Aqueous Synthesis And Photocatalytic Property Study Of Bismuth Based Semiconductor Oxides Micro/Nano-materials

Recently years, semiconductor materials have shown great application value in solving environmental pollution problem. As semiconductor materials can be able to directly use sunlight to produce substance with optical activity to degrade pollutants,extensive attentions of researchers had been put into semiconductor materials. With further development of this field, to study and develop different photocatalytic materials, to improve the photocatalytic efficiency and to realize the simple and controllable preparation of semiconductor materials have became an important issue.As a class of material in semiconductor materials, the new bismuth based semiconductor material has gradually become a hot research, due to its a larger number of advantages, such as: its very kinds of species, ability to adsorb visible light for most of materials, narrow band gap energy, low cost and non-toxicity, extremely wide range of applications. Now, The main focus of the relevant work and report is to improve the photocatalytic activity of bismuth based semiconductor materials, but these synthesis methods often have one or more disadvantages, such as: long reaction time, high requirements for equipments, complex processing technology, toxic or expensive raw materials, et al. These defects are unfavorable for the industrialization of bismuth based semiconductor materials.In this paper, by means of the liquid phase synthesis with simple synthetic treatment process, cheap and non-toxic raw materials were used to quickly and efficiently prepare bismuth based oxide semiconductor micro/nano materials with high photocatalytic performance. Based on various characterization methods for analyzing morphology, composition and properties of the as-prepared materials, the synthesis mechanism of different kinds of bismuth based semiconductor oxide micro/nano materials and the related factors of the reaction were studied. The as-prepared bismuth based semiconductor oxide micro/nano materials were used to photodegrade rhodamine B（Rh B） and colorless pentachlorophenol, and the mechanism of the photocatalytic reaction was also analyzed. The main research contents and results can be summarized as follows:1. Using ethylene glycol（EG） as the surface active agent, through simple liquid phase precipitation method, bundle α-Bi₂O₃ crystal with acicular branching structure was rapidly prepared. The amount of EG and volume of Na OH solution could be controlled to prepare α-Bi₂O₃ crystal with different degree of crystallinity andbranching growth. Directional adsorption of EG molecules on the α-Bi₂O₃ crystal promoted the occurrence of the branching growth process, and the growth mechanism of bundle α-Bi₂O₃ was proposed on the basis of theoretical analysis and experimental characterization. With increasing the degree of the branching growth, thermodynamic transition temperature of α-Bi₂O₃ was decreased, while its catalytic degradation property for Rh B under visible light was improved. Of course, other photocatalytic reaction conditions, such as: distance of the light source, amount of the catalyst,concentration and p H of Rh B solution, could also affect the photocatalytic reaction efficiency. Study on the photocatalytic degradation mechanism indicated that bundleα-Bi₂O₃ achieved the degradation of Rh B molecules through photogenerated holes（h+）in neutral solution. In the other reaction system, large rod-liked α-Bi₂O₃ sample was prepared. During the experiment, the time needed to prepare α-Bi₂O₃ could be decreased by increasing the concentration of Na OH solution or the reaction temperature, and the addition of sodium oleate（SOA） inhibited the formation of Bi₂O₃.The length of large rod-liked α-Bi₂O₃ increased with formula weight of surface active agent（polyethylene glycol） PEG increased.2. Using hexadecyl trimethyl ammonium bromide（CTAB） as the surface active agent, pumpkin-liked metastable β-Bi₂O₃ was first synthetized at 70 oC, then, short block-liked β-Bi₂O₃ was quickly fabricated at 70 oC. metastable β-Bi₂O₃ could be able to transform into stable α-Bi₂O₃, and Bi₂O₃ with different crystalline forms might be obtained by collecting samples at different reaction time. The concentration of Na OH solution, the reaction temperature and the stirring rate together played a role in the stable time of β-Bi₂O₃ exsited in the reaction system. The experimental study about synthesis at 40 oC indicated that the mount of CTAB influenced on crystal form and morphology of the as-obtained samples. Only appropriate quantity of CTAB was added,pure β-Bi₂O₃ could be prepared, at the same time, the mechanism for synthesis ofβ-Bi₂O₃ crystal induced by halogen ion was proposed based on the experimental study and theoretical analysis. One dimensional β-Bi₂O₃ crystal with different aspect ratio could be prepared by changing the concentration of Na OH solution. At the last, we focused on studying the photocatalytic property and mechanism of β-Bi₂O₃. During the experiment, the p H value（regulated by HCl） of Rh B solution was respectively controlled as 3, 5 and 7, as a result, β-Bi₂O₃ exhibited best photocatalytic efficiency for degradaing of Rh B solution when the p H value is 3, that was because HCl had promoted generation of a little of Bi OCl on surface of β-Bi₂O₃, which helped for improving the photocatalytic degradation efficiency. A detailed explanation forphotocatalytic mechanism was given. β-Bi₂O₃ with differrent size was used to degrade Rh B, the result shown that β-Bi₂O₃ with smaller size exhibited better photocatalytic efficiency. Experimental study on the comparison of photocatalysis β-Bi₂O₃ andα-Bi₂O₃ verified the former’s better photocatalytic efficiency.3. By means of the liquid phase precipitation synthesis, precursor containing bismuth was firstly separated from the mother liquor, and then reacted with precipitating agent Na OH to prepare piece-liked Bi₁₂O₁₇Cl₂ plaited by belts, the piece of Bi₁₂O₁₇Cl₂ was about 10 15 nm in thickness. Based on the characterization and analysis for the precursor obtained before addtion of Na OH and the samples obtained at different reaction time after the addtion of Na OH, it was revealed that Bi₁₂O₁₇Cl₂ was transformed from Bi OCl, the morphology and the state of materials changed before and after this kind of transformation, the piece of Bi₁₂O₁₇Cl₂ is soft, while Bi OCl is hard. The intrinsic material CO32– in Na OH solution might cause the final sample to be non pure phase Bi₁₂O₁₇Cl₂, which was not conducive to the photocatalytic degradation of Rh B. Two different synthetic processes including separation Bi OCl from mother liquid or not were used, the former is more help for rapid synthesis of Bi₁₂O₁₇Cl₂. Bi₁₂O₁₇Cl₂ has significant photocatalytic degradation ability for neutral Rh B solution, the reason of which might due to the thin thickness of Bi₁₂O₁₇Cl₂ nanoflakes to inhibit recombination of photogenerated e– and h+.4. Through inheritance of morphology, spherical architecture Bi₁₂O₁₇Cl₂ was obtained by using assemble Bi OCl sphere as template in situ reaction under the influence of OH–, the assembly unit of Bi₁₂O₁₇Cl₂ was nanoflake. By controlling the amount of raw material Na Cl, synthesis temperature of precursor and the amount of surface active agent PEG-6000, spherical assembly architectures Bi OCl and Bi₁₂O₁₇Cl₂ with differrent size and assembly degree could be prepared. For spherical assembly architecture, the thickness of its basic unit Bi OCl nanoplate was too thick（about 40 nm or more） to inhibit transformation from Bi OCl into Bi₁₂O₁₇Cl₂, while was too thin to accelerate transformation from Bi OCl into Bi2O2CO3. Based on the analysis of the characterization results and the software simulation of crystal growth, the relationship between the scale of Bi OCl and the directional growth of its（001）,（110） crystal plane was explained, and the influence of reaction conditions on the product was further analyzed. Bi₁₂O₁₇Cl₂ was stable in reaction system, and would not chang in its composition and morphology with reaction time increased. Bi₁₂O₁₇Cl₂ samples with different assembly degree were employed to degrade Rh B under visible light irradiation, the higher assembly degree of Bi₁₂O₁₇Cl₂, the better photocatalyticproperty of Bi₁₂O₁₇Cl₂. The research on the photocatalysis mechanism indicated that the h+ of the Bi₁₂O₁₇Cl₂ had played an important role in the process of photodegradation...