Preparation Of Novel Composite Oxides Nanostructures And Their Application In Photocatalysis And Adsorption

Nowadays, environmental problems have become a global concern because of their impact on public health. Among them, organic dyes removal has recently attracted considerable attention because of their complex structure, poor biodegradability, and long-term environmental toxicity. Various methods have been developed to remove organic dyes from aqueous environment, while the adsorption technique and photocatalytic degradation of organic dyes have been extensively considered as effective methods. Furthermore, the preparing methods and property investigations for the adsorbents and photocatalysts are of much significance in the chemical synthesis, new materials and environmental protection areas. In this dissertation, a series of new bismuth based photocatalysts (CHBiO₃, Bi₂WO₆, PtCl4/Bi₂WO₆, Bi_3.64Mo_0.36O_6.55, C/Bi_3.64Mo_0.36O_6.55) and adsorbent (ZnV₂O₄) were obtained through the developed solution-based chemical synthesized methods. Besides, their applications in organic dye removal were also systematically studied. The details are summarized briefly as follows:1. Hollow ZnV₂O₄ spheres aggregated by small nanoparticles were successfully synthesized through a facile one-pot template-free solvothermal method. The formation of ZnV₂O₄ hollow spheres was based on a flowerlike intermediate product supported reduction-dissolution-aggregation process at the expense of consumption of all the flowerlike intermediate products. The obtained ZnV₂O₄ hollow spheres exhibited Brunauer-Emmett-Teller (BET) specific surface areas of 105.1 m²/g and total pore volume of 0.1563 cm³/g. Their novel structures resulted in a high surface to bulk ratio and a large surface area, contributing to high adsorption capacities and faster adsorption rates. In fact, they showed a good adsorption capacity of MB organic dye, and a faste adsorption rate within 40 min, which might be attributed to their special structural feature with large surface area. The adsorption kinetics and isotherm of MB on ZnV₂O₄ hollow spheres were also studied.2. By virtue of structural understanding, bismuth oxide formate (CHBiO₃) was first put forward to be a novel photocatalyst candidate. 3D flowerlike architectures have been successfully synthesized through a facile and economical route, which was free from any surfactant and template. Besides, the formation mechanism of the CHBiO₃ flowerlike architectures was also discussed. It was believed that the formation of the flowerlike CHBiO₃ was related to its crystal structure. There was a weak nonbonding interlayer vander Waals interaction along the c axis and strong intralayer bonding in the (001) plane. Therefore, it tended to form layered structures, e.g. flakes or platelets with a high aspect ratio. Then, the flowelike CHBiO₃ was formed by self-assembly of the nanoplate in order to decrease the surface energy. From the results of photocatalytic tests, the synthesized CHBiO₃ architectures exhibited excellent photocatalytic activity for rhodamine-B (RhB) degradation under the simulated solar light irradiation. Therefore, this novel 3D flowerlike CHBiO₃ architectures show significance of potential application in environment protection problems.3. The flowerlike hierarchical Bi₂WO₆ was successfully synthesized through a facile template-free hydrothermal method. The reaction time, the amount of HAc, and the addition of HNO₃ were systematically refined, and the formation mechanism of the flowerlike hierarchical Bi₂WO₆ was also discussed. Based on the morphology evolution as a function of hydrothermal time, the formation mechanism was proposed to be as follows: First, the aggregation of the noncrystal nanoparticles; Then, the formation of crystalline nanoplates by dissolution of the noncrystal nanoparticles; Finally, organization of the formed nanoplates into flowerlike hierarchical structure in the assistant of HAc adsorption on the surface of nanoplates and the hydrogen bonds formed between carboxyls. For its special flowerlike hierarchical structure, Bi₂WO₆ can be used as photocatalyst for potential application in environment protection problems. In this work, the obtained flowerlike hierarchical Bi₂WO₆ exhibited excellent visible-light-driven photocatalytic efficiencies for the degradation of RhB within 60 minutes, which were much higher than those of TiO₂ (P25) and Bi₂WO₆ sample prepared by solid-state reaction (SSR- Bi₂WO₆). Besides, we concluded the photodegradation of RhB with two competitive processes: a photocatalytic process and a photosensitized process. Both the photocatalytic process and the photosensitized process would work concurrently under visible light irradiation, but the former was the predominant process.4. In order to further improve the photocatalytic activity of bismuth based photocatalysts, several materials were introduced to modify the surface of the photocatalysts. We modified Bi₂WO₆ with PtCl4 and Bi_3.64Mo_0.36O_6.55 with carbon, and systematically studied their influences on photocatalytic activity of bismuth based photocatalysts. (1) Flowerlike PtCl4/Bi₂WO₆ composite photocatalyst was successfully synthesized through a simple two-step method involving a template-free hydrothermal process and the following impregnation treatment. The results indicated that the introducing of PtCl4 did not affect the crystal structure and the morphology of Bi₂WO₆ photocatalyst, but it had great influences on the photocatalytic activity of Bi₂WO₆ towards RhB degradation, and also an optimal Pt species content on the surface of Bi₂WO₆ photocatalyst was discovered with the highest photocatalytic ability. The improved photocatalytic performance could be ascribed to the increased photoabsorption ability, the enhanced interfacial charge transfer and the inhibited recombination of electron-hole pairs by modified with PtCl₄. Meanwhile, a possible mechanism for RhB photocatalytic degradation over PtCl4/Bi₂WO₆ catalyst was also proposed. (2) The bismuth molybdate Bi_3.64Mo_0.36O_6.55 (BMO) was successfully synthesized by a rapid and convenient microwave-assisted method. Carbon was introduced to hybridize with BMO material through the simple combination of hydrothermal process in the presence of glucose and subsequent calcination treatment in N₂ gas at 280°C. The results indicated that carbon did not affect the final crystalline structure and morphology of BMO, but it had great influences on the photocatalytic activity of BMO towards RhB degradation. The improved photocatalytic performance could be ascribed to the synergetic effects of increased photoabsorption ability, enhanced photogenerated electron-hole separation and more RhB adsorption associated with carbon.