Solution Phase Preparation Approaches And Photocatalytic Activities Of Metallic Oixdes Hierarchical Nanostructures

Hierarchical nanostructures (HNSs) with high porosity, large surface area and good dispersibility not only can ehance the performances of the materials, but may also endow them new physical and chemical properties. Moreover, heterogeneous HNSs (hetero-HNSs) can achieve the vectorial transfer for the photogenerated charges. Thus, they are extremely promising in energy and environmental areaes, such as water treatment, photocatalysis, solar cell, lithium-ion batteries, supercapacitor, and so on. In this dissertation, considering the challenges of the oxides HNSs preparation, which possess the high melting points as well as the readily hydrolyzed processors, we have developed new, facile and efficient solution phase technologies to successfully prepare Ta2O5and Nb2O7F HNSs, Ta5N5/Ta2O5and Ag3PO4/α-Fe2O3hetero-HNSs. And, we systematically investigate their growth mechanisms and related photocatalytic activities. Generanly, the achieved research results are listed as the following.Firstly, we develop a new so-called "etching-growth" synchronous strategy to successfully prepare fluorinated Ta2O5(F-Ta2O5) HNSs composed of single crystalline nanorods. The formation rate of H2TaF7is effectively tuned by slowly etching Ta powders with HF based on the chemical stability of Ta powders and the rapid hydrolysis of the intermediate H2TaF7, and thus the quasi-equibibrium growth of Ta2O5is intelligently produced. The as-obtained F-Ta2O5HNSs with a large specific surface area have the single crystalline nannorods building units, and thus exhibit an excellent photocatalytic activity for H2production from water splitting.Next, we extend the above "etching-growth" synchronous strategy to effectively prepare Nb3O7F HNSs of single crystalline nanorods and/or nanoplates via the selective adsorption of2-propanol onto Nb3O7F crystal facets.2-propanol can adsorb onto (110) facets to make Nb3O7F crystal grow along [001] direction, and thus form the primary nanorods. Then, due to the reduced growth rate and the matching lattices between (001) and (110) facets, secondary nanorods grow on the surfaces of primary nanorods by secondarily heterogeneous nucleation and growth of the newly formed F, and thus obtain the HNSs at last. The theoretical calculation of the band structure of Nb3O7F suggest that it is suitable for photocatalytic H2production, and the experimental research confirm that it can be used as an excellent photocatalyst for H2production from water splitting by using the as-obtained Nb3O7F HNSsThen, bansed on the above research, we further develop the "etching-growth" synchronous strategy to prepare Ta2O5/Ta3N5branched hetero-HNSs (Ta2O5/Ta3N5BHNSs) by slowly etching the Ta3N5with HF under a hydrothermal environment. Under the visible light and the simulant sunlight irradiation, the as-prepared Ta2O5/Ta3N5BHNSs can separate the photogenerated charge carriers efficiently and thus exhibit excellent H2production activities from water splitting. Based on the photocatalytic H2production activities over the hetero-HNSs with different molar ratio of Ta2O5and Ta3N5, the probable mechanism for photogenerated charges separation and transportation have been proposed, and the probable reason for the enhanced photocatalytic activities have been explained. TaON/Ta2O5and TiN/TiO2hetero-HNSs also have been successfully fabricated by using the above method, which illustrates that it is a general strategy for the preparation of HNSs/hetero-HNSs with high melting points and rapid hydrolysis rates of the corresponding precursorsFinally, considering the problems in the preparation process of hetero-HNSs with unique hetero-interface, such as complicated synthesis technologies and/or the inevitable self-nucleation, etc, we rationally develop a facile and efficient "ultrasoniclly in-stiu growth strategy" to successfully prepare the Ag3PO4/a-Fe2O3NTs hetero-HNSs by ingeniously using in-situ growth induced effect arising from the adsorbed phosphate anions on the surfaces of α-Fe2O3nanotubes (NTs). This strategy open a new door for the construction of hetero-HNSs. We find that the as-prepared Ag3PO4/a-Fe2O3NTs hetero-HNSs have an efficient separation ability of photogenerated charge carriers, and thus exhibit efficiently photocatalytic activities for organic pollutant RhB degradation.