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Water-soluble small molecule co-catalyst trifluoroacetic acid accelerates hole transfer
Recently, Professor Wu Changzheng of the University of Science and Technology of China cooperated with Zhang Qun's research team to develop new water-soluble small molecule co-catalysts to accelerate the growth of photo-induced hole transfer and realized a dramatic increase in the photocatalytic performance of hydrogen production. The precious metal promoters used present new solutions. The relevant research results were published online on October 21st in Nature Comm. (2015, 6, 8647).
The efficient conversion of low-density solar energy into storable chemical energy is an important way to develop renewable energy sources. However, the recombination of photo-generated carriers severely limits the conversion efficiency of the artificial photocatalytic system. How to realize the maximum separation of photo-generated carriers becomes an important challenge to improve the photocatalytic efficiency. Supported precious metals are widely regarded as highly efficient cocatalysts. However, precious metals, as solid catalysts, tend to bring about limited contact areas, and the high cost also greatly limits their large-scale application.
In response to these challenges, Wu Changzheng's research group broke through the traditional view that high-efficiency cocatalysts are mostly concentrated on the limitations of solid-phase precious metals. For the first time, the discovery of water-soluble small molecule trifluoroacetic acid (TFA) is a new class of highly efficient molecular cocatalysts. They innovatively discovered that TFAs have reversible redox couples and exhibit a high degree of reversibility in the photocatalytic environment, which provides a new idea for the transfer of photogenerated carriers. The molecular cocatalyst TFA achieves a rapid free radical reaction between molecules through its own redox couple, accelerating the rapid transfer of holes.
On the basis of the advantages of high specific surface area of ​​potassium citrate two-dimensional nanomaterials, the photocatalytic hydrogen production performance has been successfully improved 32 times. Nuclear magnetic resonance, elemental analysis, in situ electron spin resonance and other series of characterization confirmed that the photogenerated holes in the valence band of potassium citrate reacted with the adsorbed TFA anion to generate highly active TFA radicals; meanwhile, TFA radicals transferred holes to methanol. Molecular, so as to achieve efficient separation of electron-hole pairs in the two-dimensional nanomaterial nanoparticle catalytic system of potassium niobate.
Its collaborator Zhang Qun’s research team used ultra-fast transient absorption spectroscopy and steady-state/transient fluorescence spectroscopy to measure the photocatalyst kinetics associated with hole trap states and electron trap states in this model system. Behavior and mechanism, thus confirming the rationality and effectiveness of the water-soluble small molecule cocatalyst strategy. Ultrafast kinetics analysis showed that the lifetime of the photogenerated electrons of the potassium niobate nanosheets increased nearly threefold after TFA addition, revealing that the small-molecule cocatalyst-induced efficient hole transport and electron-hole pair separation are the major photocatalytic properties of the system. The root cause of the increase. The proposal of the small molecule cocatalyst strategy is expected to get rid of the traditional precious metal cocatalyst system and open up new ways for designing a cheap and efficient photocatalytic system.
This research work was supported by the National Fund Committee, the Ministry of Science and Technology, the Chinese Academy of Sciences, the Collaborative Innovation Center for Energy Materials, and the Collaborative Innovation Center for Quantum Information and Quantum Science.
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