Titanium Dioxide/Reduced Graphene Oxide Hybrid Photocatalysts
for Efficient and Selective Partial Oxidation of Cyclohexane
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Abstract
Partial oxidation of cyclohexane
(CHA) to cyclohexanone (CHA-one)
with molecular oxygen (O<sub>2</sub>) is one of the most important
reactions. Photocatalytic oxidation has been studied extensively with
TiO<sub>2</sub>-based catalysts. Their CHA-one selectivities are,
however, insufficient because the formed CHA-one is subsequently decomposed
by photocatalysis involving the reaction with superoxide anion (O<sub>2</sub><sup>●–</sup>) produced by one-electron reduction
of O<sub>2</sub> on TiO<sub>2</sub>. Here we report that TiO<sub>2</sub>, when hybridized with reduced graphene oxide (rGO), catalyzes photooxidation
of CHA to CHA-one with enhanced activity and selectivity under UV
light (λ > 300 nm). The TiO<sub>2</sub>/rGO hybrids produce
CHA-one with twice the amount formed on bare TiO<sub>2</sub> with
much higher selectivity (>80%) than that on bare TiO<sub>2</sub> (ca.
60%). The conduction band electrons photoformed on TiO<sub>2</sub> are transferred to rGO, promoting efficient charge separation and
enhanced photocatalytic cycles. The trapped electrons on rGO selectively
promote two-electron reduction of O<sub>2</sub> and suppress one-electron
reduction. This inhibits the formation of O<sub>2</sub><sup>●–</sup>, which promotes photocatalytic decomposition of the CHA-one formed.
These properties of rGO therefore facilitate efficient and selective
formation of CHA-one on the hybrid catalyst
