Montmorillonite-chitosan composite support enhances the electron transfer and stability of loaded copper nanoparticles during the catalytic reduction of Cr(VI)

Abstract

Hexavalent chromium (Cr(VI)), a highly toxic and mobile contaminant commonly found in industrial wastewater, poses substantial environmental and health risks, and its reduction to the less harmful trivalent form (Cr(III)) is a critical remediation strategy. While copper nanoparticles (Cu NPs) offer a cost-effective alternative to expensive precious metal catalysts, their tendency to agglomerate limits their catalytic efficiency. To address this, we synthesized a Cu-MMT/CS (montmorillonite/chitosan) composite catalyst via a straightforward two-step pyrolysis method, leveraging the chelating ability of chitosan and the layered structure of montmorillonite to disperse Cu NPs. The optimized Cu-MMT/CS catalyst achieved exceptional performance, removing more than 98 % of Cr(VI) within 6 min via formic acid (FA) as a reductant, and maintained its high efficiency even in the presence of common environmental anions such as Cl^-、NO₃^-、SO₄^2-、CO₃^2-、H₂PO₄^-. The uniformly dispersed Cu nanoparticles serve as the active sites for the catalytic reaction, while the high degree of graphitization of the carrier (MMT/CS structure) and the low charge transfer resistance facilitate charge transfer between the catalyst and FA, promoting the decomposition of FA to produce active hydrogen, which in turn enhances the ability to reduce Cr(VI). This study offers a cost-effective, environmentally friendly solution for Cr(VI) reduction, advancing the design of sustainable nonprecious metal-based catalysts for wastewater treatment.