Titanium Dioxide/Reduced Graphene Oxide Hybrid Photocatalysts for Efficient and Selective Partial Oxidation of Cyclohexane

• Published in: ACS catalysis 2017-01, Vol.7 (1), p.293-300
• Main Authors: Shiraishi, Yasuhiro, Shiota, Shingo, Hirakawa, Hiroaki, Tanaka, Shunsuke, Ichikawa, Satoshi, Hirai, Takayuki
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.6b02611

Partial oxidation of cyclohexane (CHA) to cyclohexanone (CHA-one) with molecular oxygen (O2) is one of the most important reactions. Photocatalytic oxidation has been studied extensively with TiO2-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 (O2 ●–) produced by one-electron reduction of O2 on TiO2. Here we report that TiO2, 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 TiO2/rGO hybrids produce CHA-one with twice the amount formed on bare TiO2 with much higher selectivity (>80%) than that on bare TiO2 (ca. 60%). The conduction band electrons photoformed on TiO2 are transferred to rGO, promoting efficient charge separation and enhanced photocatalytic cycles. The trapped electrons on rGO selectively promote two-electron reduction of O2 and suppress one-electron reduction. This inhibits the formation of O2 ●–, 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.