钨酸铋的制备、改性以及光催化性能的研究

发布时间：2018-10-16 17:19

【摘要】：钨酸铋(Bi_2WO_6)作为一种新型的光催化材料,因其具有较窄的带隙、较高的光化学稳定性、较强的氧化能力以及成本低等优点被广泛的关注和深入的研究。本文以硝酸铋(Bi(NO3)3·5H2O)和钨酸钠(Na2WO4·2H2O)为原料合成了一系列钨酸铋和金属改性钨酸铋材料,研究了制备条件对材料活性的影响,揭示了其光催化反应机理,为制备具有高催化活性的光催化剂提供了理论依据。主要研究内容如下:(1)采用水热法,以硝酸铋和钨酸钠为原料,通过改变原料的配比、前驱液的pH值以及反应时间,来确定最佳的反应条件。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和紫外-可见漫反射光谱(DRS)对Bi_2WO_6的形貌和结构进行分析。以罗丹明B(RhB)为模拟染料废水,研究了不同制备条件对Bi_2WO_6光催化性能的影响。结果表明,当摩尔比Bi:W=2:1,前驱液pH=1,反应时间为24小时时,所制备的Bi_2WO_6纳米片晶化程度最好,相对的光催化活性也最高。(2)以银氨溶液为银源,采用两步法在已合成的Bi_2WO_6表面负载银单质,得到钨酸铋负载银,并探讨了其对罗丹明B的降解性能。结果表明,在钨酸铋表面负载的微量银单质,并没有对纯钨酸铋的结构和晶型造成很大的影响,但却在一定程度上提高了其在可见光下的降解活性,得出这种现象的原因可能是银单质的等离子共振效应提高了催化剂在可见光区的吸收范围,并且银单质作为一种导体,促进了光生电子-空穴的分离。(3)以硝酸铜为铜源,采用水热法一步合成铜改性钨酸铋,并且也探究了其在不同pH时,对罗丹明B的降解性能。结果表明,微量铜的改性对纯Bi_2WO_6的晶型和结构的影响不大,但却显著提高了其在可见光和紫外光下的降解活性,表征结果表明负载的微量铜增强了Bi_2WO_6对光的吸收,并且促进了光生电子-空穴的分离效率。通过对其机理的探究,发现在Bi_2WO_6降解罗丹明B过程中的主要活性物种是光生空穴以及羟基自由基;罗丹明B的降解主要发生在催化剂表面,因此,罗丹明B的吸附过程是光催化降解的决速步骤。
[Abstract]:Bismuth tungstate (Bi_2WO_6), as a new photocatalytic material, has been widely studied because of its narrow band gap, high photochemical stability, strong oxidation ability and low cost. A series of bismuth tungstate and metal modified bismuth tungstate were synthesized from bismuth nitrate (Bi (NO3) 3 5H2O) and sodium tungstate (Na2WO4 2H2O). It provides a theoretical basis for the preparation of photocatalysts with high catalytic activity. The main contents are as follows: (1) the optimum reaction conditions were determined by changing the ratio of raw material, pH value of precursor and reaction time, using hydrothermal method and bismuth nitrate and sodium tungstate as raw materials. The morphology and structure of Bi_2WO_6 were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and UV-Vis diffuse reflectance spectroscopy (DRS). Using Rhodamine B (RhB) as simulated dye wastewater, the effects of different preparation conditions on photocatalytic properties of Bi_2WO_6 were studied. The results showed that when the molar ratio of Bi:W=2:1, precursor pH=1, was 24 hours, the degree of crystallization of Bi_2WO_6 nanoparticles was the best, and the relative photocatalytic activity was the highest. (2) Silver ammonia solution was used as silver source. Silver loaded with bismuth tungstate on the surface of Bi_2WO_6 was prepared by two-step method. The degradation of rhodamine B was investigated. The results show that the microamounts of silver loaded on the surface of bismuth tungstate have no significant effect on the structure and crystal form of pure bismuth tungstate, but to some extent improve the degradation activity of bismuth tungstate under visible light. It is concluded that the reason for this phenomenon may be that the plasmon resonance effect of the silver element increases the absorption range of the catalyst in the visible region, and that the silver element, as a conductor, promotes the separation of photogenerated electrons and holes. (3) Copper nitrate is used as a copper source. Copper modified bismuth tungstate was synthesized by hydrothermal method, and the degradation properties of rhodamine B at different pH were also studied. The results showed that the modification of trace copper had little effect on the crystal form and structure of pure Bi_2WO_6, but significantly increased its degradation activity under visible and ultraviolet light. The characterization results showed that the supported trace copper enhanced the absorption of Bi_2WO_6. It also promotes the separation efficiency of photogenerated electrons and holes. It is found that the main active species in the degradation of Rhodamine B by Bi_2WO_6 are photogenerated holes and hydroxyl radicals, and the degradation of Rhodamine B mainly occurs on the surface of the catalyst, therefore, the degradation of Rhodamine B occurs on the surface of the catalyst. The adsorption process of Rhodamine B is the critical step of photocatalytic degradation.
【学位授予单位】：河北师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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