Biochar derived from corn residues for Cr(VI) adsorption from multicomponent systems: influence of acid functionalization

Wastewater contamination by potentially toxic elements (PTEs) poses serious environmental and public health risks. Among them, hexavalent chromium (Cr(VI)) is highly toxic, mutagenic, and carcinogenic. This study developed a sustainable adsorbent from corn residue (CR) by producing biochar (ACSB) via H₃PO₄ functionalization, followed by pyrolysis at 600°C, for Cr(VI) removal from aqueous solutions. ACSB was characterised by Proximate Analysis, SEM, BET, TGA, FTIR, and XRD, confirming the conversion of fibrous biomass into a porous, amorphous, and chemically functionalised material with a surface area of 102.5 m² g−¹. Selectivity tests showed that ACSB preferentially adsorbs Cr(VI) over competing metals, achieving effective removal of chromium from the aqueous phase. The effects of contact time, initial concentration, and adsorbent dosage were evaluated using a Design of Experiments (DOE) approach. The maximum adsorption capacity (69.39 mg g−¹) was obtained at low adsorbent dosage and high Cr(VI) concentration. Kinetic studies indicated rapid adsorption, with equilibrium reached within 180 min, and the pseudo-second-order model provided the best fit. The Freundlich isotherm (R2 = 0.960) best described the process, suggesting heterogeneous adsorption involving both physical and chemical interactions. Overall, ACSB is a promising, low-cost, and sustainable adsorbent aligned with circular economy principles.