Bamboo-Derived Activated Carbon for Dye-Contaminated Wastewater Treatment: A Comprehensive Review of Synthesis, Doping Strategies, and Photocatalytic Performance

Abstract

Industrial and domestic effluents contaminated with synthetic dyes represent a significant global environmental and public health concern, necessitating the development of efficient, cost-effective, and sustainable wastewater treatment technologies. Among various remediation strategies, activated carbon (AC) has garnered considerable attention as an effective adsorbent, owing to its high surface area, excellent porosity, and strong adsorption capacity. This review presents a comprehensive analysis of activated carbon, with a particular focus on its derivation from bamboo biomass—a renewable, abundant, and low-cost precursor. It explores the key physicochemical characteristics of bamboo-based AC, common synthesis techniques, and the role of modification strategies—particularly metal oxide doping with TiO₂, ZnO, and MoS₂—in enhancing dye removal performance. The mechanisms underlying dye remediation, including adsorption and photocatalysis, as well as the synergistic effects observed in advanced AC-based composites, are critically examined. Emphasis is placed on the degradation of commonly used textile dyes such as methylene blue (MB), rhodamine B (RhB), and reactive blue, supported by comparative analyses of efficiency, stability, and reusability across various studies. Finally, the review outlines current challenges and knowledge gaps in the field, offering perspectives on future research directions to advance the development and large-scale application of sustainable bamboo-derived activated carbon composites for effective and eco-friendly wastewater purification.

1. Introduction

The rapid pace of industrialization and population growth worldwide has led to a severe deterioration of water quality, with industrial wastewater being a primary contributor [1,2,3,4]. Industries such as textiles, cosmetics, pulp and paper, leather, and pharmaceuticals extensively utilize dyes as colorants, leading to the discharge of substantial quantities of dye-contaminated effluents into water bodies [1,2,3,4,5,6]. These synthetic dyes, numbering over 10,000, are complex organic molecules often structured to resist chemical reactions and photolysis, making them highly recalcitrant in natural environments [4,7]. The presence of dyes in wastewater alters the aesthetic quality of water, diminishes the rate of photosynthesis in aquatic plants, and poses significant health risks to humans and aquatic organisms due to their xenobiotic, toxic, and sometimes carcinogenic properties [1,2,3,4,5,6,8,9,10,11]. Furthermore, dye production and treatment often generate considerable amounts of secondary pollution, such as sludge, which requires further safe disposal [4]. Given the tightening legislative regulations and the urgent need for sustainable solutions, the development of efficient and environmentally friendly technologies for dye removal from wastewater is paramount [3,4].

Various treatment methods, including advanced oxidative processes (AOPs), photocatalysis, membrane filtration, ultra-filtration, electrochemical methods, and adsorption, have been employed to cleanse industrial wastewater [1,6,8,9,10,11,12]. Among these, adsorption is highly favored for its straightforward operation, reusability, superior proficiency, low cost, and reduced waste formation [1]. Activated carbon (AC) stands out as the standard adsorbent for wastewater treatment due to its large surface area, abundant pores, and high recycling efficiency [1,7,8,13,14,15,16]. However, commercially available ACs can be expensive, leading researchers to explore biomass-derived ACs as renewable and less costly alternatives [1,13,14].

The research methodology incorporates a mini-review focused on recent progress (research ranging from 2019 to 2025) and advances in metal-based nanophotocatalysts (ZnO, TiO₂, and MoS₂) for dye degradation. The study also included a comparative case study investigating the photodegradation of Reactive Black 5 (RB5), utilizing synthesized Molybdenum Disulfide (MoS₂), prepared commercial Titanium Dioxide (TiO₂), and commercial Zinc Oxide (ZnO) data from a previous study. The selection of literature emphasized obtaining information and results related to the project, concentrating on recent advances and employing keywords such as Photocatalysis, Nanophotocatalysts, Dye Degradation, Reactive Black 5, Metal Oxides, and Environmental Remediation to determine the most important sources.

This comprehensive review focuses on bamboo-derived activated carbon (BBAC) and its modified forms for the effective degradation of organic dyes, detailing the advantages of bamboo as a precursor and examining advanced doping strategies using metal oxides (TiO₂, ZnO, and MoS₂) to enhance performance. The flow for BBAC preparation routes is illustrated in Figure 1 below. The primary objective is to critically elucidate the synergistic adsorption and photocatalytic degradation mechanisms, provide a comparative analysis of efficiencies, stability, and reusability across various studies, and ultimately highlight current challenges and propose future research directions in the field of sustainable wastewater purification.

Bamboo, a rapidly growing woody plant, is gaining significant attention as a sustainable and inexpensive precursor for AC synthesis [1,7,8,13,17,18]. This review focuses on the use of bamboo-based activated carbon (BBAC) and its modified forms for the effective degradation of organic dyes. We will also discuss the summary of procedure in Figure 1 where it will explore the BBAC preparation which includes fundamental properties and synthesis of AC (steam and chemical), detail the advantages of bamboo as a precursor, and discuss advanced doping strategies using metal oxides (e.g., TiO₂, ZnO, MoS₂) to enhance photocatalytic and adsorptive performance [19]. The primary mechanisms of dye removal, including adsorption and photocatalysis, will be elucidated, along with a comparative analysis of efficiencies, reusability, and stability across various studies. Finally, the paper will highlight current challenges, identify knowledge gaps, and propose future research directions in this crucial field.

2. Fundamentals of Activated Carbon

Activated carbon (AC) is a highly porous, amorphous form of carbon that has been processed to possess an exceptionally high surface area and intricate pore structure, making it highly effective for adsorbing molecules from liquids and gases [8,13,17].

2.1. Structure and Properties

The unique structural characteristics of AC are crucial to its adsorption capabilities. It features an extensive network of microscopic pores, which can be categorized into micropores (<2 nm), mesopores (2–50 nm), and macropores (>50 nm) [8,13,17]. This hierarchical porosity significantly increases the internal surface area, providing numerous active sites for the physical and chemical adsorption of contaminants [8,13,20]. For instance, a high surface area (1273 m²/g) and a mesoporous structure (average pore size 3.1 nm) were reported for bamboo-based AC synthesized via steam activation [13]. Beyond physical structure, the surface of AC can contain various oxygen-containing functional groups, such as carboxyl, hydroxyl, and carbonyl groups, which play a vital role in chemical adsorption through interactions like hydrogen bonding and electrostatic forces [13,14].

2.2. Precursors for Activated Carbon

AC can be produced from a wide array of carbon-rich sources, including wood, coal, coconut shells, and peat [8,17]. In recent years, biomass materials such as wood, coconut shells, and agricultural residues like rice husks, bagasse, olive stones, plum kernels, date pits, fruit stones, nutshells, and ginger stems have garnered significant attention as precursors [1,8,13,21]. This shift is driven by their advantages of high adsorption capacity, renewability, and lower preparation cost compared to conventional non-renewable sources [1,8,13,14,16,17].

2.3. Synthesis and Activation Methods

The production of activated carbon typically involves two main steps: carbonization and activation [8,17].

Carbonization: This initial step involves heating the raw carbonaceous material in the absence of oxygen at high temperatures (typically 400–900 °C) [13,14,17]. This process drives off volatile compounds, leading to the formation of a carbon-rich char. The thermal degradation profile of bamboo powder, for example, reveals distinct stages of mass loss corresponding to moisture release and the decomposition of hemicellulose, cellulose, and lignin, ultimately forming a porous char structure [14].

Activation: This crucial step enhances the porosity and surface area of the carbonized material. Activation can be achieved through two primary methods [8,13,17].

Physical (Thermal) Activation: The carbonized material is heated to high temperatures (typically between 600 and 1200 °C) in the presence of an activating gas such as steam or carbon dioxide (CO₂) [8,13,17]. This process physically corrodes the carbon, forming and expanding pores within the material [13]. Physical activation avoids complex post-treatment of chemical reagents and is suitable for large-scale industrial production [13]. For instance, steam activation of bamboo at 860 °C successfully yielded activated carbon with a high surface area of 1273 m²/g and rich porous structure [13].

Chemical Activation: This method involves impregnating the carbonized material with an activating agent, such as potassium hydroxide (KOH), phosphoric acid (H₃PO₄), or zinc chloride (ZnCl₂), followed by heating at lower temperatures (600 to 1000 °C) [8,13,17]. The activating agent reacts with the carbon matrix, leading to pore creation and increased surface area. Chemical activation is often a one-step process, requiring lower activation temperatures and shorter times, resulting in higher yields and better porous structures compared to physical activation [8]. Examples include KOH activation of rattan hydrochar [8] and edamame shells [13], and H₃PO₄ activation of sunflower stalks [13]. However, chemical activation can pose environmental challenges due to the use of corrosive chemicals and the generation of residues that necessitate extensive washing and waste management, leading to increased production costs [8,13].

3. Natural Activated Carbon Sources

The increasing demand for sustainable and cost-effective adsorbents has spurred research into various biomass materials for activated carbon (AC) production.

3.1. Bamboo-Based Activated Carbon (BBAC)

Bamboo is an exceptionally promising and sustainable resource for AC production due to its rapid growth, abundant availability, and unique structural properties [7,8,13,17,20]. Bamboo can reach maturity in 3 to 5 years and can grow on degraded lands, preventing competition with food crops and aiding in soil restoration [17]. Its lignocellulosic content is a significant contributor to its excellent status as a raw material for biochar and AC [14,17].

3.2. Key Advantages of Bamboo as a Precursor for AC Include

Unique Structure: The hollow internodal structure and scattered vascular bundles in bamboo naturally generate micro- and mesoporous channels, which serve as templates for carbonization and activation. This facilitates the penetration of activating agents and favors the formation of a well-integrated pore network [8,17].

High Surface Area: BBAC can achieve very high BET surface areas, ranging up to 3208 m²/g, which is significantly higher than the 2000–2500 m²/g typical for conventional wood- or coal-based ACs [8,17].

Chemical Composition: Bamboo is rich in cellulose (approx. 40–50%) and relatively low in lignin (approx. 20–30%), promoting efficient carbonization and yielding carbon-rich char with low ash content and fewer volatile impurities [17].

Mechanical Strength and Uniformity: The columnar culm structure with uniform wall thickness and absence of secondary growth in bamboo ensures consistent pyrolysis outcomes. This also means AC developed from bamboo can be mechanically stronger and less prone to attrition, making it suitable for industrial applications like fixed-bed adsorbers [8].

Electrical Conductivity: The well-aligned fibers in bamboo facilitate an orderly carbon microstructure upon pyrolysis, promoting graphitization and thus electrical conductivity, making BBAC suitable for electrochemical applications [8].

Specific studies demonstrate the efficacy of BBAC in dye removal: Bamboo stem-derived AC/MoS₂ (ACM) composite showed 98% methylene blue (MB) degradation within 90 min under natural light irradiation [1]. This was significantly higher than AC alone (94%) and MoS₂ alone (33%) [1].

• Steam-activated bamboo AC (BC-860) exhibited a maximum adsorption capacity of 369.28 mg/g for MB dye at optimized conditions [13].
• Pyrolyzed bamboo charcoal (BC850), obtained at 850 °C, achieved a high maximum adsorption capacity of 216.45 mg/g for MB [14]. Despite having a lower surface area than BC800, its functional groups and pore window properties contributed to higher performance [14].
• NaOH-impregnated bamboo charcoal (BC-I) showed an enhanced maximum adsorption capacity of 220.26 mg/g for MB, while further magnetization to magnetic bamboo charcoal (BC-IM) boosted this to 497.51 mg/g [8].

These findings highlight bamboo’s immense potential as a sustainable and highly effective precursor for activated carbon in wastewater treatment.

Building upon the highly efficient adsorption and synergistic photocatalytic results already mentioned (such as the 497.51 mg/g adsorption capacity of BC-IM and the 98% degradation by AC/MoS₂), even more exceptional results have been reported utilizing bamboo charcoal composites.

For instance, a novel Cu-g-C₃N₄/BC(600) composite, prepared by calcination at 600 °C, demonstrated complete degradation of Methylene Blue (MB) and Rhodamine B (RhB) within a remarkable 10 min in a photo-Fenton system under visible light. Furthermore, surface modification of BAC using the surfactant Cetyltrimethylammonium bromide (CTAB) yielded a composite with a nearly perfect 99.87% removal rate for MB.

Lastly, a hierarchical bamboo/silver nanoparticle composite was synthesized, capable of degrading MB by more than 96.7%, showcasing the potential of bamboo as a high-surface area catalytic support.

3.3. Other Biomass Sources

Beyond bamboo, a variety of other biomass sources have been explored for AC production, contributing to the broader context of sustainable adsorbents:

Agricultural Wastes: Plum kernels, bagasse, rice husks, olive stones, date pits, fruit stones, and nutshells have been reported for AC synthesis [1]. For instance, activated carbons prepared from agricultural waste bagasse by ZnCl₂ activation demonstrated adsorption of acid dyes [1]. Rice husks have also been used to prepare AC with studies focusing on surface area and porosity [1].

Coconut Shells: Coconut shells are a common precursor known to produce activated carbon with very high surface area [8,13,17].

Wood and Other Plant Biomass: Wood-based AC is widely used, and other biomass sources like ginger stems have been investigated for biomass activated carbon (BAC) preparation, showing advantages like abundant sources, low price, and good thermal and chemical stability [21].

Waste Materials: Watermelon rinds have been utilized to produce mesoporous activated carbon with high surface area for methylene blue adsorption [13].

While these sources offer promising results, bamboo often presents superior structural and chemical features for high-performance activated carbon, such as its natural pore channels and well-aligned fibers, which provide unique advantages for applications like dye degradation [8,17].

Beyond bamboo, various other sustainable biomass sources are actively being explored, often exhibiting good performance: Coconut shells, for example, are frequently used as precursors due to their ability to produce activated carbon with a very high surface area. In terms of specific applications, activated carbons prepared from agricultural waste like bagasse (using ZnCl₂ activation) have successfully adsorbed acid dyes, while mesoporous activated carbon produced from watermelon rinds showed high surface area suitable for MB adsorption. Additionally, derivatives like Sorghum-derived carbon dots (CDs), functioning as metal-free photocatalysts, achieved 86.10% degradation of Rose Bengal (RB) dye within 120 min under UV light.

4. Doping Strategies for Activated Carbon

While activated carbon (AC) is a highly effective adsorbent, its intrinsic limitations, such as low electrical conductivity and relatively smaller surface area in some forms, can limit its overall efficiency, particularly in advanced oxidation processes [1]. Doping strategies involving the incorporation of various materials, especially metal oxides, are increasingly employed to overcome these obstacles, enhance photocatalytic activity, reduce electron–hole pair recombination, improve structural stability, and extend visible light absorption capabilities [1,5,12].

4.1. Focus on Metal Oxides (TiO₂, ZnO, MoS₂)

Molybdenum Disulfide (MoS₂): The decoration of 2H-MoS₂ on the surfaces of activated carbon derived from bamboo stem biomass waste creates a regenerative novel architecture for effective degradation of methylene blue (MB) [1]. The synthesized AC/MoS₂ (5%) composite (ACM) exhibited a remarkable 98% photocatalytic degradation efficiency for MB within 90 min under natural light irradiation [1]. This composite consists of ultra-small activated carbon nanoparticles (approximately 20 nm) and layered MoS₂ with a lateral thickness of approximately 150 nm, as revealed by HRTEM analysis [1]. The presence of MoS₂ significantly expands the AC adsorption region and increases its surface area, strengthening the catalyst during regeneration [1]. The ACM composite also demonstrated high stability, retaining 89% of its photocatalytic efficiency after three cycle of experiments, confirming its regenerative potential [1].

Copper Oxides (CuxO) and Graphitic Carbon Nitride (g-C₃N₄): A novel CuxO and g-C₃N₄ codoped bamboo charcoal (Cu-g-C₃N₄/BC) composite was developed through in situ pyrolysis of Cu²⁺/melamine modified bamboo powders [12]. This composite, specifically Cu-g-C₃N₄/BC(600), prepared by calcination at 600 °C, exhibited exceptional catalytic efficiency in a photo-Fenton system with H₂O₂. It achieved complete degradation of methylene blue (MB) and rhodamine B (RhB) dyes within 10 min, and 97.5% degradation of methyl orange (MO) within 30 min [12]. The synergistic effect of Cu₂O, CuO, and g-C₃N₄ active sites increased the density of photogenerated electrons and promoted electron–hole pair separation via heterojunctions [12]. The bamboo charcoal matrix played a critical role by adsorbing dyes and H₂O₂, facilitating H₂O₂ activation and dye degradation. Its high conductivity also aided charge transfer from active sites to H₂O₂ [12]. Electron paramagnetic resonance (EPR) tests confirmed that hydroxyl radicals (•OH) were the main active species, with minor roles played by superoxide radicals (•O₂⁻) and photogenerated holes (h⁺) [12]. This catalyst also demonstrated good reusability due to its structural stability [12].

Titanium Dioxide (TiO₂): TiO₂ is a widely preferred choice for environmental remediation due to its strong oxidative power, chemical stability, and relatively low cost, making it effective for dye degradation [10]. Unmodified TiO₂ nanoparticles can significantly enhance the photodegradation of MB under natural sunlight. One study demonstrated a degradation efficiency of up to 93% at pH 10 by using TiO₂ nanoparticles [10]. This approach leverages the photosensitivity of MB dye in the visible spectrum and pH optimization to activate the photocatalyst, thereby speeding up the degradation rate by enhancing the generation of hydroxyl radicals [10]. While TiO₂ typically exhibits photocatalytic properties under UV radiation due to its wide band gap (around 3 eV), its effectiveness under visible light (which constitutes 40% of solar radiation) can be improved through strategic modifications or by exploiting the self-degradation properties of certain dyes [10].

Zinc Oxide (ZnO): ZnO, a well-known semiconductor, has gained popularity as a photocatalyst due to its distinctive optical and electrical characteristics, modest toxicity, strong stability, and affordability [5]. However, its wide band gap (3.37 eV) and high charge carrier recombination rate limit its photocatalytic efficacy [5]. Doping with other elements, such as silver (Ag), can effectively tune the band gap and prolong the recombination time of charge carriers, thereby enhancing the degradation rate [5]. For example, a composite of Ag-loaded ZnO garnished on carbon nanotubes (Ag-loaded ZnO:CNT) was synthesized, demonstrating approximately 100% photocatalytic efficiency in 2 min against MB dye at pH 9, with a rate constant of 1.48 min⁻¹ [5]. The CNTs in the composite offer a high surface area, strong adsorptive ability, and good catalytic activity, contributing to the overall enhanced performance [5].

4.2. Other Dopants and Modifications

Magnetic Materials (Fe₂O₃, Fe₃O₄): Magnetic modification is an efficient approach to improve AC properties, particularly for easy recovery and reusability. Magnetic bamboo charcoal (BC-IM) showed superior MB adsorption capacity (497.51 mg/g) and a significantly higher catalytic degradation rate (1.542 h⁻¹) compared to raw or NaOH-impregnated bamboo charcoal [8]. Similarly, Fe₃O₄/Graphene Oxide (GO) nanocomposites synthesized from natural iron sand achieved 91.3% degradation of RhB under UV light [19]. These composites leverage the magnetic properties for convenient separation from treated water, addressing the issue of secondary pollution [8,19]. A magnetic carbon nitride nanocomposite (Ag₂CrO₄/Fe₂O₃/g-C₃N₄) also demonstrated 87.1% RhB dye degradation, with good magnetic properties [15].

Surfactants: Surface modification with surfactants can enhance the adsorption capacity of AC. Cetyltrimethylammonium bromide (CTAB)-modified bamboo-based activated carbon (BAC) showed a remarkable 99.87% removal rate for MB [2].

Silver Nanoparticles (Ag NPs): Silver nanoparticles are known for their catalytic properties. A hierarchical bamboo/silver nanoparticle composite was developed, capable of degrading MB by more than 96.7% [22]. The large specific surface area of the bamboo provides ample space for the purification reaction, while the Ag NPs act as a catalyst, promoting dye reduction [22].

Graphitic Carbon Nitride (g-C₃N₄): g-C₃N₄, a metal-free polymer semiconductor, is gaining attention for photocatalysis. An α-zirconium phosphate/graphitic carbon nitride (α-ZrP/g-C₃N₄) nanocomposite showed enhanced degradation of crystal violet (CV) dye under solar light, with a rate constant four times higher than g-C₃N₄ alone [9].

Carbon Dots (CDs): Biomass-derived carbon dots possess adjustable optical properties and impressive electron-transfer capabilities [11]. Sorghum-derived carbon dots (J 2h) demonstrated 86.10% degradation of Rose Bengal (RB) dye under UV light, highlighting their potential as photocatalysts [11].

These doping and modification strategies significantly broaden the applicability and enhance the efficiency of activated carbon materials, moving beyond simple adsorption to more complex and effective degradation mechanisms.

5. Mechanisms of Dye Removal

The removal of dyes from wastewater by activated carbon and its composites primarily occurs through two major mechanisms: adsorption and photocatalysis, often exhibiting synergistic effects in advanced materials.

5.1. Adsorption

Adsorption is a surface phenomenon where dye molecules adhere to the porous structure of the adsorbent. This process is driven by various interactions and is highly dependent on the properties of both the adsorbent and the adsorbate [8,13,20].

Physical Adsorption: This mechanism involves weak intermolecular forces, such as van der Waals forces, between the dye molecules and the adsorbent surface [20]. The high specific surface area and extensive porous structure of activated carbon, particularly bamboo-based activated carbon (BBAC), provide numerous adsorption sites, enhancing its capacity for physical adsorption [8,13,20].

Chemical Adsorption (Chemisorption): This involves the formation of stronger chemical bonds or electrostatic interactions between the dye molecules and the functional groups present on the adsorbent’s surface [13,14,20]. For instance, the oxygen-containing functional groups (e.g., carboxyl, hydroxyl) on the surface of activated carbon can interact with cationic dyes like methylene blue (MB) through electrostatic attraction and hydrogen bonding [13,14]. Additionally, π–π stacking interactions can occur between the aromatic rings of dye molecules and the graphitic layers of the carbonaceous material [11,13,14].

Influence of pH: The pH of the solution significantly affects both the surface charge of the adsorbent and the degree of ionization of the adsorbate molecules [13,18]. For cationic dyes like MB, an increase in pH (more alkaline conditions) can enhance electrostatic attraction by increasing the negative charge on the adsorbent surface, thereby improving adsorption efficiency [13,18]. Conversely, in acidic environments, while electrostatic forces might decrease, hydrogen bonding between protonated functional groups on the AC and the dye can still contribute to removal [13].

5.2. Photocatalysis

Photocatalysis is an advanced oxidation process that utilizes light energy to activate semiconductor materials, generating reactive species that degrade organic pollutants [6,9,11,12].

Mechanism: When a semiconductor photocatalyst (e.g., TiO₂, ZnO, MoS₂) is irradiated with light of sufficient energy (greater than or equal to its band gap), electrons (e⁻) in the valence band (VB) are excited to the conduction band (CB), leaving behind positive holes (h⁺) in the VB [9,10,12]. These photogenerated electron–hole pairs then migrate to the catalyst surface.

The holes (h⁺) can react with water (H₂O) or hydroxide ions (OH⁻) adsorbed on the catalyst surface to produce highly reactive hydroxyl radicals (•OH) [9,12].

The electrons (e⁻) in the conduction band can react with molecular oxygen (O₂) to form superoxide radicals (•O₂⁻) [5,12].

Both •OH and •O₂⁻ are potent oxidizing agents that can attack and break down complex organic dye molecules into simpler, less toxic compounds, eventually leading to their complete mineralization into carbon dioxide (CO₂) and water (H₂O) [3,4,6,10,12].

Light Source: Solar light-driven photocatalysis is particularly attractive due to its low cost, absence of sludge formation, and potential for complete mineralization, especially in remote areas [9,10,11]. While many photocatalysts are most active under UV light, strategies like doping or surface modification aim to shift their light absorption capabilities into the visible spectrum, which constitutes a larger portion of natural sunlight [10].

5.3. Synergistic Effects in Composites

Many advanced materials combine both adsorption and photocatalytic capabilities to achieve enhanced dye removal efficiency.

The adsorbent matrix (e.g., bamboo charcoal, activated carbon) plays a crucial role by concentrating dye molecules near the photocatalytically active sites, thereby increasing the local concentration of pollutants and facilitating their interaction with the reactive species [8,12]. This initial adsorption step can significantly improve the overall degradation rate [12,22].

Furthermore, in composite catalysts, the carbonaceous support can act as a charge transfer medium. For instance, the high conductivity of bamboo charcoal facilitates the transfer of photogenerated electrons from the active sites to the oxidants (e.g., H₂O₂) or adsorbed oxygen, effectively reducing electron–hole recombination and boosting catalytic activity [1,12].

This synergistic interplay ensures that dyes are not only effectively removed from the aqueous phase through adsorption but are also subsequently degraded into harmless substances via photocatalysis as portrayed in Figure 2, offering a more comprehensive and efficient solution for wastewater treatment [5,8,12,22].

5.4. Comparative Studies

This section presents a comparative analysis of the performance of various bamboo-based activated carbon (BBAC), specifically their adsorption performance as shown in

Table 1. Adsorption Performance of Bamboo-based Materials for Methylene Blue (MB).

Adsorbent/Composite	Precursor/Description	Max Adsorption Capacity (mg/g)/Efficiency (%)	Conditions	Reference(s)
AC/MoS2 (ACM)	Bamboo stem-derived AC with 5% MoS2	98% degradation in 90 min	Natural light, 20 ppm MB, pH 6, 10 mg catalyst	[1]
AC	Bamboo stem-derived AC	94% degradation	Natural light, 20 ppm MB, pH 6, 10 mg catalyst	[1]
MoS2	Synthesized MoS2	33% degradation	Natural light, 20 ppm MB, pH 6, 10 mg catalyst	[1]
BC-860	Steam-activated bamboo AC (860 °C)	369.28 mg/g	pH 10, 0.05 g adsorbent, 30 °C temperature	[13]
BC-I	NaOH-impregnated bamboo charcoal	220.26 mg/g	328 K	[8]
BC-IM	Magnetic (Fe2O3) bamboo charcoal	497.51 mg/g	328 K	[8]
BC850	Bamboo charcoal (pyrolyzed at 850 °C)	216.45 mg/g	pH 7, 0.25 g/L adsorbent, 20 mg/L MB	[14]
CTAB-modified BAC	Bamboo-based AC modified with CTAB (0.25 g/L)	99.87% removal	Optimized conditions	[2]

Note: Degradation efficiency for ACM, AC, and MoS₂ refers to photocatalytic degradation, while others primarily indicate adsorption capacity or removal efficiency which may include both adsorption and catalytic effects.

and doped AC materials for dye degradation, highlighting their removal efficiencies, degradation rates, and reusability which is summarised via Photocatalytic Degradation in

Table 2. Photocatalytic Degradation Performance of Doped AC and Composite Materials.

Catalyst/Composite	Dye Tested	Degradation Efficiency (%)/Rate Constant	Conditions	Reference(s)
Cu-g-C3N4/BC(600) + H2O2	MB, RhB, MO	Complete MB/RhB in 10 min, 97.5% MO in 30 min	Photo-Fenton, visible light	[12]
TiO2 nanoparticles	Methylene Blue	Up to 93%	Natural sunlight, pH 10	[10]
Ag-loaded ZnO:CNT	Methylene Blue	~100% in 2 min (rate constant 1.48 min−1)	Visible light, pH 9, 10 ppm MB, 10 wt% CNT	[5]
α-Bi2O3 microrods	Reactive Blue-4	97% in 1 h (rate constant 0.561 min−1)	Natural sunlight, pH 3	[24]
α-ZrP/g-C3N4 nanocomposite	Crystal Violet	Rate constant 4x higher than g-C3N4	Solar light, pH 6	[9]
Sorghum-derived CDs (J 2 h)	Rose Bengal	86.10% in 120 min (rate constant 0.016 min−1)	UV light, 5 mg CDs, 15 ppm RB, pH 7	[11]
In-ZnV@MWCNT	Acridine Orange	>99.60%	UV light, 20 mg catalyst, pH 3	[3]

.

5.5. SEM Test

This Figure 3 below illustrates the natural hierarchical structure of bamboo, which serves as a critical template for producing porous activated carbon. (a) Bamboo is characterized as a monocot grass with a hollow, segmented culm [25]. (b) The culm wall is functionally graded, showing an increasing density of stiff, fiber-comprising vascular bundles concentrated toward the outer epidermis [25]. (c) These vascular bundles are embedded within the ground tissue, which is composed of box-shaped parenchyma cells featuring thin primary cell walls (PL) [25]. (d–f) Detailed views of the fibers reveal thick, lignified cell walls with a polylamellar structure, including a primary cell wall layer, and up to eight secondary cell wall layers (SL) [25]. The pectin-rich middle lamella (ML) adjoins the fiber cells; the compound middle lamella (CML) is defined as the combination of ML, PL, and the first layer of the secondary cell wall (S0) [25]. This intrinsic structure of hollow channels and vascular bundles naturally generates the micro- and mesoporous network, facilitating the formation of high-surface-area activated carbon.

5.6. Reusability and Stability

Catalyst reusability is a crucial factor for sustainable and economic applications.

The AC/MoS₂ (ACM) composite demonstrated good reusability, exhibiting a slight decrease in photocatalytic efficiency to 89% after three cycle of experiments (a 9% loss from the initial 98% efficiency), indicating its high stability and regenerative potential [1].

The Cu-g-C₃N₄/BC catalyst also exhibited good reusability due to its structural stability [12].

The In-ZnV@MWCNT composite showed good stability up to five cycles for acridine orange dye degradation [3].

Sorghum-derived carbon dots (CDs) demonstrated favorable regeneration capabilities [14].

The CuO/Bi₂O₃ nanocomposite synthesized using bamboo leaves extract maintained good reusability for RhB degradation [6].

However, the Fe₃O₄/GO nanocomposites showed a decrease in degradation efficiency by an average of 12.23% over three cycles for RhB degradation [19].

These comparative studies highlight that doping strategies, especially with metal oxides, significantly boost the performance of activated carbon, both in terms of degradation efficiency and catalytic activity, while maintaining reasonable reusability and stability. The choice of dopant and precursor material, along with synthesis conditions, plays a critical role in optimizing these properties.

6. Comparative Study Findings

Bamboo-Based Activated Carbon (BBAC) offers superior advantages over AC derived from other biomass sources like wood, coconut shells, and agricultural residues due to its unique structural properties and high efficiency in dye removal. Specifically, bamboo’s hollow internodal structure and scattered vascular bundles naturally create micro- and mesoporous channels, which serve as templates for a well-integrated pore network, facilitating higher contaminant adsorption. This results in BBAC achieving very high BET surface areas, potentially up to 3208 m²/g, which significantly surpasses the 2000–2500 m²/g typical for conventional wood- or coal-based ACs. While other precursors like coconut shells also yield AC with a high surface area, and agricultural wastes like bagasse and watermelon rinds show efficacy for specific dyes, bamboo also offers greater mechanical strength and uniformity, making it better suited for industrial fixed-bed adsorbers. Regarding optimal synthesis methods for dye adsorption applications, the sources suggest that chemical activation is generally preferred as it requires lower activation temperatures and shorter times, often resulting in higher yields and better porous structures. For instance, NaOH-impregnated bamboo charcoal (BC-I) showed an enhanced maximum adsorption capacity of 220.26 mg/g for Methylene Blue (MB), which was further optimized to 497.51 mg/g when combined with magnetic materials (BC-IM). Conversely, while physical activation (steam activation) is more environmentally friendly as it avoids corrosive chemicals, the highest reported adsorption-focused capacity in the sources comes from the chemically modified magnetic bamboo charcoal (BC-IM). Therefore, for maximizing dye adsorption capacity, chemical activation combined with post-synthesis modification (such as magnetic functionalization or surfactant modification) yields the most optimal performance properties, despite the disadvantage of associated environmental challenges and complex post-treatment processes.

• Mechanistic understanding, band-gap characterization, and selectivity tuning in BBAC-metal oxide composites
  • Doping-Induced Band-Gap Changes and Charge-Carrier Dynamics

The sources discuss the concept of doping to tune the band gap and prolong the recombination time of charge carriers, as well as the intrinsic wide band gaps of TiO₂ (around 3 eV) and ZnO (3.37 eV) [5].

6.1. Mechanistic Understanding and Future Directions

To elevate the development of bamboo-based activated carbon (BBAC) photocatalysts from empirical observation to rational design, it is essential to delineate the specific physical mechanisms governing charge dynamics at the interface. The contact between semiconducting nanoparticles MoS₂ ZnO and the graphitic domains of the conductive BBAC facilitates the formation of a Schottky barrier, which rectifies electron flow and effectively suppresses electron–hole recombination. This barrier is critical in systems like the Cu-g-C₃ N₄/BC composite, where the synergistic heterojunction increases the density of photogenerated electrons available for the reduction in adsorbed O₂ into superoxide radicals O₂. Furthermore, in visible-light active systems involving dye molecules, the mechanism often relies on dye sensitization, where the dye absorbs photons and injects electrons into the semiconductor’s conduction band; here, the BBAC support aids via pi-pi interactions, preventing desorption and facilitating rapid carrier transport.

For composites incorporating plasmonic metals (e.g., Ag-loaded ZnO or Mie-resonant semiconductor particles, the degradation mechanism involves complex light-matter interactions that must be distinguished to optimize performance. Future mechanistic models for BBAC composites must account for Mie-Resonance Energy Transfer (MIRET) and distinguish between non-thermal and thermal pathways. Specifically, the decay of localized surface plasmons via Landau damping generates energetic “hot electrons” (a non-thermal effect) that can be injected directly into the adsorbate or catalyst conduction band to drive reactions. This must be differentiated from phonon-assisted decay, which results in localized photothermal heating. While bulk heating can enhance reaction rates, uncontrolled photothermal effects can be parasitic or detrimental to selectivity. Tuning the excitation wavelength to the resonance frequency is therefore crucial to maximize the electromagnetic field enhancement (non-thermal) while minimizing deleterious thermal effects.

Currently, the precise contribution of these pathways in BBAC composites is often hypothesized rather than experimentally verified. To rigorously validate the presence of hot-electron injection versus thermal heating, and to confirm the efficacy of the Schottky barrier, future research must employ advanced in situ kinetic characterization. Techniques such as Transient Absorption Spectroscopy (TAS) are necessary to resolve the ultrafast timescales of hot-electron cooling (femtoseconds) versus interfacial charge transfer. Additionally, Time-Resolved Photoluminescence (TRPL) is required to quantify carrier lifetimes and confirm the quenching efficiency attributed to the carbon matrix. Moving beyond simple radical scavenging tests to these time-resolved methods will provide the molecular-level evidence needed to confirm the roles of defect engineering and facet control in these complex heterostructures.

We have also considered concepts from the suggested articles, such as Carrier dynamics in cuprous oxide-based nanoparticles and heterojunctions and Charge separation in metal-semiconductor nanocatalytic heterojunctions, to illustrate:

• Interfacial Charge Transfer: How the BBAC’s high conductivity facilitates the transfer of photogenerated electrons from the active sites (like Cu₂O, CuO, or MoS₂) to oxidants like H₂O₂ or adsorbed O₂. [1]
• Heterojunction Efficacy: How the formation of p-n or Schottky heterojunctions promotes the separation of photogenerated electron–hole pairs, thereby reducing recombination and boosting catalytic activity. The sources provide evidence for this synergy: for example, the Cu-g-C₃ N₄/BC composite shows that the synergistic effect increases the density of photogenerated electrons and promotes separation [12].
• Distinguishing Electromagnetic Field Enhancement from Heating Effects (Advanced Mechanism): Moving beyond simple light absorption, future mechanistic studies must address the paradox of thermal vs. non-thermal effects, particularly in plasmonic or Mie-resonant composites (such as those containing Ag or Cu. Utilizing concepts from Tuning Catalytic Activity and Selectivity in Photocatalysis on Mie-Resonant Cuprous Oxide Particles, it is essential to distinguish between two concurrent light-matter interactions:

  -

  Electromagnetic Field Enhancement (Non-Thermal): The generation of strong localized electromagnetic fields (the “antenna” effect) which accelerates the non-thermal generation of electron–hole pairs and drives the catalytic reaction.

  -

  Photothermal Heating (Thermal): The generation of local heat via non-radiative decay. Quantifying the distinct role of these mechanisms is critical because while field enhancement consistently boosts catalytic rates, the heating effect can be parasitic or alter reaction selectivity. Tuning the excitation wavelength allows researchers to selectively maximize the electromagnetic field enhancement at resonance frequencies while minimizing detrimental thermal effects, a level of control necessary for developing high-selectivity BBAC photocatalysts.

• Wavelength Tuning for Selective Control: The sources confirm that different light sources were used across various studies: natural light for the AC/MoS₂ composite, visible light for the Ag-loaded ZnO:CNT composite and the photo-Fenton system using Cu-g-C₃N₄/BC, and UV light for Sorghum-derived Carbon Dots. [1,5,11,12]. The sources also acknowledge that TiO₂’s effectiveness under visible light is improved through modifications or by exploiting the self-degradation properties of certain dyes. [10].

To improve the manuscript in this aspect, we should utilize the concepts derived from the suggested article, Tuning Catalytic Activity and Selectivity in Photocatalysis on Mie-Resonant Cuprous Oxide Particles: Distinguishing Electromagnetic Field Enhancement Effect from the Heating Effect, to discuss how:

• Excitation Wavelength Dependence: Tuning the wavelength can control which reactive oxygen species are predominantly generated (e.g., favoring reductive pathways by exciting specific plasmon resonances) [1].
• Selective Degradation: Understanding this control is key for developing composite catalysts that can selectively degrade specific components in mixed dye effluents.
• Tuning Selectivity via Advanced Engineering: The sources detail extensive modification and engineering strategies, including magnetic functionalization (e.g., BC-IM), surfactant modification (CTAB-modified BAC), and heterojunction design (Cu-g-C₃N₄/BC). [4]
  • Radical Species and Modification: The Cu-g-C₃ N₄/BC composite study did use Electron Paramagnetic Resonance (EPR) tests to identify the active species resulting from its particular design. These tests confirmed that hydroxyl radicals (•OH) were the main active species, with minor roles played by superoxide radicals (•O₂⁻) and photogenerated holes (h⁺).
  • Intentional Tuning: While this confirms the resulting radical dominance, the sources do not explicitly report any study that intentionally used advanced techniques like defect engineering (e.g., creating specific oxygen vacancies) or facet control to deliberately shift the balance between •OH and •O₂⁻ or h⁺ in order to tune selectivity between different types of pollutants.

6.2. Current Challenges

High Costs and Sludge Generation: Traditional physicochemical methods like coagulation, membrane filtration, and adsorption often suffer from high operational costs, membrane fouling, and the generation of substantial amounts of secondary pollution or sludge, which then requires further treatment and disposal [4]. Activated carbon, while effective, can be economically unviable if commercially sourced [4].

Environmental Impact of Chemical Activation: Although chemical activation methods offer advantages in terms of porosity and yield, they frequently involve the use of corrosive and toxic chemical reagents (e.g., KOH, H₃PO₄, ZnCl₂). This leads to environmental pollution, complex and costly post-treatment processes, and waste management issues [8,13,20].

Optimization and Scalability: Most research is currently confined to the laboratory scale, with minimal validation at pilot or industrial levels. Scaling up production faces hurdles due to the variability of biomass precursors like bamboo (species, age, growth conditions), which can impact yield, surface chemistry, and reproducibility of performance [20]. High-temperature pyrolysis and advanced pretreatment methods also demand significant energy, increasing operational costs [20].

Limited Catalytic Efficiency and Specificity: While biological treatments are cost-effective and produce less sludge, their catalytic efficiency can be limited, and they often require specific environmental conditions (pH, dissolved oxygen, nutrients, temperature) that are difficult to maintain in real-world scenarios [4,12].

Long-term Performance and Regeneration: The long-term performance, including regeneration efficiency over multiple adsorption–desorption cycles, degradation behavior, and safe disposal or reuse strategies for spent materials, is often not deeply explored in current studies which usually can be portrayed via efficiency trend graphs as shown in Figure 4.

6.3. Knowledge Gaps

Biomass Variability and Properties: There are limited studies on how specific bamboo species, their age, and diverse growing conditions influence the physicochemical properties and performance of the resulting activated carbon [20]. This variability makes standardization challenging.

Mechanistic Understanding at a Deeper Level: While adsorption and photocatalytic mechanisms are generally understood, the precise, in situ mechanistic pathways, including charge transfer kinetics, radical formation, and surface interactions, are often hypothesized rather than experimentally verified with advanced techniques. For example, the interplay between different interaction types (electrostatic, hydrogen bonding, π-π stacking) for dye adsorption requires further elucidation [16].

Performance in Complex Real-World Matrices: The effectiveness of these materials in complex real-life wastewater matrix systems, which contain mixtures of dyes, other organic pollutants, heavy metals, varying ionic strengths, and emerging contaminants (e.g., PFAS, microplastics), is poorly studied [13].

Dye Leaching and Color-Fastness: For dyed bamboo products, there is a need to quantify dye leaching from bamboo tissue and to develop more water-tight and color-fast, weather-resistant dyes [26].

To summarize, reduced electron–hole recombination, the enhanced conductivity of the bamboo charcoal facilitating charge transfer, and the role of heterojunctions in electron–hole separation, the following spectroscopic and time-resolved experiments should be reported to quantitatively support these asserted mechanisms:

• Time-Resolved Photoluminescence (TRPL) Spectroscopy
  Purpose: TRPL is used to quantitatively measure the radiative decay kinetics of photogenerated charge carriers, providing a direct measurement of electron–hole pair recombination rates.
  • Key Observables: Longer Lifetime: A significant increase in the photoluminescence lifetime (τ) (typically measured in nanoseconds to microseconds) for the BBAC-metal oxide composite (e.g., AC/MoS₂ or Cu-g-C₃N₄/BC) compared to the pristine metal oxide (MoS₂ or TiO₂) would quantitatively confirm reduced electron–hole recombination.
  • Quenching of PL Intensity: A strong quenching (reduction) in the overall photoluminescence intensity of the composite relative to the metal oxide component provides evidence that the BBAC acts as an efficient electron sink, pulling electrons away from the semiconductor and promoting separation at the heterojunction interface.
• Transient Absorption Spectroscopy (TAS) and Ultrafast TAS (UTAS)
  Purpose: TAS and UTAS probe the non-radiative fate of photogenerated species by monitoring transient changes in absorption over time, allowing the tracking of free carriers, trapped charges, and intermediate radicals across timescales ranging from femtoseconds to milliseconds.
  • Key Observables: Interfacial Transfer Kinetics: TAS can measure the rate of charge injection or transfer across the heterojunction interface. The instantaneous decay of the semiconductor signal (e.g., the signal attributed to conduction band electrons in ZnO or TiO₂) and the simultaneous appearance of a new signal attributed to trapped electrons on the highly conductive bamboo charcoal (BBAC) surface would prove rapid and efficient interfacial charge transfer.
  • Trapped-State Lifetimes: An extended lifetime for the charge carriers trapped on the BBAC surface, compared to the bulk recombination time within the pure metal oxide, would demonstrate that the BBAC supports effective charge separation and stabilizes the required carriers for degradation, thereby enhancing catalytic activity.
• Time-Resolved Electron Paramagnetic Resonance (TR-EPR)
  Purpose: While standard Electron Paramagnetic Resonance (EPR) is cited for identifying stable, long-lived reactive species such as hydroxyl radicals (•OH), TR-EPR measures the kinetics of formation and decay of these radicals and other paramagnetic charge carriers.
  • Key Observables: Radical Formation Rate: TR-EPR would measure the rate of formation of key reactive oxygen species (•OH and •O₂⁻) immediately following light excitation in the composite compared to the pure semiconductor. A faster and higher concentration of radical species generated by the composite would quantitatively link the enhanced charge separation at the heterojunction to the increased production of the potent oxidizing agents responsible for degradation.
  • Active Site Verification: TR-EPR can confirm the role of specific trapped-hole signatures in generating •OH from adsorbed water (H₂O) or hydroxide (OH⁻) ions, providing molecular-level evidence of how the holes migrating through the heterojunction are utilized for pollutant oxidation.

In summary, adopting these advanced, time-resolved techniques is critical to moving the field beyond simply correlating high performance with hypothesized charge separation and instead generating the quantitative kinetic data necessary to rigorously validate the mechanism of interfacial charge transfer and reduced recombination in these BBAC-based photocatalysts.

6.4. Future Directions

To address these challenges and knowledge gaps, future research should focus on several key areas:

• Sustainable Synthesis and Activation Methods

Develop greener alternatives for chemical activating agents, such as bio-based activators or closed-loop recovery systems, to minimize environmental impact.

Explore novel, low-energy production routes such as solar-powered pyrolysis, mechanochemical activation, or low-temperature hydrothermal methods, aligning with circular economy principles.

Investigate the use of different waste materials for AC production, such as ginger stems, for sustainable development [8].

2.

Advanced Doping and Surface Engineering

Refine activation parameters to precisely control and maximize specific properties like surface area, pore size distribution, and the nature and density of surface functional groups [20].

Develop cost-effective and efficient methods for incorporating diverse functional groups or doping with various metals and non-metals to tailor adsorptive and catalytic properties for specific pollutants. This includes exploring combinations of pretreatments like ultrasound or hydrothermal carbonization for bamboo biochar [20].

Further research into the synergistic effects of multi-component doped composites (e.g., metal oxides with carbon nanotubes, graphene, or carbon dots) to optimize their performance and stability [5,12,17].

3.

In-depth Mechanistic Studies

Employ advanced in situ characterization techniques (e.g., X-ray absorption spectroscopy, solid-state NMR, advanced computational simulations) to experimentally verify and gain a deeper understanding of adsorption and photocatalytic degradation mechanisms at the molecular level.

Identify and quantify intermediate degradation products using advanced analytical techniques like LC-MS to elucidate complete degradation pathways and assess toxicity [3].

4.

Scalability and Real-World Applications

Translate successful laboratory-scale innovations into pilot and industrial-scale production, addressing issues of consistency and cost-effectiveness [20].

Conduct comprehensive studies on the performance of these materials in complex industrial wastewater matrices and other challenging environments (e.g., saline conditions, presence of multiple pollutants).

Develop standardization protocols for bamboo-based precursors and AC products to ensure reproducibility and market acceptance [20].

5.

Integration with Emerging Technologies

Integrate machine learning and artificial intelligence (AI) tools to predict and optimize process parameters (e.g., pyrolysis temperature, impregnation ratios, residence times) for faster material design and discovery [13,15].

Explore the application scope of BBAC beyond dye degradation to niche areas such as hydrogen storage, capacitive deionization, CO₂ capture, and biomedical applications (e.g., drug delivery, biosensing).

6.

Holistic Sustainability Assessment

Conduct interdisciplinary studies encompassing lifecycle assessments, techno-economic analyses, and risk assessments to certify the commercial viability and environmental friendliness of BBAC in comparison to conventional and other biomass-based carbons [15].

By focusing on these areas, future research can bridge existing gaps, mitigate challenges, and unlock the full potential of bamboo-based activated carbon materials for a truly sustainable and effective approach to global water purification.

7. Conclusions

The global challenge of water pollution by toxic industrial dyes necessitates the urgent development of sustainable and highly efficient treatment technologies. This review has highlighted the exceptional potential of activated carbon (AC), particularly that derived from abundant and renewable bamboo biomass, as a robust solution for dye degradation. Bamboo-based activated carbon (BBAC) offers significant advantages stemming from its rapid growth, unique natural microstructure, and favorable chemical composition, enabling the production of AC with high surface areas and well-developed porosity.

The critical analysis revealed that while adsorption plays a fundamental role, the integration of advanced doping strategies, especially with metal oxides such as MoS₂, CuxO, TiO₂, and ZnO, significantly enhances the dye removal efficiency. These dopants facilitate photocatalytic degradation by promoting the generation of reactive oxygen species (like hydroxyl and superoxide radicals), reducing electron–hole recombination, extending light absorption into the visible spectrum, and leveraging synergistic effects with the carbon matrix. For instance, AC/MoS₂ (ACM) composites demonstrated 98% MB degradation, while Cu-g-C₃N₄/BC(600) achieved complete MB and RhB degradation within 10 min. Similarly, Ag-loaded ZnO:CNT showed nearly 100% MB degradation in just 2 min, showcasing the remarkable capabilities of these advanced composites. Furthermore, surface modifications with surfactants, magnetic particles, and silver nanoparticles have been shown to drastically improve adsorption capacities and enable convenient catalyst recovery.

Despite these promising advancements, the field faces challenges related to the scalability of production, the environmental impact of chemical activators, and the need for more in-depth mechanistic understanding in complex real-world wastewater matrices. Future research must prioritize sustainable synthesis methods, including greener activation agents and low-energy routes, along with advanced characterization techniques to elucidate precise degradation pathways. Integrating machine learning for process optimization, conducting large-scale pilot studies, and performing comprehensive techno-economic and lifecycle assessments are crucial steps toward the commercial realization and widespread adoption of these innovative bamboo-based materials. By addressing these challenges, bamboo-derived activated carbon composites can profoundly contribute to environmental remediation and the advancement of a circular bioeconomy for clean water.