An eco-efficient dual-function technology: Magnetically recoverable rGO-WO3/Fe3O4 ternary heterojunction catalytic system simultaneously performing malachite green photolysis and Cr(VI) reduction

Abstract

This study focuses on developing a system that efficiently removes two contaminants simultaneously: malachite green (MG), an organic dye, and chromium (Cr) ions, which are used as oxidizing agents in the dyeing process. A dual-functional heterojunction photocatalyst was prepared by combining tungsten oxide (WO3, the main photocatalyst) and iron oxide (Fe3O4, a visible light absorber) on a reduced graphene oxide (rGO) support. The 10% rGO-WO3/Fe3O4 catalyst decomposes malachite green in 6 h and reduces Cr(VI) to Cr(III) in 2 h (both at 100 ppm). A mixed solution of MG and Cr(VI) required treatment for only 2 h, showing that the intermediates generated during the reaction positively synergized with each other. Here, the junction of WO3 and Fe3O4, which strongly induces a Z-scheme charge transfer, facilitates photo-charge separation and suppresses exciton recombination. The rGO extended the photocatalytic activity while continuously supplying electrons to the valence band of WO3. Finally, the rGO-WO3/Fe3O4 catalyst was completely recovered after the reaction using a magnet. Ultimately, this system will be useful for the quick, clean, and safe treatment of wastewater containing toxic heavy metals and organic pollutants.