Efficient degradation of orange II by ZnMn₂O₄ in a novel photo-chemical catalysis system

A ZnMn₂O₄ catalyst has been synthesized via a sucrose-aided combustion method and characterized by various analytical techniques. It is composed of numerous nanoparticles (15–110 nm) assembled into a porous structure with a specific surface area (SSA) of 19.1 m²·g⁻¹. Its catalytic activity has been investigated for the degradation of orange II dye using three different systems, i.e., the photocatalysis system with visible light, the chemocatalysis system with bisulfite, and the photochemical catalysis system with both visible light and bisulfite. The last system exhibits the maximum degradation efficiency of 90%, much higher than the photocatalysis system (15%) and the chemocatalysis system (67%). The recycling experiments indicate that the ZnMn₂O₄ catalyst has high stability and reusability and is thus a green and eximious catalyst. Furthermore, the potential degradation mechanisms applicable to the three systems are discussed with relevant theoretical analysis and scavenging experiments for radicals. The active species such as Mn(III), O₂^•−, h⁺, e_aq⁻, SO₄^•− and HO^• are proposed to be responsible for the excellent degradation results in the photo-chemical catalysis system with the ZnMn₂O₄ catalyst.[Figure not available: see fulltext.].