Arylamine organic dye-functionalized g-C3N4 formed through cycloaddition reactions and its application in photocatalytic hydrogen evolution

Abstract

Three typical arylamine organic dyes were covalently grafted onto g-C₃N₄ to form the resulting composites g-C₃N₄/TPA-CNCHO, g-C₃N₄/EtPTZ-CNCHO and g-C₃N₄/EtCz-CNCHO. They were synthesized by 1,3-dipolar cycloaddition with (E)-3-(4-(diphenylamino)phenyl)-2-formylacrylonitrile (TPA-CNCHO), (E)-3-(10-ethyl-10H-phenothiazine-3-yl)-2-formylacrylonitrile (EtPTZ-CNCHO), or (E)-3-(9-ethyl-9H-carbazol-3-yl)-2-formylacrylonitrile (EtCz-CNCHO) dyes. The experimental results show that arylamine organic dye moieties were successfully attached to g-C₃N₄, and this attachment can efficiently extend the light absorption area of pure g-C₃N₄ from approximately 460 nm to more than 650 nm. The obtained g-C₃N₄/TPA-CNCHO, g-C₃N₄/EtPTZ-CNCHO and g-C₃N₄/EtCz-CNCHO samples showed enhanced H₂ evolution activity with photocatalytic H₂ production rates that were approximately 105-, 93- and 67-fold that of pure g-C₃N₄. By combining the comprehensive analysis from experiments and density functional theory (DFT) calculations, a possible mechanism can be drawn: the introduced arylamine organic dye fragments attached to the surface of the g-C₃N₄ may acquire more light irradiation, and effective photoexcited carrier transfer from the donor dye fragments to the acceptor g-C₃N₄ could be achieved through the IFCT process. The results confirm that the covalent azomethine ylide bonds formed via 1,3-dipolar cycloaddition between the g-C₃N₄ and organic dye can truly enhance the photocatalytic H₂ evolution rate of the obtained samples. It is believed that this kind of modification can be an effective strategy for achieving other kinds of functional organic dyes grafted onto g-C₃N₄ with highly efficient photocatalytic H₂ activity.