Enhanced visible light photocatalytic hydrogen evolution of sulfur-doped polymeric g-C₃N₄ photocatalysts

Visible light-activated sulfur-doped g-C₃N₄ photocatalysts were successfully synthesized using thiourea as sulfur source. The obtained photocatalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microcopy, ultraviolet-visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy and transient photocurrent response. The sulfur-doped g-C₃N₄ photocatalysts show beneficial effects on visible light absorption, electron-hole pair generation and separation. The sulfur species doped in the samples was identified as S^2- to replace N atoms in the g-C₃N₄ framework. The photocatalytic activities of the sulfur-doped g-C₃N₄ under visible light were evaluated by hydrogen evolution from water splitting in aqueous solution containing methanol. The sulfur-doped g-C₃N₄ photocatalyst showed the highest photocatalytic performance with H₂ evolution rate of 12.16 μmol h^-1, about 6 times higher than un-doped g-C ₃N₄. It can be concluded that the sulfur species play a vital role and act as active sites in the photocatalytic reaction. This novel sulfur-doped g-C₃N₄ can be potentially used in energy and environmental applications.