Utilization of Activated Biochar from Isatis tinctoria L. for the Efficient Removal of Methylene Blue and Pb2+ from Aqueous Solutions

Abstract

This study evaluates the biochar (BC) synthesized from the branches of the plant Isatis tinctoria L. (ITL), along with active biochars (BCNa1, BCNa2), as renewable adsorbents for the adsorption of organic and inorganic pollutants, focusing particularly on methylene blue (MB) and lead ions (Pb2+). The modification of biochar with NaOH resulted in enhanced surface basicity due to an increased presence of oxygen-containing functional groups on the surface. The adsorbents were characterized by FTIR, TGA, XRD, SEM-EDX, BET, CHNS and zero charge point (pHpzc). The parameters studied were: effect of impregnation ratio, initial metal concentration, pH of the solution, adsorbent dosage, temperature, contact time, and multicomponent system. The activated biochar exhibited a Langmuir qmax value of 243 mg g-1 for methylene blue and 75 mg g-1 for Pb2+, with the Freundlich model being the most appropriate for methylene blue and the Langmuir model for Pb2+. The pseudo-second-order and Elovich models indicated a good fit, suggesting that chemical adsorption occurs for all components. The primary mechanisms of adsorption for MB and heavy metals on active biochar were identified as chemical adsorption. The remarkable adsorption capacities and high reusability properties for both organic pollutants and inorganic heavy metals position this active biochar as a potential cost-effective adsorbent for alleviating water pollution issues.