Immobilization of polyoxometalates on protonated graphitic carbon nitride: A highly efficient and reusable catalyst for the synthesis of pyridine-N-oxides

•Different contents of Cs3PW12O40 decorated on protonated graphitic carbon nitride were prepared based on the impregnation-precipitation method.•The prepared CsPW-CN catalysts achieved better catalytic activities than the pure Cs3PW12O40 in the N-oxidation of pyridine, and obtained 99% yield of pyridine-N-oxide in aqueous medium.•The intimate interaction between Cs3PW12O40 and protonated graphitic carbon nitride was verified by various characterization techniques.•The result of HRTEM revealed that the semi-embedded structure between Cs3PW12O40 and pg-C3N4 was formed.