Oxygen vacancies promoted the generation of sulfate radicals and singlet oxygen by peroxymonosulfate activation with Co3O4 quantum dots/g-C3N4 nanosheets

Abstract

Co3O4 quantum dots /g-C3N4 nanosheets nanomaterials with vacancies (VO-CoCN) were fabricated by deposition–precipitation and NaBH4 reduction. TEM and HRTEM images indicated that Co3O4 particles of about 2 nm size are uniformly distributed on the surface of the g-C3N4 nanosheets. Furthermore, the formation of oxygen vacancies was also confirmed by HRTEM, XPS, ESR and other techniques. The 0.25-VO-CoCN catalyst coupled with peroxymonosulfate (PMS) exhibits excellent sulfadiazine (SDz) removal efficiency is up to 100 % in 20 min, with a mineralization rate of 77.4 %. The cycle stability of the 0.25-VO-CoCN catalyst was also significantly improved compared to CoCN samples without vacancies for PMS activation. Moreover, the 0.25-VO-CoCN/PMS system can maintain the efficient SDz removal rate in the presence of low-concentration inorganic anions (NO3–, HCO3– and Cl-) in the pH range of 5–9. The free radical quenching experiment and EPR characterization reveal that the •SO4- radicals and 1O2 non-free radicals are the main reactive oxygen species of SDz degradation in the VO-CoCN/PMS system. The superior degradation performance is attributed to the fact that oxygen vacancies can promote the redox cycling of Co3+/Co2+, thereby increasing the formation of •SO4- and simultaneously promoting the formation of singlet oxygen species.