New insights into Cd(ii) removal from water using iron-doped chitosan biochar: synthesis, characterization, and adsorption mechanism

Abstract

An eco-friendly iron-doped chitosan biochar composite (Fe-CS@BC) was innovatively synthesized utilizing chitosan as a template for Cd(II) adsorption. The adsorption capacity for Cd(II) by biochar was significantly enhanced by the loading of iron. Under pH 6 conditions, the adsorption of 50 mg L⁻¹ Cd(II) by 0.05 g Fe-CS@BC reached equilibrium within 6 h, with an adsorption capacity of 29.89 mg g⁻¹. The characterization of the material before and after the reaction indicates that the iron species were uniformly dispersed across the unmodified biochar matrix. The loading of Fe resulted in a considerable number of pores and a more abundant pore structure on the surface of the material. The specific surface area of Fe-CS@BC was found to be 14 times that of chitosan biochar (CS@BC). The potential mechanisms for Cd(II) removal by Fe-CS@BC were comprehensively evaluated, including ion exchange, complexation reaction, electrostatic attraction and physical adsorption.