GO/Bi2O2CO3/NiWO4 with Z-scheme heterojunction: efficiently enhanced degradation of organic pollutants under visible light and DFT studies

Abstract

A ternary composite of GO/Bi2O2CO3/NiWO4 (GBCNWO) was prepared via an in-situ of Bi2O2CO3 onto the surface of NiWO4 and Bi2O2CO3/ NiWO4 being warped by GO, which was thereafter untilled as catalyst in photodegradation of organic pollutants. The microstructure, and optical properties of all the prepared samples were characterized using various techniques such as XRD, FT-IR, SEM, TEM, TG-DTG, XPS, UV-Vis, ESR, and N2-adsorption. Amongst the studied samples, GBNWO possessed the largest specific surface area, which would efficiently afford much more spaces for the exposing of active sites. Results of UV-vis and XPS suggested that GBNWO was more efficient for the adsorption and conversion of visible light, and photocurrent conduction through graphite carbon ring could lessen the recombination rate of photoelectrons and holes. Also, the minor arc radius of GBCNWO unveiled its lowest photoresistors among the composites, indicating that the GBNWO structured with GO, Bi2O2CO3 and NiWO4 has synergistic catalysis in the photodegradation. Importantly, 95.15% of degradation rate was observed under the optimized conditions (pH=7, catalyst weight of 30mg, 40mg/L of MB, 25oC). Additionally, the degradation rate of various substrates followed the order: MB (99.34%) > ciprofloxacin (97.28%) > RHB (97.01%) > indole (27.47%) > phenol (9.47%). The quenching experiment and ESR test suggested that three kinds of active species (•OH, •O2− and h+) can be photogenerated during visible light radiation. Among them, •O2− was confirmed as the key species during the photocatalytic process, which could be adduced that the existence of oxygen vacancies made the receiving photoelectrons to reduce O2, forming the superoxide radical. Finally, a Z-scheme mechanism about the production of active radicals was proposed, which was also validated by DFT calculations.