Defect engineering is recognized as an effective route to obtain highly active photocatalytic materials. However, the current understanding of defects is mainly limited to isolated atomic vacancy defects, ignoring the exploration of the functions of multivariate defects formed by the deletion of several adjacent atoms in photocatalytic system. Here, we prepared SnS2 nanostructures with the same morphology but different dominant defects, and by testing their photocatalytic performance, it was found that the multivariate defects can significantly improve the photocatalytic performance than isolated S vacancies. Combining experiments and theoretical calculations, we confirmed that the promotion of multivariate defects, especially “S-Sn-S” vacancy associates, on the photocatalytic performance is reflected in many aspects, such as the regulation of the energy band structure, the improvement of the charge separation efficiency, and the promotion of the adsorption and activation of guest molecules. SnS2 with “S-Sn-S” vacancy associates exhibits excellent photocatalytic water purification ability. Under the induction of “S-Sn-S” vacancy associates, phenol was thoroughly photocatalytically decomposed, further confirming its excellent functionality. This work not only provides new insights into identifying advantage defects in the catalyst structure, but also offers new ideas for constructing highly active photocatalysts based on defect engineering.
The shuttle effect of lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) has been hampered their commercialization. Metal oxides as separator modifications can suppress the shuttle effect. Since there is no direct electron transport between metal oxides and LiPSs, absorbed LiPSs should be diffused from the surface of metal oxides to the carbon matrix to go through redox reactions. If diffusivity of LiPSs from metal oxides surface to carbon substrate is poor, it would hinder the redox reactions of LiPSs. Nevertheless, researchers tend to focus on the adsorption and overlook the diffusion of LiPSs. Herein, same morphology and different crystal phase of TiO2 nanosheets grown on carbon nanotubes (CNTs@TiO2-bronze and CNTs@TiO2-anatase) have been designed via a simple approach. Compared with CNTs and CNTs@TiO2-anatase composites, the battery with CNTs@TiO2-bronze modified separator delivers higher specific capacities and stronger cycling stability, especially at high current rates (~ 472 mAh·g-1 at 2.0 C after 1, 000 cycles). Adsorption tests, density functional theory calculations and electrochemical performance evaluations indicate that suitable diffusion and adsorption for LiPSs on the CNTs@TiO2-B surface can effectively capture LiPSs and promote the redox reaction, leading to the superior cycling performances.
Semiconductor combination is one of the most common strategies to obtain high-efficiency photocatalysts; however, the effect mechanism of composition ratio on micro-structure and photocatalytic activity is remaining unclear. In this study, a case of g-C3N4 quantum dots@SnS2 (CNQDn@SnS2) heterojunction with different ratio of CNQD is used to uncover the origin of optimum and excess composition for photocatalysts. Research on the functional mechanism of the optimum composition shows that 0.8 wt.% CNQD are completely attached to the non-(001) facets of SnS2, which benefits the formation of type-II heterojunction, resulting in an optimal pollutant degradation and mineralization efficiency. For the excess composition, both experiments and theoretical calculations confirm that excess CNQD (the part exceeding of 0.8 wt.%) located on the (001) facet of SnS2, leading to the type-I band alignment of this heterojunction, which severely restricts the separation of photo-induced charge carriers, and thus reduces their lifetime. This work makes the functional mechanism of composition ratio on micro-structure and photocatalytic activity clearer. Related research results provide a new insight into semiconductor combination study and take an important step toward the rational design of highly active photocatalysts.