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