It is known that the rates of semiconductor-mediated photocatalytic reactions increase as the surface area of a photocatalyst increases. It is much less known if and how the atomic arrangement on the photocatalyst surface affects the photocatalytic activity and, especially, selectivity toward a particular product. In this study, tungsten sulfide WS2, atomically-layered semiconductor, was used or prepared in the form of different nanostructures exposing different surface sites. WS2 inorganic fullerenes (courtesy of R. Tenne, Weizmann Institute of Science, Israel), which are 50-150 nm hollow multilayer spheres, have sulfur-terminated close-packed basal planes on the outside. WS2 nanoslabs, 40-80 nm wide 5-10 layer thick stacks of the WS2 layers, expose two types of surface sites – basal planes and layer edges. Synthesized nanoslabs were additionally treated by annealing in various gases (H2, H2S, Ar) or by corrosive chemicals to introduce defects such as sulfur vacancies or additional edge sites. The samples were characterized by TEM, XRD, XRF, UV-vis, and IR spectroscopy. Photocatalytic performance of the WS2 materials was studied in the photocatalytic oxidation of benzyl alcohol in acetonitrile under O2 atmosphere and UV irradiation (360±50 nm). Products were identified and quantified with GC-MS and HPLC. Two major reaction routs were observed: (1) benzyl alcohol oxidation to benzaldehyde and further to benzoic acid, and (2) oxidative coupling to form hydrobenzoin (which also forms in the absence of a catalyst). WS2 nanoslabs, unmodified or modified by annealing in H2 or H2/H2S, favor the production of benzaldehyde and benzoic acid. Annealing of the nanoslabs in Ar or corrosive treatment decreases their activity and shifts the selectivity toward hydrobenzoin. WS2 fullerenes have low activity; mostly hydrobenzoin is observed. We discuss these trends from the point of view of the role of different surface sites in this photocatalytic process.

Effect of WS2 photocatalyst morphology on the activity and selectivity in photocatalytic oxidation of benzyl alcohol

2019 Spring National Meeting

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