Visible-light-driven oxidation of cyclohexane using Cr-supported mesoporous catalysts prepared via phenyl-functionalized mesoporous silica

Abstract

A series of Cr-supported mesoporous silica (Cr-PFMS) photocatalysts were prepared via phenyl-functionalized mesoporous silica (PFMS) by two steps. Namely Cr-PFMS photocatalysts were firstly assembled by co-condensation of tetraethoxysilane (TEOS) and various amounts of phenyltriethoxysilane (PTES) using PEO–PPO–PEO triblock copolymer (P123) as the template, and then loaded with chromium species with the aid of the phenyl groups. The physical and photophysical properties of the Cr-PFMS photocatalysts were characterized by various techniques including inductive couple plasma optical emission spectrometer (ICP-OES), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflection spectroscopy (DRS). The visible-light-driven (λ > 420 nm) photocatalytic performance of the Cr-PFMS materials for the cyclohexane oxidation with O₂ at room temperature was investigated. Results showed that the introduction of phenyl groups derived from PTES not only promoted the phase transition of PFMS from high-curvature hexagonal structure to low-curvature cubic structure, but also increased the loading amounts of Cr species of which Cr⁶⁺ chromate species were active sites. Consequently, the hexagonally structured Cr-PFMS photocatalysts possessed higher photocatalytic activity than their counterpart photocatalyst, Cr-SBA-15 prepared without adding PTES. Moreover, the activity of the Cr-PFMS samples with cubic structure was also higher than that of those samples with hexagonal structure. This work may provide more insight into the design of novel supported photocatalysts with high metal loading and catalytic activity for cyclohexane oxidation under mild reaction conditions.