Enhanced adsorption of Cr(VI) pollutants using CaFe2O4@rGO modified-biochar derived from mixture of black soldier flier exuviae and durian peel

Abstract

To solve the problem of hexavalent chromium (Cr(VI))-polluted water sources, mixed black soldier flier exuviae (BSFE) and durian peel (DP)-derived biochar modified with CaFe2O4@rGO (BC-CFr) was synthesized to remove Cr(VI) from wastewater. Our findings indicated that the adsorption of Cr(VI) on BC-CFr reached a maximum at a pH of 2.0, biochar dosage of 0.3 g/100 mL, and initial Cr(VI) concentration of 50 mg/L, with a Cr(VI) adsorption capacity of 30.8 mg/g, which was approximately two times greater than that on pristine biochar (PBC). The characterization results showed that the as-prepared modified biochar was rich in surface functional groups, including amine groups (−NH2) and active sites. Cr(VI) adsorption followed the Elovich kinetic and Freundlich isotherm models, illustrating the adsorption process involved multilayer on the heterogeneous surface. The thermodynamic study confirmed the adsorption process was endothermic. The proposed adsorption mechanisms included adsorption-coupled reduction, electrostatic attraction, and pore filling. This study provided a simple method to prepare compositing biochar using abundantly available agricultural by-products that dealt with the dual problems of Cr(VI)-contaminated water and agricultural solid waste. Besides, the BC-CFr exhibited high desorption performance and recyclability over five consecutive adsorption-desorption cycles, suggesting the BC-CFr is a feasible nanocomposite biochar for effectively removing Cr(VI) from wastewater in practice.