Graphitic Carbon Nitride/CdSe Quantum Dot/Iron Carbonyl Cluster Composite for Enhanced Photocatalytic Hydrogen Evolution

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.