Selectivity enhancement in the g-C3N4-catalyzed conversion of glucose to gluconic acid and glucaric acid by modification of cobalt thioporphyrazine

Abstract

g-C3N4/CoPz (cobalt tetra(2,3-bis(butylthio)maleonitrile)porphyrazine) composite was found to be highly photocatalytic active in oxidation of glucose to gluconic acid and glucaric acid using H2O2 as the oxidant under mild conditions. Under the optimal conditions, the total selectivity of gluconic acid and glucaric acid reached 79.4% with 52.1% of glucose conversion under xenon lamp irradiation within 20 min. The surface modification of g-C3N4 by CoPz displayed a significantly enhanced photocatalytic activity and improved selectivity to gluconic acid and glucaric acid in glucose oxidation in comparison to pure g-C3N4, this was attributed to the synergistic effect between g-C3N4 and CoPz. The influence of the CoPz content, H2O2 addition, glucose concentration and catalyst amount on the glucose oxidation were further evaluated and discussed. g-C3N4/CoPz composite exhibited more efficient separation of the photogenerated carriers in comparison to the individual components, which was responsible for its enhanced photocatalytic activity. The CoPz modification can enhance the adsorption of glucose and reduce the adsorption of organic acids on the surface of catalyst, more importantly, the presence of CoPz can reduce the formation of strong and nonselective hydroxyl radical (·OH), thus obtaining high selectivity of gluconic acid and glucaric acid. In addition, recyclability experiments revealed that the g-C3N4/CoPz composite photocatalyst was stable after five cycles with no apparent loss in activity or selectivity.