【作者】 杨艳青；

【导师】 张高科；

【作者基本信息】 武汉理工大学 ， 环境工程， 2012， 博士

【摘要】 光催化具有分解水制氢、还原CO2和光降解有机污染物等作用,在解决能源问题、温室效应和环境问题方面有重要的应用前景。Ti02因为具有催化活性高、化学和光稳定性好、安全无毒等优点而被作为一种常用的光催化剂。但是其较宽的禁带宽度使其只能被太阳光中少部分的紫外光所激发,另外,由于催化剂的比表面积相对较小,对低浓度污染物的富集作用比较弱,且催化剂处于悬浮体系中,不利于回收利用,限制了光催化技术在实际中的应用。因此,开发具有可见光响应的新型半导体光催化剂和解决催化剂的固载问题是环境污染和可再生能源开发利用的重要内容之一。贵金属-半导体光催化剂结合了贵金属的表面等离子体共振效应和半导体光催化活性的优点,能够提高对可见光的利用率和光催化活性。粘土矿物因其具有大的表面积,使得它们对有机污染物具有吸附性,且其来源广泛,价格低廉。因此,粘土可作为光催化剂的载体。本论文将等离子体光催化剂与粘土载体相复合,通过利用Ag-AgX表面等离子体的可见光响应以提高太阳光利用率,以及粘土的结构特性增大催化剂的比表面积和固液分离性能,防止光生活性颗粒的宏观聚集和催化剂在降解过程中被侵蚀或被洗去。从而达到提高催化剂可见光利用率和固定光催化剂的目的。本论文通过大量实验制备了一系列不同结构的光催化剂,通过各种表征手段探究晶相和物理化学性质及对其光催化活性的影响。在理论和实际应用上做了一些有益的探索。具体研究内容和研究成果如下：通过溶胶-凝胶法在低温下制备了具有吸附性能的Ti02/累托石复合催化剂,通过Ag-AgCl修饰TiO2/累托石复合物制备了具有可见光响应的Ag-AgCl-TiO2/累托石复合光催化材料。利用X射线衍射(XRD)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线光电子能谱分析(XPS)、激光拉曼光谱(Raman)、紫外可见漫反射光谱(UV-vis DRS)等测试手段对所制备的催化剂进行了表征。分别以酸性红G和4-硝基苯酚为目标降解物,研究了光催化剂在可见光下对有机污染物的光催化降解性能,探讨了复合光催化材料的结构与光催化性能之间的关系。通过紫外_可见光光谱分析和活性自由基的分析,探讨了制备的光催化剂对有机污染物的降解机理。研究表明,通过光致还原将AgCl表面部分的Ag+还原成Ag,利用贵金属Ag的等离子体共振效应可以增强对可见光的吸收,同时以粘土为载体增大了光催化剂的比表面积,从而得到了具有可见光响应的高吸附性催化剂。针对Ti02光催化剂在实际利用中所面临的可见光利用率低及纳米粉体在悬浮体系中易失活、难回收等问题,通过溶胶凝胶的方法将TiO2光催化剂负载在凹凸棒粘土上,然后通过沉淀和光还原的方法将Ag-AgCl沉积于表面,得到Ag-AgCl-TiO2/凹凸棒石复合光催化材料。采用多种表征手段对其结构和表面特性等进行了分析。这种等离子体-半导体复合光催化剂在降解罗丹明B溶液时显示出高的光催化活性,相同实验条件下,较Ag-AgCl光催化剂和Ti02/凹凸棒复合光催化材料对罗丹明B溶液有较高的吸附性能和光催化性能。该复合光催化材料综合利用表面等离子体对可见光的吸收性能和凹凸棒的吸附固载性能,在一定程度上解决了Ti02可见光利用率低的问题,以及实际应用中难于回收的问题。制备了新型的Ag-AgBr/粘土复合光催化材料,利用XRD、SEM、HRTEM、 XPS、UV-vis DRS等测试手段对所制备的催化剂进行了表征。探讨了复合光催化材料的形成过程。研究了复合光催化材料在可见光下对有机染料的光催化活性,并对其降解机理进行了分析。结果表明,纳米贵金属的等离子效应增强了复合光催化材料对可见光的吸收。相同条件下,Ag-AgBr/粘土复合光催化材料的性能要优于Ag-AgBr催化材料。这说明,粘土矿物作为载体的引入一方面起到了固定光催化剂、防止催化剂流失和提高光催化剂利用率的作用,另一方面又能增加光催化剂的有效表面积和活性点,有利于电子-空穴对的分离并增强对反应物的吸附能力。等离子体材料的可见光吸收和载体的大的比表面的协同作用提高了复合光催化材料对污染物的降解性能。更多还原

【Abstract】 Photocatalyst can be use to split water into hydrogen, photoreduced CO2and photodegrade organic pollution and so on. Therefore, the photocatalytic technology has prospect of application in solving the problem of energy shortage, global warming and environment pollution. TiO2is the most widely used photocatalyst due to its high catalytic activity, good chemical stability and non-toxicity, etc. unfortunately, it is activated only under UV light irradiation because of its large band gap. Moreover, the TiO2powder has small surface area leading to a low adsorption capacity for much diluted solutions, which take a low photocatalytic effect for low concentration wastewater treatment. And the photocatalyst in suspended system was difficult to separate from aqueous solution. These questions hindered its practical applications. Therefore, the development of new visible light-driven photocatalyst and immobilized the catalyst are essential to the control of environment pollution and the use of sustainable energies.The plasmonic photocatalyst combining the surface plasmonic resonance (SPR) properties of noble metal nanoparticles and the photocatalytic properties of semiconductors, which is expect to improve the photocatalytic activity and increase the utilization ration of visible light. Clays can serve as the host materials for catalysts because of their large surface area for adsorption of organic pollutants as well as their abundance and low cost. In this paper, Ag/AgX plasmonic photocatalyst supported on clays were studied, the photocatalyst can take full advantage of the visible light response of the plasmonic photocatalst to improve the utilization of sunlight, and can use the particular structure properties of clays to increase the surface area of the photocatalyst and the solid-liquid separation efficiency as well as avoid the formation of macroscopic aggregates of photoactive particles and protects the photocatalyst particles from erosion or washing in the photodegradation process. The present work fabricated series of visible light driven photocatalysts with various structures. The microstructure properties and the photocatalytic activities of the prepared photocataltst were measured by means of characterization methods. This work has valuable exploration in theory and practical application. The main points of the present work could be summarized as follows:In this paper, the TiO2/rectorite composites were successfully prepared by a facile and low-cost sol-gel technique at low temperature, Ag-AgCl particles were then loaded on the TiO2/rectorite to obtain the Ag-AgCl-TiO2/rectorite composite. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (HRTEM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (Raman) and UV-vis diffuse reflectance spectrum (UV-vis DRS). The photocatalytic activities of the as-prepared photocatalysts were evaluated by the degradation of acid red G (ARG) and4-nitrophemol (4-NP) in aqueous solution under visible light irradiation. The relationship between the photocatalytic activity and the structural features of the prepared catalysts was investigated through a systematic characterization analysis. A possible photocatalytic mechanism was discussed through UV-vis spectrum analysis and active species analysis in the photocatalytic reaction. The results indicated that the photoreduction method can reduce partial ions to Ag0species, which can effectively improve the absorption of visible light. And the clay as the supports of the composites can improve the adsorption capacity of organic pollutants. Therefore, this paper explores a new way to prepare a visible light responsive photocatalyst with high adsorption.Conventional TiO2photocatalyst requires near-ultraviolet irradiation for effective photocatalysis and difficult to separate from aqueous solutions thereby severely limiting its practical application. At first, TiO2immobilized on attapulgite was prepared by sol-gel method, and then deposited Ag-AgCl on the surface of TiO2/attapulgite by a precipitation and photoreduction method to obtain the Ag-AgCl-TiO2/attapulgite photocatalyst. The composite were characterized by some characterization methods. The prepared photocatalyst exhibits an efficient visible light photocatalytic activity for degradation of Rhodamine B and has a higher adsorption and photocatalytic activity than the Ag-AgCl and TiO2/attapulgite powders under the same condition. The experiments confirmed the composite was beneficial to enhancing the adsorption activity and the utilization of sunlight, which has a beneficial effect on the practical application of photocatalytic technology.Ag-AgBr/clay composite was synthesized and characterized by XRD, SEM, TEM, XPS and UV-vis DRS methods. And the strategy for the fabrication of Ag-AgBr/clay composite was proposed. The visible light driven photocatalytic activity of this composite material was investigated by the photocatalytic decomposition of azo dyes and the photocatalytic mechanism of the reaction was also discussed. It was obvious that the photocatalytic activity of Ag-AgBr/clay was higher than that of Ag-AgBr under the same conditions. The results indicate that the surface plasmon resonance of Ag can enhance the visible light adsorption of photocatalyst. The clay function as a substrate for Ag-AgBr particles can stabilized photocatalyst to avoid catalyst loss and thus improve the utilization of the catalyst. Moreover, the specific surface area, the active sites, the separation of electron-holes and the adsorption properties are improved by the carrier. The performance photocatalytic activity of the composite can be attributed to the synergetic effect of the visible light adsorption of the plasmon materials and the large specific surface area of the clay.更多还原