Photocatalytic behaviour of Ag3PO4, Fe3O4 and Ag3PO4/Fe3O4 heterojunction towards the removal of organic pollutants and Cr(VI) from water: Efficiency and light-corrosion deactivation

Abstract

This work aims to synthesize and study the photocatalytic behaviour of Ag3PO4, Fe3O4 and Ag3PO4/Fe3O4 to oxidize organic pollutants (diclofenac sodium and acid green 25) and photoreduction of Cr(VI). In terms of organic pollutants oxidation, Ag3PO4/Fe3O4 composite showed higher efficiency than bare Ag3PO4 and Fe3O4. Based on the reactive oxygen species scavenging experiments, it was found that Ag3PO4/Fe3O4 can enhance the photogeneration of −O2 species, solving the low ability of bare Ag3PO4 to reduce O2 into −O2 because of its lower conduction band compared to the redox potential of O2/−O2. As a result, it was claimed that the Z-scheme heterojunction is more plausible than type II heterojunction system for enhancing photoproduced charges separation and photoactivity in Ag3PO4/Fe3O4 platform. In terms of photoreduction of Cr(VI), Fe3O4 and Ag3PO4/Fe3O4 were more effective than bare Ag3PO4 under solar light. The deactivation tests carried out comparatively on Ag3PO4 and Ag3PO4/Fe3O4 for successive oxidation of diclofenac sodium under solar light showed that Ag3PO4/Fe3O4 has better long-term use. At the same time, Ag3PO4 lost its activity significantly along with a total change of its colour from green to black because of the strong light corrosion. On top of the high stability and easy magnetic recovery of Ag3PO4/Fe3O4, the coating of Ag3PO4 on low-cost Fe3O4 can have an economic benefit at large scale.