Co3O4 with Different Morphologies: Synthesis and Performances in Activating Peroxymonosulfate for Methylene Blue Degradation

Three methods (urea hydrothermal-calcination, chemical bath deposition-calcination, and oxalate pyrolysis) were used to prepare CO3O4 powder materials with different morphologies, which were named CO3O4-A, CO3O4-B, and CO3O4-C, respectively. All of them were taken as catalysts to activate peroxymonosulfate (PMS) for the degradation of methylene blue (MB). It is found that these CO3O4 materials were quite different in their catalytic performance. Under the assistance of CO3O4-A, CO3O4-B, and CO3O4-C, the PMS decomposition reaction rate constants were measured as 0.047 1, 0.217 4, and 0.003 7 min(-1), while the degradation ratios of MB were 91.25% (reaction time: 50 min), 100.00% (reaction time: 25 min), and 31.55% (reaction time: 50 min), respectively. That is, CO3O4-B had the best catalytic performance. To make clear the difference in the catalytic ability of CO3O4 a series of characterizations were carried out. It is discovered that these CO3O4 materials are different in many ways such as crystallinity, microstructure, specific surface area, surface oxygen vacancy concentration, and surface hydroxyl density. And it is confirmed that the primary factor influencing the catalytic performance of CO3O4 is the surface hydroxyl density. In addition, the optimized parameters for MB degradation in the CO3O4-B/PMS reaction system were determined as follows: reaction temperature 25 degrees C, catalyst dosage 0.02 g.L-1, and PMS dosage 0.6 mmol.L-1, where the MB degradation ratio was as high as 98.33%. Moreover, the reactive oxygen species center dot SO4-, center dot OH, center dot O-2(-) and O-1 were all detected in the CO3O4-B/PMS system according to the quenching experiments and electron paramagnetic resonance tests, and sulfate radicals were identified as the primary reactive oxygen species.