In an effort to find sustainable and affordable solutions for treating water contaminated with toxic organic pollutants, researchers Fateh Barbari and colleagues investigated the use of biochar created from Vicia Faba (broad bean) stems. The results, published in Scientific Reports, establish that this biochar, produced through direct pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More is a highly effective adsorbent for phenol removal from aqueous solutions. Phenol is a pervasive and harmful organic pollutant originating from various industrial activities, including petrochemical and pharmaceutical manufacturing, and its elimination from water is crucial for protecting human and ecological health.

The prepared Vicia Faba Stem Biochar (VFSB) was thoroughly characterized to understand the properties that contribute to its performance. It was found to possess a high carbon content of 83.1% and a significant specific surface area of 144.34m²/g. Structural analysis revealed a highly porous, irregular surface texture and a composition categorized as a mesoporous material. The surface also exhibits a point of zero charge of 6.0, meaning the surface is electrically neutral at this pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More but becomes positive in more acidic conditions and negative in more alkaline conditions.

Adsorption experiments confirmed the VFSB’s efficacy, demonstrating a maximum phenol removal efficiency of 88.86% at pH 6.0. The process was found to be rapid, reaching equilibrium within a short contact time of 180 minutes (three hours). The maximum adsorption capacity was determined to be 44.25mgg^-1 at the equilibrium time, an increase in capacity of 45.82% across the studied pH range of 2–12. The optimal pH of 6.0, which matches the biochar’s pHpZC, suggests that non-electrostatic interactions are primarily responsible for the adsorption at this condition, as the surface has almost no net charge and phenol is predominantly in its neutral form of 9.95.

A detailed analysis of the adsorption kinetics and isotherms provided key insights into the mechanism of phenol uptake. The kinetic data for the adsorption process showed an excellent fit with the pseudo-second-order (PSO) model. This superior fit suggests that chemisorption, or chemical adsorption involving the formation of chemical bonds between the phenol molecules and the biochar surface, is the dominant rate-limiting step. Analysis of the equilibrium data further revealed that the Freundlich isotherm model provided the best representation of the experimental data . This result points to a mechanism of multilayer adsorption occurring on the heterogeneous surface of the biochar, consistent with the observed porous and irregular structure. The Freundlich constant n (2.217), which is greater than 1, further confirms the favorable nature of the adsorption under the tested conditions.

Thermodynamic investigations, revealed that the adsorption of phenol onto VFSB is a spontaneous and endothermic process. The overall adsorption is governed by a combination of non-electrostatic mechanisms, including pi-pi interactions, hydrogen bonding between the phenol and the biochar’s functional groups ,Van der Waals forces, and the physical process of pore filling.

Finally, the study demonstrated the practical utility and sustainability of VFSB by testing its reusability. After four consecutive adsorption cycles, the phenol removal efficiency decreased from its initial maximum. However, after a simple regeneration step involving soaking the saturated biochar in a sodium hydroxide solution and rinsing, the material recovered most of its performance, achieving a high removal rate in the first regeneration cycle. These findings underscore the potential of Vicia Faba stem biochar as a reusable, cost-effective, and practical adsorbent, opening avenues for future research into enhancing its surface properties and exploring its use in complex, multi-pollutant real-world wastewater treatment systems.

Source: Barbari, F., Khechana, S., Hecini, L., Bacha, N., Halati, M. S., Babes, B., Alghamdi, A., Alsharef, M., Althobiti, A., & Gedefie, B. A. (2025). Kinetic and isothermal insights on phenol removal via biochar from Vicia Faba stems. Scientific Reports, 15(40591).