A Review of Recent Advances in Biomass-Derived Porous Carbon Materials for CO₂ Capture

Abstract

With the intensifying global climate crisis and the urgent demand for carbon neutrality, carbon dioxide (CO₂) capture technologies have received growing attention as effective strategies for mitigating greenhouse gas emissions. Carbon-based porous materials are widely regarded as promising CO₂ adsorbents due to their tunable porosity, high surface area, and excellent chemical and thermal stability. Among them, biomass-derived porous carbon materials have received growing attention as sustainable, low-cost alternatives to fossil-based adsorbents. This review provides a comprehensive overview of recent advances in biomass-derived porous carbon materials for CO₂ capture, emphasizing the fundamental adsorption mechanisms, including physisorption, chemisorption, and their synergistic effects. Key synthesis pathways, such as pyrolysis and hydrothermal carbonization, are discussed in relation to the development of biomass-derived porous carbon materials. Furthermore, performance-enhancing strategies, such as activation treatments, heteroatom doping, and templating methods, are critically evaluated for their ability to tailor surface properties and improve CO₂ uptake capacity. Recent progress in typical biomass-derived porous carbon materials, including active carbon, hierarchical porous carbon, and other innovative carbon materials, is also highlighted. In addition to summarizing recent advances in porous carbon synthesis, this review introduces a unified techno-economic framework that integrates cost, sustainability, and performance-driven benefits. Overall, this review aims to provide systematic insights into the performance of biomass-derived porous carbon materials and to guide the rational design of efficient, sustainable adsorbents for real-world carbon capture applications.

1. Introduction

The emission of greenhouse gases, primarily carbon dioxide (CO₂), is causing profound and irreversible impacts on the Earth’s ecosystems and climate balance [1,2]. These effects, manifested in global temperature rise, more frequent extreme weather events, sea-level rise, and biodiversity loss, have become one of the most urgent environmental challenges facing humanity [3,4]. The fundamental cause of excessive CO₂ emissions lies in the continued dominance of fossil fuels such as coal, oil, and natural gas within the global energy mix [5,6,7,8,9]. Their extraction, processing, and combustion consistently release large amounts of greenhouse gases [10,11,12]. Although clean energy sources such as solar [13,14,15], wind [16,17,18,19], and nuclear power [10,20,21,22] have made remarkable progress in recent years, they still face significant technical and economic challenges related to stability, infrastructure development, energy density, and storage technologies, making a complete substitution for fossil fuels infeasible in the short term. Consequently, during this transitional phase of the global energy system toward low-carbon development, the effective control and management of “unavoidable carbon emissions” has become a central component of current carbon mitigation strategies. Against this backdrop, carbon capture, utilization, and storage (CCUS) technologies have attracted increasing global attention as an essential transitional pathway toward achieving carbon neutrality [23,24,25,26]. By efficiently capturing CO₂ from industrial emissions or energy conversion processes, followed by subsequent utilization or safe storage, CCUS can significantly reduce overall greenhouse gas emissions [27,28]. In recent years, substantial progress has been achieved in critical areas including the development of high-performance capture materials, process optimization, system integration, and pilot-scale demonstrations. As a result, CCUS has evolved from laboratory-scale research to engineering applications, offering a practical and scalable solution for achieving deep decarbonization worldwide [29,30,31,32,33,34,35].

In the CCUS system, efficient carbon capture represents the prerequisite and core step of the entire process. Only by achieving effective separation and concentration of CO₂ can reliable support be provided for subsequent utilization and long-term storage. Therefore, the development of low-cost, efficient, and renewable CO₂ capture materials and processes is of great significance for promoting the large-scale deployment and commercialization of CCUS technologies. Among various CO₂ capture approaches, compared with alkaline and amine-based absorbents as well as emerging materials such as amine-functionalized adsorbents, covalent organic frameworks (COFs), and porous organic polymers (POPs), carbon-based porous materials offer several benefits, including low production cost, wide availability of precursors, high thermal and chemical stability, reversible adsorption–desorption behavior, moisture resistance, and excellent reusability [36,37,38,39,40,41].

Traditional precursors for porous carbon materials have primarily relied on petroleum pitch, coal, and synthetic polymer resins [42,43]. Although these materials offer stable performance and high controllability, they are non-renewable and their preparation processes are often accompanied by high energy consumption and environmental burdens, which hinder the realization of green and low-carbon development goals. To address these challenges, an increasing number of researchers have explored biomass as a sustainable carbon source to replace conventional precursors for the fabrication of high-performance CO₂ adsorbents [37,44]. Biomass resources are abundant, easily accessible, low-cost, and environmentally friendly [45,46,47]. Beyond serving as precursors for carbon materials, biomass also functions as a versatile feedstock for producing a wide range of high-value bioenergy products, including solid biomass pellets [48], biocoal [49], biodiesel [50], bioethanol [51,52], biohydrogen [53,54], biogas [55,56], and syngas [57,58], highlighting its broader roles within sustainable energy system. Furthermore, due to their intrinsic microstructures, such as cellular cavities and fibrous channels, and the presence of heteroatoms, biomass materials are particularly advantages for carbonization and activation into porous carbons with favorable pore frameworks and functional sites [40,59]. These features endow biomass-derived porous carbons with high surface area and tunable surface chemistry, enabling a wide range of applications, including CO₂ capture [60], batteries [61,62,63,64], supercapacitors [65,66,67], and environmental remediation [68,69,70]. Among these, improvements in CO₂ capture performance by biomass-derived porous carbon has been significant [60,71,72]. Calvo-Muñoz et al. synthesized a series of porous carbon materials from biomass waste and systematically evaluated their CO₂ adsorption performance under post-combustion conditions [73]. The results demonstrated that these materials exhibited adsorption capacities comparable to those of complex carbon materials or inorganic adsorbents. Notably, activated carbon fibers derived from lignin not only achieved high CO₂ uptake but also allowed rapid and complete desorption under standard conditions, indicating excellent regenerability and practical application potential. Similarly, Ahmed et al. reported the preparation of ultramicroporous biomass-derived porous carbon materials using environmentally friendly, green technologies [74]. These materials retained favorable physicochemical properties while exhibiting excellent CO₂ adsorption performance, demonstrating the potential for low-cost, sustainable, and efficient conversion of biomass into CO₂ capture materials.

Despite these advances, existing reviews mainly focus on general preparation methods or broad applications of biomass-derived porous carbons, while a systematic and targeted review specifically addressing recent progress in their CO₂ capture performance is still lacking. In particular, the latest progress in performance enhancement through precise structural regulation, such as pore size distribution, and functional modifications, such as surface chemistry tuning, have not yet been comprehensively and critically summarized. To address this gap, this review systematically analyzes and integrates studies published over the past decade, with an emphasis on revealing the structure–function–performance relationships of biomass-derived porous carbons for CO₂ capture and providing guidance for future material design. It first introduces the fundamental CO₂ capture mechanisms of biomass-derived porous carbon materials, followed by an overview of common biomass feedstocks and their characteristics, key carbonization processes, and various performance tuning strategies. Subsequently, representative biomass-derived porous carbon materials currently applied for CO₂ capture and their research progress are highlighted. Finally, the review discusses major challenges and future directions from both technical and economic perspectives. By integrating techno-economic considerations with material development, this review proposes directions for scalable and cost-effective material design and process optimization. Such a combined materials-process-techno-economic perspective is intended to facilitate the translation of laboratory advances into industrial practice. By providing systematic insights and technical guidance, this work aims to accelerate the development and practical application of biomass-based CO₂ capture materials, thereby contributing to global efforts toward carbon neutrality and sustainable environmental management.

2. Data Collection and Methodology

This study was conducted through a systematic process encompassing information collection, classification, analysis, and summarization. The information was extensively sourced from peer-reviewed journal articles and conference proceedings retrieved from major academic databases, including Web of Science and Scopus. The publications reviewed were primarily concentrated within the past decade, with certain foundational concepts and technologies extending back approximately twenty years. After collection, the information was organized according to several key thematic categories, including the fundamental mechanisms governing CO₂ adsorption by biomass-derived materials, classifications of biomass feedstocks, technologies for producing biomass-derived porous carbons, and recent technological advancements in this field. Based on this framework, a detailed analysis was carried out to summarize the characteristics of different biomass feedstocks, the features of various production technologies, and the corresponding progress achieved to date in typical porous carbons for CO₂ capture. Furthermore, the current challenges associated with biomass-derived porous carbons were clarified, and potential directions for future improvement were proposed.

3. Overview of CO₂ Capture Mechanisms by Biomass-Derived Porous Carbon Materials

The capture of CO₂ by biomass-derived porous carbon materials primarily relies on adsorption processes [38]. The adsorption mechanisms are influenced by factors such as the type of biomass precursor, synthesis method, and surface modification strategies, which result in variations in pore structure and surface chemistry. Consequently, different carbon materials exhibit diverse adsorption behaviors during CO₂ capture. Overall, these behaviors can be categorized into three main mechanisms: physisorption, chemisorption, and a combined physisorption-chemisorption synergistic process [75,76].

Physisorption refers to the process in which CO₂ molecules interact with the surface of carbon materials through non-covalent forces such as van der Waals interactions or dipole-induced dipole interactions [77]. This type of adsorption typically occurs on micropore-rich materials with pore size below 2 nm and is highly sensitive to specific surface area and pore volume [78,79,80]. Physisorption offers advantages such as reversibility, good regenerability, and low operational energy consumption [81]. Additionally, the corresponding synthesis methods are relatively mature and cost-effective. However, the adsorption capacity is limited by the physical pore structure, and their performance can deteriorate under high-temperature or high-humidity conditions due to weakened physical interactions or competitive adsorption. Moreover, their weak specific interactions with CO₂ lead to low selectivity [82].

Chemisorption involves the formation of covalent or ionic bonds between CO₂ molecules and active sites on the carbon surface [83,84,85]. This process is often exothermic and accompanied by electron rearrangement [86]. Compared with physisorption, chemisorption provides higher selectivity and stronger adsorption strength, maintaining stability and high adsorption capacity under elevated temperatures or variable pressure conditions. Moreover, during synthesis and optimization, surface active sites can be deliberately tailored to facilitate electron donor-acceptor interactions with CO₂, thereby enhancing affinity and adsorption performance. However, chemisorption also has limitations: the process can be irreversible or require high energy for regeneration, cyclic stability is generally lower than that of physisorption, and functionalization adds complexity and cost to material preparation [87,88].

In most practical applications, CO₂ capture by biomass-derived porous carbon materials is not dominated by a single mechanism but results from the synergistic effect of physisorption and chemisorption [89]. By rationally designing pore structures and surface functionalities, this synergistic mechanism can achieve high adsorption capacity, selectivity, and stability, making it particularly suitable for CO₂ capture and separation in complex gas environments. Nevertheless, material design must balance pore structure control with chemical functionalization, and performance is highly dependent on the structural-component synergy. Therefore, synthesis becomes more complex, and production costs are higher.

Table 1. Mechanisms and performance characteristics of CO₂ capture on biomass-derived porous carbon materials.

Capture Mechanism	Interaction	Advantages	Disadvantages	References
Physisorption	van der Waals forces, dipole interactions	Reversible and good regenerability; Low energy consumption; Mature, low-cost synthesis	Low selectivity; Limited capacity by pore structure; Less stable at high temperature or humidity	[77,81,82]
Chemisorption	Chemical bonds (covalent or ionic)	High selectivity; Stable at elevated temperature/pressure; Tunable surface sites enhance CO2 affinity	May be irreversible or energy-intensive to regenerate; Lower cyclic stability; Complex, costly functionalization	[83,84,85,87,88]
Physisorption–Chemisorption Synergy	van der Waals forces, dipole interactions, and chemical bonds	High capacity; Strong selectivity; Good cyclic stability; Effective across wide temperature/pressure ranges	Complex design balancing pores and functionality; Performance depends on structure-component synergy; Higher production cost	[89,90]

summarizes the characteristics of physisorption, chemisorption, and the combined physisorption-chemisorption mechanism.

4. Feedstocks and Preparation Techniques of Biomass-Derived Porous Carbon Materials

Biomass-derived porous carbon materials have attracted widespread attention due to their high CO₂ adsorption performance and favorable environmental adaptability. Compared with conventional carbon materials, biomass-based carbons offer abundant, low-cost, and environmentally friendly resources [37,44,46]. In addition, some biomass features intrinsic porous structures and rich heteroatom content, which provide a unique foundation for the development of high-performance CO₂ adsorbents [40,59].

The general preparation process of biomass-derived porous carbon materials for CO₂ capture is illustrated in Figure 1 and typically involves feedstock selection, carbonization, and performance tuning. Common biomass feedstocks include agricultural residues, forestry wastes, municipal solid waste, algae, and animal-derived biomass. Pyrolysis and hydrothermal carbonization are the most commonly used carbonization methods for converting biomass into carbon-based materials. To overcome the inherent limitations of primary carbon materials, such as low specific surface area, suboptimal pore structure, or insufficient surface active sites, various performance optimization strategies are employed, including activation, heteroatom doping, and templating techniques. These strategies can be implemented at different stages of the carbonization process: pre-treatment before carbonization, co-treatment or in situ treatment during carbonization, and post-treatment after carbonization. The resulting porous carbon materials typically exhibit high specific surface area, abundant functional groups, and excellent thermal and cyclic stability, meeting the requirements for efficient and sustainable CO₂ capture.

4.1. Biomass Feedstocks

According to their source types, the biomass feedstocks commonly used for preparing carbon materials for CO₂ capture mainly include agricultural residues, forestry residues, municipal solid waste, algal biomass, and animal-derived biomass.

Table 2. Characteristics of different biomass feedstocks for porous carbon materials.

Feedstock Type	Resource Ability	Key Features	Advantages for Carbon Materials	References
Agricultural residues	Seasonal availability; Abundant and widely accessible	Rich in cellulose, hemicellulose, and lignin; High carbon content; Low ash and sulfur	Easily pyrolyzed; Tunable pore structure; High carbon yield	[91,92,93,94]
Forestry residues	Large quantities; Widely distributed; Stable supply	High lignin content; High carbon content; Low ash, sulfur, and heavy metal contents; Uniform structure	Suitable for high surface area activated carbon; Low impurity levels; Stable pore structure; Excellent adsorption performance	[95,96,97,98]
Municipal solid wastes	Massive quantity; Diverse sources; High recycling potential	Complex composition; Pretreatment required; High proportion of organic components	Promotes waste valorization; Strong environmental co-benefits	[99,100,101]
Algae	Short growth cycle; High light-use efficiency; Obtainable via enriched water bodies or cultivation	High carbon, low lignin; Nitrogen-rich; Easily doped/modified	Biomass can capture CO2; Nitrogen-rich carbon favors chemisorption sites and enhances performance	[102,103,104]
Animal-derived biomass	High-value utilization potential	Rich in nitrogen, phosphorus, sulfur; Easily self-doped	Naturally multi-heteroatom-doped; High surface activity; Favorable for CO2 chemisorption and catalytic reactions	[105,106]

summarizes the key properties of these biomass resources.

Agricultural residues are among the most common and abundant biomass resources, primarily including crop straws [94,107,108], fruit shells [109,110,111], seed coats [112,113,114], and husks [115,116,117], and corncobs [91,92,93]. Forestry residues are organic waste by-products generated during logging and wood processing activities [74,118]. They mainly include wood chips [98,118,119], sawdust [96,97,120], and bark [95,121,122]. These residues are widely distributed and generated in large quantities, making them major sources of solid biomass wastes.

Municipal solid wastes have emerged as an important potential source for biomass-derived carbon materials and have attracted increasing attention in recent years. Municipal solid wastes consist primarily of carbon-rich components such as organic kitchen waste, paper, and green waste, which, after appropriate treatment, can be converted into porous carbon materials for applications in environmental purification and greenhouse gas mitigation. Compared with incineration or landfill disposal, valorizing municipal solid wastes into carbon-based adsorbents not only helps reduce environmental burdens but also adds functional value to waste materials. Although the global generation of municipal solid wastes is enormous, their recycling and high-value utilization rates remain relatively low [123], highlighting the urgent need to develop efficient municipal solid wastes valorization pathways. Studies have shown that biochar materials prepared from the organic fraction of municipal solid wastes through composting or pyrolysis exhibit good CO₂ adsorption capacity and regenerability [99,100,101]. Low-cost and abundant municipal solid wastes serve as promising precursors for sustainable CO₂ adsorbents in the circular economy.

In addition to agricultural, forestry, and municipal solid wastes, algae and animal-derived biomass show significant potential as precursors for carbon materials. During growth, algae can efficiently capture CO₂ from the atmosphere or industrial flue gases through photosynthesis, achieving a “carbon-negative” effect [72,124]. After carbonization, the resulting porous carbon materials exhibit high specific surface areas and micropore volumes suitable for physisorption, while their rich nitrogen- and oxygen-containing functional groups confer excellent chemisorption properties [102,103,104]. Algae comprise diverse species and are characterized by fast growth, high carbon content, and abundant nitrogen [125], making them highly suitable for carbon adsorbent production. Animal-derived biomass, such as silkworm cocoons, shells, and bones, is rich in proteins, chitin, and collagen, naturally containing nitrogen, phosphorus, and sulfur [105,106]. Upon carbonization, these feedstocks yield multi-heteroatom-doped carbon materials that demonstrate excellent adsorption and catalytic performance in CO₂ capture and electrochemical energy storage. Algal and animal biomass provide abundant feedstocks and versatile structural tuning strategies, offering new avenues for the sustainable development of biomass-based CO₂ capture technologies.

4.2. Biomass Carbonization Techniques

The key step in converting biomass into carbon materials is carbonization, whose primary goal is to remove volatile components from the biomass through thermochemical processes, enrich the carbon content, and form a carbon framework with porous structures. Carbonization not only determines the fundamental skeleton of the carbon material but also significantly influences key structural parameters such as specific surface area and pore size distribution, thereby directly affecting the CO₂ adsorption capacities. Currently, the commonly used carbonization methods include pyrolysis and hydrothermal carbonization. Each method has distinct advantages in terms of suitable feedstock types, energy consumption, and product properties, making them adaptable to different types of biomass resources.

4.2.1. Pyrolysis

Pyrolysis is one of the most mature thermochemical conversion technologies [126]. This process is typically conducted at the temperature range of 300 to 800 °C under oxygen-deficient or inert conditions. Biomass is heated to high temperatures, promoting the decomposition and separation of internal moisture, volatile components, and unstable organic matter, ultimately yielding carbon-rich and structurally stable char materials. During pyrolysis, biomass is converted into three product phases: gas (syngas), liquid (bio-oil), and solid (char) [126]. The solid char is rich in carbon, possesses a certain porous structure and thermal stability, and serves as a key precursor for carbon-based adsorbents, widely applied in CO₂ capture and other environmental remediation processes. Recent studies also indicate that pyrolysis under a CO₂ atmosphere, rather than strictly oxygen-deficient or inert conditions, can better preserve the carbon and nitrogen content in the biomass [126].

The main components of biomass, including lignin, cellulose, and hemicellulose, exhibit different thermal decomposition temperature ranges and reaction characteristics during pyrolysis, leading to variations in product distribution.

Table 3. Pyrolysis characteristics and product features of different biomass components.

Biomass Components	Pyrolysis Temperature (°C)	Thermal Stability	Product Characteristics	References
Hemicellulose	200–350	Low	Low char yield; Produces abundant volatile small molecules; Unstable char structure	[126,133]
Cellulose	300–400	Moderate	Moderate char yield; Forms lamellar structures with well-developed porosity	[126,134]
Lignin	>400	High	High char yield; Stable carbon framework; Rich in aromatic structures	[126,135]

summarizes the pyrolysis characteristics of these three major components. It is important to note that biomass pyrolysis is not a simple superposition of the individual component behaviors, but rather a complex synergistic reaction system. This synergy manifests in several ways. First, volatile compounds released early from hemicellulose (e.g., acetic acid, phenolics) may interact with cellulose or lignin, affecting their decomposition rates [127,128]. Second, intermediate products generated during the decomposition of each component, such as free radicals, can further participate in condensation or cross-linking reactions [129], influencing the structure and stability of the final char. In addition, aromatic free radicals produced from lignin pyrolysis contribute to the aromatization of the carbon material [130], enhancing its porous structure and thermal stability. Finally, inherent inorganic minerals in the biomass and gases generated during pyrolysis, such as CO₂ and H₂O, also affect the reaction atmosphere and kinetics, exerting a notable influence on product distribution [131,132].

Depending on the heating rate and the residence time of the material at high temperature, the pyrolysis process can be categorized into slow, fast, and flash pyrolysis [126]. The major products obtained from these different modes vary significantly.

Table 4. Characteristics and product distributions of different pyrolysis processes.

Pyrolysis Process	Heating Rate	Residence Time	Feedstock Characteristics	Main Products	References
Slow pyrolysis	0.1–1 °C/s	Several minutes to hours	Dense, low-moisture, lignocellulosic-rich biomass	Mainly biochar	[126,137]
Fast pyrolysis	10–200 °C/s	0.5–10 s	Light, low- to moderate-moisture, high-volatile-matter biomass	Mainly bio-oil	[126,136]
Flash pyrolysis	>1000 °C/s	<1 s	Fine, low-moisture, high-volatile-matter biomass	Bio-oil and gases	[126,136]
Microwave-assisted pyrolysis	Rapid (system-dependent and adjustable)	Several seconds to minutes	Broad feedstock adaptability; Tolerant to high-moisture or heterogeneous biomass	Biochar, bio-oil, and gases	[126,138,140]

summarizes the key parameters and main product characteristics of these pyrolysis processes. Fast and flash pyrolysis, characterized by rapid heating and short residence times, primarily yield bio-oil and combustible gases [126,136], making them suitable for liquid fuel production. In contrast, slow pyrolysis involves longer reaction times and more complete thermal decomposition, resulting in a higher proportion of solid products (biochar), with char yields typically ranging from 30% to 50% [126,137]. Consequently, it is widely employed for preparing carbon material precursors. In addition, a novel alternative approach, microwave-assisted pyrolysis, can achieve uniform heating by directly penetrating the biomass and interacting with polar molecules via microwave irradiation [138,139,140]. Compared with conventional conductive heating, microwave-assisted pyrolysis offers advantages such as higher heating rates, lower energy consumption, and improved reaction efficiency [126,140]. It is particularly suitable for processing biomass with high moisture content, effectively minimizing the energy loss associated with water evaporation at the initial stage [138,141,142]. However, several challenges remain for its practical application. The system design is relatively complex, operational parameters must be precisely controlled, and the biochar yield is generally lower than that obtained from conventional slow pyrolysis. Further research and optimization are needed to enhance its scalability and ensure consistent performance of the resulting carbon materials.

4.2.2. Hydrothermal Carbonization

Hydrothermal carbonization is a sustainable and energy-efficient thermochemical conversion technology. The process is typically conducted in a sealed reactor using water as the reaction medium, under moderate conditions with temperatures in the range of 180 to 250 °C and the corresponding autogenous pressure. Hydrothermal carbonization simulates the natural processes of humification and coalification and is often referred to as “accelerated coalification” or “wet pyrolysis” [143,144]. Under these relatively mild conditions, biomass undergoes dehydration and decarboxylation reactions that progressively remove hydrogen and oxygen, enriching its carbon content. Ultimately, the biomass is converted into a solid carbonaceous material known as hydrochar [145,146]. During this process, small amounts of liquid-phase products, mainly aqueous solutions containing organic acids and phenolic compounds, and gaseous products, predominantly CO₂ with minor light hydrocarbons, are also generated [147,148].

The resulting hydrochar serves as an important precursor for the preparation of carbon materials with CO₂ adsorption capability. Its microstructure primarily consists of a matrix and small coke microparticles [149,150]. Specifically, the matrix originates from partially unhydrolyzed biomass and is formed through dehydration, condensation, and decarboxylation reactions, often retaining some of the original structural features. The hydrolyzed organic molecules first polymerize to form aromatic structures, which then aggregate to generate primary microcores [151]. The surfaces of these microcores are rich in polar functional groups, such as hydroxyl (–OH), carbonyl (C=O), and carboxyl (–COOH), which can further undergo condensation reactions with small molecules in the liquid phase, such as furans, ultimately forming densely structured coke microparticles [152,153,154]. Due to the abundance of oxygen-containing functional groups on the hydrochar surface, it exhibits strong potential for surface functionalization and high CO₂ affinity, making it an ideal precursor for adsorption-type carbon materials [155,156].

4.2.3. Comparison of Carbonization Techniques and Biomass Feedstock Suitability

Pyrolysis and hydrothermal carbonization, as two primary pathways for biomass carbonization, both are capable of producing carbonaceous solid products, but they differ significantly in reaction environment, product characteristics, and feedstock suitability. Pyrolysis is typically conducted under dry, oxygen-limited, high-temperature conditions, making it well-suited for low-moisture biomass such as agricultural and forestry residues. These feedstocks are rich in cellulose and lignin with relatively uniform structures, enabling high carbon yields and stable pore networks. In contrast, hydrothermal carbonization can directly process high-moisture biomass, including municipal solid wastes and algae, substantially reducing the energy required for pre-drying and allowing efficient conversion under wet conditions. Animal-derived biomass has moderate moisture content and is rich in proteins and heteroatoms; both pyrolysis and hydrothermal carbonization can be applied, but hydrothermal carbonization is advantageous for preserving nitrogen, phosphorus, and sulfur, facilitating the production of multi-heteroatom-doped carbon materials. The structural and surface chemical properties of the resulting carbon materials vary between these two methods, influencing their subsequent CO₂ adsorption performance.

Table 5. Key characteristics of pyrolysis and hydrothermal carbonization.

Carbonization Techniques	Pyrolysis	Hydrothermal Carbonization
Reaction Temperature	300 to 800 °C	180 to 250 °C
Reaction Pressure	Atmospheric pressure	Autogenous pressure
Reaction Medium	Dry, oxygen-limited or inert	Water
Energy Consumption	High	Low
Suitable Biomass	Low-moisture biomass	High-moisture biomass, processed directly
Main Products	Biochar, bio-oil, syngas	Hydrochar, liquid organics, small amount of gas
Characteristics of solid carbon products	Rich porous structure and aromatic frameworks suitable for physisorption	Rich functional groups suitable for chemisorption

summarizes the key characteristics of pyrolysis and hydrothermal carbonization, as well as the suitability of different biomass feedstocks, providing guidance for material selection and process optimization.

4.3. Performance Tuning Techniques for Biomass-Derived Porous Carbon Materials

Through pyrolysis or hydrothermal carbonization, primary carbon materials typically exhibit some degree of micro- and mesoporosity and a moderate specific surface area, making them suitable for CO₂ adsorption under low-demand conditions. However, these materials often suffer from limited surface area, suboptimal pore structures, insufficient surface active sites, and relatively poor thermal and cycling stability, which constrain their adsorption capacity and overall performance. To improve CO₂ adsorption selectivity and efficiency, various performance tuning strategies are commonly applied, including activation, heteroatom doping, and templating methods.

4.3.1. Activation

Activation is an effective strategy to develop and enhance the pore structure of carbon materials, significantly increasing their specific surface area [157,158]. Depending on the type of activating agent and reaction conditions, activation is commonly classified into two main categories: physical activation and chemical activation [157]. Physical activation typically employs gaseous media at high temperatures to induce carbon structural reorganization, whereas chemical activation involves the introduction of chemical reagents that react with the carbon precursor to develop a well-defined porous structure.

Physical activation is typically carried out after carbonization, at high temperatures of 800 to 1000 °C, by introducing activating gases that “etch” the carbon framework through gas–solid reactions, thereby generating a well-developed porous structure and significantly enhancing the specific surface area and adsorption performance. Common gaseous activating agents include CO₂, steam (H₂O), and air (O₂), each exhibiting distinct reaction mechanisms, activation characteristics, and effects on the pore structure of the resulting carbon materials [159].

Table 6. Characteristics of three physical activation methods.

Activation Method	Core Reaction Mechanism	Activation Features	Effect on Carbon Material Porosity	References
CO2 Activation	C + CO2 → 2CO	Conducted at 800–1000 °C; Slow gas etching; Mild reaction; Relatively long activation time	Suitable for creating stable microporous structures	[160,161,162]
Steam Activation	C + H2O → CO + H2	Conducted at 700–900 °C; Stronger etching effect; Faster reaction; High activation efficiency	Suitable for developing micropores, mesopores and macropores	[163,164,165,166]
Air Activation	C + O2 → CO2	Conducted at 400–600 °C; Simple operation; Lower temperature and equipment requirements; Vigorous reaction	Suitable for mild or preliminary activation; Uncontrolled conditions may damage pore structure	[159]

provides a detailed comparison of the features of these three physical activation methods.

Unlike physical activation, which is typically performed after carbonization, chemical activation can be carried out in two ways: a one-step activation, in which the activating agent is mixed with the raw biomass before thermal treatment so that carbonization and activation occur simultaneously; and a two-step activation, in which the activating agent is introduced after biomass carbonization, followed by a second thermal treatment, similar in sequence to physical activation [167]. Based on the chemical nature of the activating agents, chemical activation is generally classified into acid, alkaline, and salt activation [168]. These agents induce the formation of specific pore structures, and some also promote the development of surface functional groups in biomass-derived carbon materials through distinct thermochemical mechanisms.

Table 7. Characteristics of three chemical activation methods.

Activation Method	Representative Activating Agent	Activation Mechanism	Effect on Carbon Material Porosity	References
Acid Activation	H3PO4, H2SO4, HNO3	Acids promote dehydration, crosslinking, and suppress tar formation	Mainly mesoporous/macroporous; Well-defined pore structure, high yield; Surface enriched with acidic functional groups enhancing CO2 adsorption selectivity	[169,170,171,172]
Alkaline Activation	KOH, NaOH, amino (–NH2)	Reacts with carbon to generate CO, H2, metal salts, and gas evolution creates micropores	Mainly microporous; High surface area, small pore size, excellent adsorption performance; Some basic surface groups retained or introduced to improve chemical CO2 adsorption	[173,174,175,176]
Salt Activation	ZnCl2, FeCl3, MgCl2	Inhibits charring, promotes thermal cracking and pore formation, enabling porous carbon formation at lower temperatures	Micro- and mesopores coexist; Loose and porous structure; Partial salt residues can introduce metal oxides or surface functional groups, enhancing adsorption and catalytic potential	[177,178,179,180]

provides a detailed comparison of the characteristics of these three chemical activation approaches.

Table 8. Comparison of physical and chemical activation.

Activation Method	Physical Activation	Chemical Activation
Activation Mechanism	Gas–solid reaction between activating gas and carbon selectively “etches” the carbon structure, forming micropores	Chemical agents react with the carbon precursor, generating gases and intermediates that dissolve and rearrange the carbon structure to form abundant porosity
Activation Procedure	Carbonization first, followed by gas activation	Two approaches: (1) One-step: chemical agent pre-mixed with raw biomass for simultaneous carbonization and activation; (2) Two-step: biomass is carbonized first, then mixed with chemical agent for activation
Typical Activation Temperature (°C)	800 to 1000	400 to 800
Advantages	Simple process, no chemical residues, environmentally friendly	Rich pore structure, high activation efficiency, suitable for high-performance carbon materials
Disadvantages	Limited control over pore structure, high temperature required, high energy consumption	Chemical residues require washing, process is more complex, potential environmental impact

provides a comparison of physical and chemical activation. Overall, physical activation offers advantages such as relatively simple operation, mature technology, low cost, and environmental friendliness. However, because it relies on gas–solid reactions between activating gases and the carbon precursor at high temperatures, the process is constrained by gas diffusion rates, the distribution of reactive sites, and heat transfer efficiency. As a result, precise control over pore size and distribution is difficult to achieve. In contrast, chemical activation involves intimate contact and reaction between a chemical activating agent and the organic framework of the precursor, promoting carbon skeleton reconstruction, dehydration, etching, and cross-linking at relatively lower temperatures, thereby forming more developed microporous and mesoporous structures. Since the activating agent can be uniformly distributed within the precursor, chemical activation provides significant advantages in controlling porosity, adjusting specific surface area, and achieving uniform pore size distribution. Additionally, certain chemical activators can introduce surface functional groups, further enhancing the carbon material’s affinity for CO₂ [181,182]. Nevertheless, chemical activation typically involves corrosive reagents, requiring post-treatment washing to remove residues, which imposes higher demands on environmental and cost management. Therefore, both methods have distinct strengths and limitations, and the choice or combination of techniques is generally guided by the specific application requirements.

4.3.2. Heteroatom Doping

Heteroatom doping, as a chemical modification strategy, introduces non-carbon elements such as nitrogen (N), phosphorus (P), sulfur (S), or boron (B) into carbon materials, effectively tuning the surface electronic structure and the distribution of polar functional groups, thereby enhancing CO₂ affinity and selective adsorption [183]. Due to the significant differences in atomic radius, electronegativity, and hybridization compared with carbon, the doping process disrupts the original six-membered ring structures and π-conjugated systems in the carbon framework, generating structural defects [184,185]. These defects break the symmetry of surface charge distribution, creating polar sites and unsaturated bonds that increase CO₂ adsorption activity [186,187]. Additionally, heteroatom incorporation promotes the formation of active sites, such as oxygen-containing functional groups, further strengthening interactions between CO₂ and the material surface [188]. In summary, heteroatom doping enhances CO₂ adsorption through a synergistic mechanism of defect induction and functional group modulation. Figure 2 provides schematic illustrations of carbon materials doped with various heteroatom species.

Heteroatom doping can be classified into two main approaches based on the timing and method of introducing dopants: in situ doping and post-treatment doping [189,190]. In situ doping involves the incorporation of heteroatoms directly into the carbon framework during the carbonization of biomass. This can be achieved through methods such as precursor co-mixing, solution impregnation followed by carbonization, or gas-phase doping [191,192,193]. The approach ensures uniform distribution and good dispersion of dopants, making it suitable for large-scale production. However, at high temperatures, dopants may partially volatilize or undergo functional group rearrangements, which can limit precise control over doping levels. In contrast, post-treatment doping is performed after the carbon material has been formed, introducing heteroatoms via chemical reactions or thermal treatments. Common techniques include gas-phase post-treatment, liquid-phase impregnation, and plasma-assisted methods [194,195,196,197,198]. This approach allows more precise control over surface functional groups and the design of specific surface functionalities, which is advantageous for tailored applications. Nevertheless, the doping depth is often limited, and the overall efficiency is lower compared to in situ methods. The mechanisms of commonly used in situ and ex situ heteroatom doping techniques are illustrated in Figure 3.

The impact of heteroatom doping on the performance of carbon materials depends not only on the type and method of doping but also critically on the amount of dopant introduced. An appropriate dopant concentration helps balance the introduction of active sites with the preservation of the porous structure, thereby optimizing CO₂ adsorption performance. Conversely, an excessive level of heteroatom doping can compromise the structural integrity of carbon materials, leading to pore collapse and a subsequent decrease in adsorption efficiency [199]. In addition, different types of heteroatoms and the functional groups they form exhibit varying stability during thermal treatment and multiple adsorption–desorption cycles, significantly influencing the material’s regenerability and long-term performance. Therefore, carefully controlling the dopant loading and thermal treatment conditions is essential for the design of high-performance, reusable carbon-based adsorbents.

4.3.3. Templating

To achieve precise control over pore size distribution and specific morphologies, the templating method, a structure-directing strategy, is widely employed for the fabrication of biomass-derived carbon materials with ordered pore structures, high specific surface areas, and tunable shapes [200]. The fundamental principle involves introducing an appropriate template either before or during carbonization, which guides the formation of the desired pore structure and morphology by replicating the template architecture. The resulting carbon materials exhibit uniform pore sizes, high surface areas, and well-defined channels, thereby enhancing CO₂ adsorption capacity and mass transfer efficiency.

Depending on the template properties and formation mechanism, the templating method is generally classified into hard templating and soft templating [201,202]. In hard templating, rigid and non-decomposable inorganic materials serve as templates. Biomass is first physically or chemically confined within the surface or pores of the template and then carbonized, allowing the carbon precursor to form a specific structure within the confined space. The template is subsequently removed by acid or base treatment, such as using HF, HCl, or NaOH, leaving a carbon framework that replicates the template structure. Soft templating uses flexible organic molecules, such as surfactants, and block copolymers [203,204]. These molecules interact with the biomass carbon source through intermolecular forces such as electrostatic interactions, hydrogen bonding, or van der Waals forces, and self-assemble into ordered aggregates. After drying to form gels or precursors, the carbon source solidifies within the microstructure defined by the soft template during carbonization, producing ordered or hierarchical porous structures. The soft template molecules decompose thermally during carbonization, eliminating the need for additional removal steps and yielding carbon materials with well-defined mesoporous structures. Figure 4 illustrates the processes for producing porous carbon materials via hard and soft templating methods.

As the demand for precise pore structure control in porous carbon materials has increased, the dual-templating method has been developed to integrate the advantages of both hard and soft templating [205]. This approach typically introduces soft templating agents into an inorganic hard-template framework to further tailor pore size distribution, channel connectivity, and carbon skeleton morphology. In practice, the hard template provides macroporous or mesoporous structural support, while the soft template guides the formation of mesopores or micropores at the nanoscale. After carbonization, the soft template is thermally decomposed, and the hard template is chemically removed, resulting in hierarchical porous carbon materials with high surface area and large pore volume.

Table 9. Characteristics of hard templating, soft templating, and dual-templating methods.

Templating Type	Template Property	Common Template Materials	Pore Formation Mechanism	Advantages	References
Hard Templating	Rigid inorganic materials	SiO2, MgO, Al2O3, CaCO3, metal oxides	Biomass is molded within the confined space of the template, which is later removed chemically	Well-defined pore size, high structural stability, controllable morphology	[201,202,206]
Soft Templating	Flexible organic molecules or polymers	Pluronic F127, P123, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG)	Soft templates self-assemble with carbon precursors to form an ordered precursor, and subsequently decompose during carbonization	Simple process, suitable for hierarchical porous structures	[202,203,207]
Dual Templating	Combination of inorganic hard template and organic soft template	SiO2 + CTAB, MgO + P123, etc.	Hard template provides structural support, while soft template regulates micro/mesopores through combined confinement and self-assembly effects	Tunable hierarchical porosity, large surface area, improved pore connectivity and mass transfer	[205]

provides a detailed comparison of the characteristics of hard templating, soft templating, and dual-templating methods.

4.3.4. Comparison of Performance Tuning Strategies

Activation treatment, heteroatom doping, and templating represent three key performance tuning strategies for constructing high-performance biomass-derived porous carbon materials for CO₂ capture.

Table 10. Comparison of performance tuning strategies for biomass-derived porous carbon materials.

Technique	Activation	Heteroatom Doping	Templating
Tuning Objective	Increase specific surface area and pore volume	Enhance polarity interactions and chemisorption capability	Construct ordered pore space and specific morphological structures
Mechanism	Physical or chemical etching of the carbon framework to generate abundant micropores or mesopores	Introduce non-carbon elements to increase surface active sites and CO2 affinity	Use template materials to direct the formation of carbon frameworks, with ordered pores formed after template removal
Implementation Stage	Post-/Co-treatment	Pre-/Co-/Post-treatment	Pre-/Co-treatment
Advantages	Mature process, easy to operate, significantly enhances adsorption capacity	Tunable surface chemistry, improved selective adsorption performance	Controllable pore size, ordered structure, high surface area, favorable for diffusion and mass transfer
Limitations	Excessive micropores may hinder diffusion; Potential risk of structural damage	Difficult to precisely control doping concentration and distribution; May affect pore structure	High cost of templates; Challenges remain for green and scalable fabrication
Behavior under Dry/Humid Conditions	Humidity reduces CO2 uptake via pore blocking; Stable under dry conditions	Hydrophilic doped sites increase humidity sensitivity via CO2-H2O competitive adsorption	Templating improves CO2 adsorption kinetics under dry or low-humidity environments but is hindered by pore blocking under high humidity
Behavior at Low/High Temperature	Adsorption capacity decreases noticeably at elevated temperatures	Stronger chemisorption enables better retention at moderately elevated temperatures	Adsorption decreases with temperature due to physical adsorption dominance
Tolerance to impurities (SO2, NOx, etc.)	Acidic impurities cause deactivation by occupying active sites and blocking pores	Basic sites preferentially adsorb acidic gases, reducing CO2 selectivity	Large mesopores improve mass transfer and impurity removal but may reduce CO2 selectivity

provides a detailed comparison of these methods in terms of their modification mechanisms, implementation stages, advantages, and limitations, as well as their performance under various operating conditions, including dry/humid environments [208,209,210,211,212], low- and high-temperature conditions [38,213,214,215], and tolerance to gas impurities [216,217,218]. Each approach offers distinct benefits: activation treatment is simple to operate and enhances the overall specific surface area; heteroatom doping strengthens chemisorption capability; and templating enables precise control over pore structure.

In addition, surface acidity and basicity significantly influence CO₂ adsorption performance [219,220,221,222]. Physical activation primarily modifies pore structure, increasing micropore and mesopore volume and overall surface area, but has minimal effect on surface chemical properties. Templating methods mainly optimize pore size distribution and hierarchical pore structure, with limited influence on surface chemistry. In contrast, chemical activation can simultaneously adjust both pore structure and surface chemistry. For example, alkaline activation (e.g., KOH or NaOH) generates abundant micropores and introduces basic sites (–OH, –O⁻), whereas acid activation (e.g., H₃PO₄ or H₂SO₄) creates acidic functionalities (–COOH, –PO_x) while also developing porosity. Heteroatom doping primarily modifies surface chemical properties by introducing basic or acidic sites, with only limited influence on pore structure.

It is important to note that CO₂ is known to be a Lewis acid and preferentially interacts with basic surface sites through acid-base interactions [223]. Khosrowshahi et al. investigated the role of surface chemistry on CO₂ adsorption in biomass-derived porous carbons using experimental measurements and molecular dynamics simulations [224]. They found that basic surface sites introduced via nitrogen doping are the primary drivers of CO₂ chemisorption. Different nitrogen functionalities contributed synergistically: graphitic nitrogen alone achieved an uptake of 3.39 mmol/g, pyridinic nitrogen increased it to 3.72 mmol/g, and the coexistence of both types further raised adsorption to 4.34 mmol/g. Other basic functionalities, including hydroxyl and alkoxide groups, also enhanced adsorption through acid-base interactions and improved surface polarity [225]. In contrast, acidic functionalities such as carboxylic and phosphate groups provided only auxiliary effects by modulating surface polarity and electrostatic interactions, resulting in moderate increases in uptake. For instance, adding carboxyl groups to hydroxyl-containing surfaces increased adsorption from 3.39 to 3.60 mmol/g [224]. Overall, basic sites are more effective than acidic ones for CO₂ capture, as excessive acidic activation can partially degrade the carbon framework, reduce micropore volume, and limit adsorption under high loading conditions [226,227]. Therefore, while acidic functionalities can fine-tune surface properties, basic functionalization remains the key strategy for maximizing CO₂ adsorption performance.

These performance tuning techniques can be applied individually or combined synergistically to optimize multi-scale structural and functional properties. For example, Zhu et al. integrated KOH chemical activation with nitrogen/sulfur co-doping during hydrothermal carbonization, where activation increased the specific surface area and doping enhanced surface polarity and electron transport properties [228]. The cooperative effect of activation and heteroatom doping significantly improved the microporous structure and surface chemistry of the biomass-derived carbon, providing an effective strategy for developing high-performance CO₂ adsorbents. Similarly, Chen et al. combined the hard-templating method with KOH activation and nitrogen doping to construct porous carbon materials with dual mesoporous structures and abundant nitrogen functionalities [229]. The synergistic effects of these three techniques enable precise control over both pore structure and surface chemistry, demonstrating the feasibility of multi-technique integration for developing high-performance carbon materials.

5. Typical Biomass-Derived Porous Carbon Materials and Research Progress

Porous carbon materials can be classified in various ways depending on their characteristics. In this study, to systematically review CO₂ capture performance, biomass-derived porous carbons are categorized into three main types based on their structural and pore features: activated carbons, hierarchical porous carbons, and other innovative carbons. This section discusses the properties and research progress of each category.

5.1. Activated Carbons

Activated carbons represent the most mature and widely applied class of biomass-derived porous carbons. Their preparation typically involves the carbonization of biomass precursors, followed by physical or chemical activation to construct a micropore-dominated network within the material [230]. Due to their well-established production methods, activated carbons show promising applications in CO₂ capture [231,232]. Recent advances have shifted research focus from conventional activated carbons to design of nanoporous activated carbons with smaller and more controllable pore sizes, as well as functionalized variants. These innovations aim to further enhance CO₂ adsorption capacity and selectivity, representing the latest trends in the field.

5.1.1. Conventional Activated Carbons

Conventional activated carbons are typically prepared from common biomass sources such as agricultural and forestry residues through well-established carbonization and activation processes [150,233]. These carbon precursors have been long preferred due to their high carbon content, dense structure, and abundant availability. Recent research on conventional activated carbons has primarily focused on optimizing biomass precursors and improving material performance.

Research on activated carbons derived from agricultural residues has focused on optimizing activation conditions, controlling pore structures, and functionalizing surfaces to enhance CO₂ adsorption capacity, selectivity, and cyclic stability under mild conditions. Coconut shells have been proven to be a highly advantageous biomass source due to their high lignin and cellulose content, which facilitates the formation of well-ordered microporous structures with strong carbon frameworks, providing superior adsorption performance and stability compared to high-ash precursors such as straw or rice husks. Their pore structure can be finely tuned through KOH activation [234] and further enhanced by surface modification with basic oxides (e.g., BaO, MgO, CuO), introducing chemical adsorption sites while retaining physical adsorption and enabling synergistic effects for improved CO₂ capacity and selectivity [235]. Corncobs are another particularly representative, as they are widely available and produced in stable quantities, and the resulting carbon materials exhibit not only high CO₂ adsorption capacity but also excellent cyclic stability and regeneration performance [236]. In addition, other novel biomass sources, including tropical fruit seeds [237] and various agricultural residues [238], have been explored to produce high-surface-area activated carbons with diverse pore structures, demonstrating the broad potential of biomass valorization for CO₂ capture.

Research on forestry residues as valuable precursors for carbon materials has focused on optimizing key parameters in their carbonization and activation processes. For example, Quan et al. prepared activated carbon from pine sawdust via pyrolytic carbonization and KOH activation at different temperatures, finding that higher activation temperatures increased surface area and pore volume, with the 700 °C sample showing the best CO₂ capture due to abundant meso- and micropores and surface functional groups [120]. High-microporosity activated carbons have also been obtained from birch wood and pine cones using pyrolysis or hydrothermal carbonization incorporating activation with superheated water vapor (SWVA), which creates narrower sub-nanometer pores and significantly improves CO₂ uptake [239]. Another study has developed high-performance activated carbon from forestry residues and waste wood via ZnCl₂ impregnation and one-step pyrolysis, achieving high surface areas, high microporosity, and oxygen-rich surfaces conducive to CO₂ adsorption; a two-step acid washing can remove over 99% of residual Zn²⁺ and recycle ZnCl₂ [240]. Additionally, waste eucalypt poles treated with chromated copper arsenate (CCA) preservatives have been converted into activated carbons via pyrolysis-phosphoric acid activation, yielding moderate CO₂ adsorption capacity with rapid adsorption–desorption kinetics [241]. These materials are suitable for pressure swing adsorption (PSA) systems and enable resource recovery and detoxification of heavy-metal-containing residues.

In recent years, driven by the increasing demand for waste valorization and novel biomass sources, research has expanded beyond conventional agricultural and forestry feedstocks toward emerging and non-traditional biomass sources, particularly municipal solid waste and algae to achieve both high adsorption efficiency and environmental benefits. Plastic-based wastes in municipal solid waste, due to their high carbon content and thermal stability, have been investigated as precursors for activated carbon, yielding promising results [242,243]. In contrast, the biomass fractions of municipal solid waste, such as food waste and compost, are generated in large quantities and pose significant disposal challenges. Rich in proteins, inorganic salts, and minerals, these materials can introduce nitrogen, sulfur, and metal elements during pyrolysis, offering potential for the fabrication of functionalized carbon materials. However, their high moisture content, ash content, and impurities make processing and activation more complex, and studies on these feedstocks remain relatively limited. Notably, Karimi et al. applied Mechanical-Biological Treatment (MBT) to composted municipal solid waste biomass, followed by sulfuric acid treatment and high-temperature activation, to successfully produce activated carbons with well-developed porosity [244]. The optimized materials exhibited CO₂ uptake of approximately 2.6 mol/kg at 40 °C and 3 bar and demonstrated excellent dynamic adsorption performance in PSA cycles, highlighting the feasibility and engineering potential of valorizing urban organic waste for CO₂ capture.

Algal biomass, particularly microalgae, contains high proportions of proteins, polysaccharides, and lipids, making it inherently rich in nitrogen. This characteristic allows the direct production of nitrogen self-doped activated carbons via pyrolysis or hydrothermal carbonization, without the need for additional nitrogen sources, thereby simplifying the doping process. For example, high-sugar microalgae Chlorococcum sp. have been used as a precursor to prepare nitrogen-doped activated carbons with high specific surface area through hydrothermal carbonization combined with KOH activation [245]. XPS analysis revealed a pyridinic nitrogen content of up to 58.3%, and the resulting activated carbon exhibited excellent CO₂ adsorption capacity and stable performance over seven adsorption–desorption cycles. Similarly, Taihu blue algae have been used to produce nitrogen self-doped activated carbons rich in graphitic nitrogen sites via in situ pyrolysis [103]. Experimental and Density Functional Theory (DFT) analyses indicated that the graphitic nitrogen content in these materials is significantly higher than in carbons derived from agricultural residues, with abundant graphitic nitrogen sites enhancing CO₂ adsorption energy and performance. Beyond relying on intrinsic nitrogen, some studies have further increased nitrogen content and functional group distribution using external nitrogen sources, such as urea, to enhance CO₂ adsorption performance [246]. This strategy, combining native algal nitrogen with external doping, provides a flexible route to high-performance nitrogen-doped carbon materials. These studies highlight the unique advantages of microalgae for nitrogen-doped activated carbon production, offering a green and cost-effective pathway for high-performance CO₂ adsorbents.

5.1.2. Nanoporous Activated Carbons

Although conventional activated carbons possess well-developed porosity and abundant resource availability, their CO₂ capture performance remains limited by insufficient selectivity and adsorption capacity. In recent years, significant efforts have been devoted to precisely tailoring pore-size distributions toward the sub-nanometer scale, with particular emphasis on constructing ultramicropores smaller than 1 nm [247]. Given that the kinetic diameter of a CO₂ molecule is approximately 0.33 nm [248], these recent developments in nanoporous structures represent a key technological advance in next generation activated carbon materials for high-efficiency CO₂ capture.

The preparation of biomass-derived nanoporous activated carbons remains centered on the core processes of carbonization and activation. Numerous studies have achieved the development of nanoporous activated carbons by precisely optimizing key parameters in these processes, including pyrolysis temperature, residence time, and the ratio of activating agent to biomass [118,249,250]. For instance, Dobele et al. prepared nanoporous activated carbons from birch wood residues through a combination of low-temperature pre-carbonization and finely controlled NaOH activation [118]. The process began with pre-carbonization under nitrogen at 375–550 °C, which reduced oxygen-containing functional groups in lignocellulosic materials that readily react with NaOH, thereby minimizing activator consumption. Simultaneously, it generated initial micropores that facilitated subsequent NaOH impregnation and diffusion. The pre-carbonized product was then mixed with 40 wt.% NaOH solution at 50–215 wt.% of the raw biomass and activated at 575–800 °C. Precise control of activation temperature and the NaOH/biomass ratio proved crucial: excessively high temperatures caused over-etching of pore walls and micropore widening, whereas lower temperatures led to insufficient surface area. Similarly, insufficient NaOH loading hindered the formation of a continuous microporous network, while excessive loading promoted meso-/macropore formation and broadened the pore-size distribution. Through this optimization, the resulting activated carbons achieved surface areas exceeding 1000 m²/g with narrow pore-size distributions concentrated in the 1–1.7 nm range. The materials exhibited CO₂ adsorption capacities of 11–16 wt.% under post-combustion conditions and up to 91 wt.% under pre-combustion conditions. This study demonstrated that refined parameter control within conventional carbonization-activation frameworks can significantly narrow pore-size distributions and stabilize nanoporous structures, providing a feasible route for large-scale production of high-performance nanoporous activated carbons. Additionally, Al-Ghurabi et al. utilized date-palm leaflets as precursors and employed response surface methodology (RSM) to systematically evaluate the individual and interactive effects of activation temperature, activation time, and KOH dosage on the pore structure, surface chemistry, and CO₂ adsorption performance of nanoporous activated carbons [249]. By preparing and analyzing 20 samples under different parameter combinations, the optimal synthesis conditions yielding the highest CO₂ adsorption capacity were identified, representing the best production parameters for this biomass source. This study successfully integrated process optimization with application performance enhancement. Moreover, the use of RSM offers strong generalizability, providing a versatile framework to rapidly determine optimal preparation conditions for CO₂-capture-oriented nanoporous activated carbons derived from various biomass precursors.

In addition, to achieve more stable nanoporous architectures in activated carbons, recent studies have focused on coupling precise activation techniques with supplementary processes that reinforce nanopores while simultaneously enhancing material performance. A representative example is the combined alkaline activation and iron-catalyzed graphitization strategy. The core concept involves first creating a high proportion of nanopores in the carbon matrix through alkaline activation, followed by introducing iron salts to catalyze graphitization. This partial transformation of the carbon framework into ordered graphitic layers substantially improves pore-wall stability, structural durability, and electrical conductivity without sacrificing porosity. Two main process routes are typically adopted: sequential and simultaneous activation-graphitization. In the sequential route, activation precedes graphitization. For instance, Souza et al. employed acai stone, an abundant agro-industrial residue, as a biomass precursor and used KOH chemical activation to construct an ultramicroporous structure. Subsequent Fe-catalyzed graphitization significantly improved pore-wall ordering and structural stability [251]. In contrast, the simultaneous route integrates activation and graphitization within a single step, where both alkaline and iron salts act concurrently. For example, Gunasekaran et al. used bamboo bagasse as a biomass precursor and employed potassium ferrocyanide together with KOH as activating agents, enabling in situ graphitization during pore formation [252]. Both approaches yield structurally robust nanoporous activated carbons with high surface areas (>1300 m²/g), narrow pore-size distributions (<2 nm), and excellent electrochemical and adsorption properties, extending their potential applications in energy storage and environmental remediation.

Recent progress in nanoporous biomass-derived activated carbons for CO₂ capture is characterized by fine-controlled activation, statistical optimization (e.g., RSM), and structural reinforcement through in situ graphitization, which together represent a new generation of preparation technologies. These advances enable more controllable pore structures, improved stability, and better scalability, offering a clearer pathway toward industrially viable CO₂ adsorbents.

5.1.3. Functionalized Activated Carbons

To further enhance CO₂ capture performance, functionalized activated carbons have been developed. This approach introduces surface functional groups and heteroatom doping to impart additional chemical reactivity and polar active sites, thereby strengthening both physical and chemical interactions with CO₂.

Oxygen and nitrogen functional groups are key for enhancing CO₂ adsorption in activated carbons, with oxygen increasing pore polarity for physical adsorption and nitrogen providing chemical sites for selective adsorption. These functional groups can be effectively introduced through an acid pre-treatment followed by precise activation. For example, using Arundo donax as a precursor, sulfuric acid pre-treatment removes inorganic impurities and promotes biomass dehydration and condensation, stabilizing the carbon framework while introducing abundant oxygen-containing groups such as carboxyl and hydroxyl [253]. Subsequent KOH activation generates highly uniform and size-controlled nanopores. The synergy between oxygen functional groups and narrow micropores enhances CO₂ affinity at low pressures, resulting in high adsorption capacity and selectivity [253]. Functionalization can also be achieved by leveraging the inherent chemical composition of the biomass. For instance, nitrogen-rich Acai fruit shells can be carbonized and then activated via wet impregnation or dry mixing with KOH or NaOH [109]. During carbonization and activation, nitrogen from the precursor is retained and converted into surface nitrogen functional groups, enhancing CO₂ affinity and synergistically improving selective adsorption. The resulting nanoporous activated carbons exhibit high specific surface area up to 2251 m²/g and a nitrogen content of 13.9 wt%, achieving excellent CO₂ adsorption capacity [109].

Self-doping and external doping of heteroatoms are common strategies to enhance the CO₂ adsorption performance of functionalized activated carbons, with nitrogen doping being the most extensively studied [189]. Unlike other heteroatoms that require external introduction, nitrogen is widely present in various natural biomass sources, such as proteins, peptides, and amino acids, and can be incorporated in situ during carbonization. By selecting biomass precursors with high nitrogen content and structural stability, the intrinsic nitrogen can be efficiently utilized to improve CO₂ adsorption. In addition to microalgae, nitrogen-rich agroforestry residues, such as pomelo peel, leaves, and poplar fluff, as well as animal by-products, including poultry feathers and leather waste, can serve as low-cost precursors for self-doped nitrogen activated carbons with excellent adsorption performance [103,254,255]. Furthermore, studies have shown that naturally formed oxygen functional groups during carbonization can synergistically interact with nitrogen doping to optimize surface chemistry [256,257]. Guo et al. prepared N/O co-doped activated carbons from corn silks via acid treatment, Na₂CO₃-assisted chemical activation, and high-temperature pyrolysis under N₂, producing porous carbons that maintain high porosity while exhibiting superior adsorption capacity and selectivity [256], as illustrated in Figure 5.

In addition, some studies have improved the hydrothermal carbonization strategy to enhance carbon yield and doping efficiency by using bio-oil rich in organic components as a medium instead of water [258]. Co-carbonization of algae with bio-oil enables in situ nitrogen self-doping while significantly increasing solid yield and the density of active sites. After subsequent activation, the resulting materials exhibit excellent CO₂ adsorption and electrochemical performance, demonstrating the dual advantages of efficient resource conversion and the preparation of functionalized carbon materials.

Recent advances in functionalized activated carbons combine heteroatom doping, self-doping, co-carbonization with bio-oil, and controlled nanopore formation. These innovative strategies enhance the pore uniformity, functional group density, CO₂ affinity, and solid yield of biomass-derived activated carbons.

5.2. Hierarchical Porous Carbon Materials

Hierarchical porous carbon materials are developed through the integration of precise design and regulation strategies to construct interconnected micro-, meso-, and macroporous structures. Compared with conventional activated carbon, hierarchical porous carbons offer greater tunability in pore structure. This tunability allows rational control over pore size distribution and connectivity to optimize adsorption performance. The micropores play a dominant role in CO₂ capture, while mesopores and macropores provide efficient mass-transfer channels, significantly improving gas diffusion and adsorption–desorption kinetics. This synergistic interaction among micro-, meso-, and macropores allows hierarchical porous carbons to outperform conventional activated carbons in balancing adsorption capacity and rate, making them particularly suitable for dynamic industrial CO₂ adsorption processes and a focal point of recent research.

The templating method is a key strategy for regulating the pore structure of carbon materials. In recent years, researchers have improved the functional performance of templated hierarchical porous carbons through heteroatom doping and precursor modification [259,260]. In addition, multiscale templating techniques have been developed [261,262,263]. By combining templates of different sizes, these methods enable precise control of macroporous and mesoporous structures.

When the templating method is used in combination with other approaches, the CO₂ adsorption and electrochemical properties of hierarchical porous carbons can be further enhanced. For example, Yue et al. utilized nitrogen-, oxygen-, and sulfur-rich Spirulina as a biomass precursor and calcium carbide slag (a CaC₂ byproduct) as a hard template to synthesize N/O/S self-doped three-dimensional hierarchical porous carbon via a one-step carbonization-activation process [259]. In this study, micropores were primarily formed through the self-pore-forming mechanism of the carbon source during carbonization, while the introduction of the hard template significantly increased the mesopore and macropore volumes. The naturally high heteroatom content of the biomass precursor contributed to a total doping amount of 12.58%. The synergistic effect of the hierarchical pore structure and heteroatom doping markedly enhanced CO₂ adsorption capacity. This study not only demonstrates the high-value utilization of waste resources but also provides a green and efficient pathway for the pore-structure regulation and heteroatom doping of hierarchical porous carbons. In another study, Sevilla et al. further optimized hierarchical porous carbon materials by integrating templating, heteroatom doping, and precursor selection strategies [260]. In this work, glucose and glucosamine mainly generated micropores and macropores, while soya flour and microalgae produced micro-, meso-, and macropores. During carbonization, potassium oxalate served as an activating agent that reacted with the carbon precursor, whereas calcium carbonate nanoparticles acted as hard templates to guide macropore formation. The morphology and size of the template particles were further regulated by in situ formed double carbonates, resulting in an open, macroporous foam-like structure. The mesopores were created both through redox reactions between carbon and potassium oxalate and through the reaction between carbon and released CO₂. Meanwhile, the inherent nitrogen content of microalgae enabled in situ nitrogen self-doping. Overall, this integrated strategy offers a sustainable and efficient route to high-performance hierarchical porous carbon materials.

The multiscale templating strategy achieves hierarchical pore structures by combining templates of different sizes, such as pairing a hard template with a soft template or combining two hard templates [264,265,266], thereby enabling precise control over the synergistic formation of macropores and mesopores. In addition, Esteves et al. innovatively proposed a combination of ice templating and hard templating to further enhance the controllability and uniformity of macropores and mesopores [267]. This approach integrates ice templates, hard templates (colloidal silica), and physical activation to produce hierarchical porous carbon materials, as illustrated in Figure 6. During rapid freezing, ice crystal growth pushes the biomass-derived carbon precursor and hard template particles into the interstitial spaces, forming an interconnected macropore network. Simultaneously, the instantaneous freezing process locks the particles and carbon source in place, effectively reducing aggregation. Subsequent carbonization and physical activation yield hierarchical structures with highly interconnected macropores and mesopores and tunable pore sizes. In this system, the hard template forms the mesopore network, whose pore size distribution can be controlled by adjusting the silica particle size or the carbon-to-template ratio, while physical activation regulates the micropore structure, achieving optimized connectivity among all three pore scales and a high specific surface area. This strategy not only retains the advantages of conventional dual-templating methods but also improves pore uniformity and tunability through physical means, providing a new pathway for high-performance hierarchical porous carbon materials in CO₂ adsorption and electrochemical applications.

In addition, some studies have successfully obtained hierarchical porous carbons by fully exploiting the intrinsic properties of biomass, without using external templates [255,268]. Liang et al. utilized the natural structural features of silkworm cocoons to directly carbonize the material, producing hierarchical porous carbon [268]. During carbonization, the original material composed of nanoscale carbon particles retained microporous structures, while the dense and loose aggregations of carbon particles formed mesopores and macropores, respectively. Additionally, the staggered arrangement of the carbon material generated an interconnected macropore network, resulting in a hierarchical structure of interconnected micro-, meso-, and macropores, as illustrated in Figure 7. Sun et al. used carp fish scales as a precursor and developed a method combining hydrothermal pre-mixing activation with single-step carbonization to produce hierarchical porous carbon [255]. During the hydrothermal stage, a small amount of KOH was added to allow activating ions to penetrate the biomass uniformly and form activation sites. Subsequent medium-temperature single-step carbonization achieved simultaneous carbonization and pore-structure formation. This process takes advantage of the natural layered organic-inorganic structure of fish scales, with hydrothermal pre-mixing and KOH activation substituting for an external template. During carbonization, protein pyrolysis forms the carbon skeleton and promotes in situ nitrogen doping, while gases released from KOH simultaneously etch the carbon framework, generating hierarchical micro- to mesoporous structures. By adjusting the carbonization temperature and KOH ratio, the method produced uniform hierarchical porous carbon materials with a high specific surface area and large pore volume. This approach features a simplified process, low activator usage, uniform structure, and in situ doping, demonstrating the feasibility and economic potential of efficiently producing high-performance hierarchical porous carbons from animal-derived biomass for CO₂ adsorption applications.

Recent advances in hierarchical porous carbons for CO₂ capture highlight innovative strategies in precise pore-structure design and multifunctionalization. Key technological breakthroughs include multiscale templating, heteroatom self-doping, and template-free approaches that leverage the intrinsic structures of biomass. These methods create tunable micro-, meso-, and macropore architectures with enhanced connectivity, uniform distribution, and simultaneous functionalization, leading to significantly improved CO₂ capture efficiency.

5.3. Other Innovative Carbon Materials

Recent research has increasingly focused on improving CO₂ capture performance through functional and morphological innovations in porous carbon materials. These materials can be broadly categorized into three types: functionally enhanced biomass-derived carbons, morphologically engineered biomass-derived carbons, and carbon materials integrating functional and morphological innovations.

5.3.1. Functionally Enhanced Biomass-Derived Carbons

In addition to the previously discussed approaches for improving CO₂ capture performance in biomass-derived carbons, such as the introduction of specific functional groups and heteroatom doping, recent research has explored the incorporation of metal components to enhance functional properties to these materials. Following this strategy, biomass-metal composite carbons have attracted increasing attention, including biomass-derived carbon/metal oxide (C-MO), carbon/metal (C-M), carbon/metal hydroxide (C-M(OH)_x), and carbon–metal–organic framework (C-MOF) composites. These materials not only maintain or enhance high CO₂ adsorption capacity but also endow the carbon matrix with multifunctionality, enabling simultaneous CO₂ capture and catalytic conversion, selective separation, or other additional functions. This further broadens the potential applications of biomass-derived carbons in environmental remediation and energy utilization.

Biomass-derived carbon/metal oxide composites have recently emerged as promising materials for CO₂ capture [269]. Metal oxides, such as MgO, CaO, and ZnO, can chemically adsorb CO₂ via their basic sites [270,271], while carbon materials provide high surface area and abundant porosity, offering physical adsorption sites and facilitating gas transport. The combination of these two components generates a significant synergistic effect. The carbon phase enhances the dispersion and stability of the metal oxide, while the metal oxide improves the chemical adsorption capacity of the carbon. The synergy between pore structure and surface chemistry endows biomass derived carbon/metal oxide composites with high adsorption capacity, excellent selectivity, and good cyclic stability, thereby substantially enhancing CO₂ capture efficiency [230].

It is noteworthy that the preparation pathways for biomass derived carbon/metal oxide composites for CO₂ capture are diverse. These materials can be constructed either by using metal oxides as the primary component with the incorporation of biomass-derived carbon to enhance structure and performance, or by using biomass-derived carbon as the primary matrix onto which metal oxides are loaded. In the approach where metal oxides serve as the main component, Creamer et al. proposed a strategy for the biomass-assisted synthesis of nanoscale MgO to achieve efficient CO₂ capture [272]. The core idea is that the introduction of biomass carbon enables the in situ formation and stable dispersion of MgO nanoparticles during the thermal decomposition of MgCl₂·xH₂O, resulting in a biomass-derived carbon/metal oxide composite with synergistic adsorption properties. In this study, sugarcane bagasse was used as the biomass carbon source, mixed with anhydrous MgCl₂ solution, dried, and subjected to stepwise pyrolysis under an inert atmosphere. A dehydration step at 200 °C facilitated the conversion of MgCl₂·xH₂O to the intermediate Mg(OH)Cl, followed by thermal treatment at 600 °C to achieve complete decomposition and formation of active MgO nanoparticles, while the biomass underwent pyrolysis to form a carbon framework, yielding an in situ carbon-supported MgO composite. The resulting composite exhibited excellent CO₂ adsorption performance at low temperatures, with capture capacities significantly exceeding those of the control sample without biomass. This demonstrates that biomass-derived carbon not only serves as a physical support but also regulates MgO formation and dispersion at the nanoscale, enhancing both adsorption reactivity and material stability.

Strategies using biomass-derived carbon as the primary matrix with metal oxide loading have also shown excellent CO₂ capture performance. Nowrouzi et al. developed an activated biomass derived carbon/metal oxide composite using Persian ironwood biomass for efficient CO₂ capture [269]. The biomass was first chemically activated with H₃PO₄ and pyrolyzed at 500 °C to produce highly porous activated carbon with abundant micropores and high surface area, providing a basis for physical CO₂ adsorption. Single or binary metal oxides, including Al₂O₃, MgO, CuO, NiO, and their combinations, were then loaded onto the carbon and thermally treated, introducing basic sites on the carbon surface to enable chemical adsorption. Metal loading could be precisely controlled by adjusting the type, ratio, and thermal treatment of the metal precursors. Compared to single metal oxides, binary metal oxide systems exhibited superior performance: synergistic interactions between the two metal oxides provided complementary basic sites; the presence of two metals helped inhibit particle sintering, ensuring more uniform dispersion on the carbon surface and increasing the number of active sites; meanwhile, microstructural adjustments induced by gas release and volume expansion during thermal treatment optimized pore structure and mass transport, further enhancing CO₂ adsorption kinetics. Similarly, another study used walnut shells as the carbon source, chemically activated with H₃PO₄ to produce activated carbon, and subsequently loaded MgO or MgO-Al₂O₃ to form composites [273]. By adjusting the metal oxide loading ratio and thermal treatment conditions, MgO nanoparticles or MgO-Al₂O₃ were uniformly dispersed on the carbon pores, and dynamic CO₂ adsorption tests were used to optimize synthesis parameters. The activated carbon/MgO-Al₂O₃ composite exhibited excellent CO₂ capture performance at low temperatures over single metal oxide-loaded materials. Overall, these studies show that metal oxide-loaded biomass-derived carbon enables synergistic effects and highlights the potential of various biomass sources and metal combinations for optimizing CO₂ capture.

Studies have shown that biomass carbon sources can be combined with soluble metal salts under specific conditions to produce biomass derived carbon/metal [274] or biomass derived carbon/metal hydroxide composites [275]. In these materials, the metal or hydroxide can influence the pore structure during pyrolysis or activation through particle growth, reduction, or volatilization, subtly modifying the micropore distribution. This structural modulation, together with the chemical activity of the metal/hydroxide sites, enhances both physical and chemical adsorption, resulting in excellent CO₂ capture performance. Ma et al. proposed an in situ activation strategy for preparing porous carbon from tobacco stalks, where hydrothermal treatment enables coordination between the C-OOH and C-OH functional groups in the biomass and Zn²⁺ ions, successfully forming Zn-hydrochars [274]. The introduction of Zn²⁺ not only enhanced the thermal stability of the hydrochar but also, at intermediate to high temperatures, formed ZnO/carbon composites and, at higher temperatures, generated metallic Zn via carbothermal reduction and volatilization. This process synergistically modulated the micro- and ultramicroporous structure of the carbon, optimizing pore size distribution and active site placement, thereby significantly enhancing CO₂ capture capacity. Experimental results showed CO₂ uptake of up to 209 mg/g at 0 °C and 146 mg/g at 25 °C under 1 bar, with CO₂/N₂ selectivity ranging from 16.4 to 26.6, while also exhibiting excellent adsorption of low-concentration benzene. Similarly, Creamer et al. prepared C-M(OH)_x composites using cottonwood as the biomass carbon source via an in situ composite strategy, aiming to develop efficient and low-cost CO₂ adsorbents [275]. Different concentrations of metal salts (Al³⁺, Fe³⁺, Mg²⁺) were dissolved in water to allow thorough adsorption onto the biomass, followed by high-temperature pyrolysis under nitrogen to convert the biomass into biochar and generate metal hydroxide nanoparticles uniformly distributed on the carbon surface. This composite structure significantly enhanced CO₂ adsorption, with AlOOH-biochar achieving a maximum uptake of 71 mg/g, while enabling efficient desorption at low temperatures for cost-effective cyclic use. By directly combining biomass carbon with metal hydroxides, this approach achieves synergistic optimization of material structure and surface chemistry, providing a feasible route for efficient, recyclable CO₂ capture with potential for scalable production.

Biomass-derived carbon–MOF composites represent a promising research direction in the field of CO₂ capture [276]. MOFs can form highly controllable porous structures and abundant chemical functional sites by tuning the type and arrangement of metal centers and organic ligands. Their channels provide a large surface area for physical adsorption, while metal sites or functional groups such as amines and carboxyls can selectively adsorb CO₂ via acid-base interactions, hydrogen bonding, or coordination effects. Combined with molecular sieving and the quadrupole moment of CO₂, these materials achieve high adsorption capacity and selectivity [26]. Integrating MOFs with biomass-derived carbon further exploits the advantages of both components: the carbon matrix offers high surface area, rich porosity, good mechanical strength, and macroscopic support, while the MOF provides tunable micropores and functionalized sites. This combination maintains excellent CO₂ adsorption performance while improving particle morphology and engineering operability, significantly enhancing practical applicability in real adsorption systems. Choudhary et al. comprehensively reviewed cellulose, a biomass carbon source, in cellulose/MOF composites, covering preparation strategies, cellulose derivative types, MOF species and synthesis methods, and key material properties including porosity, chemical functionality, mechanical stability, and biodegradability [277]. The review also covers advances in applications including water treatment, gas adsorption, energy storage, biomedicine, and other emerging fields, providing guidance for the design of functionally innovative biomass-derived carbon–MOF composites. Yue et al. used rice straw as a raw material to extract plant fibers via alkaline treatment and prepare nitrogen-doped porous carbon, providing a reliable basis for efficient CO₂ adsorption [278]. On this basis, Co-MOF-74 was innovatively introduced, and a MOF-assisted granulation technique was employed to convert the porous carbon into carbon microspheres. This innovation served a dual purpose: the MOF-modulated pore structure enhanced CO₂ adsorption capacity up to 3.87 mmol·g⁻¹ at 1 bar, 25 °C, while granulation significantly improved mechanical strength with particle strength increased more than fivefold, effectively addressing the common issues of aggregation and reactor clogging associated with conventional powdered porous carbon. This approach balances adsorption performance with material processability, providing a new technical route for the practical application of biomass-derived carbon–MOF composites in carbon capture.

5.3.2. Morphologically Engineered Biomass-Derived Carbon Materials

Enhancing the CO₂ capture performance of biomass-derived carbon materials through morphological innovations is another research avenue with significant potential. Novel morphologies, such as flexible aerogels, layered carbons, and carbon fibers, construct high surface area and efficient mass-transfer channels, not only markedly improving adsorption kinetics but also facilitating the large-scale integration and modular application of these materials.

Flexible carbon aerogels, as morphology-innovative biomass-derived carbon materials, exhibit remarkable advantages in CO₂ capture due to their three-dimensional network structure and hierarchical porosity obtained through gelation-based synthesis. Zhuo et al. used cotton linter to develop a cellulose-based carbon aerogel with a hierarchical pore structure [279], providing a novel morphology-engineering strategy for CO₂ capture. In this study, cellulose was first self-assembled into a 3D network aerogel via a Dis-gel and freeze-drying process [280], providing a structural framework for subsequent pore regulation. A one-step carbonization-activation treatment under a CO₂ atmosphere then produced a hierarchical porous structure with interconnected macropores, mesopores, and micropores, along with a high specific surface area. Compared with traditional solid activators such as NaOH or KOH, CO₂ activation eliminates the need for complex post-treatment and reduces processing costs. The resulting carbon aerogel exhibited remarkable CO₂ adsorption capacity, high specific surface area, and excellent electrochemical performance, demonstrating the advantages of flexible, hierarchically porous aerogels in mass transfer, adsorption kinetics, and cyclic stability. By combining the renewability of cellulose, the 3D porous network of aerogels, and the eco-friendly CO₂ activation route, this work provides a sustainable and high-performance pathway for biomass-derived carbons in CO₂ capture and energy storage applications. Building on this foundation, a study further optimized cellulose-based carbon aerogels through heteroatom co-doping, synthesizing a novel N, B co-doped porous biochar (NBCPB) [281]. Using cotton linter cellulose, the researchers first prepared a cellulose aerogel with in situ N and B co-doping via a modified alkali-urea method. The resulting aerogel possessed a three-dimensional porous network, which was subsequently carbonized at 400 °C under N₂ to form a precursor and then activated with potassium citrate. Serving as both a green activator and a salt template, potassium citrate enabled controlled pore development and hierarchical porosity while avoiding the corrosion and waste issues associated with traditional activators. By adjusting the activation temperature (550–700 °C) and the mass ratio of activator to precursor, a series of NBCPB materials were obtained. The optimized sample exhibited a high surface area of 891 m²·g⁻¹, a large micropore volume of 0.40 cm³·g⁻¹, and an excellent CO₂ adsorption capacity of 4.19 mmol·g⁻¹ at 100 kPa and 25 °C, along with superior CO₂/N₂ selectivity (>97.5%), cyclic stability, and outstanding electrochemical performance in supercapacitors. This study not only enhanced the functional versatility of flexible, hierarchically porous carbon aerogels but also demonstrated a feasible route to simultaneously achieve structural and chemical optimization for dual applications in CO₂ capture and energy storage.

Layered carbon materials derived from biomass have demonstrated significant advantages in CO₂ capture owing to their unique sheet-stacked architecture and locally ordered carbon arrangements [282]. The planar alignment of carbon atoms forms graphitic-like layers with varying degrees of graphitization, where the interlayer spacing can be tailored through graphitization control or heteroatom doping [283,284,285,286,287,288]. Such structural tunability promotes gas diffusion and adsorption between layers, while simultaneously enhancing electronic conductivity, thermal stability, and structural integrity over multiple adsorption–desorption cycles. These combined effects lead to efficient CO₂ uptake and excellent cyclic stability, offering new design insights for developing high-performance biomass-derived carbon sorbents. For example, Singh et al. developed a porous carbon with nanosheet morphology using waste pistachio shells as a carbon source, employing an integrated activation-graphitization process [289]. Iron acetate acted as a graphitization promoter, while potassium acetate generated a porous structure during high-temperature treatment. The resulting layered carbon exhibited high electronic conductivity, excellent thermal stability, and abundant micro/mesopores, facilitating CO₂ diffusion and adsorption between layers. Consequently, the material achieved a remarkable CO₂ uptake of 16.7 mmol·g⁻¹ at 0 °C and 30 bar. Moreover, when applied as a lithium-ion battery anode, it showed high specific capacity, highlighting the multifunctional potential of biomass-derived carbon materials. Some studies further explored the potential of using various biomass precursors and multistep thermal treatment strategies for the development of layered carbon materials [290]. Arunpandian et al. developed two types of layered carbon materials: graphitized carbon with multilayer graphene structures (DG) and nitrogen-doped graphitized carbon (NG), from dead leaf biomass through a multi-step thermal treatment strategy [290]. The process began with pre-pyrolysis at 400 °C, followed by either hydrothermal impregnation in deionized water or solvothermal impregnation in ammonia water, both containing KOH and KMnO₄. The presence of ammonia in the solvothermal system introduced nitrogen species into the carbon framework, leading to the formation of nitrogen-doped graphitized carbon, whereas the hydrothermal route yielded non-doped graphitized carbon. In both routes, KMnO₄ acted as a transition metal catalyst to promote graphitization and partial graphene formation, while KOH served as a chemical activator to generate hierarchical porosity. Controlled stepwise pyrolysis from 400 °C to 1000 °C facilitated simultaneous carbonization, activation, graphitization, and graphenization, resulting in layered, highly graphitized structures. The resulting DG and NG materials exhibited high specific surface areas of 1400 m²·g⁻¹ and 947 m²·g⁻¹, respectively, along with excellent CO₂ adsorption capacities of 50 mg·g⁻¹ for DG and 70 mg·g⁻¹ for NG. They also demonstrated outstanding electrochemical performance, with specific capacitances of 184 F·g⁻¹ and 206 F·g⁻¹, respectively. These results highlight a sustainable and high-performance strategy for fabricating biomass-derived layered carbon materials applicable to environmental remediation, gas adsorption, and energy storage.

Biomass-derived carbon fibers represent another important class of structure-oriented carbon materials, owing to their excellent structural stability and controllable morphology. They exhibit diverse morphologies, including platelet-like, herringbone, and tubular structures, as shown in Figure 8, which not only demonstrate their structural versatility but also enhance CO₂ capture by improving surface area, mass transfer efficiency, and accessibility of adsorption sites. These fibers are commonly derived from biomass precursors such as cellulose, lignin, or natural polysaccharides. Electrospinning is a widely used technique for producing carbon fibers and nanofibers [291,292,293,294]. However, it suffers from complex procedures, low yield, and limited scalability. Recently, researchers have explored alternative strategies that exploit the intrinsic fiber structure of biomass to fabricate carbon fibers [295,296,297,298]. Gelfond et al. demonstrated that biomass carbon fibers derived from bamboo cellulose can achieve efficient carbon fixation and superior electrical conductivity [297]. In this method, cellulose fibers are first pretreated with formic acid to obtain macroscopic fibers, which are then stabilized and carbonized, followed by rapid graphitization at around 2000 °C using Joule heating. This process significantly enhances the degree of graphitization and the electrical performance of the fibers. The resulting carbon fibers exhibit highly oriented nanostructures and excellent conductivity, offering a sustainable material with both carbon capture functionality and high-performance application potential. Additionally, the lignin byproduct can be further converted into electrode materials or bio-based polymers, enabling diversified utilization of biomass resources. Further research has focused on introducing hierarchical porosity into carbon fibers, yielding biomass porous carbon fibers (BPCFs) with enhanced specific surface area and pore connectivity to improve CO₂ adsorption and diffusion. For example, natural spider silk has been used as a carbon source to prepare nanoporous carbon fibers with high surface area and functionalized surfaces through KOH chemical activation [298]. In this approach, spider silk is first washed, dried, and carbonized at 800 °C under nitrogen to form preliminary carbon fibers. Subsequent KOH activation significantly increases surface area and pore volume while introducing oxygen-containing functional groups on the fiber surface, enhancing adsorption of CO₂, CH₄, and H₂. This strategy fully exploits the highly oriented protein fiber structure and intrinsic heteroatoms of spider silk, enabling the activated fibers to retain their morphology while developing abundant micro- and mesopores that create fast mass transfer pathways. The resulting nanoporous carbon fibers exhibit CO₂ adsorption capacities of 23.6 mmol·g⁻¹ at 0 °C and 25 bar, and 15.4 mmol·g⁻¹ at 25 °C and 25 bar, along with excellent CH₄ and H₂ storage capabilities. Moreover, they maintain nearly full adsorption capacity over multiple adsorption–desorption cycles, demonstrating outstanding regenerability.

5.3.3. Carbon Materials Integrating Functional and Morphological Innovations

Building on the optimization of biomass-derived carbon materials for CO₂ capture through either function or morphology design, composite carbon materials that integrate both functionality and morphology can fully exploit synergistic effects to achieve superior performance.

Constructing biomass-derived carbon–MOF composites into favorable structural morphologies, which can simultaneously enhance adsorption capacity, mass transfer efficiency, and multifunctionality, has shown promising progress. Huang et al. reported the design of biomass-derived carbon–MOF composites in the form of aerogels to achieve synergistic optimization of both functionality and morphology [300]. Renewable biomass resources, cellulose and chitosan, were used to construct a three-dimensional aerogel network that provides stable support for the embedding of a bimetallic MOF (Mg/Co-MOF-74). Cellulose- and chitosan-based aerogels (CSA) are prepared via directional freeze-drying, producing a three-dimensional, highly porous network with abundant oxygen- and nitrogen-containing functional groups. These functional groups act as pre-binding sites for metal ions, enabling uniform incorporation of Co²⁺ and Mg²⁺ prior to MOF growth. The bimetallic Mg/Co-MOF-74 is then grown in situ within the aerogel matrix using a mild one-pot solvothermal method, ensuring intimate contact between the MOF and the carbonaceous scaffold. This approach combines the hierarchical porosity of the aerogel with the microporous structure and chemically active sites of the MOF, resulting in a composite with optimized mass transfer, high surface area, and enhanced CO₂ adsorption capacity. Additionally, the procedure allows tunable MOF loading by repeating the in situ growth steps, providing flexibility in controlling functional density without compromising the aerogel’s structural integrity.

Some studies have exploited the intrinsic structural features of biomass fibers to construct nanofibrous biomass-derived carbon–MOF composites [301,302]. Shezad et al. grew Cu-MOF nanocrystals in situ on wood-derived cellulose nanofibers (WCNFs) or bacterial cellulose nanofiber lamellas (BCNFLs), exploiting their natural structural characteristics [302]. WCNFs possess hierarchical fibrous structures derived from wood, while BCNFLs form highly oriented, ultrafine nanofiber networks through microbial fermentation. These features provide robust, high-surface-area, and interconnected scaffolds that support uniform MOF growth and create efficient mass transfer pathways, significantly enhancing adsorption kinetics and diffusion. The anchored MOF nanoparticles offer abundant micropores and highly active adsorption sites. The resulting composites exhibited CO₂ adsorption capacities of approximately 1.00 mmol/g for MOFs/BCNFLs and 1.19 mmol/g for MOFs/WCNFs at 1 bar, maintaining stability over multiple cycles. This study highlights the potential of nanofibrous biomass-derived-MOF materials to achieve synergistic functional and structural optimization for CO₂ capture.

6. Challenges and Future Directions

With the growing global concern over CO₂ emissions, biomass-derived porous carbon materials have attracted considerable attention in the field of CO₂ capture. In recent years, continuous advancements in the preparation techniques of biomass-based porous carbons have led to significant improvements in their CO₂ adsorption performance. Some biomass-derived porous carbon materials have reached laboratory-scale maturity in terms of material synthesis and CO₂ adsorption testing. However, reports of pilot- or industrial-scale deployment are very limited, and large-scale implementation remains largely unexplored [303]. Several challenges remain for their practical application, including the diversity and effective utilization of biomass feedstocks, waste management during synthesis, the need for further enhancement of material performance, and concerns over production and implementation costs. These factors jointly contribute to skepticism regarding the large-scale production and industrial feasibility of such materials [304].

6.1. Technical Challenges and Prospects

Agricultural and forestry residues remain the most commonly used biomass feedstocks for the preparation of porous carbon materials. However, their supply may be affected by seasonal and regional variations, while the costs associated with collection and transportation may limit large-scale applications. Future research should focus on diversifying feedstock sources, such as fully utilizing abundantly available and widely distributed municipal solid waste, as well as fast-growing, environmentally adaptable algae, to enhance the sustainability and accessibility of biomass resources. Differences in carbon content, ash composition, and impurity levels among various feedstocks directly influence the efficiency of carbonization, the pore structure of the resulting materials, and their CO₂ adsorption performance. Therefore, pretreatment, carbonization and activation processes should be optimized based on the specific characteristics of each feedstock. For instance, municipal solid waste can be improved through sorting and impurity removal to increase carbon content and reduce contamination, while algae can be cultivated on a large scale using wastewater or industrial CO₂ to promote biomass accumulation and accelerate its valorization as a carbon source. Moreover, the combined effects of economic feasibility, environmental sustainability, and feedstock characteristics on the final material performance should also be considered to achieve efficient and diversified utilization of biomass resources.

The high production cost and waste treatment issues during the preparation of carbon materials remain major obstacles to their large-scale application. Pyrolysis, as the most mature and commonly used carbonization technique, often requires high energy input, resulting in elevated costs that reduce the overall economic profitability of the resulting carbon products. In contrast, microwave-assisted pyrolysis can achieve carbonization within a shorter duration and at lower energy consumption. Studies have demonstrated that this method not only improves product yield but also enhances material quality, making it a promising low-energy and cost-effective alternative to conventional pyrolysis [305,306,307]. Future research directions should emphasize a systematic understanding of the suitability of various biomass feedstocks and the optimization of critical process parameters to validate the scalability and industrial applicability of microwave-assisted pyrolysis.

During the activation stage, the use of acidic or alkaline activating agents often leads to equipment corrosion, waste liquid treatment challenges, and environmental safety concerns. Alternatively, salt-based activating agents such as ZnCl₂ and Na₂CO₃ can mitigate equipment corrosion and simplify waste treatment, and are therefore considered relatively mild and environmentally friendly activation methods. Nevertheless, the activation efficiency of salt-based methods is generally lower than that of acid and alkaline activation. To enhance the performance of salt activation and make it a viable substitute for conventional methods, future research should focus on optimizing salt type and dosage, incorporating auxiliary activating agents or additives, improving heating strategies, and precisely controlling activation temperature and duration. These improvements could enhance the specific surface area, pore volume, and adsorption capacity of the resulting materials, while reducing equipment degradation and waste treatment burdens, ultimately promoting a more efficient and sustainable approach to carbon material production.

Templating methods are among the most effective approaches for precisely regulating the pore structure of carbon materials. However, commonly used techniques, such as hard templating, soft templating, and dual templating, often involve expensive templates, complex and time-consuming removal steps, and potential environmental pollution, all of which significantly limit their economic feasibility and environmental sustainability for large-scale production. To address these challenges, increasing attention has been directed toward utilizing the intrinsic structural features of biomass to obtain hierarchical porous carbons under template-free conditions. In particular, biopolymer-based non-templating strategies represent a promising research direction, focusing on the development of sustainable, template-free synthesis routes derived from renewable biomass precursors to construct tunable three-dimensional hierarchical pore architectures [308]. This approach not only enables the synergistic optimization of surface area, pore network, and functional group distribution, but also promotes the sustainable development of carbon materials in terms of environmental compatibility and cost-effectiveness.

In terms of further enhancing the performance of carbon materials, future research could focus on developing composite materials that integrate both physical adsorption and chemical absorption. This can be achieved by introducing functional groups, such as amines and quaternary ammonium salts, onto the surface of biomass-derived porous carbons [309]. These functionalities enable the chemical conversion of adsorbed CO₂ into stable carbonates or bicarbonates, thereby realizing a synergistic adsorption-fixation effect. Such material designs should balance improvements in adsorption–desorption kinetics with the maintenance of high cyclic stability. This strategy not only has the potential to enhance CO₂ capture efficiency at low concentrations but also provides a controllable platform for subsequent CO₂ conversion into fuels or chemicals, expanding the application of biomass-derived porous carbons in sustainable carbon utilization, environmental remediation, and clean energy technologies. Moreover, algae represent a renewable biomass resource with multifaceted functions in CO₂ capture. In addition to being directly converted into carbon-based materials for CO₂ adsorption, algae can be integrated with other bio-based porous materials to construct innovative carbon capture systems, thereby expanding their potential in carbon recycling [72]. For instance, the combination of chemically modified biomass cellulose aerogels with immobilized algal systems has demonstrated efficient CO₂ capture and biotransformation [310], highlighting a promising direction for the synergistic application of algal biomass and bio-based porous materials in carbon capture and circular carbon utilization.

6.2. Industrial and Economic Barriers to Scale-Up and Techno-Economic Assessment

From an industrial perspective, the production cost and waste-treatment issues associated with biomass-derived porous carbons remain major obstacles to large-scale application. Current studies evaluating production costs across different feedstocks and fabrication techniques are still limited, yet such analyses are essential for assessing the feasibility of scale-up. Key factors influencing the final cost per unit mass include biomass processing, energy consumption, reagent usage, labor, equipment depreciation and maintenance, waste treatment and environmental compliance, transportation and logistics of both raw materials and final products, material yield and efficiency, and the sensitivity of these components to energy-source and price fluctuations.

Capital expenditure, operating expenditure, and scale effects from laboratory to industrial production further shape economic viability. At present, the lack of detailed techno-economic assessments (TEAs) incorporating these dimensions creates substantial uncertainty regarding the true cost of biomass-derived porous carbons and their competitiveness relative to conventional adsorbents [311,312]. Such uncertainty limits the ability to evaluate their practical viability and to benchmark them against alternative CO₂ capture technologies. Addressing these gaps through systematic techno-economic analysis will therefore be essential for guiding process design, optimization, and scale-up, and for determining the realistic industrial potential of biomass-derived porous carbons for CO₂ capture.

A comprehensive TEA is hence essential for determining whether biomass-derived porous carbons can transition from laboratory demonstrations to industrial CO₂ capture applications. Although many studies highlight their promising adsorption performance, systematic evaluations of production costs, energy requirements, scalability, and long-term operational stability remain limited.

From an economic perspective, carbonization and activation routes differ markedly in energy demand, capital cost, and scalability, leading to distinct cost structures. Feedstock choice further introduces substantial variability due to differences in availability, pretreatment needs, logistics, and conversion efficiency. However, these upstream and process-related cost drivers are still insufficiently quantified in most existing studies. Integrating such parameters into comprehensive TEA frameworks is therefore essential for a realistic assessment of the cost–benefit potential of biomass-derived porous carbons. Sustainability-related advantages, such as waste valorization, carbon neutrality, and long-term reductions in environmental burden, represent not only environmental benefits but direct economic value that is often omitted from current TEA studies [313,314]. While these gains are frequently described qualitatively in the materials literature, they can in fact be rigorously monetized. For example, reductions in CO₂ emissions, landfill loads, or wastewater discharge generate measurable financial returns under existing carbon-pricing and regulatory incentive structures. Incorporating these benefit streams fundamentally changes the cost–benefit profile of biomass-derived porous carbons, especially when compared with sorbents that incur high regeneration energy penalties or produce secondary waste.

This insight is reinforced by established economic valuation frameworks. The social cost of carbon (SCC) provides a standardized method for assigning monetary value to avoided CO₂ emissions, with contemporary estimates [314] widely used in policy and industrial decision-making, as reflected in regulatory applications by the U.S. Environmental Protection Agency. Likewise, marginal abatement cost (MAC) curves, such as those developed by McKinsey [315], offer a practical measure of the economic benefit associated with reducing one metric ton of CO₂ across competing abatement pathways. Together, SCC and MAC approaches enable sustainability benefits to be expressed in quantitative economic terms rather than treated as qualitative externalities, thereby aligning environmental performance with industrial decision metrics.

These economic valuation tools also complement emerging engineering frameworks that integrate TEA with life-cycle analysis (LCA). Recent studies highlight the importance of jointly considering material performance, energy use, emissions intensity, and end-of-life impacts to achieve a full-system appraisal of CO₂ capture materials [316]. Leveraging such interdisciplinary methodologies enables TEA models to move beyond cost minimization toward ecological-economic optimization, providing a more accurate reflection of the long-run industrial competitiveness of biomass-derived porous carbons.

While sustainability advantages reshape the long-run economic profile of biomass-derived carbons, an equally important yet frequently overlooked dimension concerns the economic value generated by technological improvements themselves. Most materials-focused studies emphasize adsorption capacity, regeneration efficiency, or structural stability, but rarely quantify how the performance gains translate into economic benefits, such as reduced energy demand, lower replacement frequency, or minimized waste generation [317,318]. Incorporating such benefit-side contributions is essential for accurately evaluating the overall techno-economic viability of biomass-derived porous carbons relative to conventional alternatives.

Importantly, the same economic valuation principles used to monetize sustainability benefits, including the SCC, MAC frameworks, and market-based carbon pricing, apply directly to performance-driven improvements. Enhancements in adsorption efficiency or regeneration energy reduction, for example, effectively lower the marginal cost of CO₂ capture and thereby generate measurable economic returns when evaluated through SCC or MAC metrics.

Market evidence reinforces this point. Empirical analyses of carbon-trading systems, such as the EU Emissions Trading System, demonstrate that firms respond to carbon prices by investing in more efficient abatement technologies [319]. This implies that materials offering higher adsorption performance and longer durability possess not only engineering value but also economic advantages under realistic policy and market conditions.

Taken together, monetizing the economic value of performance improvements allows TEA to capture both cost reductions and benefit enhancements, enabling a more decision-relevant evaluation of the competitiveness of biomass-derived porous carbons. A comprehensive economic framework should therefore jointly consider direct process costs, performance-derived benefits, and long-term sustainability effects.

Horizontally, TEA should integrate both sides of the economic ledger: direct expenditures (energy input, capital investment, pretreatment, activation, regeneration) and measurable benefits arising from improved efficiency, lower emissions, reduced waste generation, extended material lifetime, and avoided reinvestment. Vertically, the framework must account for life-cycle effects: long-term stability, reduced environmental liabilities, carbon-abatement value, and the durability-driven decline in replacement frequency. Such temporal considerations are essential for capturing the cumulative economic advantages of sustainable production routes, many of which only emerge when evaluated over multi-year operational horizons.

Quantifying these benefit pathways has been well-established in environmental economics through approaches such as the social cost of carbon, marginal abatement cost curves, carbon market pricing, and ecological valuation of emission reduction. Integrating these established methods into TEA enables a more accurate determination of net value creation, moving beyond a narrow cost-minimization perspective toward a full ecological-economic appraisal of biomass-derived CO₂ capture materials.

A unified TEA model should therefore integrate material performance metrics with energy consumption, capital investment, feedstock logistics, regeneration cost, and environmental credits. Such models should also support direct comparison with existing CO₂ capture technologies, including amine scrubbing, activated carbon systems, and advanced solid sorbents, to evaluate their relative economic attractiveness, consistent with established benchmarking frameworks [311]. System-level evaluations of this kind can identify economically limiting steps, highlight process components in need of optimization, and support the design of industrial pathways that capitalize on both the environmental and techno-economic strengths of biomass-derived porous carbons. Such an integrated economic system enables transparent comparison across CO₂ capture technologies and supports evidence-based decisions for industrial deployment.

7. Conclusions

Biomass-derived porous carbon materials capture CO₂ primarily through adsorption, which can occur via physisorption, chemisorption, or a synergistic combination of both. Physisorption offers fast, reversible adsorption with low energy consumption, while chemisorption provides higher selectivity and stronger binding but often requires more energy for regeneration. By rationally designing pore structures and surface functionalities, these materials can exploit the synergistic mechanism to achieve high adsorption capacity, selectivity, and stability, making them highly effective for CO₂ capture applications.

Agricultural and forestry residues are currently the most commonly used feedstocks for the production of biomass-derived porous carbon materials for CO₂ capture. Municipal solid wastes, algae, and animal-derived biomass provide additional sustainable feedstocks, with municipal solid wastes being widely available and low-cost, algae offering high carbon content and rapid growth, and animal biomass naturally containing heteroatoms, enabling the synthesis of functionalized porous carbons with tailored adsorption properties.

Pyrolysis and hydrothermal carbonization are two commonly used methods for converting biomass into carbon materials. Pyrolysis is typically performed at high temperatures under dry, oxygen-limited conditions, making it suitable for low-moisture biomass and producing carbon materials with well-developed aromatic and porous structures. In contrast, hydrothermal carbonization operates at relatively lower temperatures in a water medium, allowing the direct processing of high-moisture biomass, yielding hydrochar with abundant surface functional groups and moderate porosity.

Activation, heteroatom doping, and templating are three representative performance tuning strategies for biomass-derived porous carbon materials for CO₂ capture. Activation enhances surface area and porosity, heteroatom doping introduces active sites to improve chemical affinity, and templating enables precise control of pore architecture. Their synergistic integration allows the simultaneous optimization of surface chemistry and hierarchical structure, leading to superior CO₂ adsorption performance.

Activated carbons, including conventional, nanoporous, and functionalized types, have demonstrated significant potential for CO₂ capture due to their high surface area, tunable porosity, and the possibility of surface chemical modification. Advances such as the use of diverse biomass precursors, precise pore-size control, heteroatom doping, and innovative activation methods have enabled the preparation of carbons with enhanced adsorption capacity, selectivity, and stability.

Hierarchical porous carbons, with integrated micro-, meso-, and macroporous structures, offer enhanced tunability in pore architecture and significant potential for CO₂ capture. Recent advances have further improved their functional performance by combining templating methods with heteroatom doping and precursor modification, employing multiscale templating techniques, or exploiting the intrinsic structures of biomass without external templates.

Apart from activated carbons and hierarchical porous carbons, other innovative biomass-derived carbon materials for CO₂ capture can be broadly classified into functionally enhanced, morphologically engineered, and functionally–morphologically integrated carbons. Functionally enhanced biomass-derived carbons improve CO₂ adsorption by incorporating metal components. Examples include biomass-derived carbon/metal oxide, carbon/metal, carbon/metal hydroxide, and carbon–MOF composites, all demonstrating enhanced adsorption functionality. Morphologically engineered biomass carbons feature novel architectures such as flexible aerogels, layered carbons, and carbon fibers, which provide high surface areas and efficient mass-transfer channels, significantly improving adsorption kinetics and facilitating large-scale integration. Composite carbon materials that integrate both functional and morphological innovations exploit synergistic effects to achieve superior performance. In particular, constructing biomass-derived carbon–MOF composites with favorable structural morphologies have shown promising progress.

Despite significant progress in developing biomass-derived porous carbons for CO₂ capture, challenges remain in achieving scalable, cost-effective, and environmentally sustainable synthesis suitable for large-scale applications. Future research should therefore emphasize the development of low-energy carbonization processes, sustainable activation strategies, and template-free synthesis routes, while further optimizing the structural and functional properties of the resulting materials. Meanwhile, integrated techno-economic assessment is essential to guide scale-up and industrial deployment. By integrating TEA with material performance and sustainability metrics, the industrial feasibility of biomass-derived porous carbon materials for CO₂ capture can be evaluated in a more systematic and quantitative manner.