Preparation And Photocatalytic Properties Of Novel Nanostructured Photocatalysts

Ever since the1970s, steadily worsening environmental pollution and energy shortages have raised awareness of a potential global crisis. For the sustainable development of human society, the development of both pollution-free technologies for environmental remediation and alternative clean energy supplies is an urgent task. Among the wide variety of green earth and renewable energy projects underway, semiconductor photocatalysis has emerged as one of the most promising technologies because it represents an easy way to utilize the energy of either natural sunlight or artificial indoor illumination, and is thus abundantly available everywhere in the world. The potential applications of photocatalysis are found mainly in the following field such as photolysis of water to yield hydrogen fuel, photo-decomposition or photo-oxidization of hazardous substances, artificial photosynthesis and photoelectrochemical conversion. Nanostructured semiconductor photocatalytic materials due to the many special properties of nano size such as high surface area, high reactivity, easily dispersed and fast diffusion exhibit more enhanced photocatalytic activities compared with macro bulk materials. It is generally believed that the physical and chemical properties of nanomaterials depend on not only their chemical composition, but also their structures, including phase, size, size distribution, morphology, and dimensionality. Therefore, the design and fabrication of novel Nano-photocatalytic materials with ideal morphology, controllable size and stable sucture are particularly crucial to semiconductor photocatalysts and provide a new way for the design of novel efficient and stable nano-photocatalytic materials.In this dissertation, a series of novel semiconductor photocatalysts nanostructures have been successfully prepared by the hydrothermal method, chemical precipitation, microwave hydrothermal method and chemical etching. Moreover, these photocatalysts materials exhibit a superior photocatalytic properties ascribed to their unique nanostructures. Through a series of characterization, the crystal phase, morphology, microstructure and surface chemical state and optical properties have been analyzed. The relation between highly efficient photocatalytic performance and shape, electronic structure and surface states has been discussed in detail via the methods such as XPS, UV-Vis diffuse reflectance spectroscopy and theoretical calculation. The main contents are as follows:Novel three-dimensional (3D) hierarchical Nb3O7(OH) nanostructures with a sheaf-like nanoarchitecture were fabricated for the first time by a hydrothermal process. Interestingly, the nanosheafs are composed of nanorods with an average diameter of about25nm. The as-prepared3D hierarchical nanostructures possess a high surface area of77m2g-1with pore diameters of ca.4.2-12.5nm. A possible growth mechanism based on the combined Ostwald ripening and self-assembly process was proposed. It is found that both the valence-band top and the conduction-band bottom consist of O2p and Nb4d orbitals. Importantly, the3D hierarchical Nb3O7(OH) nanostructures exhibit enhanced photocatalytic activity for degradation of Rhodamine B (RhB) under UV-visible light, which is attributed to the unusual hierarchical structure, high surface area, and hybridization of energy bands.A facile biomaterial-assisted method has been developed to fabricate AgCl@Ag concave cubes. The biomaterial of agar gel was used to moderate the reaction process by providing a reaction matrix to mediate the diffusion of reactants and confine the growth of AgCl@Ag concave cubes. The whole reaction process was performed under a mild condition without heat treatment or organic additives. The as-formed AgCl@Ag concave cubes as a photocatalyst exhibit effective activity for photocatalytic degradation of methyl orange (MO) under visible-light irradiation, which is mainly attributed to the surface plasmon resonance (SPR) of Ag nanoparticles.Self-assembled hierarchical nanostructures of BiO1.84H0.08spheres have been successfully synthesized by a rapid, one-pot, low-temperature hydrothermal route under microwave irradiation. The as-prepared hierarchically nanostructured BiO1.84H0.08possesses a high surface area of113m2g-1.By adjusting the reaction temperature and reactant concentration, the morphology of the as-formed BiO1.84wH0.08nanostructures can be tailored. As a new photocatalyst, the flower-like spherical BiO1.84H0.08exhibits enhanced photocatalytic activity for degradation of Rhodamine B (RhB) under UV-visible light. The synthetic procedure is simple, efficient, and scalable for mass production. Therefore, the as-formed BiO1.84H0.08hierarchical nanostructures may offer great potential applications for decomposition of organic contaminants.Lastly, we have successfully fabricated hierarchical porous g-C3N4by a chemical etching method with KOH as activator. Compared to the bulk g-C3N4, the hierarchical porous g-C3N4with high porosity and specific surface area and a hierarchical pore size distribution of mesopores and macropores exhibits enhanced photocatalytic activity and good stability. Besides, the excellent photocatalytic performance of hierarchical porous g-C3N4nanostructure ascribes to several aspects:a high surface area, hierarchical pore structure and nano lamellar structure. These factors will promote the utilization efficiency of light absorption, improve the generation of photo-generated carriers and facilitate the separation of electrons and holes, which sequentially enhance the photocatalytic activity.