Highly efficient charge transfer through a double Z-scheme mechanism by a Cu-promoted MoO3/g-C3N4 hybrid nanocomposite with superior electrochemical and photocatalytic performance

Abstract

Herein, a novel Cu-MoO₃/g-C₃N₄ hybrid nanocomposite was successfully synthesized by a two-step strategy of one-pot pyrolysis followed by the impregnation method. The structure, phase, morphology and electronic environment of MoO₃, g-C₃N₄ and Cu in the composite were determined by various characterization methods. The oxygen vacancies of MoO₃ were ascertained by UV-DRS, Raman, and XPS analysis. The formation of the heterostructure was characterised by electrochemical measurements. The photocatalytic performance of the composite was investigated by the water reduction reaction and the reduction of an important inorganic pollutant, Cr(VI). In the presence of Cu NPs, the H₂ evolution of the MoO₃/g-C₃N₄ hybrid was found to be 652 μmol h⁻¹ with an apparent energy conversion efficiency of 13.46%, and up to 95% of Cr(VI) was reduced using citric acid as a hole scavenger. The remarkably enhanced photocatalytic performance was attributed to the combined effect of the double Z-scheme mechanism and defective MoO₃. The in situ formation process of the MoO₃/g-C₃N₄ hybrid followed a direct Z-scheme charge transfer by generating a great number of defects at the solid–solid interface, similar to that of a conductor, and offered low electrical resistance, whereas loading of Cu NPs built up an indirect Z-scheme charge transfer to establish the double Z-scheme charge transfer mechanism. This hybrid material produces a photocurrent density of 12.1 mA cm⁻², in good agreement with the photocatalytic activity. This study highlights the facilitation effect of MoO₃ due to oxygen vacancies and charge transfer through the double Z-scheme mechanism to open up a new window in the field of 2D nanostructured photocatalytic materials.