Introduction of CoCl2·6H2O into Co3O4 for enhancement of hydroxyl radicals and effective charge separation

Abstract

Porous sphere-like tricobalt tetraoxide (Co₃O₄)–cobalt chloride hydrate (CoCl₂·6H₂O, CCH) heterojunctions are obtained using a one-step facile solution combustion route. The heterostructure is confirmed by XRD, HRTEM, and XPS measurements. Their photocatalytic performances are evaluated by the degradation of methyl orange (MO) and the reduction removal of Cr(VI) ions under visible light irradiation. The heterojunction containing 81.5 wt% Co₃O₄ and 18.5 wt% CCH exhibits the highest photocatalytic performance, for which the pseudo-first-order reaction rate constant is 10.0 and 8.7 times that of pure Co₃O₄ towards MO degradation and Cr(VI) reduction, respectively. This enhancement in activity can be attributed to the effective electron transfer from the conduction band of Co₃O₄ to that of CCH, which is verified with a double increase of the photocurrent valve of the heterojunction sample electrode in comparison with the bare Co₃O₄ sample electrode. Electron paramagnetic resonance, fluorescence spectrophotometry and scavenger experiments indicate that photo-induced holes, and hydroxyl and superoxide anion radicals are the active species responsible for the photo-oxidation of MO. The reasons for the formation of these species are discussed and proposed based on the band gap structures of Co₃O₄ and CCH. The recycling experiment results indicate that the activity can be regained by a remedial experiment.