Large-scale synthesis of visible light responsive ZnS by one-step molten salt method

Abstract

It still remains a big challenge for the large-scale synthesis of visible light responsive ZnS. In this work, a simple one-step molten salt method is developed for large-scale synthesis of visible light responsive ZnS, in which the as-obtained sample at T oC is named as ST (T = 200, 300, 400, 500, 600 °C). The degradation reaction of Rhodamine B (RhB) is used to evaluate photocatalytic activity under visible light (λ ＞ 400 nm). Among the samples, S200 shows the highest visible light activity. Under visible light irradiation (λ ＞ 400 nm), 70% of RhB can be degraded by S200 after 90 min. Typically, the visible light activity of S200 is 28.2 times higher than that of S600. The higher activity of S200 is mainly attributed to more sulfur vacancies (VS), wider light absorption range, higher charge separation efficiency and larger BET area. Specifically, the BET area of S200 (44.4 m2 g−1) is 4.1 times higher than that of S600 (8.7 m2 g−1), thus S200 can provide more active sites. Meanwhile, the photocurrent for S200 is 6 times higher than that of S600, demonstrating that S200 has a higher charge separation efficiency mainly caused by more surface VS. Density functional theory (DFT) calculation further demonstrates that VS is favorable thermodynamically for the adsorptions of O2 and H2O, which benefits the generation of •OH and •O2– active species, leading to an improved activity. After three cycles of RhB degradation, S200 shows outstanding stability with 95% visible-light activity remained. The molten salt method is simple and productive, which can be used for large-scale synthesis of photocatalysts in practice.