Biochar-derived activated carbon, abbreviated BAC in the literature, begins its life as ordinary biomass. Feedstocks are converted to biochar through pyrolysis—heating in the absence of oxygen—or through hydrothermal carbonization, a wet process that uses pressurized water at moderate temperatures. Each route leaves a distinct fingerprint on the resulting material. Pyrolysis tends to produce more aromatic, carbon-rich structures, while hydrothermal carbonization yields hydrochars with abundant oxygen-containing functional groups and is particularly well suited to wet feedstocks such as food-industry sludge and sewage. The review emphasizes that the choice of feedstock matters enormously: lignin-rich woods behave differently from cellulose-rich agricultural residues, and the mineral content of the original biomass—its inherent potassium, calcium, or silica—can itself influence pore development during subsequent processing.

The real magic happens during activation, the step that converts a relatively inert char into a highly porous adsorbent. Physical activation uses steam or carbon dioxide at high temperatures, gently gasifying the carbon skeleton and carving out an intricate network of pores. Chemical activation, by contrast, impregnates the char with agents such as potassium hydroxide, phosphoric acid, or zinc chloride before heating, dramatically accelerating pore formation and often producing far higher surface areas. The review notes that chemical activation with KOH remains the workhorse of the field, generating microporous materials with exceptional adsorption capacities, but it comes at an environmental cost: corrosive chemicals, substantial water consumption for washing, and energy-intensive heating. Physical activation with CO2, while yielding lower surface areas, is considerably greener—and, intriguingly, studies cited in the review show that CO2-activated carbons can outperform KOH-activated counterparts in certain electrochemical applications, suggesting that greener is not always worse.

One of the most important conceptual contributions of the review is its insistence that the widely reported BET surface area—a standard measure of internal surface derived from nitrogen gas adsorption—is an incomplete predictor of adsorption performance. Two carbons with identical surface areas can behave very differently in real water treatment. What matters is pore accessibility: whether contaminant molecules can actually reach the adsorption sites. Micropores, those smaller than two nanometers, are ideal traps for small molecules and hydrated metal ions, but they can exclude or slow the diffusion of larger contaminants. Mesopores, between two and fifty nanometers, act as transport highways that speed larger molecules such as dyes and pharmaceuticals toward the interior. The most effective adsorbents are often hierarchically porous, combining both regimes in a single particle. Crystallinity and the degree of structural disorder also play a role, as does the transport behavior of water within the pore network.

Surface chemistry is the second pillar of the framework. Oxygen-containing groups such as carboxyl, hydroxyl, and carbonyl functionalities can dramatically enhance the uptake of polar contaminants and heavy metals through electrostatic attraction, hydrogen bonding, and complexation. Nitrogen doping introduces basic sites that bind acidic pollutants, while sulfur and phosphorus functionalities offer additional binding chemistries. The review stresses that these groups are not merely decorative; they determine the point of zero charge of the material, its wettability, and its affinity for specific classes of pollutants. For heavy metals such as lead, manganese, iron, and zinc, surface complexation with oxygen groups often dominates. For organic dyes such as methylene blue and Rhodamine B, a combination of pi-pi stacking interactions with the aromatic carbon skeleton and electrostatic interactions with charged surface groups governs uptake.

Perhaps the most timely section of the review concerns per- and polyfluoroalkyl substances, the notorious PFAS family of ‘forever chemicals’ that includes PFOA and PFOS. These compounds, used for decades in non-stick coatings, firefighting foams, and water-repellent fabrics, are extraordinarily resistant to degradation and have contaminated water supplies worldwide. Adsorption is currently one of the most practical remediation strategies, and the review highlights that PFAS capture is strongly influenced by hydrophobic and fluorophilic interactions rather than simple pore filling. The fluorinated tails of PFAS molecules seek out hydrophobic carbon domains, while the charged head groups interact with surface functionalities. Recent studies cited in the review demonstrate that biochar-derived carbons—including those made from invasive water hyacinth and from microalgae residues left over after lipid extraction—can achieve meaningful PFOS removal under neutral pH conditions, particularly when activated by microwave-assisted methods that rapidly develop the right pore architecture.

The breadth of contaminants addressed by BAC is remarkable. The reviewed literature documents successful removal of pharmaceuticals such as amoxicillin, ibuprofen, acetaminophen, tetracycline, and fluoroquinolone antibiotics; industrial dyes; the herbicide glyphosate; the endocrine disruptor bisphenol A; arsenic from contaminated drinking water in Pakistan; and phosphate recovered from wastewater for reuse as fertilizer. In many cases, adsorbents made from humble feedstocks—mango seeds, olive stones, tea stalks, date palm waste, ginkgo leaves, potato peel—achieve removal efficiencies approaching those of commercial activated carbon, at a fraction of the cost and with the added benefit of valorizing waste streams. Kinetic and thermodynamic analyses across these studies consistently show that adsorption is fast in the initial stages, slows as sites fill, and follows pseudo-second-order kinetics in many systems, indicating chemisorption contributions alongside physical adsorption.

Yet the review is refreshingly honest about the sustainability challenges that stand between laboratory success and real-world deployment. Chemical activation consumes large quantities of corrosive reagents and generates acidic or alkaline wastewater that must itself be treated. Pyrolysis and activation furnaces are energy-hungry, and if that energy comes from fossil fuels, the net environmental benefit shrinks. Regeneration of spent adsorbent—essential for economic viability—often requires thermal treatment that can degrade surface functionality and collapse pore structure. Scale-up remains the elephant in the room: a synthesis that works beautifully with grams of feedstock in a muffle furnace may fail economically at the ton scale. The authors argue that rigorous life cycle assessment and techno-economic analysis must become standard companions to adsorption studies, rather than afterthoughts.

To overcome these hurdles, the review proposes three forward-looking strategies. Hybrid activation, which combines mild chemical pre-treatment with physical activation, can reduce chemical consumption while preserving high porosity. Low-chemical processing routes, including mechanochemical activation—where ball milling induces porosity without liquid reagents—and microwave-assisted heating, which delivers energy directly to the carbon and slashes processing times, offer greener alternatives. Most intriguingly, the authors highlight artificial intelligence as an emerging tool: machine learning models trained on published datasets can predict how feedstock composition and process parameters will shape pore structure and adsorption capacity, allowing researchers to navigate the vast design space of biomass, activation agent, temperature, and residence time far more efficiently than trial and error. Evolutionary algorithms have already been used to optimize co-pyrosis of biomass with plastic wastes, and similar approaches are being applied to porous carbon design for energy storage, a field whose insights transfer readily to adsorption.

The vision that emerges from this review is one of circular economy chemistry at its most elegant: agricultural waste becomes a purification material, contaminated water becomes clean, and the carbon locked in biomass is kept out of the atmosphere in the process. Biochar itself is increasingly recognized as a carbon sequestration tool, and diverting a portion of biochar production into high-value adsorbents could improve the economics of carbon removal schemes. For the billions of people who lack access to safely managed drinking water, and for the ecosystems degraded by industrial effluents, the prospect of cheap, locally produced adsorbents made from regional waste streams is genuinely transformative. The Indonesian-led team, supported by the country’s Ministry of Higher Education, Science and Technology, has provided the field with a coherent roadmap—one that links the molecular details of activation chemistry to the global challenge of clean water, and that makes clear the path forward runs through smarter processing, honest sustainability accounting, and a willingness to let machines help us design the materials of a cleaner future.

Subject of Research: Biochar-derived activated carbon for sustainable water purification and contaminant adsorption

Article Title: Green activated carbon from biochar waste: linking activation pathways, surface chemistry, and adsorption performance for water purification

Article References: Zharvan, V., Ihsan, N., Subaer, S., Samnur, S., Sutikno, S., Diantoro, M., Suryana, R., & Sujiono, E. H. (2026). Green activated carbon from biochar waste: linking activation pathways, surface chemistry, and adsorption performance for water purification. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38281-y

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38281-y

Keywords: activated carbon, biochar, water purification, adsorption, PFAS, pyrolysis, hydrothermal carbonization, surface chemistry, porous materials, circular economy, wastewater treatment, sustainability