Photocatalytic Energy Materials Based On Hierarchical Oxides:Design,Optimization And Property Study

Energy issues and environmental problem is becoming more and more rigorous, which is induced by the large scale using of the fossil fuel, meanwhile, the emission of CO₂ has leaded to the housewarming effect. Hence, it is very necessary to develop clean, environment friendly and sustainable fuels energy.In order to develop new generation solar technology, the photocatalytic oxides materials exploitation becomes importantly. The hierarchical inorganic photocatalytic materials of oxides are successful to make the solar conversion become more easily. However, because of the limitation of the exploration of advanced materials, how to make further development in the efficiency and recycle or regeneration is a key of novel materials. Based on these basic knowledges, we focus our eyes on the design and optimization of photocatalytic system, through researching hierarchical structure, surface defects, and controlling the heterojunction effect of semiconductor, then applied in photocatalytic O₂ and H₂ generation. On the way of development new system and optimized design, we fortunately found MOFs derived carbonized materials which can be used in the application of CO₂ reduction. All in all, with the development and researching of the photocatalytic system, the new photocatalytic technology gives us a reference to make it into practical application. This work includes several aspects:1. A novel and simple "self-templating" strategy was developed to fabricate multi-shelled CeO₂ hollow spheres. When these multi-shelled CeO₂ hollow spheres are used as the photocatalystic material for water splitting, an obvious improvement in oxygen evolution is achieved compared to those photocatalysts based on single-shelled and double-shelled CeO₂ hollow spheres or commercial CeO₂ nanoparticles. We find that the enhance oxygen evolution activity and durability of multi-shelled CeO₂ can be attributed to the more effective light harvest and special structure. Furthermore, based on the design of CeO₂ nanostructure materials, CeO₂ nanorods ?NRs? with tunable surface defects are successfully prepared. Impressively, compared with the CeO₂ NRs obtained under Ar-H₂ mixed gas at 800? exhibit superior catalytic activity towards water oxidation under visible light, which is 10 times higher than that of CeO₂ NRs treated under air. Detailed characterization and theoretical analysis reveal that the rich surface defects including surface oxygen vacancies and Ce³⁺ ions are the origin of the enhanced water oxidation performance.2. Based on the design of structure and surface prosperity, ultrafine Cu₂O clusters are in situ uniformly grown on the surface of TiO₂ nanoplatesvia one-pot hydrothermal method. The morphology and structure of Cu₂O/TiO₂ products are investigated by different characterization techniques. Furthermore, detailed study on photocatalytic H₂ generation demonstrates that the charge transfer of TiO₂ with Cu₂O loading is significantly accelerated, leading to high charge separation efficiency. Impressively, Cu₂O/TiO₂ exhibits superior catalytic activity towards water reduction, which is even higher than that of TiO₂ loaded with noble metal Au nanoparticles. The strategy, facilitating charge transfer by construction of heterojunction interface with cheap Cu₂O, will offer the opportunity toward-practical application of nanomaterials in energy conversion.3. Finally, it is further to control the structure and contents of photocatalytic materials, Co-MOF74 was fabricated by ultra-sonication methods, following the post-treatment of carbonized to synthesize the tunable contents of Co@C/Co-C composites materials. Subsequently, after analysis of the CO₂ reduction results, it is shown that the best performance of Co-C hybrids material is carbonized at 1200 ?. The reason is due to metal cobalt active site and super electronic conductivity from the graphite carbon. This synergetic effect promotes the photocatalytic CO₂ reduction into CO more enhanced. And it is the first time to propose metallic material combined with Ru?bpy?32+, which is used to obtain a superior photocatalytic CO₂ reduction.