Research on Direct Air Capture: A Review

Abstract

Direct Air Capture (DAC) technology plays a crucial role in reducing atmospheric CO₂, but large-scale deployment faces challenges such as high energy consumption, operational costs, and slow material development. This study provides a comprehensive review of DAC principles, including chemical and solid adsorption methods, with a focus on emerging technologies like Metal–Organic Frameworks (MOFs) and graphene aerogels. MOFs have achieved adsorption capacities up to 1.5 mmol/g, while modified graphene aerogels reach 1.3 mmol/g. Other advancing approaches include DAC with Methanation (DACM), variable-humidity adsorption, photo-induced swing adsorption, and biosorption. The study also examines global industrialization trends, noting a significant rise in DAC projects since 2020, particularly in the U.S., China, and Europe. The integration of DAC with renewable energy sources, such as photovoltaic/electrochemical regeneration, offers significant cost-reduction potential and can cut reliance on conventional heat by 30%. This study focuses on the integration of Artificial Intelligence (AI) for accelerating material design and system optimization. AI and Machine Learning (ML) are accelerating DAC R&D: high-throughput screening shortens material design cycles by 60%, while AI-driven control systems optimize temperature, humidity, and adsorption dynamics in real time, improving CO₂ capture efficiency by 15–20%. The study emphasizes DAC’s future role in achieving carbon neutrality through enhanced material efficiency, integration with renewable energy, and expanded CO₂ utilization pathways, providing a roadmap for scaling DAC technology in the coming years.

1. Introduction

Climate change has been identified as one of the most significant risks to human civilization due to its profound and widespread impacts. Since the Industrial Revolution (around 1760), the use of fossil fuels has caused a sharp rise in carbon dioxide (CO₂) emissions [1], the primary greenhouse gas driving climate change, which has increased from a pre-industrial concentration of 280 ppm [2], growing at a rate of 2.4 ppm per year [3]. By 2022, CO₂ levels had exceeded 420 ppm, and by 2024, they surpassed 426 ppm [4], marking the highest concentration in at least 2 million years [5]. This rapid increase in CO₂ levels has led to more frequent extreme weather events, rising sea levels, and significant ecosystem disruption.

Global warming, however, is driven by a basket of greenhouse gases with diverse sources and atmospheric behaviors. Energy-related activities (electricity and heat production, industry, and transport) dominate global emissions and are responsible primarily for CO₂ and CH₄ releases, while agriculture and other land uses are major sources of nitrous oxide (N₂O), and industrial processes emit a wide range of fluorinated gases (F-gases) [6,7,8] markedly in radiative efficiency and lifetime: a substantial fraction of anthropogenic CO₂ persists in the climate system for centuries to millennia, whereas CH₄ has an atmospheric lifetime of about a decade, N₂O on the order of a century, and many fluorinated gases can remain for hundreds to thousands of years [6]. As a result, deep emissions reductions are required across all greenhouse gases, but the stock-like behavior and long atmospheric lifetime tail of CO₂ make it particularly necessary to develop carbon dioxide removal (CDR) and negative emissions technologies to counteract its cumulative warming effect [9,10].

Over the past three decades, climate mitigation strategies have incorporated a diverse portfolio of CO₂ reduction and removal options, including renewable energy, Carbon Capture and Storage (CCS), Bioenergy with CCS (BECCS), and nature-based solutions [11]. While each approach contributes to decarbonization, they also face distinct limitations-such as geographical constraints, land use implications, infrastructure dependencies, or vulnerability to reversal-highlighting the need for complementary technologies that can address these gaps [11].

Although traditional greenhouse gas reduction strategies have provided some progress, their limitations are becoming increasingly apparent. Consequently, there is an urgent need for more innovative and scalable solutions to reduce atmospheric CO₂ concentrations and meet global climate targets. Direct Air Capture (DAC) has emerged as a flexible carbon removal option that operates independently of emission sources, capturing CO₂ directly from ambient air (≈400 ppm) using regenerative sorbent processes [12]. Its modular and location-agnostic nature allows co-location with renewable energy and storage sites, avoiding long-distance CO₂ transport and enabling deployment in regions where other mitigation options are less feasible [13]. Moreover, DAC is not affected by flue gas pollutants, which often complicate traditional CCS applications [14]. However, as an emerging technology, the path for DAC is not linear. Its large-scale deployment faces significant scientific, engineering, and economic challenges, rendering it a highly dynamic and focused field of research.

The potential of DAC extends beyond technical carbon management; it aligns with broader sustainable development objectives. By providing a pathway to counterbalance residual and hard-to-abate emissions, DAC is a direct contributor to Sustainable Development Goal 13 (Climate Action). Furthermore, its sustainable integration fosters progress across other SDGs: it advances SDG 7 (Affordable and Clean Energy) by creating demand for and coupling with renewable power systems; and supports SDG 11 (Sustainable Cities and Communities) by offering a scalable solution for managing distributed urban emissions and enabling sustainable industrial planning [15,16]. Thus, positioning DAC within the global mitigation portfolio strengthens the synergy between climate action and sustainable development.

DAC is now considered essential in global net-zero pathways, with its projected capacity and academic interest growing exponentially [17,18], as shown in Figure 1 and Figure 2. Since Klaus S. Lackner’s seminal 2002 paper [19], nearly 2000 academic papers have been published [20], with leading contributions from the United States, China, the United Kingdom, Germany, and Canada. This burgeoning body of literature reflects not merely a linear accumulation of knowledge but a highly volatile and rapidly evolving research landscape. The field’s dynamism is evidenced by shifting research thrusts (from fundamental material science to scale-up and cost reduction), a competitive landscape of technological pathways (ongoing optimization and debate between solid sorbent vs. liquid solvent systems regarding energy use and stability), and evolving research foci (with increasing emphasis on system integration, energy optimization, and life-cycle assessment). Research communities are actively grappling with core challenges: how to break the energy intensity bottleneck, dramatically reduce capture costs, and ensure permanent sequestration and environmental co-benefits. It is precisely these persistent debates, iterations, and unresolved questions-rather than settled conclusions-that define the current state of DAC research and underscore the need for this comprehensive review.

This review provides a comprehensive analysis of DAC technology, focusing on current research and applications. It covers the core principles of DAC, key technological developments, adsorption materials and equipment, system energy consumption characteristics, and potential interdisciplinary integration pathways. The review aims to establish a solid theoretical foundation for the development of efficient, low-carbon DAC systems and offers essential guidance for future engineering applications and the sustainable development of DAC technology.

2. DAC Principles and Key Technologies

2.1. DAC Principle

Currently, the main technologies for direct air capture (DAC) of CO₂ are as follows.

Liquid Absorption: This method uses strong alkaline solutions to chemically react with CO₂. It is a well-established and efficient technology, but it is energy-intensive and can cause corrosion.

Solid Adsorption: This approach employs porous solid materials to adsorb CO₂ at low temperatures, with regeneration achieved by heating or reducing pressure. It offers lower energy consumption and flexible equipment design, though its adsorption capacity and cycle stability need improvement.

Membrane Separation: This technique uses selective permeation membranes to separate CO₂. The process is simple and energy-efficient, but its efficiency in capturing low-concentration CO₂ is insufficient, and the technology is still immature.

Additionally, emerging technologies like electrochemical capture and cryogenic capture are under research. The former shows potential for lower energy use, while the latter is limited by its high energy demands [21].

In summary, liquid absorption, solid adsorption, and membrane separation are the core DAC methods in use today, with electrochemical and cryogenic technologies representing potential future directions.

2.2. Key DAC Technologies

2.2.1. Liquid Absorption Method

Adsorption materials used in liquid absorption methods include alkali metal-based adsorbents, amine solution adsorbents, and amino acid salt solutions. These materials are highly effective in capturing carbon dioxide and forming stable compounds, which results in high adsorption capacity and selectivity [22]. However, their effectiveness comes with the trade-off of higher energy consumption.

DAC Technology for Alkaline Hydroxide Solutions

Alkaline hydroxide solutions are among the earliest and most studied DAC adsorbents. The capture mechanism relies on the chemical reaction between hydroxide ions and CO₂, demonstrating a high CO₂ removal capacity [23]. Zeman and Lackner were the first to propose the use of alkaline hydroxide solutions (such as NaOH or KOH) for directly capturing CO₂ from the air. This technology involves two cyclical reactions: first, atmospheric CO₂ reacts with an alkaline hydroxide solution (NaOH or KOH) to form water-soluble CaCO₃; second, the alkaline hydroxide is regenerated through a causticization reaction, and the resulting calcium carbonate (CaCO₃) is heated above 900 °C to release CO₂ [24].

Figure 3 shows the KOH solution DAC process flow diagram [24]. This process, based on the widely used Kraft process in the paper industry, involves four chemical reactions-absorption, causticization, calcination, and digestion-carried out in an air contact tower. CO₂ from the air is absorbed by the KOH solution and converted into K₂CO₃. This K₂CO₃ undergoes causticization in a granular reactor, regenerating KOH. The CaCO₃ produced during causticization decomposes into CaO and CO₂ under high temperatures in the calcination furnace [25]. Finally, CaO reacts with water in the digestion reactor to form Ca(OH)₂, completing the cycle.

The regeneration of solvents in hydroxide-based Direct Air Capture (DAC) is highly energy-intensive [26,27]. Zeman [28] found that this single step consumes about 58% of the total energy required (256 kJ/mol), which is significantly higher than the theoretical minimum of 109.4 kJ/mol [26]. The need to process large volumes of air due to low CO₂ concentration presents another challenge [29]. To reduce costs, the air contact tower design can be optimized with efficient packings and distributors [24] (as shown in Figure 3), and renewable energy should be used for the thermal regeneration process.

Due to the high energy consumption of strong alkaline solution DAC technology, Rinberg et al. [30] proposed the Alkaline Solution Concentration-based DAC (ACSDAC) technology. This system includes a CO₂ absorption unit, an alkalinity concentration unit, a CO₂ extraction unit, and an alkalinity dilution unit. The primary energy-consuming step in ACSDAC is solution concentration. This can utilize seawater desalination techniques, such as reverse osmosis [31], capacitive deionization [32], and electrodialysis. The energy consumption for ACSDAC using reverse osmosis ranges from 160 to 190 kJ/mol, while membrane capacitive deionization requires between 170 and 380 kJ/mol.

Conventional KOH absorbers require high-temperature regeneration (900 °C), increasing costs, while porous adsorbents like MOFs suffer from limited stability and high price [33,34]. To address these issues, Li et al. [35] developed “charged adsorbents,” where active hydroxide ions are fixed within porous carbon electrodes. This allows for direct air capture and regeneration at a significantly lower temperature (90–100 °C), offering a promising new design concept. However, further work is needed to understand the adsorption mechanism and validate performance through long-term cycling tests [23].

Amino Acid Solution DAC Technology

Currently, most research focuses on solid adsorbents, with limited development in chemical adsorption [36]. Among the liquid adsorbents, amino solutions are the most well-known. Amine-based absorption has become one of the most reliable methods for carbon dioxide reduction and is widely used in industrial applications [33,34].

The regeneration of ammonia-based CO₂ capture requires significant energy at about 120 °C [37], a common issue shared with amine scrubbing, where stripping consumes ≈70% of operating costs [38,39]. However, amine adsorbents offer a superior path for DAC [40,41,42]. Their surface chemistry can be optimized for high selectivity and fast capture of dilute CO₂ [43,44]. Crucially, their regeneration energy is lower, and they have low corrosion potential [45], making them widely applicable in carbon capture [46,47].

Amine-based adsorbents are favored for DAC for their high selectivity [48] and enthalpy [49]. Research focuses on three classes with distinct trade-offs: while Class 1 adsorbents (amine-impregnated) have high capacity [50,51,52], they suffer from amine degradation during regeneration [53]. Class 2 adsorbents (amine-grafted) improve stability but at the cost of lower capacity [54,55]. In contrast, Class 3 adsorbents (with grafted polyamines on an inorganic carrier) are emerging as a promising option, typically offering higher capacity, better regeneration performance, and easier synthesis for long-term stability [56,57,58,59].

Beyond solid amine adsorbents, liquid amine solutions, especially monoethanolamine (MEA), are commonly used in DAC systems [60]. Figure 4 shows the typical absorption-regeneration process for MEA-based DAC [24], which is simpler than the alkaline hydroxide-based DAC process. During the absorption phase, the MEA solution reacts chemically with CO₂ from the air, forming carbamate or bicarbonate intermediates [61].

Amino Acid Salt Solution DAC Technology

Despite their promising properties for DAC, such as rapid kinetics, low toxicity, and resistance to oxidative degradation [62,63], amino acid salt solutions (also known as Bis-iminoguanidines (BIGs)) face significant scaling challenges. A core issue is the low solvent-to-air flow ratio required to capture dilute CO₂ [64]. Furthermore, the high temperatures (120–140 °C) needed for regeneration lead to substantial energy costs and risk thermal degradation, reducing cycling stability [65,66]. Addressing these regeneration challenges is therefore critical for practical deployment.

To address these challenges, Seipp et al. [61] introduced a novel DAC method using amino acid salt solutions combined with BIGs. The process employs BIGs as a solvent, where CO₂ reacts to form insoluble carbonate crystals via guanidino hydrogen bonds, enabling easy separation. As shown in Figure 5, the three-stage process [63] involves: 1. CO₂ absorption by the amino acid salt solution to form bicarbonate. 2. Reaction of bicarbonate with BIGs, regenerating the amino acid solvent and precipitating carbonate crystals [67]. 3. Low-temperature (80–120 °C) crystal decomposition, releasing high-purity CO₂ and regenerating BIGs for reuse [68].

DAC Technology for Alkalinity Concentration Variation

The Alkalinity Concentration Swing (ACS) process, introduced by Rinberg et al. [30] (Figure 6), offers a low-energy alternative to thermal calcination for DAC [69]. It operates through a cycle: First, a dilute alkaline solution absorbs CO₂ from the air. Second, the solution is concentrated using desalination techniques such as reverse osmosis (RO) [70], capacitive deionization (CDI) [71], or electrodialysis [72]. This concentration increases the partial pressure of the dissolved CO₂. Third, the absorbed CO₂ is released by reducing the system pressure. Finally, the concentrated solution is diluted to restore its original alkalinity, closing the loop.

Compared to traditional calcination-based regeneration methods, ACS-DAC technology avoids high-temperature steps and enables cycle switching through low-energy processes like membrane separation. This approach holds significant potential for thermal integration and compatibility with renewable energy sources. As a result, ACS-DAC offers a novel pathway for developing more energy-efficient and sustainable DAC systems.

2.2.2. Solid Adsorption Method

In contrast to liquid absorbents that degrade over cycles, solid physical adsorbents offer a promising path for DAC [73]. Due to low regeneration energy [74] and fast kinetics, CO₂ is captured via weak physical forces (e.g., van der Waals) on high-surface-area materials like zeolites [75], MOFs [76,77,78], COFs [79], and activated carbon [80,81]. However, their performance is highly sensitive to temperature [82,83,84] and humidity [85,86], and the energy cost for capturing ultra-dilute CO₂ remains a major bottleneck for commercialization [87,88].

Solid Alkali (Alkali Earth) Metal DAC Technology

Solid alkali metal adsorbents offer several advantages, such as low cost, non-corrosiveness to equipment, and the potential for methane formation [89], making them a highly studied material in DAC technology [90,91,92].

The adsorption of CO₂ by solid alkali metals involves a carbonation reaction, with regeneration requiring high calcination temperatures (650–890 °C) [72,93] as shown in Figure 7. However, metal oxides face kinetic limitations, transitioning from a fast chemical-controlled reaction to a slow diffusion-controlled phase [94], and Ca-based adsorbents suffer from poor cycle stability [95]. Using solid hydroxides like Ca(OH)₂ can overcome this kinetic barrier. This approach is thermodynamically feasible and sustainable [96], especially when paired with solar energy for regeneration [97].

Oxides/hydroxides of alkali/alkaline earth metals like CaO and NaOH are common solid adsorbents for CO₂ capture. The process, exemplified by CaO, cyclically involves carbonation (forming CaCO₃) and calcination (releasing CO₂). While applicable to air capture, the extremely low CO₂ concentration in ambient air compared to flue gas significantly increases energy consumption, posing a major challenge for DAC.

In conclusion, while alkaline (alkaline earth) metal oxide adsorbents perform excellently in traditional industrial flue gas applications, overcoming kinetic limitations and reducing energy consumption are essential for their successful implementation in direct air capture. Future progress in this technology is expected through novel material designs and the integrated use of renewable energy sources.

Solid-State Amine Adsorption DAC Technology

Solid amine adsorbents, a major research focus in DAC, involve loading amine groups onto porous supports [98]. They offer significant advantages over liquid systems by enabling regeneration at milder temperatures (<110 °C) [99], avoiding the high-energy (>800 °C), oxygen-rich conditions required by traditional methods [100,101]. They provide high capacity, fast kinetics, and good selectivity, especially under humidity [102]. However, their strong CO₂-amine affinity leads to higher regeneration energy and preparation costs, limiting wider application [103].

Solid amine adsorbents, created by functionalizing porous carriers with amine groups, are the most extensively studied DAC technology [104]. They effectively capture low-concentration CO₂ via chemical reactions (forming carbamate [105], or carbonate species [106]), and are easier to regenerate than liquid absorbents. A typical engineering application uses Temperature-Vacuum-Swing Adsorption (TVSA), as shown in Figure 8 [24]. Although steam heating increases energy use, it enhances desorption efficiency and CO₂ purity, achieving an optimal balance between energy input and product quality.

DAC Technology for MOF Materials

MOFs, composed of metal ions and organic linkers, are notable for their tunable pore sizes and surface properties [107]. Their CO₂ capture capability stems from a dual mechanism: physical adsorption via van der Waals forces on the pore surfaces [108] and enhanced chemical adsorption at uncoordinated metal sites [109]. This combination often yields superior adsorption properties [110]. Furthermore, compared to traditional porous materials, MOFs generally possess larger specific surface areas and broader pore size distributions, contributing to their high performance [111].

Over the past two decades, significant advancements in MOFs’ structural design and functionalization have extended their applications beyond gas separation to energy storage and humidity regulation, highlighting their potential for moisture adsorption and humidity control [112]. Compared to conventional porous materials such as zeolites or amine-functionalized porous silica, MOFs show higher CO₂ adsorption capacities at low partial pressures and better adsorption enthalpies. However, their performance under low CO₂ partial pressures still requires further optimization to meet the energy efficiency and stability demands for DAC systems.

Building upon the material design strategies proposed by Liu et al. [113], Ozkan et al. [114] classified MOFs for CO₂ capture into three categories: MOFs with Open Metal Sites (OMS), Hybrid Ultramicroporous Materials (HUMs), and MOFs with Amine-functionalized Sites (AFS). OMS and HUMs operate via physical adsorption mechanisms and are suitable for applications with high CO₂ concentrations.

Recently, MOFs have emerged as a research hotspot in DAC technology. Research led by Shekhah et al. [115] shows that strategic material design, such as reducing pore size (e.g., Cu-centered MOF capacity = 1.24 mmol/g vs. Zn-centered = 0.13 mmol/g), drastically improves CO₂ uptake. Ding et al. [116] found that the capacity of ultramicroporous MOFs is greatly enhanced at specific low temperatures (−78 °C and 0 °C). Advancing this, Zhang et al.’s [117] new material, NbOffIVE-1-Ni, achieves a high capacity of 1.3–1.5 mmol/g at the challenging but realistic condition of 400 ppm CO₂ and 25 °C, confirming the practical potential of MOFs for DAC.

These findings collectively highlight the tunability and structural versatility of MOFs, positioning them as one of the most promising classes of materials for next-generation DAC systems aimed at achieving higher selectivity, lower energy penalties, and greater operational stability.

As MOFs transition from laboratory research to pilot-scale and industrial applications, continuous optimization is necessary, particularly in areas such as adsorption capacity at low concentrations, moisture stability, kinetic performance, and cycle life.

Graphene Adsorbent DAC Technology

Graphene’s use in CO₂ capture is limited by its stacked structure, which impedes gas diffusion, and its nonpolar nature, which reduces CO₂ selectivity [118]. To address this, methods like chemical activation and thermal treatment have been used to modify its properties and enhance its adsorption performance and tolerance to flue gas components [119]. Unfortunately, these modifications often cause irreversible damage to the graphene structure—such as pore collapse and reduced surface area—which ultimately hinders CO₂ access to active sites and degrades adsorption efficiency.

To address existing limitations, a novel N₂/H₂ plasma modification method was developed. The effectiveness of this technique is demonstrated by a direct comparison: unmodified graphene oxide aerogel had a post-combustion CO₂ capacity of 1.6 mmol/g and a direct air capture capacity of 0.14 mmol/g. After modification, the graphene aerogel’s performance increased to 3.3 mmol/g and 1.3 mmol/g, respectively. The modified material also provides superior CO₂ selectivity and faster heating, leading to significantly lower regeneration energy consumption [120,121].

In summary, N₂/H₂ plasma-treated graphene aerogel demonstrates exceptional CO₂ adsorption performance, making it highly competitive in both post-combustion and direct air capture scenarios. This presents a new direction for graphene material applications in DAC technology.

Activated Carbon Adsorption DAC Technology

Activated carbon is a commonly used physical adsorbent in DAC technology. The CO₂ adsorption process on activated carbon is reversible, but its effectiveness can be affected by water vapor [122]. Enhancing the adsorption capacity and selectivity of activated carbon remains a key research area [123,124].

2.2.3. Other DAC Technologies

Beyond traditional methods, innovative approaches like Direct Air Capture and Methanation (DACM) have been proposed. Introduced by Duyar et al. [125], it utilizes Dual-Function Materials (DFMs) which combine CO₂ adsorption and catalytic components on a high-surface-area carrier. DFMs can directly capture CO₂ from ambient air and, when supplied with H₂ and heat, convert the captured CO₂ into methane (CH₄) in situ [126]. This integrated capture-and-conversion process reduces the need for separate CO₂ compression and transport, lowering overall costs [127].

Another approach, variable-humidity adsorption DAC, utilizes the free energy from water evaporation as the energy source for desorption. Since water and CO₂ exhibit opposite adsorption behaviors, this method eliminates energy losses typically associated with co-adsorption of water [128], significantly reducing DAC energy consumption. Lackner projects that a variable-humidity adsorption DAC could achieve a future cost of $30 per ton of CO₂ captured. Hou et al. [129] developed a swing adsorption DAC unit (capturing ≈30 kg/d CO₂) integrated with agricultural fertilization systems. The optimal operating conditions were identified as a desorption temperature of 45 °C and a CO₂ volume fraction of around 3% in the desorbed gas stream, achieving a minimum energy demand of 35.67 kJ/mol and an integrated cost of only $34.68 per ton of CO₂.

In recent years, Light-induced Swing Adsorption (LISA) regulates CO₂ adsorption/desorption by using light to switch molecular structures within porous materials [130]. Most research focuses on high-concentration CO₂ [131,132,133], with few studies on ultra-dilute air capture. Addressing this, Li et al. [134] modified a mesoporous material (SBA-15) with polyethyleneimine (PEI) and azobenzene. After 10 light/dark cycles, the material with 70% PEI content achieved a CO₂ desorption capacity of 0.6 mg/g, demonstrating stable, light-controlled DAC performance. This research lays the foundation for further studies into light-induced oscillating DAC technology.

Sun et al. [133] proposed a novel DAC technology (MI-DAC) integrating phytoplankton nitrate assimilation with CO₂ dissolution. Laboratory cost analysis indicates that the operational cost of MI-DAC is approximately $30.54 per ton of CO₂, showing significant potential for large-scale DAC deployment.

Biological utilization, one of nature’s primary methods for CO₂ fixation, includes processes such as photosynthetic bacteria, higher plant photosynthesis, and algal photosynthetic uptake. Microalgal cultivation presents a scalable DAC method with low energy requirements [135], simultaneously sequestering captured CO₂ into biomass. Controlled cultivation of microalgae can be performed in photobioreactors (PBRs) [136,137,138], enabling the sequestration of substantial amounts of CO₂ [139].

2.2.4. Comparison of Advantages and Disadvantages of Various DAC Technologies

Each of the DAC technologies mentioned above has its unique advantages and challenges, as summarized in Appendix A 

Table A1. Comparison of Various DAC Technologies.

DAC Technical Designation	Advantages	Disadvantages	Reference
DAC technology for alkaline hydroxide solutions	Technologically mature, with a high absorption rate	High regeneration temperature and high energy consumption during regeneration result in significant water loss	[28,32]
Amines solution DAC technology	The absorption rate is relatively high	Accompanied by the volatilization of the amine solution, and with relatively low regeneration efficiency	[32]
Amino acid salt solution DAC technology	High absorption rate, low regeneration temperature, minimal solvent loss	Energy consumption is relatively high, and capture efficiency varies depending on the amino acid salt solution	[32,69]
Alkalinity concentration variation DAC technology	High absorption rate, low regeneration temperature, and energy consumption, suitable for collaboration with seawater desalination research	Capture efficiency correlates with solution concentration techniques, requiring substantial water consumption	[69,109]
Solid alkali (alkali earth) metal DAC technology	High adsorption efficiency, good regeneration stability	Regeneration entails higher energy consumption and associated costs	[28]
Solid-state amine adsorption DAC technology	Technologically mature, featuring high adsorption rates and low regeneration temperatures	The thermal stability of adsorbents warrants further enhancement	[28]
Metal–organic framework materials DAC technology	Offers application advantages at lower temperatures	Capture efficacy is significantly influenced by ambient water content, with relatively high raw material costs	[109]
Dewet absorption DAC technology	High adsorption and desorption rates, coupled with low regeneration temperatures and energy consumption	High water consumption with stringent water quality requirements, yielding a low partial pressure of carbon dioxide	[28,32]
DAC combined ethaneation technology	Enables simultaneous carbon dioxide capture and conversion, with minimal humidity sensitivity	Requires elevated regeneration temperatures, with catalysts playing a decisive role	[32,109]
Light-Induced oscillatory adsorption DAC technology	Low regeneration energy consumption	Requires the incorporation of photoreactive elements within the material	[69]
DAC technology for nitrate assimilation in phytoplankton	Low regeneration energy consumption, suitable for seawater applications	Capture efficiency is primarily dependent on microbial activity	[69,109]

. When selecting the most suitable technology, factors such as technical costs, maturity, environmental impact, and application scenarios must be considered together.

3. DAC Technology Equipment and Adsorption Materials

3.1. DAC Technology Equipment

From a patent perspective, the United States leads the world in DAC patent applications, accounting for nearly 30% of the total. After years of steady growth, China now ranks second globally. Other countries and regions with significant application shares include Canada and developed European nations [140], as shown in Figure 9.

In 2004, Lackner et al. first developed a laminar flow scrubber device for the direct capture of carbon dioxide from air [141], as illustrated in Figure 10. This air scrubber unit consists of a layered air collector and a liquid reservoir. The adsorbent material flows downward along layered sheets while the air stream passes through the narrow spaces between them. Chemical reactions occur between the air and the adsorbent material, leading to the removal of carbon dioxide.

Subsequently, Lackner et al. further improved the design by using open-cell foam as an air-liquid exchanger [142], as shown in Figure 11.

Carbon Engineering is currently the only commercial company worldwide utilizing liquid DAC technology. The company developed a CO₂ capture device and method [143], as shown in Figure 12. This device incorporates a plate-shaped packing structure and at least one liquid source. The liquid source directs the flow of CO₂ absorbent liquid through the packing plates, where the absorbent liquid and CO₂ gas flow in a cross-flow configuration relative to each other. Compared to conventional counter-current tower structures, this operational mode improves overall energy efficiency by more than threefold.

Climeworks’ carbon capture technology involves deploying devices in the atmosphere that capture CO₂ from the air and react it with various compounds to separate the CO₂. The company developed a low-pressure-drop structure for granular adsorbent beds used in gas separation processes [144], which reduces the pressure drop in gas flow and enhances mass transfer rates between the gas phase and the adsorbent material’s surface [145], as shown in Figure 13.

Global Thermostat’s rotary multi-bed system, optimized into a Continuous Rotary DAC (CR-DAC) technology, offers low operating costs and high reliability for scalable applications [146], as shown in Figure 14. In a different approach, Deng et al.’s device, based on bipolar membrane electrodialysis, achieves higher carbon capture efficiency and purity, with the added advantage of adaptability to diverse operating scenarios [147,148], as shown in Figure 15.

Zhou et al. [149] developed a solar-powered CO₂ capture and recycling system. This system enhances CO₂ capture efficiency by increasing the mass transfer rate between the CO₂ capture liquid and the atmosphere, while reducing energy consumption in the CO₂ adsorption/desorption process. Ultimately, it achieves zero emissions and the reuse of CO₂ after desorption [150].

Linhe Climate Technology (Beijing) Co., Ltd. (Beijing, China) has developed a DAC system based on wet-regenerating adsorbents [151], as shown in Figure 16. This system enables continuous CO₂ capture and storage while reducing energy consumption and costs associated with adsorbent regeneration, improving space utilization. The company has successfully operated two DAC units in Xi’an, with capture capacities of 700 kg/a and 2000 kg/a, respectively.

Lei’s team [152] proposed a CO₂ capture technology based on the pH gradient in a water electrolyzer, as shown in Figure 17. The device uses a partition to create separate CO₂ capture (near cathode) and release (near anode) chambers. Both electrodes are constructed with layered structures (cover, gas diffusion layer, electrode, membrane). The key advancement is the integration of ion-exchange membranes, which minimize the distance between electrodes, thereby reducing the operating voltage and overall energy consumption.

Wang et al. [153] proposed an energy-saving system for direct air capture of CO₂ featuring precise ion control. The system layout, as shown in Figure 18, comprises an air delivery device, an air distribution device, and a CO₂ adsorption device connected in sequence. The CO₂ adsorption device incorporates a spray system.

The DAC technology from Beijing Deruncheng Environmental Technology Co., Ltd. (Beijing, China) [154] is based on a spherical solid-phase amine thin-layer moving bed, as shown in Figure 19. Its compact design reduces space occupation and eliminates waste, lowering investment and operational costs. The system is highly efficient, achieving a CO₂ capture rate of 70–90% and product purity of 95–99%. Notably, it consumes less adsorption/desorption thermal energy, air transportation energy, and auxiliary energy per unit of CO₂, giving it a significant advantage for large-scale applications [155].

McQueen et al. [92] proposed a method to directly capture CO₂ from the air by repeatedly calcining and carbonizing magnesite (MgCO₃) feedstock. As shown in Figure 20, the CO₂ capture potential could reach at least 2–3 billion tons per year. Calcining MgCO₃ produces MgO and high-purity CO₂, which is then spread onto land, where it reacts with atmospheric CO₂ to form MgCO₃, enabling a closed-loop mineralization process. The high-purity CO₂ and H₂O generated as byproducts can be sold, with condensation yielding 0.3 tons of H₂O per ton of CO₂ captured from the air.

3.2. DAC Adsorption Materials

The high energy consumption of DAC, driven by low CO₂ concentration, makes the selection of adsorption materials critical. These materials fall into two main categories: solid adsorbents (e.g., silica gel, zeolites, MOFs) and liquid absorbents. Furthermore, based on the adsorption mechanism, solid adsorbents can be classified as physical or chemical. Physical adsorbents operate through weak van der Waals interactions, while chemisorbents utilize reversible chemical reactions, typically providing greater selectivity and capacity at the cost of higher regeneration energy. The differences in their pore structure, surface chemistry, and stability dictate their suitability for various DAC applications.

Appendix A 

Table A2. Summary of DAC Adsorption Material Properties [156].

Material Properties	Material Type	Characteristics	Cost	Renewable Energy
Physical adsorption materials	MOFs	Its structure is stable, exhibiting a high specific surface area and porosity, enabling efficient CO2 capture through structural modification	High production costs	Due to its adjustable porosity and moderate regenerative energy
	Activated carbon	Its large specific surface area and porosity enable low-cost, efficient capture of CO2	Low cost	Due to the high specific surface area and mild activation, the regeneration energy is low
	Silica gel	It is frequently employed for dehumidification and air purification due to its low cost	Low cost	Due to its stable and reusable nature, the regeneration energy is low
	Molecular sieve	Adsorption facilitates separation and purification by screening molecular sizes	Moderate cost	High regeneration energy may be attributable to specific adsorption properties
	Zeolite	Adsorption capacity can be enhanced through ion exchange and other modification techniques	Moderate cost	Regeneration energy varies according to type and modification method
	Mesoporous silica	Despite its high porosity, weak interactions with CO2 result in limited adsorption capacity Consequently, surface modification presents an attractive strategy for improving CO2 capture efficiency in DAC	Low cost	Additional energy is required for surface modification to enhance CO2 capture
Chemical adsorption materials	Alkali metal-based adsorbents	It can capture CO2 and form stable compounds. Its adsorption capacity and selectivity	Due to raw material costs, the expense is moderately high	Due to raw material costs, the expense is moderately high
	Solid amine adsorbents	Despite the considerable cost associated with desorption, it exhibits a high adsorption rate	Owing to the higher temperatures required, regeneration energy consumption is elevated	Owing to the higher temperatures required, regeneration energy consumption is elevated

summarizes the key characteristics of various adsorbent materials used in DAC processes [156]. This table is crucial for understanding the performance differences and mechanisms between materials in CO₂ capture. By comparing their properties, adsorbents with the highest application potential in terms of energy efficiency and capture effectiveness can be identified, providing a scientific basis for optimizing DAC system design and material selection.

Research findings indicate that physical adsorbents are effective for CO₂ capture from CO₂-rich mixed gases. However, the presence of atmospheric moisture, which competes with CO₂ for adsorption sites, significantly reduces the performance of physical adsorbents in DAC processes. Previous studies suggest that regulating the pore structure and surface chemistry of materials through crystal engineering could enhance their CO₂ selective adsorption performance [157]. While physical adsorbents exhibit relatively low CO₂ adsorption capacities, their potential for rapid regeneration and low-energy operation partially compensates for this limitation.

Alnajjar et al. [158] treated wood-plastic composite surfaces with chromic acid, introducing oxygen-containing functional groups that enhanced interfacial bonding with epoxy nanocomposite coatings, improving mechanical modulus, scratch resistance, and reducing water absorption. This inspires the design of DAC adsorbents: through targeted surface modifications—such as adding basic sites or hydrophobic coatings—it is possible to maintain high CO₂ selectivity while effectively suppressing competitive adsorption from moisture, thereby improving capture efficiency under real atmospheric conditions.

Future adsorbent development should focus on reducing regeneration temperatures and energy consumption while enhancing cycle stability and durability. Additionally, research into low-water or non-aqueous absorption systems, such as mixed amine solutions and ionic liquids, is of great importance. This requires the concurrent development of corresponding process and material adaptation technologies to improve the economic viability and practicality of the overall system [159]. Yu et al. [160] found that triethanolamine (TEA) acts as an efficient carbonation promoter through a dual-action mechanism: it greatly increases CO₂ solubility in water and promotes Ca²⁺ leaching via complexation. This enables carbonation rates at atmospheric pressure to match or exceed those at elevated pressures. This insight informs DAC liquid absorbent design: developing multifunctional additives like TEA, which can simultaneously enhance CO₂ chemisorption and interfacial mass transfer, could enable high capture efficiency under milder conditions, significantly lowering system energy consumption.

Since CO₂ capture from air generally occurs at ambient temperatures, physical adsorbents have limited adsorption capacity and selectivity [161]. Chemical adsorbents, on the other hand, rely on chemical bonding forces for adsorption, offering stronger adsorption capacities [162], but desorption of CO₂ requires breaking these strong chemical bonds, leading to higher energy consumption during regeneration [163].

The practical application of adsorbents requires synergistic development with process engineering. Introducing promising materials into process models is key to understanding their real-world impact, yet a significant gap exists, as many advanced materials lack evaluation under specific DAC conditions. Future advancement hinges on integrating high-performance adsorbents with systemic innovations [164]. This includes designing materials with high surface areas and stability from a lifecycle perspective, simplifying synthesis for cost reduction, and coupling DAC with renewable energy. In summary, future DAC breakthroughs will depend not only on material optimization but also on synergistic innovations across process and energy utilization.

4. DAC Adsorption Efficiency, Energy Consumption, and Costs

4.1. Adsorption Efficiency and Energy Consumption of DAC

The overarching challenge of DAC is the inherent difficulty of efficiently capturing CO₂ from its highly diluted state in the atmosphere, which is both thermodynamically and economically demanding. Within this challenge, two parameters are paramount: adsorption efficiency, which dictates the system’s capacity and kinetics, and energy consumption, which is the primary determinant of operational costs and environmental footprint. While advances in material science and process engineering offer promising pathways, a systematic and critical evaluation of the interplay between efficiency and energy use is crucial to identify true bottlenecks and guide future R&D.

A clear illustration of the energy burden can be found in liquid solvent systems, such as those using NaOH, where the calcination step in the solvent regeneration process dominates the total energy demand. AspenPlus simulations underscore this point: for instance, Renata et al. [165] reported that calcination accounts for approximately 90% of the total energy input, while Jin et al. [166] identified it as the largest consumer at 5.64 GJ/t CO₂. This consensus highlights that optimizing the thermal efficiency of the regeneration process, particularly calcination, is a critical lever for improving the economic viability of liquid-solvent-based DAC.

Beyond energy, the environmental footprint of DAC systems involves critical trade-offs between different resource inputs. For example, while Giesen et al. [167] demonstrated the high carbon efficiency (73%) of amine solutions, suggesting their technical feasibility, other studies reveal high ancillary costs. Terlouw et al. [168] found that solar-powered DACCS requires substantial land area, and Liao et al. [169] highlighted water consumption as a pivotal factor, with estimates for chemical absorption systems being notably high. These trade-offs necessitate a holistic assessment that extends beyond mere capture efficiency.

A critical analysis of the energy consumption profiles, as delineated in Table 1, reveals a fundamental dichotomy between S-DAC and L-DAC technologies that transcends mere total energy figures. Solid Sorbent Direct Air Capture (S-DAC) and Liquid Solvent Direct Air Capture (L-DAC) show significant differences in system characteristics, operational modes, and energy consumption [170]. Each system has its own set of advantages and limitations, as detailed in

Table 2. Key characteristics of S-DAC and L-DAC technical approaches [49].

Methods of Carbon Dioxide Separation	Solid Adsorbent	Liquid Adsorbent
Energy consumption per unit (GJ/tCO2)	7.2–9.5	5.5–8.8
Proportion of thermal energy consumption (%)	75–80	80–100
Energy consumption per unit (GJ/tCO2)	7.2–9.5	5.5–8.8
Proportion of electricity consumption (%)	20–25	0–20
Regeneration temperature	80–100 °C	900 °C
Land requirements (km2/MtCO2)	1.2–1.7	0.4
Life-cycle emissions (tCO2 emitted/tCO2 captured)	0.03–0.91	0.1–0.4

. The energy requirements for S-DAC and L-DAC [171] are shown in Figure 21.

While S-DAC systems typically exhibit a lower total energy demand, their profile is characterized by a significant electrical load (e.g., for air movement and creating a vacuum for regeneration). This makes their operating costs highly sensitive to electricity prices. In contrast, L-DAC systems, while often more energy-intensive overall, are dominated by thermal energy requirements, particularly the high-grade heat needed for solvent regeneration and calcination. This distinction is not merely quantitative but strategic: it dictates the optimal energy sourcing and integration pathways for each technology. S-DAC is a natural partner for low-grade waste heat or solar thermal, coupled with low-carbon electricity. L-DAC’s viability, however, is inextricably linked to the availability of cost-effective, high-temperature, zero-carbon heat sources, such as advanced geothermal or nuclear energy [172].

Therefore, the choice between these pathways cannot be based on a simple comparison of GJ/t CO₂; it must be evaluated within the context of the specific energy ecosystem and infrastructure available at the deployment site.

Table 1. Comparative Analysis of Energy Consumption Profiles: Solid Sorbent vs. Liquid Solvent DAC Systems (Basis: 1 Mt CO₂/year).

Parameter	Solid Adsorbent [173]	Liquid Solvent [174]	Analysis and Implications
Total energy requirement (MW)	126–188	315–439	Solid systems are usually more energy-efficient.
Electrical requirements (MW)	18–35	23–52	Electricity is the core cost for solids, making them price-sensitive. Thermal energy dominates for liquids, so power costs matter less.
Thermal energy requirements (MW)	108–152	291–386	Solid systems are more energy-flexible, able to use low-grade or renewable heat, while liquid systems require high-grade, demanding heat sources.
Energy consumption structure	Electricity Combined electrical and thermal consumption	Thermal consumption is the absolute dominant factor.	Cost reduction strategies differ: solids must optimize electricity use, while liquids need affordable, low-carbon heat.
Primary energy consumption stages	Adsorption bed forced ventilation, vacuum regeneration, temperature swing	Solution pumping, solvent regeneration (particularly calcination)	The process bottlenecks differ fundamentally: liquids are limited by the thermodynamics of high-temperature calcination, while solids are constrained by mass transfer kinetics.
Technology Maturity	mid-to-low	mid-to-high	Liquid solvent technology is more mature but has a high energy ceiling. Solid adsorbent technology is novel with greater optimization potential, but its scalability is uncertain.

Table 1. Comparative Analysis of Energy Consumption Profiles: Solid Sorbent vs. Liquid Solvent DAC Systems (Basis: 1 Mt CO₂/year).

Parameter	Solid Adsorbent [173]	Liquid Solvent [174]	Analysis and Implications
Total energy requirement (MW)	126–188	315–439	Solid systems are usually more energy-efficient.
Electrical requirements (MW)	18–35	23–52	Electricity is the core cost for solids, making them price-sensitive. Thermal energy dominates for liquids, so power costs matter less.
Thermal energy requirements (MW)	108–152	291–386	Solid systems are more energy-flexible, able to use low-grade or renewable heat, while liquid systems require high-grade, demanding heat sources.
Energy consumption structure	Electricity Combined electrical and thermal consumption	Thermal consumption is the absolute dominant factor.	Cost reduction strategies differ: solids must optimize electricity use, while liquids need affordable, low-carbon heat.
Primary energy consumption stages	Adsorption bed forced ventilation, vacuum regeneration, temperature swing	Solution pumping, solvent regeneration (particularly calcination)	The process bottlenecks differ fundamentally: liquids are limited by the thermodynamics of high-temperature calcination, while solids are constrained by mass transfer kinetics.
Technology Maturity	mid-to-low	mid-to-high	Liquid solvent technology is more mature but has a high energy ceiling. Solid adsorbent technology is novel with greater optimization potential, but its scalability is uncertain.

In conclusion, the choice between intermittent S-DAC and continuous L-DAC is a strategic one, hinging on the specific deployment scenario and resource availability. Despite their differences, both technologies face the universal challenge of optimizing the trade-off between adsorption efficiency and energy demand. To overcome this, a multi-pronged approach is essential. First, next-generation adsorbents must simultaneously achieve high CO₂ selectivity, stability, and faster kinetics. Second, process engineering must focus on intensifying mass transfer and integrating low-carbon energy sources to drastically cut regeneration costs. These advancements in materials and process integration will be pivotal in reducing costs and enabling DAC to fulfill its potential as a vital tool for negative emissions.

4.2. DAC Costs

The economic trajectory of Direct Air Capture (DAC) is influenced by a complex interplay of technological innovation, economies of scale, and policy support. While long-term cost reduction is anticipated, a critical analysis of current cost assessments reveals significant uncertainties, with estimates ranging from ≈100 to over 600 per tonne of CO₂. These disparities are not mere errors but stem from fundamentally different underlying assumptions across studies, making direct comparison unreliable without a clear analytical framework.

To better understand DAC’s economic performance under different conditions,

Table A3. Comparison of Energy Consumption, Efficiency, and Costs for DAC Technologies [158].

Capture Capacity	Adsorbent	Desorption Temperature (°C)	Energy Consumption	Cost (USD/tonne)	Scale Assumption	Region Factors
1 Mt/a	KOH	900	8.81 GJ/t	94–232	Medium scale	Standard
1 Mt/a	KOH	900	5.25 GJ/t + 366 kWh/t	94–232	Medium scale	Standard
1 Mt/a	KOH	900	1535 kWh/t	186	Medium scale	Standard
0.291 t/h	MEA	123.1	1452 kWh/t	676	Small scale	Standard
0.36 Mt/a	K2CO3	80–100	7.5 GJ/t + 694 kWh/t	135–177	Small scale	Low-cost regions
3600 t/a	K2CO3	80–100	7.5 GJ/t + 694 kWh/t	203–244	Large scale	Low-cost regions
-	CaO	875	2.09 GJ/t	-	Medium scale	Standard
-	K2CO3/γ-Al2O3	150	7.3 GJ/t + 0.27 GJ/t	-	Medium scale	Standard
300 t/a	Amino groups	100	5.4–7.2 GJ/t + 200–300 Wh/t	Expected on a large scale 75	Small scale	Standard
-	Amino polymers	85–95	4.2–5.1 GJ/t + 150–260 Wh/t	<113	Small scale	Standard
-	Amino polymers	75	-	≤50	Small scale	Standard
140 g/day	Metal–organic frameworks (MOFs)	80, Vacuum	-	34–350	Small scale	Standard
166.08 t/h	Wet-activated adsorbents + amine solutions	-	306 GJ/t	93.1	Medium scale	High-efficiency
365 t/a	Wet-activated adsorbents	Wet	316 kWh/t	99	Medium scale	Standard
-	Wet-activated adsorbents	45	0.81 GJ/t	34.68	Medium scale	Standard
-	Amino acid salt solutions/m-BBIG	60–120	8.2 GJ/t	-	Medium scale	Standard
-	Amino acid salt solutions/PyBIG	80–120	6.5 GJ/t	-	Medium scale	Standard

in Appendix A provides a comprehensive summary of the energy consumption, efficiency, cost differences, as well as scale assumptions and region factors across various DAC technologies [159]. Furthermore, Figure 22 illustrates the variation in capture costs at different CO₂ concentrations, offering additional insights into how these factors impact the economic feasibility of DAC technologies under different operational scenarios [175].

From a cost perspective, the operational costs of Direct Air Capture (DAC) systems range between $94 per ton CO₂ and $232 per ton CO₂ [175], which is significantly higher than the costs associated with traditional Carbon Capture and Storage (CCS) technologies. The high energy demand in DAC primarily stems from the energy required for adsorbent regeneration. To assess DAC’s economic viability, it is crucial to compare its energy consumption, process requirements, and cost structures with those of CCS, considering the specific characteristics of the capture source.

In CCS, the initial step typically involves extracting and concentrating CO₂ from flue gases or other sources, followed by compression, transportation, and permanent storage. Approximately 75% of the total CCS costs are attributed to the energy-intensive processes of compression and transport [176]. In contrast, DAC faces challenges due to the lower concentration of CO₂ in ambient air and the need to operate near atmospheric pressure and temperature. These factors limit the applicability of many separation and concentration technologies commonly used in CCS [53].

Benito et al. [177] performed a preliminary cost assessment of the Amino Acid Salt-Ionic Liquid Direct Air Capture (AHA-ILs DAC) system, using advanced process modeling with AspenPlus software (the latest available version of Aspen Plus software is Aspen Plus V14). Their analysis considered costs for air contactors (ranging from $2000 to $50,000 USD/m³) and thermoelectricity prices (ranging from $0.01 to $0.10 USD/kWh), ultimately calculating the carbon capture costs for different operational scenarios. This assessment highlights the economic complexity of DAC systems, which must be optimized to reduce costs through advancements in material science and process integration.

Looking forward, as breakthroughs continue in material science and system optimization, DAC systems are expected to benefit from synergies with more mature Bioenergy with Carbon Capture and Storage (BECCS) technologies. The integration of DAC with BECCS offers significant potential for achieving negative carbon emissions. Figure 23 illustrates the combined effects of solid adsorbent (S-DAC) and liquid solvent (L-DAC) DAC systems when integrated with BECCS technology [174]. This figure demonstrates that both S-DAC and L-DAC technologies can enhance capture capacity within the BECCS system, improving energy consumption, material efficiency, and large-scale deployment potential.

The BECCS system comprises a biomass gasification unit, gas purification and conditioning units, and power generation facilities integrated with CO₂ capture infrastructure. In the BECCS process, atmospheric CO₂ is removed through plants and trees. Biomass can be combusted to generate heat and electricity, with most of the CO₂ released during combustion being captured and sequestered or used for fuel production [178]. This approach holds significant potential for achieving net-negative greenhouse gas emissions and offsetting existing temperature overshoot [179]. However, biomass cultivation may compete with food production, water use, and fertilizer requirements, while carbon emissions from cultivation, harvesting, and processing may also cause substantial social and environmental impacts [180].

Research indicates BECCS offers the highest net energy yield (18.08 GJ/t CO₂), followed by biochar (15.08 GJ/t CO₂), whereas DAC consumes energy without generation. However, DAC excels in water efficiency (8 m³/t CO₂ vs. BECCS’s 3.03 Mm³ and biochar’s 2.3 Mm³) and cost-effectiveness, with average costs of 206 million versus 408 million (BECCS) and $392 million (biochar) [174]. DAC’s operational and installation costs are 30% and 40% lower, respectively. While BECCS faces land and resource competition constraints, DAC’s primary challenge remains high energy demand. Technology selection should align with specific scenarios and resource availability [178].

Despite continuous breakthroughs in DAC technology worldwide, significant uncertainties remain in its cost assessment. DAC systems involve multi-stage energy consumption, material usage, and complex operating conditions, making accurate economic estimation challenging. Existing studies primarily rely on modeling under specific conditions or calculations from demonstration plants, which have led to significant variations in results. Keith et al. [181] estimated the cost of CO₂ capture in DAC systems (200–500 USD/t) based on the material and electricity prices at the time of their research. Later, Keith et al. [175] conducted a comprehensive cost analysis of CE’s KOH solution DAC system using a levelized cost estimation method (Such as Equation (1)). This method considers levelized capital costs, non-fuel operational and maintenance costs, and energy costs.

$$C_P=I_C{\displaystyle \frac{C_{RF}}{U}}$$

(1)

In the equation, C_p represents the levelized cost; I_c denotes capital intensity (i.e., the annual cost per ton of CO₂ captured), C_RF signifies the capital recovery factor, which is calculated as the annual levelized capital expense divided by the overnight capital cost, and U represents energy costs, which vary significantly across regions. Keith’s findings indicate that the CO₂ capture cost for this system ranges from 94 to 232 USD/t. Sutherland [182] projected that the cost of capturing 1 ton of CO₂ could fall below USD 60 by 2024.

To reconcile the wide range of DAC cost estimates reported in the literature, this chapter adopts a scenario-based comparative framework. Four stylized deployment scenarios are defined to make explicit the underlying assumptions regarding energy source, scale, and regional context, and to highlight how these assumptions drive differences in cost, energy use, and net CO₂ removal performance, as shown in

Table 3. Scenario-based comparative analysis of DAC performance under different assumptions.

Scenario	Energy Source	Scale Assumption	Regional Factors	Indicative Cost (USD/t CO2)	Energy Intensity	Key Risks and Uncertainties
S1-Current Baseline DAC	Grid electricity and fossil-based heat; limited access to renewables	Small to medium-scale plants (≈104–105 t CO2/yr)	Fossil-dominated power systems; immature supply chains	300–600 (sometimes up to 1000 USD/t CO2)	1500–2500 kWh/t CO2 (≈8–10 GJ/t)	High CAPEX and OPEX; high electricity prices; limited operational experience; low technology maturity
S2-Near-term Optimized DAC	Mixed energy (part renewables, part fossil); partial use of waste heat	Medium to large-scale (≈105–106 t CO2/yr)	Emerging renewable regions (Europe, North America, China)	230–400	1200–1800 kWh/t CO2 (≈6–9 GJ/t)	Uncertain pace of cost reduction; limited low-carbon energy supply; evolving policy support
S3-Large-scale Low-carbon DAC	Predominantly renewable or nuclear electricity + low-carbon heat (solar/geothermal)	Large commercial plants or clusters (≈106–107 t CO2/yr)	Regions with abundant low-cost renewables and CO2 storage sites (e.g., North Sea, Australia, Middle East)	200–300	800–1500 kWh/t CO2	Large upfront capital investment; CO2 transport and storage infrastructure; regional siting and permitting constraints
S4-Optimistic Future DAC	Fully decarbonized energy systems; integration of waste heat and advanced regeneration	Gigaton-scale deployment (>106 t CO2/yr per cluster); modular mass manufacturing	Regions with strong policy incentives, abundant renewables, and CO2 storage (e.g., U.S., Gulf States, Australia)	230–540 (policy targets < 100 USD/t CO2 are unlikely near term)	<800–1000 kWh/t CO2 (best-case projections)	Dependence on rapid innovation and subsidies; resource competition (materials, land, water); uncertain long-term policy stability

.

5. Development Status and Industrialization of DAC

5.1. Analytical Methodological Framework

To ensure the authenticity and objectivity of the research, the data and information cited in Section 5 have been obtained and verified through the following approach: the data is primarily sourced from companies’ publicly available technical white papers, reports from government agencies, research by international academic institutions, or literature-supported materials, which are treated as indicative of technological potential rather than confirmed commercial outcomes. Methodologically, a triangulation approach cross-references announcements from companies’ publicly available technical white papers, academic model studies, and authoritative industry reports (e.g., IEA, IPCC) to verify credibility and identify broader trends. This methodology aims to objectively present the actual progress, ongoing challenges, and strategic intentions within the industrialization of DAC technology.

5.2. Global Landscape and Regional Policy Drivers

The development of DAC technology is currently transitioning from research and development (R&D) and demonstration projects to early-stage industrialization, driven by varying policy frameworks across different regions. North America, particularly the United States, leads in the number of projects and scale of investment, largely supported by strong policy incentives like the Inflation Reduction Act, which has positioned DAC as a core strategy for achieving climate goals. This has resulted in a near-term surge in project announcements.

In contrast, while the Asia-Pacific region is seeing growing momentum in promoting carbon capture, utilization, and storage (CCUS) technologies, progress remains uneven. For instance, China faces significant challenges in advancing DAC, primarily due to imperfect market mechanisms and insufficient policy incentives, with current activities still dominated by traditional carbon capture projects. One key driver for DAC’s expansion is the availability of financial incentives, research grants, and subsidies, which support the initial stages of DAC technology development and deployment [13].

Moreover, tax credits and carbon pricing mechanisms play a crucial role in reducing the operational costs of DAC, making it more competitive with other emissions reduction methods. However, despite these efforts, there are significant challenges, including a fragmented policy landscape, the immaturity of carbon removal markets, and inadequate infrastructure for CO₂ transport and storage, which hinder large-scale DAC deployment [12,13]. Furthermore, global cooperation is essential, especially in the development of CO₂ storage and transportation infrastructure, as well as in establishing international carbon removal markets. Addressing these gaps and integrating DAC with renewable energy initiatives and carbon market frameworks will be crucial for realizing its potential as a major tool in mitigating climate change (National Aeronautics and Space Administration [4,5].

5.3. Analysis of Key Corporate Players: Technology Pathways and Commercialization Strategies

The current industrialization effort is led by a few pioneering companies, which exemplify different technological pathways and commercial strategies. Table 4 provides a comparative summary.

Climeworks (Zurich, Switzerland), as an industry pioneer, has pursued a strategy of validating the feasibility of its solid-sorbent technology through several pilot and demonstration projects (e.g., supplying CO₂ for greenhouses [183]). Its early projects successfully demonstrated engineering feasibility and operational experience.

Carbon Engineering (Squamish, BC, Canada) represents an alternative path, focusing on scaling up its liquid solvent technology directly to megatonne-scale facilities. This reflects a strategy centered on achieving rapid cost reduction through economies of scale.

Other players, such as Global Thermostat and Susteon, seek differentiation in technology or business models. For example, Susteon’s focus on “capture and utilization” creates a contrast to the “capture and storage” model emphasized by others, highlighting the industry’s ongoing exploration of viable business cases.

Table 4. Comparison of Major Global DAC Companies: Technologies and Strategies.

Company/Location	Year Founded	Primary Technology	Example Project/Capacity	Commercialization Strategy and Notes
Climeworks (Switzerland) [20].	2009	Solid Sorbent	900 t CO2/year (2017, Switzerland)	Incremental deployment, starting with small-to-medium pilots to validate technology and serve niche markets (e.g., greenhouses, beverages).
Carbon Engineering (Canada) [169]	2009	Liquid Solvent	Planning megatonne-scale projects	Scale-up path, aiming for low-cost capture directly via large-scale facilities, targeting geological storage.
Global Thermostat (New York, NY, USA) [184]	2010	Ion-Exchange Sorbent	≈100 t CO2/plant per year	Multi-project approach, leveraging a differentiated technology and exploring various scales and applications.
Susteon (Morrisville, NC, USA) [185]	2008	Solid Sorbent (similar to Climework)	Not Applicable (focus on integrated solutions	Business model innovation, focusing on integrated “capture-and-utilization” solutions, complements DACCS pathways.

Table 4. Comparison of Major Global DAC Companies: Technologies and Strategies.

Company/Location	Year Founded	Primary Technology	Example Project/Capacity	Commercialization Strategy and Notes
Climeworks (Switzerland) [20].	2009	Solid Sorbent	900 t CO2/year (2017, Switzerland)	Incremental deployment, starting with small-to-medium pilots to validate technology and serve niche markets (e.g., greenhouses, beverages).
Carbon Engineering (Canada) [169]	2009	Liquid Solvent	Planning megatonne-scale projects	Scale-up path, aiming for low-cost capture directly via large-scale facilities, targeting geological storage.
Global Thermostat (New York, NY, USA) [184]	2010	Ion-Exchange Sorbent	≈100 t CO2/plant per year	Multi-project approach, leveraging a differentiated technology and exploring various scales and applications.
Susteon (Morrisville, NC, USA) [185]	2008	Solid Sorbent (similar to Climework)	Not Applicable (focus on integrated solutions	Business model innovation, focusing on integrated “capture-and-utilization” solutions, complements DACCS pathways.

In summary, the global DAC industry is undergoing a critical transition from proof-of-concept to large-scale deployment. Governments and companies worldwide continue to drive policy incentives, capital investment, and technological innovation, propelling the rapid evolution and diversification of various technical pathways. Currently, 28 DAC plants and demonstration projects are operational worldwide [186], as shown in

Table 5. Current DAC Factories and Demonstration Projects in the World [187,188,189,190,191,192].

Affiliated Factory	State	Carbon Dioxide Capture Volume t·yr−1
Global Thermostat	United States	500
Global Thermostat	United States	1000
Global Thermostat	Canada	365
Climeworks	Germany	1
Climeworks	Germany	50
Climeworks	Switzerland	900
Climeworks	Iceland	50
Climeworks	Switzerland	600
Climeworks	Switzerland	3
Climeworks	Italy	150
Climeworks	Germany	3
Climeworks	Netherlands	3
Climeworks	Germany	3
Climeworks	Germany	50
Climeworks	Germany	50
Climeworks	Germany	3
Climeworks	Germany	3
Climeworks	Iceland	4000
Ordos Test Site	China	Thousand-tonne class
MissionZeroTechnologies	United Kingdom	Thousand-tonne class
INPEX Hokkaido pilot scheme	Japan	Hundred-tonne class
Heirloom Carbon Technologies	United States	1000
Climeworks	Iceland	36,000
Removr-Carbfix DAC pilot	Iceland	300
Removr-industrial pilot at Technology Centre Mongstad (TCM)	Norway	300
Mission Zero Technologies	United Kingdom	50
CarbonCapture Inc. -Leo-series DAC module	United States	500–700
AspiraDAC-pilot DACCUS facility	Australia	≈365

and Figure 24. The distribution and scale of these facilities not only reflect regional policy differences and resource endowments but also indicate that DAC technology is gradually moving from laboratory research toward commercial application.

5.4. Assessment of Industrialization Level and Key Challenges Discussion

As of 2025, a total of 28 DAC plants have been commissioned worldwide [Source Needed: e.g., IEA or Global CCS Institute, 2025 Report]. While this marks a significant increase from just a few years ago and indicates the technology’s transition from proof-of-concept to preliminary commercialization, the overall scale remains minimal. The average capture capacity of these facilities is approximately 1.0 × 10⁴ t CO₂·yr⁻¹ (10,000 tons per year). Critically, the collective annual capture capacity of all operational DAC plants accounts for less than 0.1% of the annual capture volume required by 2030 in IPCC scenarios to stay on track for the 1.5 °C climate target [193]. This vast gap underscores the monumental scaling challenge ahead.

The primary bottleneck to scaling remains economic viability. As of 2023, the levelized cost of DAC ranged from approximately 600 to 1000 per ton of CO₂ captured, with variations depending on the technology pathway, plant configuration, and, most significantly, local energy prices [193]. Widespread commercialization and market acceptance are contingent upon radical cost reduction. A commonly cited target is to bring the cost below $100 per ton, which is expected to require breakthroughs in material science, process optimization, and the deployment of dedicated low-cost renewable energy sources, enabling larger-scale demonstrations and eventual gigatonne-scale deployment [194].

The Capacity Gap: The total annual capture capacity of all currently operational facilities is orders of magnitude smaller than the single-plant megatonne-scale capacities being planned. This underscores the significant technical and engineering challenges that remain in bridging the gap from “demonstration” to “scale-up”.

Limitations of Data: Future plans announced by companies should be understood as strategic roadmaps. Their realization is highly dependent on sustained policy support, capital investment, and actual future cost reductions, introducing significant uncertainty.

Persistent Challenges: High costs, high energy demands, and associated indirect emissions remain the core constraints on widespread DAC commercialization and its full acceptance by the public and environmental groups. The primary goal of current projects is to prove technical feasibility and explore business models, not to achieve immediate economic competitiveness.

5.5. Summary of Industrialization Status

In summary, the global DAC sector is in a dynamic but nascent phase of industrialization, characterized by policy-driven regional disparities and diverse technological and strategic explorations by leading companies. However, it is crucial to contextualize the optimistic forecasts based on corporate claims against the currently limited scale of actual deployment. The future of DAC industrialization will hinge on the ability to effectively bridge the demonstration scale with cost-competitive, large-scale commercial facilities through continued technological innovation, robust policy support, and developed capital markets.

6. Discussion and Future Perspectives

6.1. DAC and the Energy Industry

6.1.1. DAC and the Traditional Energy Industry

The traditional energy sector primarily includes fossil fuel-based electricity generation, oil and gas extraction, processing, and supply operations, with core activities spanning energy production, conversion, and distribution. Within the global energy framework, these companies are commonly referred to as “traditional energy giants”, possessing vast energy assets and infrastructure.

DAC technology is becoming deeply integrated into the energy systems of these companies, not only optimizing carbon reduction pathways but also introducing a new paradigm for the deep decarbonization of energy systems. Through technological complementarity, resource integration, and business model innovation, DAC is helping to build a symbiotic “negative-carbon energy” ecosystem. The traditional energy sector provides low-carbon energy supplies for DAC systems, while DAC, in turn, creates carbon offset opportunities for fossil fuel systems, forming a closed-loop, mutually beneficial relationship. For example, waste heat from coal-fired power plants (80–150 °C) can replace conventional electric heating for the regeneration of MOF materials. Germany’s RWE Group, for instance, converted its coal-fired units into “cogeneration-DAC” hybrid power plants, utilizing 120 °C flue gas waste heat to drive adsorbent desorption, reducing regeneration energy consumption to 27.3 kJ/mol [195].

The deep integration of DAC with traditional energy industries shifts carbon management from a focus on “passive reduction”-reducing the carbon emissions intensity of energy production-to “active removal” of CO₂ from the atmosphere. This transition allows traditional energy companies to move beyond merely lowering emissions and instead take an active role in carbon capture and sequestration. By utilizing DAC systems, these companies can remove significant amounts of CO₂ from the air, effectively offsetting their own emissions. As a result, the role of these companies evolves from being “carbon emitters” to “carbon infrastructure operators”, where they not only produce energy but also play a crucial part in the global carbon cycle, contributing to the transition toward a net-negative carbon energy system. DAC will become the core technological lever reshaping the energy value chain.

6.1.2. DAC and the New Energy Industry

The new energy industry encompasses the production, conversion, transmission, distribution, and application of energy derived from renewable sources such as wind, solar, wave, geothermal, and biomass. Its goal is to provide low-carbon, sustainable energy solutions. DAC’s substantial energy demands for capturing dilute CO₂ necessitate a low-carbon power source, which the new energy industry provides. This integration is mutually beneficial. Renewables (wind, solar, etc.) enable low-carbon DAC operation and facilitate deployment in remote areas. Conversely, DAC serves as a flexible load to absorb variable renewable output, stabilizing the grid. Thus, their synergy is crucial for achieving true lifecycle negative emissions and constructing sustainable energy-carbon systems.

6.2. DAC and Artificial Intelligence

The large-scale deployment of DAC technology is currently constrained by several practical bottlenecks, including high energy consumption, substantial operating costs, lengthy cycles for material screening, and complex system operations. Fortunately, the rapid advancement of Artificial Intelligence (AI) provides a transformative toolkit to address these multifaceted challenges.

This section systematically elucidates the paradigm shift brought about by artificial intelligence in DAC technology development, transitioning from traditional trial-and-error experimentation to a new paradigm of “data-driven, deep integration of theoretical computation and intelligent prediction”.

6.2.1. DAC Challenges and AI Opportunities

The large-scale deployment of DAC technology faces multiple bottlenecks, including long material development cycles, high process energy consumption, and system complexity. Artificial intelligence, particularly machine learning and deep learning, is emerging as a transformative tool that is revolutionizing DAC development through data-driven approaches. A key application lies in the accelerated discovery and optimization of adsorbents and catalysts. For instance, the DeepMind team employed Graph Neural Networks (GNNs) to predict the CO₂ adsorption capacity and selectivity of Metal–Organic Frameworks (MOFs), reducing the conventional research and development cycle by 60%. In a similar vein, Hyun Park et al. developed a high-performance AI framework [196], as illustrated in Figure 25, which streamlines the design of MOFs by screening for high CO₂ uptake and synthesizability. Beyond materials science, AI-driven process modeling and optimization can enhance the energy efficiency of adsorption–desorption cycles, thereby lowering operational energy demands and uncertainties. This section will systematically elaborate on the revolutionary progress driven by AI across various levels of DAC, including material design, process optimization, and system integration.

6.2.2. Innovative Method 1: High-Throughput Virtual Screening and Molecular-Level Rational Design

The integration of AI with computational methods has created new paradigms in material discovery. Sriram et al. [197] introduced a paradigm shift by combining Density Functional Theory (DFT) with machine learning on the Open DAC 2023 dataset, replacing traditional Force Fields (FF) with ML and enhancing high-throughput screening efficiency by 2–3 orders of magnitude. This approach provides a scalable computational framework for the rational design of DAC materials, enabling systematic optimization at the molecular level. Davis et al. [198] further advanced this field by combining ML with high-throughput atomic-scale modeling (Figure 26), computing CO₂ binding enthalpies for thousands of nitrogen-containing molecules, and using surrogate ML models to rapidly screen over 1.6 million binding sites. Their work identified nearly 2500 novel materials suitable for DAC integration while assessing synthesizability and experimental feasibility.

Integrating synthesizability metrics (e.g., SA/SC Score-type) and linker availability into the screening criteria can significantly improve the “computation-to-experiment” hit rate. A recent high-throughput machine learning study focused on DAC sorbent discovery screened more than 1.6 million nitrogen-containing binding sites while explicitly filtering candidates based on synthesizability, ultimately identifying approximately 2500 viable materials, demonstrating that AI pipelines incorporating practical constraints can yield shortlists of experimentally tractable candidates [198].

6.2.3. Innovative Method 2: Intelligent Generative and Inverse Design

Beyond screening approaches, AI enables generative design of novel materials. Park et al. [199] developed a method combining deep reinforcement learning with molecular simulations to reverse-engineer MOFs for DAC. Their framework employs a dual-generator strategy that balances exploration and exploitation, iteratively optimizing MOF structures based on CO₂ adsorption heat and selectivity predictions with mean absolute errors of 2.87 kJ/mol and 0.64, respectively. This represents a significant shift from traditional screening methods toward active design of optimal materials, successfully narrowing the search within the vast chemical space of MOFs.

6.2.4. Paradigm Upgrade: SMART Framework and Closed-Loop R&D

The integration of DAC with artificial intelligence is driving a paradigm shift through the SMART (Scalable Modeling, Artificial Intelligence, Rapid Theoretical Calculations) technology framework [200]. Research demonstrates that AI enhances DAC system R&D efficiency through multidimensional innovation, enabling intelligent adsorbent screening with efficiency gains of 2–3 orders of magnitude over traditional methods [201]. Transfer learning effectively addresses experimental data scarcity, improving the CO₂ adsorption capacity prediction model generalization by 37% [202]. The introduction of an active learning framework creates a closed-loop optimization system of “computational prediction-experimental validation-model iteration”, which has surpassed the Robeson upper bound in Mixed-Matrix Membrane development, boosting CO₂/N₂ selectivity by 58% [203]. Furthermore, Large Language Models enable intelligent extraction of unstructured experimental data, increasing literature utilization from <15% to 93% [204].

The data-driven paradigm upgrade extends beyond accelerating material discovery to enabling system-level optimization and intelligent process design. To illustrate this shift from isolated material properties to integrated performance engineering, an illustrative energy ledger is presented to quantify the thermal penalty associated with co-desorbing water during the temperature-vacuum swing adsorption (TVSA) regeneration of a direct air capture (DAC) sorbent.

Assuming a desorption temperature 95 K above ambient, the sensible heat requirement is approximately 397 kJ kg⁻¹ of H₂O (based on a heat capacity of 4.18 kJ kg⁻¹ K⁻¹), and the latent heat of vaporization is 2257 kJ kg⁻¹, yielding a total of approximately 2654 kJ kg⁻¹ of H₂O. For the capture of one metric ton of CO₂, the additional regeneration energy demand is a direct function of the molar H₂O-to-CO₂ co-desorption ratio, R:

At R = 0.5, ≈205 kg of H₂O must be desorbed, requiring an additional ≈0.54 GJ t CO₂⁻¹.

At R = 3.0, the required water desorption rises to ≈1228 kg, increasing the energy penalty to ≈3.26 GJ t CO₂⁻¹.

This analysis highlights a significant operational lever. For instance, a climate-aware adsorption schedule—such as shifting regeneration cycles to periods of lower ambient relative humidity and re-optimizing TVSA parameters—that reduces by 12% would yield energy savings in the range of approximately 0.065 to 0.39 GJ t CO₂⁻¹ across the examined R = 0.5–3.0 range. These order-of-magnitude estimates are consistent with co-adsorption models that demonstrate strong humidity dependence and underscore the potential of weather-aware optimization frameworks for DAC [205]. The absolute values are, of course, contingent on specific sorbent properties and process configuration; the figures shown serve to quantify the scale of the potential energy savings.

This example epitomizes the SMART framework and closed-loop R&D: predictive models quantify the impact of a material property (water affinity) on a key system-level metric (energy cost), thereby creating a feedback loop. The insight that a 12% reduction in R translates to a specific energy saving provides a clear, quantified target for both materials chemists (to design hydrophobic sorbents) and process engineers (to develop smart operating protocols), closing the loop between molecular design and system-level performance.

The SMART idea (“Scalable Modeling, Artificial Intelligence, Rapid Theoretical calculations”) in CCUS literature refers to joining high-throughput physics, ML surrogates, and reusable data/feature pipelines so materials, process, and system models can co-evolve. It is increasingly cited as a cross-disciplinary blueprint rather than a single tool.

6.2.5. Concluding Remarks and Outlook for AI in DAC

The deep integration of AI and DAC signals a notable shift in the development of carbon removal technologies, with the potential to enhance efficiency and reduce costs in material discovery, process optimization, and system management. However, this integration remains largely transitional, moving from experimental research toward scaled implementation amid significant practical challenges. For instance, while AI accelerates the design of novel sorbents such as MOFs, their industrial feasibility—including stability, longevity, and regeneration energy requirements—has yet to be thoroughly demonstrated. Moreover, AI models rely on extensive, high-quality operational data, which remains scarce for DAC systems under real-world variable conditions, affecting their reliability and adaptability. Despite advances in algorithms, computing power, and interdisciplinary collaboration, the path to large-scale deployment is constrained by persistent issues such as high energy demands, system integration complexity, and uncertain economic viability. Therefore, while AI-enabled DAC offers a promising pathway toward global carbon neutrality, its transition from pilot-scale to meaningful industrial implementation will require overcoming substantial technical, operational, and infrastructural hurdles.

6.3. Lifecycle Environmental Performance and Societal Acceptance

A comprehensive appraisal of DAC requires looking beyond process performance and costs to its lifecycle environmental and social implications. Following standards (ISO 14040/14044 [206,207]) life-cycle assessment (LCA) principles ensures consistent system boundaries, functional units, and impact categories, and aligns the evidence base with policy and market disclosure needs [206,207]. In addition, recent assessments emphasize that carbon dioxide removal (CDR) options, including DAC, should be judged not only by gross removal but by net climate benefit and interactions with sustainable development dimensions [208,209,210]. Building on these frameworks, this subsection synthesizes DAC-specific evidence on greenhouse-gas (GHG) balances, water consumption, land occupation, and societal acceptance, and proposes reporting conventions to support responsible scale-up.

6.3.1. Lifecycle Greenhouse-Gas Balance of DAC

Plant-level LCAs indicate that DAC can already deliver net negative emissions when powered by low-carbon energy. For temperature-vacuum swing adsorption (TVSA) systems, measured carbon capture efficiencies of 85.4% (Hinwil) and 93.1% (Hellisheiði) have been reported; with low-carbon electricity and heat, adsorbent manufacture and plant construction dominate the residual footprint, underscoring the importance of materials choice and design for circularity [211]. For strong-alkali (KOH) solvent routes, cradle-to-gate analyses show that overall carbon efficiency hinges on heat and power supply, kiln integration, and chemical makeup cycles [175]. Where captured CO₂ is converted to fuels, LCAs find sizable intensity reductions relative to fossil benchmarks only when low-carbon H₂ and electricity are used; because the CO₂ is re-emitted on combustion, such pathways do not constitute durable removal, and should be reported separately from DAC with geological storage (DACS) [212].

It is recommended that project outcomes be quantified in terms of net removal efficiency—defined as gross captured CO₂ minus cradle-to-grave lifecycle emissions per metric ton of CO₂—under explicitly stated energy mix scenarios. Results should also be reported using clearly defined system boundaries that distinguish between DAC with storage (DACS) and DAC with utilization pathways, in accordance with relevant ISO standards on lifecycle assessment.

6.3.2. Water Consumption and Water-Related Risks

Water demand is technology- and site-dependent. In KOH-based configurations, process water is required for causticization, cooling, and solids handling; TVSA systems with solid amines generally have lower intrinsic process water needs but may be sensitive to ambient humidity and employ humidification or cooling in hot-dry climates [175,209,210]. At scale, water use interacts with energy choices (e.g., wet vs. dry cooling for power/heat supply) and local basin conditions.

It is recommended that analyses of direct air capture (DAC) configurations consistently report both blue and green water footprints per metric ton of CO₂ captured, accompanied by explicit disclosure of the assumed heat and power sources. Siting evaluations should incorporate basin-scale water-stress indicators to assess local hydrological impacts. Where feasible, water recovery and heat integration measures should be integrated into baseline designs to reduce freshwater withdrawals, particularly in water-scarce regions.

6.3.3. Land Occupation and Siting

Direct land occupation by DAC units is typically modest; the dominant driver of total land use is the energy system providing heat and electricity [208,213]. Modeling of deep-mitigation pathways shows that large-scale DAC deployment can avoid some of the land-competition pressures characteristic of land-intensive CDR options, provided that siting leverages low-land-intensity energy (e.g., geothermal, nuclear, industrial waste heat) and/or regions with strong renewable resources and existing grid capacity [213,214].

Recommendations should include the adoption of a unified metric expressed as “plant footprint + energy-system footprint” (in units of m²·year per t-CO₂ removed). Additionally, siting criteria should be developed that integrate grid carbon intensity, water stress, and land use conflict, thereby facilitating the identification of locations exhibiting optimal multi-criteria performance.

6.3.4. Societal Acceptance and Distributional Aspects of DAC

Experience with low-carbon infrastructure indicates that social acceptance can constitute a critical determinant of project viability. The “triangle of social acceptance”-comprising socio-political, community, and market acceptance-provides a valuable framework for analysis: (i) socio-political acceptance relies on credible measurement, reporting, and verification (MRV) as well as transparent life-cycle assessment (LCA) reporting; (ii) community acceptance is influenced by local perceptions of risks and benefits, such as traffic impacts, landscape alterations, long-term storage monitoring requirements, and employment opportunities; and (iii) market acceptance depends on the confidence of investors and consumers in certified net-removal claims and alignment with recognized taxonomiest [215]. Research on carbon management projects demonstrates that early and inclusive stakeholder engagement, coupled with equitable benefit-sharing arrangements, enhances the “social license to operate”. Furthermore, concerns regarding moral hazard, specifically, the risk that carbon removal could substitute for emission reductions, can be mitigated through policy sequencing that prioritizes rapid decarbonization [210,215].

Recommendations should integrate community participation and distributional impact assessments into the siting and permitting processes for direct air capture (DAC) facilities. Policy incentives for DAC deployment should be coupled with safeguards that prioritize emissions reduction efforts, ensuring a “mitigation-first” approach. In addition, independent third-party verification of net removal claims should be mandated to enhance credibility and align with emerging carbon removal certification standards.

6.3.5. Policy and Accounting Frameworks Relevant to DAC

Lifecycle-based accounting is increasingly integrated into climate policy frameworks. In the United States, the Inflation Reduction Act (IRA) has enhanced $45Q tax credits for DAC, offering greater incentives for Dedicated Geological Storage (DACS) compared to utilization pathways, contingent on robust measurement, reporting, and verification (MRV) and secure storage compliance [216]. In the European Union, the proposed Carbon Removal Certification Framework (CRCF) aims to establish standardized quantification, monitoring, reporting, and verification requirements for certified carbon removals, explicitly recognizing DACS as a permanent removal category [217]. At the international level, strategic policy documents increasingly frame DAC as part of a broader portfolio of climate solutions, whose overall sustainability is influenced by energy sources, project siting, and the integrity of MRV systems [218].

It is recommended that DAC system analyses consistently report a set of standardized lifecycle-based metrics-including net greenhouse gas emissions (in gCO₂e per t-CO₂ removed), water consumption (m³ per t-CO₂), and land occupation (m²·year per t-CO₂)-in accordance with ISO 14040 and ISO 14044 guidelines, while clearly distinguishing DAC with storage (DACS) from DAC with utilization (DAC-to-X). Furthermore, we advise defining a multi-criteria sustainability envelope, integrating thresholds for net removal efficiency, water use, land use, and local community impacts, to inform engineering design choices and investment prioritization.

6.4. Future Perspectives

In the future, DAC technology is expected to play a pivotal role across various sectors, including industry, energy, transportation, and construction. With ongoing technological advancements and optimization, the cost of DAC technology is anticipated to decrease further, while both adsorption efficiency and energy utilization efficiency will see significant improvements. This will enhance its economic competitiveness and environmental sustainability. As a result, DAC technology is set to become one of the key pillars in global carbon reduction efforts, providing crucial support for achieving sustainable development goals. This paper outlines the future development of DAC technology from the following perspectives:

Regarding Carbon Neutrality and Negative Emissions Targets:

As global attention to climate change intensifies, numerous countries and enterprises have set ambitious carbon neutrality and negative emissions targets. DAC technology can play a vital role in achieving these goals by directly capturing CO₂ from the atmosphere, thereby reducing carbon emissions and enabling negative carbon emissions.

Regarding Technological Advancement:

DAC technology is currently undergoing rapid development and optimization. Scientific progress is expected to significantly enhance the performance of adsorbents, further improve adsorption and desorption efficiency, and lead to more mature and efficient equipment designs. These technological improvements will help lower operational costs, increase capture efficiency, and accelerate the broader adoption of DAC technology.

Regarding Commercialization and Scaling:

As the technology matures and costs decrease, DAC is on the path to achieving commercial viability and large-scale deployment. Leading companies have already made significant strides toward commercialization, and more enterprises are expected to enter the DAC market, further accelerating its commercialization process.

Regarding Synergistic Applications with Other Technologies:

DAC can be integrated with other carbon reduction technologies to form comprehensive mitigation strategies. For example, combining DAC with carbon CCS enables the permanent underground sequestration of captured CO₂, achieving long-term carbon storage [186].

Based on recent observations and research, DAC technology is expected to evolve into a development model that decouples from central energy sources and does not rely on non-renewable resources. It will feature modular equipment and easily stackable products, allowing for rapid cost reduction. This developmental trajectory mirrors the technical path taken by new energy vehicles. Furthermore, the cost of DAC technology serves not only as the “ceiling” for the costs of various decarbonization technologies but also as a regulator for society-wide decarbonization funding. As the costs gradually decrease, the financial aspects of DAC technology will become increasingly important.

At the same time, DAC technology is poised to become a core component of future closed-loop carbon cycle industrial chains. Its application scenarios will promote the emergence of zero-carbon and negative-carbon industries, creating diverse business models. Empowered by AI, mobile, unmanned, and automatically matched DAC systems are expected to evolve into an indispensable “smart zero-carbon infrastructure” in future societies.

7. Conclusions

(1) Chemical adsorption materials exhibit high adsorption capacity and selectivity for carbon dioxide; however, they face challenges related to high costs. Solid adsorption methods show significant potential for widespread adoption in Direct Air Capture (DAC) applications due to their high energy efficiency and potential cost advantages. Enhancing adsorption capacity and regeneration stability remain core research priorities. Among solid adsorbents, novel Metal–organic Frameworks (MOFs) are advancing rapidly, achieving optimal adsorption capacities up to 1.5 mmol/g. Modified graphene aerogels have shown significantly improved post-combustion CO₂ adsorption capacity, reaching 3.3 mmol/g, while maintaining approximately 1.3 mmol/g in ambient air conditions. In addition to solid adsorption, emerging technologies like Direct Air Carbonation with Methanation (DACM), variable-humidity adsorption DAC, photo-induced swing adsorption, and biosorption are advancing quickly. However, challenges still exist in achieving low-cost and large-scale production of adsorbents. Overall, continuous innovation in adsorbent materials will directly influence the economic viability and industrialization potential of DAC technology. The United States leads the global DAC field, accounting for approximately 30% of worldwide patent applications, with China ranking second. Currently, North America, Europe, and Asia are jointly advancing DAC Research and Development (R&D) and industrialization, creating a technology-dominated landscape centered on the US, China, and Europe. Globally, 28 DAC plants and demonstration projects are operational, marking DAC’s gradual transition toward commercial application.

(2) The path to enhancing DAC adsorption efficiency has shifted from traditional trial-and-error experimentation to data-driven intelligent design, enabling dynamic system optimization for optimal energy performance. Current analyses, often utilizing tools like AspenPlus for process simulation, underscore a fundamental dichotomy between Solid Sorbent (S-DAC) and Liquid Solvent (L-DAC) technologies, extending beyond total energy figures to their distinct energy profiles. S-DAC typically has a lower total demand but relies heavily on electricity, making it sensitive to power prices, whereas L-DAC is dominated by thermal energy, particularly high-grade heat for solvent regeneration. This divergence dictates strategic energy sourcing: S-DAC pairs with low-carbon electricity and low-grade heat, while L-DAC’s viability hinges on affordable, high-temperature, zero-carbon heat sources. Economically, DAC operational costs (≈$94–232/t CO₂) remain higher than conventional CCS, with disparities arising from differing assumptions on energy, scale, and location. Future cost reduction—over 30% in marginal costs through adsorbent synthesis, equipment integration, and process optimization—is achievable. Furthermore, integration with BECCS enhances system synergy, improving capture capacity and deployment potential. Ultimately, advancing DAC requires a multi-pronged strategy: developing next-generation adsorbents with superior selectivity and kinetics, intensifying process engineering to slash regeneration energy, and conducting scenario-specific assessments that holistically weigh energy, water, and land use to enable DAC’s scalable role in achieving net-negative emissions.

(3) Direct Air Capture (DAC) is undergoing a profound transition from an experimental technology to a scalable climate solution, defined by the synergistic evolution of data-driven intelligent design, systematic energy integration, and rigorous full lifecycle sustainability. The technological paradigm has been fundamentally reshaped by artificial intelligence, which has shortened new material development cycles by 60%, increased adsorption process efficiency by 15–20% through intelligent control, and boosted the utilization of fragmented knowledge from less than 15% to 93%. In system integration, DAC demonstrates its potential as a central hub, with plants achieving carbon capture efficiencies between 85.4% and 93.1% and optimization reducing regeneration energy demands to levels as low as ≈27.3 kJ/mol. Its ultimate climate value, however, is contingent on its full lifecycle net removal efficiency, emphasizing the necessity of transparent governance under stringent standards like ISO 14040/14044. Only through this integrated evolution can DAC reliably fulfill its potential as a critical pillar for achieving global net-zero emissions.

This research demonstrates that DAC technology can overcome traditional limitations through multidisciplinary innovation (materials science, energy engineering, and artificial intelligence). Future efforts should focus on understanding material degradation mechanisms, optimizing adaptability to renewable energy fluctuations, and extending carbon product value chains. These advancements will help drive DAC’s transformation from an “energy-consuming” to a “resource-creating” technology, providing environmentally beneficial and economically viable solutions for achieving global carbon neutrality goals.