Photocatalytic oxidation of glucose in water to value-added chemicals by zinc oxide-supported cobalt thioporphyrazine

Abstract

A new composite photocatalyst, ZnO/CoPzS₈, was obtained by immobilizing cobalt tetra(2,3-bis(butylthio)maleonitrile)porphyrazine (CoPzS₈) onto the surface of home-prepared ZnO. The ZnO/CoPzS₈ composite was well characterized by X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. It turned out that CoPzS₈ was successfully loaded onto the ZnO surface and there existed an interaction between ZnO and CoPzS₈. By using the ZnO/CoPzS₈ composite photocatalyst, the photocatalytic oxidation of glucose to value-added chemicals in pure water was conducted under simulated sunlight irradiation without adding any acid or base. The ZnO/CoPzS₈ composite exhibited a higher photocatalytic activity in comparison to pure ZnO and pure CoPzS₈ owing to the synergistic effect between ZnO and CoPzS₈. Gluconic acid, arabinose, glycerol and formic acid were all observed as oxidation products when pure ZnO or ZnO/CoPzS₈ composite was used. More importantly, glucaric acid was also obtained in the ZnO/CoPzS₈ photocatalytic system, indicating that the presence of CoPzS₈ changed the glucose reaction pathway. In addition, the active species generated in the photocatalytic process were further identified by electron spin resonance (ESR) technology and scavenger experiments. A possible photocatalytic conversion pathway of glucose has been proposed according to the experimental results.