Hexavalent Chromium Adsorption on Adsorbent Derived From Biomass of Fabaceae Plant in Vietnam: Effect of Preparation Conditions on Equilibrium Adsorption Capacity

The present work is devoted to examining the potential of Sesbania sesban biochar produced through slow pyrolysis for 120 min at 300°C in removing hexavalent chromium from the aqueous phase. The physicochemical characteristics of biochar were analyzed utilizing a variety of analytical tools including SEM, BET, and FTIR. Results revealed that the biochar had a smooth surface, an even stacking pattern with a porous texture, a large BET surface area equal to 562 m²/g, and a pH_pzc of 6.9. The biochar efficiency in eliminating Cr (VI) was investigated through several variables, including biochar dosage (0.1–0.4 g), pH (2–8), initial chromium ion concentration (10–40 mg/L), and adsorption time (15–120) min. The results identified the best conditions for adsorbing Cr (VI): an initial concentration of 10 mg/L, an absorbent dosage of 0.3 g, a pH solution of 2, and a reaction time of 90 min. The experiment achieved a Cr (VI) removal efficiency of over 90% by applying these conditions. The adsorption isotherm data were analyzed and showed a strong correlation coefficient (R² = 0.985) for Langmuir monolayer model, in which the maximum adsorption capacity achieved was 5.3 mg/g. According to the kinetic investigation, the adsorption of Cr (VI) was adapted to a pseudo-second-order model having a high R² value of 0.998. These results demonstrate that Sesbania sesban biochar has excellent potential as a cost-effective and highly efficient adsorbent for removing hexavalent chromium and improving water quality.