【作者】 郭鹏；

【导师】 王祥生； 郭洪臣；

【作者基本信息】 大连理工大学 ， 工业催化， 2010， 博士

【摘要】 TiO2半导体作为光催化材料,因其具有较高的光敏性、化学稳定性等诸多优点一直备受研究者们的关注,是目前应用最广泛的一种光催化剂。与体相TiO2相比,纳米TiO2颗粒有利于提高光子产率,因而具有更高的光催化活性。但纳米TiO2颗粒极易团聚,并对有机物的吸附能力较弱,这使其光催化效率受到限制。采用将TiO2负载到具有高表面积的多孔载体上的方法,可实现其分散、吸附、催化的有机结合。而系统研究载体性质与TiO2活性组分及底物分子性能间的关系,对于发展光催化材料并实现催化反应动力学上的调变具有指导意义。本文利用偶氮染料甲基橙探针分子的吸附和光降解反应,结合多种表征方法,系统地考察了ZSM-5沸石载体的硅铝比、晶粒度、表面酸度等性质对负载型TiO2复合光催化剂的制备及性能的影响,并在此基础上着重研究了载体吸附位的本质,以及吸附键强度的调变对提高TiO2光催化剂活性的意义。主要研究结果如下：1.与SiO2和Al2O3无定形氧化物,以及5A和Y沸石分子筛载体相比,ZSM-5沸石结构是负载TiO2的最佳载体。2.利用ZSM-5沸石载体微孔结构对水分子的吸附和缓释作用,可控制负载过程中TiO2的溶胶-凝胶过程。此法可提高复合光催化剂中TiO2的负载量和分散度,制得的负载型TiO2复合光催化剂对甲基橙具有更高的光催化降解活性。3.甲基橙分子主要吸附在ZSM-5沸石载体外表面较强的酸中心上。降低ZSM-5沸石的硅铝比可提高载体酸中心数量,因此制得的负载型TiO2光催化剂的吸附量和比活性呈明显的增加趋势。减小ZSM-5沸石的晶粒度可增大沸石载体的外表面。纳米ZSM-5沸石载体因具有更大的外表面和更多的表面酸性位,故制备的负载型TiO2光催化剂具有更大的甲基橙吸附量,因而可促进低浓度底物溶液的光催化降解。同时较大的外表面也提高了TiO2的负载量和分散度。TiO2/ZSM-5复合催化剂的最高比活性对应于适当的负载量,在以硅铝比为68、晶粒度<100 nm的ZSM-5沸石为载体时,负载量为6.5 wt%的TiO2/ZSM-5复合光催化剂具有最高的光催化比活性。4.通过Na+改性调变ZSM-5沸石载体的表面酸度发现：吸附在强酸中心的甲基橙分子很难脱附,不利于提高负载型TiO2的光催化活性；而吸附在中等强度酸中心(NH3-TPD图中350-400℃区域)上的甲基橙分子在室温下即可脱附,属于可逆吸附,有助于负载型TiO2的光催化反应的进行。TiO2/1.1%Na-HZSM-5复合光催化剂中载体对甲基橙的吸附主要为可逆吸附,故在制备的催化剂中具有最高的甲基橙光催化降解活性。更多还原

【Abstract】 semiconductor as a typical photocatalyst, which has been extensively concerned due to its many advantages such as high photosensitivity and chemical stability, has become a most widely-used photocatalytic material. Fine TiO2 particle shows higher photocatalytic activity than bulk TiO2 particle for it’s easy to increase photon yield. However, the fine TiO2 particles have the tendency of aggregation. In addition, the bare TiO2 generally has very small adsorption capacity toward organic compounds. These inherent disadvantages make it less efficient in photocatalysis. The load of TiO2 on porous solid supports with large surface area carries out the combination of dispersion, adsorption and catalysis. It is instructively significant for the development of photocatalyst and the modulation of reaction kinetics to systematically investigate the relationship of support’s properties with the characters of TiO2 active constituent and substance molecule. This paper concerns the effect of ZSM-5 zeolitic support’s properties (ie. crystal size and acidity) on the preparation and performance of TiO2/ZSM-5 composite photocatalyst. Various characterization techniques were employed to investigate the physicochemical and photoresponse properties of the samples. The adsorption capacity and photodegradation activity of the samples are measured using methyl orange (MO) aqueous solution. Focuses are given to the nature of zeolite supports’adsorption toward MO, and the effect of the strength of adsorption bond on TiO2 photocatalytic activity. The main results obtained in this dissertation are as follows:1. ZSM-5 zeolite was found to be the optimal support in comparison to SiO2, Al2O3,5A and Y zeolite.2. TiO2 loading and dispersion can be increased by the capillarity of zeolitic micropore structure which can adsorb and gentlely release water to control TiO2 sol-gel process. As-prepared TiO2/ZSM-5 composite phototcatalyst has much higher MO photodegradation activity.3. MO adsorption mainly takes place on the relatively strong acid sites of the ZSM-5 external surface. The acid sites of ZSM-5 grow more with SiO2/Al2O3 decreasing, and the adsorption capacity and TiO2 specific photoactivity of TiO2/ZSM-5 are enhanced. The decrease in zeolite crystal size can increase the external surface of zeolite. The high adsorption capacity of nanosized zeolitic support can be attributed to the large amount of acid sites on the large external surface of nanosized zeolite, which can promote photodegradation in dilute substance solution. In addition, large external surface is helpful to increase TiO2 loading and dispersion. The highest TiO2 specific activity of TiO2/ZSM-5 nano-composite depends on the proper TiO2 loading, and the optimal value is 6.5 wt% when TiO2 is supported on ZSM-5 with SiO2/Al3O2 molar ratio of 68 and crystal size of less than 100 nm.4. Results of the adjustment of ZSM-5 external suface acidity by Na+modification indicate: MO molecules adsorbed by strong acid sites are difficult to desorb, which is not helpful to enhance the photoactivity of supported TiO2. Whereas the adsorption of MO by medium strong acid sites (the range of 350-400℃in NH3-TPD profile) can desorb at room temperature, belonging to reversible adsorption. The reversible adsorption of the substrate is significant in promoting the photocatalytic activity of supported TiO2. The MO adsorption by the support is mainly reversible adsoption at Na+content of 1.1 wt%, so TiO2/1.1%Na-HZSM-5 exhibits the highest photodegradation activity among prepared nano-composite photocatalysts.更多还原