In a recent study published in BiomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More and Bioenergy, Shubhangi Umare, Ajay K. Thawait, and Sumit H. Dhawane detailed the development and optimization of sustainable activated biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More (AB) synthesized from pigeon pea stalk waste (PPSW) for the highly efficient removal of the Methylene Blue (MB) dye from water. This research addresses the twin challenges of valorizing India’s substantial annual agricultural waste—which is often burned or landfilled—and tackling water pollution with a cost-effective, high-performance material. The authors utilized a dual chemical activation strategy, synthesizing two types of AB using sodium hydroxide (NaOH), a strong alkali, and zinc chloride (ZnCl2​), a Lewis acid, to enhance the raw biochar’s adsorption properties.

The synthesis process was rigorously optimized using the L9​ orthogonal array design within the Taguchi method, a statistical technique that minimizes experimental runs while identifying the dominant parameters. Four critical factors were evaluated: activation temperature, activation time, reagent-to-carbon ratio, and stirring speed. The ANOVA (Analysis of Variance) results confirmed the statistical significance of the models, with activation temperature and the reagent-to-carbon ratio exerting the strongest influence on the biochar’s performance, primarily by controlling pore development and surface functionalization.

The optimization revealed distinct pathways for the two activating agents. For NaOH/AB, the highest adsorption capacity (AC) of 7.54 mg/g and a 100% RE were achieved under relatively mild thermal conditions, specifically at 40∘C and 12 h with a 4:1 reagent-to-carbon ratio. Conversely, ZnCl2​/AB performed best at a higher temperature of 80∘C for 12 h with a 6:1 ratio, reaching an AC of 7.51 mg/g and virtually complete removal (99.9% RE). This difference is attributed to their distinct mechanisms: NaOH facilitates chemical etching and preserves micropores essential for adsorption under mild heat, while ZnCl2​ requires higher heat to act as a dehydrating agent, promoting aromatization and stable, high-porosity carbon frameworks.

Characterization confirmed the success of the chemical activation, particularly highlighting the dramatic improvement in textural properties. The BET surface area of the raw PPSW was a mere 25.42 m2/g, but it increased more than two-fold to 53.83 m2/g with NaOH activation and over four-fold to 110.23 m2/g with ZnCl2​ activation. The FESEM images visually corroborated this, showing that both AB types developed extensive, well-defined, interconnected porous networks, with pore diameters falling within the 2 to 50 nm mesoporous range—an ideal size for accommodating and diffusing the MB dye molecules. Adsorption isotherm analysis reinforced these findings, showing that both biochars exhibited excellent correlation (R2>0.95) with the Langmuir model, indicating monolayer adsorption on a homogeneous surface. The maximum monolayer adsorption capacity (qm​) was found to be 88.49 mg/g for NaOH/AB and a slightly higher 92.59 mg/g for ZnCl2​/AB. Kinetic studies further demonstrated that the process is best described by the pseudo-second-order kinetic model (R2≈0.99), implying that chemisorption, driven by electron sharing or exchange between the MB dye and the biochar’s surface functional groups (like hydroxyl and carboxyl groups), is the dominant mechanism. The primary driving force was identified as electrostatic attraction between the positively charged MB molecules and the negatively charged AB surface.

From a sustainability perspective, both biochars showed exceptional promise. The production cost was estimated to be only $4.037/kg for NaOH/AB and $4.246/kg for ZnCl2​/AB, making them competitive with and often cheaper than commercial adsorbents. Furthermore, the regeneration and reuse study confirmed their durability, with MB removal efficiency decreasing by only 15% for NaOH/AB and 17% for ZnCl2​/AB after five consecutive cycles, ensuring long-term applicability and reduced waste generation. The study successfully established PPSW-derived activated biochar as an environmentally benign, cost-effective, and technically viable solution for wastewater remediation, strongly supporting the transition toward circular bioeconomy principles by converting waste into a high-value product.

Source: Umare, S., Thawait, A. K., & Dhawane, S. H. (2026). Development and optimization of sustainable activated biochar from waste pigeon pea stalks for efficient adsorptive removal of methylene blue from water. Biomass and Bioenergy, 204, 108385.