Sustainable Valorization of Pb(II)-Loaded Inga edulis Biomass: From Adsorption to Oxygen Evolution Electrocatalysis

Abstract This work reports on the removal of Pb(II) ions from aqueous solution using Inga edulis biomass modified with sulfuric acid (BMIGA), evaluating its performance in a fixed-bed system and potential ecotoxicological effects after the adsorption process. Physicochemical characterization of the material showed that the modification increased the amount of active functional groups, consequently enhancing interaction with metal ions. Batch adsorption tests indicated a strong influence of pH on the removal efficiency, with an optimal pH close to 6.0. The adsorption capacity increased with decreasing particle size and adequate adsorbent dosage. The Thomas and Yoon-Nelson models provided the best fits the experimental data obtained in fixed-bed adsorption experiments, with coefficients of determination close to 0.99 indicating high performance of the system. After the adsorption process, the material saturated with Pb(II) was applied as an electrocatalyst for the oxygen evolution reaction (OER), exhibiting reduced overpotential and a significant improvement in current density. In ecotoxicological tests with Daphnia similis, an EC50.48h value of 13.6 μg L–1 indicated the toxicity of Pb(II), while no acute effects were observed for the post-adsorption supernatants, demonstrating the efficiency of BMIGA in completely removing the metal. It can be concluded that BMIGA represents a sustainable and effective alternative material for the treatment of lead-containing effluents, exhibiting a maximum adsorption capacity of 222.14 mg g–1. In addition to its excellent adsorptive performance, BMIGA also shows potential for reuse as an electrocatalyst and presents favorable environmental safety characteristics.