A g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite has been successfully constructed. The structure and chemical composition of the composite were investigated via, inter alia, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The ability of the assembly to act as a photocatalyst for proton reduction to form hydrogen gas was studied. With visible light irradiation for 4 h, the total H2 production catalyzed by the g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite was found to be 9 times as high as a corresponding CdSe/[Fe2S2(CO)6] assembly and significantly higher than either the CdSe quantum dots or g-C3N4 alone. The g-C3N4 support/matrix was found to enhance the stability and efficiency of the CdSe quantum dot/iron carbonyl cluster assembly in the photocatalytic hydrogen evolution process. Results from recycling tests showed that the g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite is a sustainable and robust photocatalyst, maintaining the same activity after three cycles. The photoinduced charge carrier transfer dynamics in the g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite system has been investigated by transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopies. The spectroscopic results indicate efficient hole transfer from the valence band of the excited CdSe quantum dots to the molecular iron carbonyl clusters and from the defect state of the quantum dots to g-C3N4 in the g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite, which significantly inhibits the recombination of photogenerated charge carriers in CdSe quantum dots and boosts the photocatalytic activity and stability for hydrogen evolution. Energy transfer from g-C3N4 to the CdSe quantum dot/[Fe2S2(CO)6] assembly with a time constant of 0.7 ns also contributed to the charge transfer process.
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