Selective oxidation of cyclohexane to cyclohexanol by BiOI under visible light: Role of the ratio (1 1 0)/(0 0 1) facet

The development of semiconductors capable of photocatalytic activity under visible light is very important, because such materials are potentially useful for performing photocatalytic conversion under solar illumination. However, these processes are frequently unselective because they involve the production of free radicals. Reports suggest that the selectivity of the photocatalytic processes may be adjusted through modification of the structural parameters of the semiconductor photocatalysts by the preferential exposure of certain crystalline planes. The present work focuses on the relationship between the preferential exposure of the (1 1 0) and (0 0 1) facets of bismuth oxyiodide and the cyclohexanol produced by the photocatalytic oxofunctionalization of cyclohexane. For this purpose, four bismuth oxyiodide photocatalysts (BiOI-4, BiOI-6, BiOI-10, and BiOI-12) were synthesized at different pH levels and characterized (via X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy, and the Brunauer–Emmett–Teller surface area). All BiOI photocatalysts showed higher selectivity for cyclohexanol. Additionally, a linear dependence between the cyclohexanol yield and peak intensity (1 1 0)/(0 0 1) ratio was established and related to the relative amount of hydroxyl radicals formed in the photocatalytic system.