Type II heterojunction in hierarchically porous zinc oxide/graphitic carbon nitride microspheres promoting photocatalytic activity

Graphitic carbon nitride (g-C3N4) is a visible light active semiconductor. However, low conductivity and high recombination rate of photogenerated electrons and holes limit its application in photocatalysis. In this work, we design and synthesize hierarchically porous zinc oxide/graphitic carbon nitride (ZnO/g-C3N4) microspheres with type-II heterojunction to effectively degrade rhodamine B (RhB) via increasing the charge-separation efficiency. The ultraviolet-visible (UV–Vis) absorption spectra, Mott-Schottky plots and valence band X-ray photoelectron spectroscope confirm the formation of type-II heterojunction between ZnO nanocrystals and g-C3N4 nanosheets. As a result, the 1.5-ZnO/g-C3N4 composite (the mass ratio of zinc acetate dihydrate to g-C3N4 is 1.5) exhibits the highest photocatalytic activity with good stability and higher photocatalytic degradation rate comparing to pure g-C3N4 and pure ZnO. In addition, our results confirm that O2− and h+ are the main active species for ZnO/g-C3N4 in degradation of RhB.