What is the transfer mechanism of photogenerated carriers for the nanocomposite photocatalyst Ag3PO4/g-C3N4, band-band transfer or a direct Z-scheme?

The separation mechanisms of photoexcited carriers for composite photocatalysts are a hot point in the photocatalytic field. In this paper, the Ag3PO4/g-C3N4 nanocomposites with different main parts (Ag3PO4 or g-C3N4) were synthesized using a facile in situ precipitation method. The photocatalysts were characterized by X-ray powder diffraction, UV-vis diffuse reflection spectroscopy, transmission electron microscopy and Brunauer-Emmett-Teller methods. The photocatalytic performance was evaluated by the degradation of methylene blue under visible light irradiation. When the main part of the Ag3PO4/g-C3N4 photocatalyst is Ag3PO4, the transfer mechanism of photogenerated electron-hole takes generic band-band transfer, and the photocatalytic activity is decreased. However, when the primary part of the Ag3PO4/g-C3N4 photocatalyst is g-C3N4, the migration of photogenerated electron-hole exhibits a typical Z-scheme mechanism, and the photocatalytic activity is increased greatly. The separation mechanisms of photogenerated carriers were investigated by the electron spin resonance technology, the photoluminescence technique and the determination of reactive species in the photocatalytic reactions. It is hoped that this work could render guided information for design and application of Z-scheme photocatalysts with excellent photocatalytic performance.