Efficient photocatalytic oxidation of cyclohexane to KA oil by carbon nitride hybridized decatungstate under visible light

Abstract

The highly selective synthesis of KA oil (cyclohexanol and cyclohexanone) from the oxidation of cyclohexane (CHA) with O₂ under mild conditions is still a very important and challenging research topic. This paper discloses that the hybrid (DTCN) is easily prepared by inducing carbon nitride (CN) in the synthesis of decatungstate (DT) and is found to be efficiently photo-catalyst for the above selective oxidation in acetonitrile. After illumination (LED of 405 nm) for 2 h, the best DTCN-0.5 can achieve 41.03 % CHA conversion and greater than 95 % KA oil selectivity with an apparent quantum efficiency of 25.52 %, which is much superior to the pure DT (12.46 % CHA conversion). Also, it is active for the selective oxidation of other substrates containing inert C(sp³)-H bonds. A series of characterizations, free radical trapping and isotope tracing tests as well as DFT calculations support that the doped CN can construct a built-in electric field with DT to accelerate the separation of the photo-generated charge, thus hoisting the photo-excited quantum efficiency of DT. Furthermore, it also plays a key role in converting O₂ into superoxide (•O₂^–) radical as the active oxygen donor. Additionally, the doped CN also contributes to the limited participation of water as a weak oxygen donor in the selective oxidation of CHA to cyclohexanol. It is hoped that this work will be informative for advancing the key technology of selective oxidation of saturated hydrocarbons under mild conditions.