Defective g-C3N4 Prepared by the NaBH4 Reduction for High-Performance H2 Production

Defects play a significant part in promoting photocatalytic activity for H2 production. Various methods such as chemical reduction have been performed to metal oxide based photocatalysts. Herein, we present the NaBH4 reduction route to introduce the defects into the graphitic carbon nitride (g-C3N4) to enhance photocatalytic activity. A new −C≡N group is observed in the FTIR spectra of treated g-C3N4 nanosheets indicating the presence of structural defects. At the same time, the B signal appears in the X-ray photoelectron spectroscopy analysis, suggesting that B is doped in the g-C3N4 during the treatment. All these results manifested that multiple types of defects are introduced in the g-C3N4 during the NaBH4 treatment. The UV–vis spectra illustrate that the absorption band edge of g-C3N4 is extended from 420 to 450 nm after NaBH4 treatment. This demonstrates that the band gap of g-C3N4 turns narrow owing to the introduction of defects. Photocatalytic H2 production of defective g-C3N4 is ∼5-fold better than that of pristine g-C3N4. To understand the enhanced mechanism, the apparent quantum efficiency, photoluminescent spectra, transient photocurrent and electrochemical impedance spectra are investigated. The results show that the charge separation efficiency is greatly strengthened in the defective g-C3N4. Upon these findings, the enhancement of catalytic activity can be attributed to both the broad light adsorption range and highly efficient charge separation process.