Abstract
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.
Highlights
The generation of solar fuels and energy carriers via photocatalytic water splitting is currently subject to intense research efforts
The separation of photogenerated electron−hole pairs to suppress charge recombination is essential to efficient photoreactions.[5]. Such systems include photocatalysts that can directly convert solar energy through photocatalytic water splitting, including CdSe, ZnO, and MoS2.6 The catalytic activity of established semiconductor photocatalysts can be drastically improved by their integration with co-catalysts or the formation of composites between semiconductors and other materials.[7]
The structures of the composites were identified by transmission electron microscopy (TEM)
Summary
The generation of solar fuels and energy carriers via photocatalytic water splitting is currently subject to intense research efforts. For pure CdSe quantum dots, the fastest component with a lifetime of 0.61 ns represents the charge transfer from the band edge to the defect states as it is identical to the rise of the defect emission kinetics of the same sample (Figure S10), while the long lifetime around 40 ns refers to the intrinsic band edge radiative recombination.[51,52] The middle component with a lifetime of around 4 ns refers to the interquantum dot energy transfer, which has been reported in a previous study.[53] The photoluminescence decay of the CdSe quantum dot/[Fe2S2(CO)6] assembly is faster than pure quantum dots due to the hole transfer from CdSe to the iron cluster.[13] when carbon nitride was introduced to the system, the photoluminescence decay of the ternary system became slower than the binary system. The energy transfer from g-C3N4 to CdSe quantum dot/[Fe2S2(CO)6] assembly contributes to the recombination process, i.e., g-C3N4 can harvest more light and convert it into photogenerated charge carriers
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