Magnetic porous nitrogen-doped biochar derived from natural loofah sponge activated by potassium hydroxide for efficient adsorption of Pb2+, Cd2+, Cu2+

This study demonstrates a facile one-step carbonization route for converting loofah sponge into magnetic porous nitrogen-doped biochar (FeN@BC-KOH) for the removal of Pb 2+ , Cd 2+ , and Cu 2+ from aqueous solutions. The proposed method integrates KOH activation, nitrogen doping and Fe-based magnetization in a single step, thereby simplifying the preparation procedure relative to conventional multi-step modification strategies. Systematic characterizations confirm the formation of mesoporous structure with high specific surface area, along with abundant oxygen/nitrogen functional groups and Fe-N x active sites. The synergistic contribution of porous structure, nitrogen-containing moieties and magnetic confers the biochar with enhanced adsorption capacity and facile magnetic separation performance. Adsorption conditions were optimized using Box-Behnken Design (BBD). Kinetic investigations demonstrated that the adsorption process adhered to a pseudo-second-order model (R²>0.9688). Meanwhile, the isotherm data were most appropriately characterized by the Freundlich model (R²>0.8723), implying that multilayer adsorption governed by chemisorption was predominant. The principal adsorption mechanisms encompassed complexation, precipitation, ion exchange. FeN@BC-KOH demonstrated excellent reusability (8 cycles). This work provides a green, scalable, and high-efficiency strategy for valorizing agricultural waste loofah sponge into high-performance adsorbents, which exhibits good application potential in the remediation of actual heavy metal-contaminated water.