2D/3D ZnS/SnO2 photocatalyst with Z-scheme heterojunction for efficient degradation of organic pollutants

A series of 2D/3D ZnS/SnO2-T (T = 400 degrees C, 500 degrees C, 600 degrees C, 700 degrees C) samples were synthesized, which were further applied as photocatalysts to degrade the organic pollutants. The crystal structures, particle morphologies, interfacial and photoelectric properties of the ZnS/SnO2 semiconductor photocatalysts were characterized by XRD, SEM, FT-IR, XPS, UV-Vis, CV and electrochemical impedance spectra (EIS). The catalytic performance of the ZnS/SnO2 photocatalysts was performed using methylene blue (MB) and rhodamine B (RhB) as the target pollutants, of which the ZnS/SnO2-500 exhibited the highest photocatalytic degradation performance, capable of degrading 95.02 % of MB and 59.80 % of RhB, respectively. The degradation of MB was consistent with firstorder kinetics, with a degradation rate constant of 0.587 h- 1 under optimal conditions (20 mg/L of MB, pH = 5, 40 mg of catalyst, 30 degrees C). This was attributed to the higher photoresponsive ability and lower electrochemical impedance as well as the enhanced visible light absorption capability of ZnS/SnO2-500 sample. Importantly, the ZnS/SnO2-500 photocatalyst can also be used to degrade various colorless pollutants including indole, tetracycline, norfloxacin, and ciprofloxacin, with degradation efficiencies of 46.65 %, 75.23 %, 53.98 %, and 59.19 %, respectively. Moreover, the presence of oxygen vacancies in the ZnS/SnO2 solid was confirmed according to the results of XPS and ESR analyses, which played a key role in the photocatalytic process and promoted the generation of superoxide radicals and hydroxyl radicals. Finally, the high separation and distribution of electron-hole pairs of DFT calculations suggested that the electron was transmitted from SnO2 to ZnS via the newly-formed Sn-S-Zn bond between the interfacial structures, further confirmed the proposed Z-scheme mechanism.