Origin of the enhanced visible-light photocatalytic activity of CNT modified g-C3N4 for H2 production.

Graphitic carbon nitride (g-C3N4) hybridized with a small number of multi-walled carbon nanotubes (CNT) was synthesized using cyanamide as precursor. The optimal CNT content is found to be ∼0.2 wt% in the composite, which displays a 2.4-fold enhancement in photocatalytic water splitting over pure g-C3N4. Characterizations by a series of joint techniques including Raman spectra, UV/vis diffuse reflectance spectra, steady and time-resolved fluorescence emission spectra, and photocurrent responses were carried out, aiming to reveal the determinative factor for the improved visible-light response. Our results indicate that the increased photoactivity originates from the enhanced charge-transfer effect due to the intimate interactions between g-C3N4 and conjugated CNT. The presence of CNT in the hybrids is beneficial for improving electron-hole separation on the excited g-C3N4 by prolonging the lifetimes of charge carriers and improving the population distribution of short-lived and long-lived charge carriers.