【作者】 李瑞；

【导师】 樊彩梅；

【作者基本信息】 太原理工大学 ， 化学工程， 2014， 硕士

【摘要】 作为一种新型光催化材料,BiOBr因其独特的开放式层状结构、间接跃迁模式以及适中的能带结构,受到了研究者的广泛关注,被认为是一种极具竞争力和应用前景的光催化材料。为了深入了解制备条件对于BiOBr粉末晶型结构、外观形貌及光催化活性的影响,本文以简单的BiBr3水(醇)解法在低温下制备出了不同结晶度和形貌结构的BiOBr粉末,并通过考察催化剂在模拟太阳光下对甲基橙(MO)的降解效果,确定出了适宜的制备条件。同时为了克服纳米粉末催化剂固液分离难的缺陷,本文采用简单方便、能耗低、无污染的醇解-涂覆固定化技术,通过调节反应溶剂、醇解温度及焙烧温度,制备出了一系列具有不同(110)与(102)特征峰比例的BiOBr薄膜催化剂,通过比较催化剂在紫外灯下对MO的降解效果,确定出了适宜的固定化条件,掌握了制备条件对薄膜催化剂活性影响的基本规律,具体结论如下：1.采用BiBr3水(醇)解法在不同溶剂及温度下制备出了具有不同形貌、结晶度、晶面取向且活性较好的BiOBr粉末光催化剂,该方法低温环保、经济实用。2.通过比较催化剂在模拟太阳光下对甲基橙的降解效果发现：以水为溶剂时,催化剂对MO的降解率在75mmin内均可达到90%以上,且催化剂的循环性和稳定性较好,四次循环后降解率仍保持在90%以上；以醇为溶剂时,所制催化剂的活性则随着醇种类及醇解温度的变化而变化,且以异丙醇为溶剂、在60℃下醇解时所得催化剂活性最佳,75min即可降解98%以上的MO,但此种催化剂的活性在第一次使用后有明显降低,而在此后三次循环中基本保持不变,均为120min内降解98%以上的MO。3.通过SEM、XRD等现代光谱表征手段可以发现：以水为溶剂时,所制催化剂为均匀整齐的片状结构,且催化剂的结晶度和晶面取向随水解温度的变化不明显；以醇为溶剂时,通过不同溶剂的选取可以达到催化剂形貌和结晶度的可控,且催化剂的结晶度随醇解温度的升高而升高。同时以醇为溶剂所制催化剂的晶面取向与以水为溶剂所制催化剂的晶面取向有明显差别,故结合相关文献可以得知,以水为溶剂所制催化剂活性高是由于其良好的结晶度和特殊的晶面取向所致,而以醇为溶剂时催化剂活性高是因为其特殊的形貌结构和较好的结晶度,且其循环性差是由于其吸附性能和结晶度的改变所致。4.采用醇解-涂覆法制得了具有类花状形貌的四方晶相BiOBr薄膜光催化剂,样品由Bi、O及Br三种元素构成,且元素组成比例与BiOBr的化学计量比相近。5.通过调节反应溶剂、醇解温度和焙烧温度,可以达到BiOBr薄膜(110)与(102)特征峰比例可控,进而表现出不同的光催化活性,其中以异丙醇为溶剂在60℃下醇解、不经高温焙烧时所制BiOBr薄膜具有最佳的光催化活性,在紫外灯下照射2.5h后可降解98.5%的MO,且此种薄膜具有良好的稳定性,五次循环后仍可达到90%以上的降解率。6.通过对类花状薄膜形成机理的推测,可以看出异丙醇在BiOBr薄膜的形成过程中起到了降低团聚趋势及粒径大小的作用,使得纳米片在固定化的过程中进行了自主旋转和重新组装,从而形成了类花状结构,并保留了薄膜催化剂的纳米尺寸效应。更多还原

【Abstract】 BiOBr as a novel semiconductor photocatalytic material, has drawn considerable attention and been considered to a competitive and promising photocatalytic material, due to its open-layered structure, indirect transition mode and moderate energy band structure. In order to thoroughly understand the effect of preparing conditions on crystal structure, morphology and photocatalytic activity of BiOBr powder, this paper proposed a facile hydrolysis (alcoholysis) method to synthesize BiOBr with different morphologies and crystallinity using BiBr3as precursor at a low temperature. At the same time, the photocatalytic activities of BiOBr have been evaluated by the degradation of methyl orange (MO) under simulated sunlight and the optimum conditions for the preparation of BiOBr have been determined. Furthermore, in order to overcome the solid-liquid separation defects of conventional nano-powder catalysts, we also prepared BiOBr thin film photocatalyst using an alcoholysis-coating method, which is simple, pollution free and low energy consumption. In addition, through controlling the reaction and calcining temperatures, the BiOBr thin films with different intensity ratios of (110) to (102) peaks were synthesized, and furthermore through the evaluation of MO degradation under UV light irradiation, we have obtained the optimum immobilization conditions of BiOBr thin films and mastered the basic regularity of the influences of the preparation conditions on the membrane catalytic activity. All the obtained results are listed as follows:1. The BiOBr photocatalysts with higher activity and different morphologies, crystallinity and crystalline facets orientation are synthesized using BiBr3as precursor at different solvent and reaction temperature. This method is lower temperature, environmentally friendly, economical and practical.2. According to the photocatalytic efficiency of BiOBr for decomposing MO under simulated sunlight, we find when distilled water is used as solvent, the degradation of MO can reaches90%in75min. and the as-prepared BiOBr also displays good stability, its photocatalytic activity still remains above90%after being used five times. When alcohol is used as solvent, the photocatalytic efficiency of BiOBr will change according to alcoholysis reaction temperature and species of alcohols. And the best photocatalytic degradation efficiency of MO for as-prepared BiOBr-60(IPA) is98%under75min simulated sunlight irradiation. But the photoactivity of the BiOBr decreased in the first recycling experiment, and no significant loss in the next three recycling reactions, the degradation efficiency of methyl orange (MO) also can reaches98.5%in120min.3. According to the SEM, XRD characterization, we find that when distilled water is used as solvent, the as-prepared BiOBr is composed of flake structure. The crystallinity and the crystalline facets orientation both have no significant changed with the temperature of the hydrolysis reaction increases. However when alcohols are used as solvent, the morphology and the crystallinity make noticeable changes along with the different solvents. In addition, the crystallinity was increased with the rising of alcoholysis reaction temperature. Furthermore, the crystalline facets orientation of BiOBr powders changes with solvents, and shows a big difference between distilled water and alcohols. So, the high photocatalytic efficiency of BiOBr, which is prepared in distilled water, should be attributed to the best crystallinity and unique crystalline facets orientation, while the high photocatalytic efficiency of BiOBr, which is prepared in isopropyl alcohol, should be ascribed to the specific structural characteristics and a better crystallinity. In addition, the photoactivity of BiOBr-60(IPA) decreased in the first recycling experiment due to the change of surface adsorption ability and crystallinity.4. The flower-like morphology BiOBr thin films have been prepared via a facile alcoholysis-coating method using BiBr3as the raw material and isopropyl alcohol as the solvent. And we can find that the sample was composed by Bi, O and Br three elements, and has a ratio close to the stoichiometric ratio of BiOBr.5. The intensity ratios of (110) to (102) peaks of BiOBr thin films can be controlled by the choice of solvents, the reaction and calcination temperatures, and further indicated the different photocatalytic activity. The degradation experimental results confirmed that the film prepared at60℃in isopropyl alcohol solvent posses the best photocatalytic activity and the degradation efficiency of MO can reach98.5%under2.5h UV irradiation. In addition, the BiOBr sample also displays good stability and its photocatalytic activity still remains above90%after being used five times.6. A possible formation mechanism of BiOBr thin film was also inferred and the results suggested that the isopropyl alcohol solvent can decrease the crystallite size and significantly inhibit the agglomeration of nanosheets, resulting in the nanosheets independently-rotating and reassemble, finally, the stable micro-nano-structure BiOBr thin film are formed and the nano-size effects of BiOBr thin film are remained.更多还原