【作者】 刘瑜；

【导师】 殷永泉；

【作者基本信息】 山东大学 ， 环境科学与工程， 2016， 硕士

【摘要】 近年来,工农业发展过程中产生的大量挥发性有机物(VOCs)严重危害了大气环境质量和人体健康。在众多VOCs中,苯系物属于环境空气中浓度较高、危害较大且难降解的一类。光催化氧化技术是一种绿色高级氧化技术,具有能耗低、效率高、降解彻底等优点,在污染物治理和能源开发方面具有广泛的研究和应用,溴氧化铋(BiOBr)作为一种新型的光催化材料,因其独特的层状结构和内部电场、间接跃迁模式及优良的光催化性能,引起了研究者们的关注。因此,找到一种简单有效的方法制备出具有优异的光催化性能的BiOB r,探讨其对苯的光催化降解性能的影响因素,以期为光催化技术的推广和高活性的催化材料的开发提供理论依据和实验基础。采用硝酸铋作为铋源,十六烷基三甲基溴化铵(CTAB)作为溴源,无水乙醇作为溶剂介质制备得到纳米溴氧化铋(BiOBr)粉末。制备过程中通过改变溶剂热温度和反应物Bi/Br摩尔比,得到不同形貌结构的BiOBr粉末。通过XRD、 SEM、TEM、BET、UV-Vis等表征手段,系统地研究了制备过程中溶剂热温度及反应物Bi/Br摩尔比对BiOBr的结构、形貌、比表面积及光吸收性质的影响,初步探讨了BiOBr结构的形成机理。结果表明,在反应物Bi/Br摩尔比为1：6时,制得的溴氧化铋为纳米片层状堆叠结构,且随着溶剂热温度的变化,溴氧化铋的晶型结构有一定的转变,纳米片厚度和对紫外光的吸收强度都随温度的的增加而减小。其中,120℃下制备得到的BiOBr具有最好的光催化活性,对苯进行紫外光降解反应90min,苯的去除率可达到65%,而Ti02光催化降解苯的效率仅为18%。测试制得的BiOBr稳定性时,发现催化剂重复使用三次后,BiOBr对苯的催化效率降低不到1%,说明BiOBr的稳定性良好。当溶剂热温度为120℃时,随着Bi/Br摩尔比的提高,溴氧化铋的结构形貌由层状渐渐交错成花球状,且球的粒径随之变小,比表面积则相应增大,光催化相应地增强。Bi/Br比为2：1时,苯的光催化去除率最高可达80%,光催化性能最好。采用制备得到的性能最优的BiOBr探讨了光催化过程中催化剂投加量、反应物初始浓度、水蒸气含量和光强对光催化降解苯的影响。结果表明,在一定范围内,催化剂投加量越多,光催化效率越高,当达到一定量时,去除效率不再明显增加,反应界面面积大小不再是影响光催化效率的主要因素。反应物初始浓度增加,光催化效率提高,增加到2.3g/m3,去除效率最大达到90%,继续增加浓度,催化效率不再提高,这是因为催化剂能提供的活性中心是有限的,过量的苯分子之间形成了相互竞争的关系。体系中存在一定量的水蒸气,可以提高光催化降解效率,水蒸气过量时,则会制约BiOBr的光催化性能。随着紫外光光强的增大,体系中光子数增多,苯的降解率提高。最后对苯的光催化过程进行了动力学研究,结果表明,苯的光催化过程符合一级反应动力学方程。更多还原

【Abstract】 In recent years, lots of volatile organic compounds (VOCs) that are formed during the industrial and agricultural developing processes are seriously harmful to air quality and human health. Among so many VOCs, Benzene series is very pernicious and difficult to degrade, and has a high concentration in the ambient air. The photocatalytic oxidation technology, that is an advanced green oxidation method, has the advantages of low energy consumption, high efficiency and complete degradation. It has been widely researched and used in the field of pollutant treatment and energy developing. BiOBr, as a new photocatalytic material, because of the special lamellar structure, inner-electric field, indirect transition model and good photocatalytic capability has been concerned by many researches. So, it is meaningful to find a simple and effective method to produce BiOBr that has excellent photocatalytic capability and analysis the impact factors of its photocatalytic capability during the processes of degrading Benzene. And this will provide theoretical and experimental basics for generalizing the use of photocatalytic technology and developing highly reactive catalytic materials.BiOBr powders were prepared by solvothermal method using Bismuth Nitrate as Bismuth resource, cetyltrimethylammonium bromide (CTAB) as Bromo source and absolute ethylalcohol as solvent. In the producing process, BiOBr powders with controlled morphologies and structures have been synthesized by changing the solvothermal temperature and the reactant Bi/Br molar ratio. Then the effects of the solvothermal temperature and the Bi/Br molar ratio that influence its morphologies, structures and light adsorption properties were researched and characterized by the means of XRD, SEM, TEM, BET, UV-Vis, etc. The results showed that the prepared BiOBr had nano-lamellar stacked structures when the Bi/Br molar ratio was 1:6. With the increase of solvothermal temperature, the crystallographic structure of BiOBr changed in some degree. The thickness of nano layers and the absorption intensity of ultraviolet light decreased with the increase of temperature. Under the comparison of other temperatures, BiOBr prepared at 120℃ in 90 minutes had the best photocatalytic active ability. Benzene photodegradation efficiency on this BiOBr was 65%, but only 15% on TiO2.BiOBr above prepared still had high Benzene removal efficiency and the photodegradation efficiency reduced less than 1% after recycling three times. At the preparing temperature of 120℃, the morphologies and structures of BiOBr changed from lamellar to flower-like gradually. The particle size decreased, and specific surface area increased with the increase of preparing temperature. The photocatalytic active ability improved with the increase of the Bi/Br ratio. When the Bi/Br ratio was 2:1, the catalyst showed the highest photocatalytic capability, with Benzene photodegradation efficiency of 80%.The several important effects of photocatalytic degradation, including catalyst quantity, initial concentration of solution and water vapor content, were also discussed by using the prepared BiOBr under 120℃ and the Bi/Br ratio of 2:1. The results showed that photocatalytic efficiency increased with increase of catalyst quantity within a certain range. When the catalyst reached a certain amount, the removal efficiency would not increase obviously and the size of reaction area was not an important factor of influencing the photocatalytic efficiency. With the increase concentration of initial reactant, the photocatalytic efficiency improved. When the initial reactant concentration reached 2.3g/m3, the maximum removal efficiency was 90%. After that concentration, the photocatalytic efficiency would not improve with increasing concentration, because the catalyst had limit active ability and the competitions were formed between excessive Benzene molecules. In the system, some amounts of water vapor can help to improve the photocatalytic efficiency, but too much water vapor would restrict the photocatalytic capability of BiOBr. With the increase of UV light intensity, the number of photons in the system increased, and the degradation rate of benzene increased. Finally, kinetics analyses were studied during the processes of catalyzing Benzene, with one order reaction kinetics equation.更多还原