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.

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.

Efficient toxicity elimination of aqueous Cr(VI) by positively-charged BiOClxI1-x, BiOBrxI1-x and BiOClxBr1-x solid solution with internal hole-scavenging capacity via the synergy of adsorption and photocatalytic reduction.

The ecological toxicity of photocatalysts and toxicity reduction of Cr(VI) have attracted much attention. The development of environmentally-friendly photocatalysts with adsorption and internal hole-scavenging capacity for toxicity reduction of aqueous Cr(VI) via facile preparation method is desirable. In this study, visible-light-active BiOClxBr1-x, BiOClxI1-x and BiOBrxI1-x solid solutions were prepared by simple solvothermal strategy. The BiOCl0.3Br0.7, BiOCl0.7I0.3 and BiOBr0.7I0.3 solid solutions exhibited excellent adsorption capacity and photoreduction ability. The removal efficiency of Cr(VI) by BiOCl0.3Br0.7 was 97.7% within 60 min. BiOCl0.7I0.3 and BiOBr0.7I0.3 can remove Cr(VI) almost completely within less than 30 min, which were much higher than those by BiOCl (81.6%) and BiOBr (67.4%) due to joint effect of adsorption and photoreduction. More importantly, the toxicity evaluation confirmed nontoxicity of BiOClxBr1-x, BiOClxI1-x and BiOBrxI1-x, and rapid toxicity elimination process of Cr(VI).