【作者】 刘艳；

【导师】 王西奎；

【作者基本信息】 济南大学 ， 环境工程， 2011， 硕士

【摘要】 自20世纪60年代光催化现象被人们发现以来,人们对其展开了广泛的研究,并发现光催化可用于降解环境中的无机或者有机污染物质。研究证明,卤化银不仅能用于摄影技术,还可用于光催化,尤其AgCl是近年来发现的一种新型光催化剂。半导体光催化剂能够光催化降解很多有机污染物,使它们快速彻底矿化为CO₂,H₂O以及一些小分子有机物。当半导体光催化剂吸收足够能量的光子时,其价带电子从价带跃迁到导带,这便产生了光生电子（e-）和空穴（h+）,而光生电子和空穴是良好的还原剂和氧化剂,能够引起表面催化反应。其中纳米TiO₂半导体光催化剂倍受人们青睐。科学家在利用AgCl光催化分解水时发现,在近紫外光照射下,AgCl会产生光生电子和空穴,这与二氧化钛的光催化过程相似,于是人们推测,AgCl光催化降解环境中有机污染物的机理应该与纳米TiO₂相类似。本文通过硝酸银与氯化钠在水溶液中直接反映制备AgCl光催化剂,考察了它对有机染料甲基紫及直接湖蓝5B的吸附作用及光催化降解效果,并与空白实验进行了对照。通过照射前后AgCl的X射线衍射（XRD）、扫描电子显微镜（SEM）及紫外可见漫反射光谱扫描（DRUVS）对AgCl光催化剂进行了表征,反应前后的AgCl其自身性质几乎没有发生变化,但是经照射后,颗粒表面的AgCl会部分分解产生许多Ag团簇,Ag团簇的粒径分布广泛,从而使样品在可见光区域有广泛吸收,使得光催化剂能更有效地利用光源。由吸附实验可知,AgCl对染料的吸附曲线属于典型的IUPAC II型等温线。实验过程中,我们研究了不同光源、pH、催化剂用量、染料浓度等因素对染料光催化降解的影响,并与纳米TiO₂对甲基紫及直接湖蓝5B的光催化效果做了比较。结果表明,AgCl在紫外光及可见光照射下都有良好的光催化活性,pH对AgCl的光催化活性影响不大,加大催化剂的用量能够提高光催化效果,染料浓度越大降解速率越小。由降解不同时间的染料溶液的紫外可见吸收光谱扫描图可知,AgCl光催化甲基紫的降解较为彻底;直接湖蓝5B的降解过程中产生了在400nm波长处有吸收峰的中间产物,并且在AgCl光催化剂存在条件下,该中间产物经长时间的紫外或者可见光照射都不能被完全去除。本文通过研究乙醇对AgCl的光催化的影响及AgCl在经紫外及可见光照射后的荧光谱图,探讨了AgCl的光催化的机理,结果表明,AgCl光催化机理并非同纳米TiO₂一样是由于产生了具有强氧化性的羟基自由基（·OH）,而是由于产生了氯自由基（Cl·）。更多还原

【Abstract】 The photocatalysis phenomenon was discovered in the 1960’s, since then, extensive investigations has been conducted. It is found that photocatalysis can be used to degrade inorganic or organic pollutants in the environment. Researches have shown that silver halides can be used not for only photography, but also for photocatalysis. In particular, AgCl is a new type of photocatalyst which was studied recently by researchers.Some researches had suggested that the semiconductor photocatalyst are able to degrade a wide range of organic pollutants in the environment through photocatalysis effectively and mineralize them into CO₂, water and certain types of small molecule organic materials. When a semiconductor absorbs the photon with enough energy, transion of electron from valence band to conduction band occers , and then a photoelectron （e-） and a hole （h+） generate, which are powerful reductants and oxidants, and are capable to lead to surface catalyst reactions. Titanium dioxide is one of the semiconductor photocatalysts which has been paid extensive attentions. The electron-hole pair on AgCl photocatalyst was found by scientists during the water splitting processes under the UV radiation which was similar to TiO₂. So it was deduced that the photocatalytic mechanism of AgCl used as photocatalyzer to degrade the organic contamination in solution may be the same as TiO₂.In the paper, the AgCl photocatalyst was synthesized by adding of a small excess amount of AgNO₃ to an NaCl aqueous solution with continuous stirring. Characterizations of as-prepared AgCl sample before and after irradiation were carried out by X-ray diffraction （XRD）, scanning electron microscopy （SEM） photographs and UV-visible diffuse reflectance spectroscopy （DRUVS） , and the results showed that AgCl was stable and had not been destroyed in the photocatalysis. But after irradiation there are many silver nanoparticles generated on the surface of the AgCl particles, the broad distribution of the silver particle size makes it have strong absorption in the visible-light region, which makes the AgCl photocatalyst use sunlight better. The adsorption and photocatalytic degradation of organic dyes including methyl violet and the direct sky blue 5B by AgCl was investigated. At the same time, the blank tests without the catalyst were done as control. The results showed that the adsorption isotherm for methyl violet and the direct sky blue 5B on AgCl in the dark exhibited a typical IUPAC type II isotherm shape. It was found that the photocatalytic activity of AgCl catalyst in aqueous under the UV and visible light irradiation was very good; the pH had very little impact on AgCl photocatalytic activity; the increase of catalyst dosage was able to improve the photocatalytic effect; the higher the dyestuff concentration was, the smaller the degradation rate was. Via the UV-visible absorption spectrum of dye solutions at different degradation times, the photocatalytic degradation of methyl violet with AgCl photocatalysis was more thorough, but an intermediate product with absorption peak at 400nm wavelength was found and could not be eliminated totally during the photocatalytic degradation of the direct sky blue 5B.Through the study of the effect of ethanol on the photocatalytic activity of AgCl, and the fluorescence spectra of benzene-1, 4-dicarboxylic acid solution with AgCl before and after irradiation, we research the mechanism of using AgCl as the photocatalyst. The results showed that, photocatalytic mechanism of AgCl is not the same as TiO₂, which produced the powerful oxidizing hydroxyl radicals （?OH）, but because of producing the chlorine radicals （Cl?）.更多还原