Regulating superoxide radicals and light absorption ability for enhancing photocatalytic performance of MoS2@Z by CeO2 rich in adsorbed oxygen

Abstract

Nano molybdenum disulfide (Nano-MoS2) can be as a photocatalyst for antibiotic removal under visible light. However, the low energy of visible light and limited radicals restrict the applications of nano-MoS2. In this study, ceria dioxide (CeO2) rich in adsorbed oxygen was introduced into MoS2@Z (MoS2@Zeolite) to synthesize full-spectrum CeO2/MoS2@Z photocatalysts (CeO2/MoS2@Zs). The CeO2/MoS2@Z-3 (Ce: 1.5 mmol; Mo: 3.5 mmol) shows the best photocatalytic ability (98.32%) for tetracycline within 150 min, which is 18.20% improvement over MoS2@Z. The UV–vis diffuse reflection spectra of photocatalysts shows that the ultraviolet absorption ability of CeO2/MoS2@Z-3 improved when CeO2 was introduced. The active species trapping experiment and electron paramagnetic resonance (EPR) test prove h+ and superoxide radicals (•O2−) are the main active species, and CeO2 rich in adsorbed oxygen improves the amounts of •O2− in photocatalytic process. Moreover, singlet oxygen (1O2), producing by oxygen vacancies of CeO2, also plays an important role. The enhanced photocatalytic activity is attributed to full-spectrum (200 nm–800 nm) absorption performance, improved content of •O2−, and electron-hole (e−/h+) pairs separation. After five times recycle, the photodegradation efficiency of CeO2/MoS2@Z-3 only decreased by 2.59%. Meantime, the proposed three photocatalytic pathways show that tetracycline eventually degraded into small organics (like C5H8O3), H2O and CO2 by dehydration, demethylation, deamination, dihydroxylation, deamidation, ring-opening reaction and carbonylation. The results show that CeO2/MoS2@Z-3 may become a high efficiency, stable, and promising photocatalyst for tetracycline wastewater treatment.