| The main challenge in photocatalytic conversion of solar energy is to extract the photo-generated charges competitively with their recombination, and thus in-depth understanding of the photogenerated carriers separation and migration processes is of great importance in designing efficient photocatalysts. In this dissertation, on the basis of nanomaterials solid-state chemistry, we choose well-defined two-dimensional ultrathin nanomaterials as the research model, combining with in situ characterization methods, such as the time-resolved spectroscopy, spin trapping, to understand the effect of organic-inorganic interface, surface microstructure, small organic molecules on the carriers separation and migration processes in semiconductors. Hopefully, our developed strategies can provide theoretical support for the design of high-efficient photocatalytic systems. The dissertation includes the following several aspects:1. We propose that low-dimensional strategy is an effective way to accelerate the charge separation. In particular, two-dimensional materials with atomic thickness, allow high specific surface area, short carrier diffusion distance, enhanced absorption, Based on the structural similarity of CuSe and CuInSe2, we realize the first controllable synthesis of non-layered chalcopyrite-type CuInSe2nanoplatelets. The highly anisotropic CuSe nanoplate is not only a template on morphology, but also as a structural template for manipulating the thickness of these nanoplatelets. The intimately contacting interface and the staggered energy levels of CuInSe2nanoplatelets and P3HT effectively promote the separation of carriers, and thus flexible hybrid photodetectors constructed with CuInSe2nanoplatelets and P3HT exhibit excellent photo-response properties, even under severe bending. The use of ultrathin light-harvesting layers is a noteworthy approach to reduce costs realistically, and in turn enables the mechanical flexibility of devices.2. We highlight that surface oxygen vacancies can capture photo-generated electrons, thus contributing to efficient separation of charge carriers. As an example, K4Nb6O17ultrathin nanosheet with well-defined structure is chosen as an ideal platform to investigate the relationships between surface defects and photocatalytic properties of semiconductors. Photocatalytic H2evolution results confirm that defective K4Nb6O17ultrathin nanosheets exhibit a H2evolution rate of1661μmol·g-1·h-1, which is enhanced by20times compared to the defect-free bulk counterpart, while6times compared to that of defect-free nanosheets. Moreover, the insights gained from the effect of spatial distribution of oxygen vacancies on the catalytic properties have solved the long-standing controversy on the role of oxygen vacancies. Oxygen vacancies in bulk serve as carrier recombination centers, while surface oxygen vacancies promote carriers separation, suppressing electron-hole recombination. This study highlights the decisive role of the defects’spatial location in determining the photocatalytic activities, providing an important guideline for the design of high performance photocatalysts.3. We propose a water-soluble molecule co-catalyst strategy to accelerate hole transfer kinetics. Using trifluoroacetic acid (TEA) as a water-soluble molecule co-catalysts, K4Nb6O17nanosheet photocatalysts achieve a significantly improved H2generation rate of6344p.mol/g/h, up to32times in comparison with the blank experiment. The reversible redox couple TFA·/TFA, which is confirmed by in-situ spin trapping technique and theoretical analysis, shuttles the hole from K4Nb6O17nanosheet to the hole scavenger, eventually leading to a longer lifetime of photo-generated electrons, as verified by femtosecond transient absorption spectra and photoluminescence spectra, giving a clear physical picture of photocatalytic reaction process for molecular co-catalyst. Homogeneous molecular co-catalysts represent a general route to design high-efficient photocatalytic systems. |
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