Mg-doped keratin-based biochar@hydrogel composite: An efficient cadmium and lead adsorbent

Heavy metal contamination in water and soil can be remediated using biochar, however, the limited adsorption capacity and difficult separation of raw biochar restrict its practical application. To address these challenges, this study developed a recyclable magnesium-doped keratin-based biochar@hydrogel composite (MBC@HG) via a facile one-pot synthesis method. The composite features a three-dimensional network structure that ensures excellent mechanical strength and environmental stability. The specific surface area, Mg content, total basic metal content, and adsorption capacities for Cd²⁺ and Pb²⁺ all increased proportionally with the mass ratio of Mg-doped keratin-based biochar (MBC) within the MBC@HG composite. Adsorption kinetics for MHG (the best mass ratio of biochar/acrylamide) followed the pseudo-second-order kinetic model. Notably, the adsorption capacity achieved 80% of the equilibrium adsorption capacity within the first hour. The Cd²⁺ and Pb²⁺ maximum adsorption capacities of MHG in isotherm experiments were 141 mg g^-1 and 291 mg g^-1, respectively. The primary adsorption mechanisms were identified as surface complexation, ion exchange, and precipitation. This work presents a novel and sustainable strategy that simultaneously enables keratin waste valorization and production of an efficient, easily separable adsorbent for heavy metal removal.