Valorization of citrus waste: Use in catalysis for the oxidation of sulfides

Abstract

The utilization and valorization of industrial waste is an effective strategy for environmental protection. Since the juice industry generates a huge amount of citrus waste, we studied the application of thermally treated orange peel in catalysis. On the other hand, Keggin heteropolyacids are excellent oxidant catalysts used as a replacement for conventional oxidants; however, their solubility in polar solvents and the low specific area limit their use as heterogeneous catalysts. The utilization of treated orange peel as heteropolyacid support for the selective oxidation of sulfides is presented here. Firstly, orange peel was thermally treated, and then it was incorporated with heteropolyacids (PMo) during the silica synthesis by the sol-gel method. Therefore, SiO2-PMo, SiO2-OP100-PMo, and SiO2-OP200-PMo were obtained, characterized by FTIR, SBET, XRD, and potentiometric titration, and were tested as heterogeneous catalysts in the selective oxidation of sulfide to sulfoxide in a greener process: H2O2 as oxidant and ethanol as solvent, at 25 °C.