AgBr基复合光催化剂的性能与稳定性研究

发布时间：2018-05-13 02:24

  本文选题：AgBr + 空穴转移　； 参考：《华东师范大学》2017年硕士论文

【摘要】：近年来,环境污染、能源紧缺与社会发展和人类安居之间的矛盾日益严峻,环境修复和清洁能源的开发已成为全人类所面临的亟待解决的难题。半导体光催化技术是最近几十年兴起的可以利用太阳能实现对污染物的有效降解和产氢的技术,因其操作简便、环境友好和应用前景广阔受到了越来越多的关注。溴化银(AgBr)作为传统的半导体材料,具有优良的光敏性能,但在光照下很不稳定,光腐蚀现象严重,阻碍了其在光催化方面的实际应用。目前以AgBr为主体的复合光催化剂的研究主要集中于Ag/AgBr。然而,Ag/AgBr在光催化的过程中依旧受到较为严重的腐蚀。因而,AgBr基光催化剂的性能与稳定性的研究对于AgBr基光催化剂的实际应用具有重要的意义。本文通过缓慢分解Cu(OH)2生长CuO,从而在AgBr微米颗粒表面修饰几十纳米的CuO颗粒。结果显示CuO/AgBr样品在光催化过程中反应速率常数为纯AgBr的4.3倍,对甲基橙(MO)的最终降解率达到91.2%,与纯AgBr相比光催化性能得到了明显的提高。光催化后溶液的pH值显示CuO/AgBr样品中光生空穴与Br-结合生成Br0的量明显降低,光催化后的样品没有纯AgBr明显的分解再生长现象,三次循环实验以后依旧保留了 85.1%的降解率,表明CuO/AgBr的光催化稳定性得到了明显的改善。进一步的自由基检测显示空穴在CuO/AgBr体系中起主导作用,其机制来源于CuO与AgBr紧密接触后在界面处形成p-n异质结,产生的内建电场方向由n-AgBr指向p-CuO,从而AgBr中的光生空穴能够转移到CuO中。因此,CuO/AgBr复合光催化剂的性能与稳定性的主要来源是空穴的转移。在接下来的工作中我们通过液相超声剥离块状MoS2至少数几层,并包覆在KBr的表面,然后利用离子交换法和还原法合成了 MoS2/Ag/AgBr,成功制备了 MoS2平均厚度为4nm左右的复合光催化剂。样品的相结构与微观形貌分别通过XRD和SEM进行了表征,样品中的MoS2以及层数通过激光拉曼光谱进行测定,紫外-可见吸收光谱显示MoS2/Ag/AgBr样品对光的吸收能力明显优于Ag/AgBr,光催化性能评价显示复合样品的光催化活性提高了 50%左右。在进一步的光催化机制探讨中,我们发现超薄的MoS2够转移Ag/AgBr中的光生电子,从而改善了 Ag/AgBr的光催化性能。
[Abstract]:In recent years, the contradiction between environmental pollution, energy shortage, social development and human security has become increasingly severe. Environmental restoration and clean energy development have become a difficult problem to be solved urgently. Semiconductor photocatalytic technology is a technology that can effectively degrade pollutants and produce hydrogen by solar energy in recent decades. Due to its simple operation, environmental friendliness and wide application prospects, more and more attention has been paid to semiconductor photocatalytic technology. As a traditional semiconductor material, silver bromide (AgBrB) has excellent properties of Guang Min, but it is unstable in illumination and serious in photocorrosion, which hinders its practical application in photocatalysis. At present, the study of composite photocatalyst based on AgBr is mainly focused on Agr / AgBr. However, Agr / AgBr is still seriously corroded in the process of photocatalysis. Therefore, the study on the performance and stability of AgBr based photocatalysts is of great significance for the practical application of AgBr based photocatalysts. In this paper, dozens of nanometers of CuO particles were modified on the surface of AgBr micron particles by slow decomposition of Cu(OH)2. The results show that the reaction rate constant of CuO/AgBr sample is 4.3 times of that of pure AgBr, and the final degradation rate of methyl Orange MOA is 91.2. The photocatalytic performance of CuO/AgBr sample is obviously improved compared with pure AgBr. The pH value of the solution after photocatalysis showed that the amount of photogenerated holes combined with Br-to form Br0 in the CuO/AgBr sample was obviously decreased, and the photocatalytic sample did not undergo the decomposition and growth of pure AgBr, and the degradation rate of 85.1% was still retained after three cycles. The results show that the photocatalytic stability of CuO/AgBr is obviously improved. Further free radical detection showed that holes play a leading role in the CuO/AgBr system, and the mechanism originates from the formation of p-n heterojunction at the interface between CuO and AgBr after close contact. The direction of the generated built-in electric field is directed from n-AgBr to p-CuO, so that the photogenerated holes in AgBr can be transferred to CuO. Therefore, the main source of performance and stability of CuO / AgBr composite photocatalyst is hole transfer. In the following work, we used liquid phase ultrasound to peel off at least a few layers of bulk MoS2 and coated it on the surface of KBr. Then we synthesized MoS _ 2 / AgR _ (R) by ion exchange method and reduction method. The composite photocatalyst with average MoS2 thickness of about 4nm was successfully prepared. The phase structure and microstructure of the samples were characterized by XRD and SEM respectively. The MoS2 and the number of layers in the samples were measured by laser Raman spectroscopy. The UV-Vis absorption spectra showed that the photocatalytic activity of MoS2/Ag/AgBr samples was better than that of AgR / AgBr.The photocatalytic performance evaluation showed that the photocatalytic activity of the composite samples was increased by about 50%. In the further study of photocatalytic mechanism, we found that ultra-thin MoS2 can transfer photogenerated electrons in Ag/AgBr, thus improving the photocatalytic performance of Ag/AgBr.
【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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