Ionic liquids assisted synthesis of graphite carbon nitride for one-pot aerobic oxidation of cyclohexane to adipic acid

Abstract

Adipic acid (AA) is a crucial intermediate in the production of nylon monomers, which is generally obtained by the oxidation of cyclohexane. However, difficult C-H activation and easy overoxidation make it extremely challenging to obtain highly selective AA. Herein, ionic liquid (IL) assisted synthesis of graphitic carbon nitride (g-C3N4) was designed for one-pot oxidation of cyclohexane to AA. The incorporation of C and S elements and the formation of N vacancies were brought with the presence of IL. 26.1% conversion and 51.2% AA selectivity were achieved over [Bmim][HSO4] (1-Butyl-3-methylimidazolium hydrogen sulfate) modified g-C3N4, which significantly increased AA selectivity by 18% compared to unmodified g-C3N4. The changes in electronic structure of g-C3N4 were assumed resposible for the improvement of AA selectivity by increasing the adsorption of cyclohexanone. Besides, the reduction of alkaline sites caused by the introduction of S atoms and N vacancies was benefit to remove AA avoiding excessive oxidation.