Tuning of the photocatalytic performance of g-C3N4 by polyoxometalates under visible light

Abstract

Carbon nitride (g-C₃N₄), as a rising star of metal-free photocatalysts, has received considerable attention. However, for practical application, the photocatalytic efficiency of g-C₃N₄ remains to be further improved. Herein, a series of Keggin-type polyoxoanion (polyoxoanions = SiW₁₂O₄₀⁴⁻, PW₁₂O₄₀³⁻, PMo₁₂O₄₀³⁻) modified g-C₃N₄ (POM/C₃N₄) composites have been successfully prepared. The results of XRD, TEM, XPS and EDAX reveal that a small amount of polyoxoanions was modified on the surface of g-C₃N₄ with electrostatic and hydrogen bonding interactions. Photocatalytic experiments indicate that these composites exhibit enhanced methyl orange (MO) degradation photocatalytic activity and water splitting H₂ production under visible light irradiation. The loading amount and the type of polyoxoanion can tune the photocatalytic performance of the composites. Among these catalysts, 5% SiW₁₂O₄₀⁴⁻ (SiW₁₂)-modified g-C₃N₄ has the best photocatalytic performance, which is 4.4 times higher than that of pure g-C₃N₄ for the degradation of MO. The photocatalytic mechanism reveals that polyoxoanions can act as electron traps, which can efficiently promote the separation of photogenerated electrons and holes of C₃N₄, thus resulting in the enhanced photocatalytic performance of the composites.