Design and synthesis of robust Z-scheme ZnS-SnS2 n-n heterojunctions for highly efficient degradation of pharmaceutical pollutants: Performance, valence/conduction band offset photocatalytic mechanisms and toxicity evaluation

• Published in: Journal of hazardous materials 2020-06, Vol.392, p.122345, Article 122345
• Main Authors: Xia, Baihui, Deng, Fang, Zhang, Shuqu, Hua, Li, Luo, Xubiao, Ao, Meiying
• Format: Article
• Language: English
• Subjects: Pharmaceutical pollutant; Photocatalytic activity; Valence/conduction band offset; Z-scheme band alignment; ZnS-SnS2 heterojunction
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2020.122345

[Display omitted] •ZnS-SnS2 n-n heterojunctions with Z-scheme band alignment was successfully prepared.•The (1:1) ZnS-SnS2 exhibits the highest catalytic activity in tetracycline degradation.•Fukui index was aided in inferring degradation pathways of tetracycline.•Toxicity of tetracycline was greatly reduced during the photocatalysis process.•VB and CB offset were first introduced in photocatalytic mechanism of ZnS-SnS2. Petal-like ZnS-SnS2 heterojunctions with Z-scheme band alignment were prepared by one-pot solvothermal strategy. The optimal (1:1) ZnS-SnS2 can degrade 93.46 % of tetracycline and remove 73.9 % COD of pharmaceutical wastewater under visible-light irradiation due to the efficient production of H, O2−, h+ and OH. The toxicity evaluation by ECOSAR prediction and the growth of E. coli indicates efficient toxicity reduction of tetracycline by photocatalysis and the non-toxicity of ZnS-SnS2. The attacked sites on tetracycline by reactive species were analyzed according to Fukui index, and two degradation pathways of tetracycline were inferred via the identification of intermediate products. Tetracycline degradation efficiency and the energy consumption in different water bodies were compared, and it was found that the electrical energy per order (EE/O) was the lowest in Ganjiang River. The valence band offset (ΔEVBO) and conduction band offset (ΔECBO) of ZnS-SnS2 were 1.02 eV and 0.22 eV, respectively. The probable photocatalytic mechanism of ZnS/SnS2 heterojunctions with Z-scheme band alignment based on ΔEVBO and ΔECBO was first presented.