【作者】 张雯；

【导师】 付贤智； 王绪绪；

【作者基本信息】 福州大学 ， 物理化学， 2004， 博士

【摘要】 如何解决TiO₂半导体光催化过程量子效率低下的问题是当前光催化科学发展所面临的重大挑战。为光催化反应施加电场、微波场及超声波场已被证明可以明显提高光催化降解体系的量子效率，然而迄今关于磁场对光催化过程的影响尚未见到报道。本文以Pt／TiO₂为催化剂，考察了磁场对苯光催化降解过程的影响。 采用改进的溶胶—凝胶技术制备了TiO₂溶胶，并利用浸渍法将贵金属Pt负载到TiO₂干凝胶表面制成Pt／TiO₂光催化剂。用XRD（X—射线衍射）表征了样品的晶相组成和晶粒尺寸；通过N₂吸附法测定了样品的BET比表面积。采用连续流动微分反应系统考察了在磁场对苯的光催化降解反应活性的影响，采用直流光电导（DC photoconductivity）、诱导荧光（induced luminescence）及原位傅立叶变换红外（in—situ FTIR）技术研究了光-磁共同作用下样品表面的光生载流子寿命、表面羟基自由基的生成速率以及反应中间体和产物分布。 结果表明，对Pt／TiO₂催化剂施加59.42 mT的磁场时，苯的光催化稳态转化率从无磁场时的15.5％提高到18.0％，特别是苯的矿化率从19.0％提高到52％；而在同样条件下，对TiO₂没有观察到明显的磁场效应；同时发现在低磁场强度下，苯的转化率随磁场强度的增强而降低，但当磁场强度高于23mT时，却随磁场强度的增强而提高。为了揭示磁场对光催化反应影响的本质原因，研究了磁场对载流子动力学以及载流子寿命的影响。样品在磁场存在下的光电导谱结果表明，外加磁场可延长光生载流子的寿命，无磁场时载流子有效寿命为2.11ms，当施加强度为85.7mT的磁场时，其寿命可提高到5.67ms，而且随着磁场强度的增强而延长。通过诱导荧光技术考察了磁场对光照催化剂表面的羟基自由基·OH生成速率的影响，表明外加磁场可使样品表面羟基自由基的生成速率提高11.67％。采用原位傅立叶变换红外反应技术考察了磁场对苯光催化降解路径的影响，表明外加磁场不改变光催化降解反应的机理，但可以明显加快某些中间体的转化。施加磁场一定时间后，检测到苯的红外吸收带相对强度从单纯光催化反应下稳态值的0.82降低到0.57，同时CO₂红外吸收带相对强度则从28.3增加到42.78；两个主要的中间体醌和苯酚的特征峰强度增加，但它们的相对强度从0.96提高到1.05，说明外加磁场不仅有利于苯的转化，而且有利于苯酚向苯醌的转变。上述所有结果表明，外加磁场通过改变中间体和产物分布影响了后续反应，致使苯环更容易开环降解，从而提高了样品的光催化降解苯的效率，特别是深度氧化能力。 本研究首次将磁场引入气相光催化降解有机污染物领域，发现了光催化过程的磁场效应，初步揭示了磁场效应的本质原因，这为提高光催化量子效率提供了一条崭新的途径。更多还原

【Abstract】 To improve the quantum efficiency of the TiO2 photocatalytic process, the external fields involving electric field, microwave field, ultrasonic field and so on, have b een applied s uccessively i n t he p hotocatalytic d egradation s ystem. H owever, there is less study concerning the effect of magnetic field on the heterogeneous photocatalytic reactions,In this paper, the magnetic field effect (MFE) on heterogeneous photocatalytic degradation of benzene over Pt/TiO2 has been observed.Titanium dioxide sol was prepared by a sol-gel technique and platinized titania (Pt/TiO2) was synthesized by impregnation method. XRD characterized the dominant crystal phase and the average crystal size, while the BET specific surface areas of the platinized titania particles was got by nitrogen adsorption. On-line GC, DC photoconductivity, induced luminescence and in -situ FTIR were used to investigate the influence of magnetic field on the degradation reactivity, photogencrated charge carrier lifetime, surface hydroxy radical formation and the product distribution.The results showed that in the presence of the magnetic field the conversion reached to 18% from 15.5%, and the production of CO2 was increased to 175 ppm from 52 ppm. Accordingly, the mineralization of benzene was up to 52% from 19%. In addition, the magnetic field intensity influences the conversion of benzene and production of CO2 in different modes. To verify the magnetic field effect on the charge carrier dynamic and lifetime, photoconductivity was used to illustrate the MFE on the generation, recombination, trapping and interface charge transfer, and on the lifetime of the excess charge carriers. In the condition of external magnetic field (85.7 mT), the effective lifetime was prolonged to 5.67 ms from 2.11 ms without MF. And the lifetime was increased with the increase of the magnetic field intensity. The induced-luminescence technology was adopted to test the MFE on the rate of the hydroxy radical photo-formed on the surface of the catalyst, and the results showed that the application of the external magnetic field accelerated the production of the mentioned radical by 11.67%, compared to the reaction in the absence of MF. In situ FTIR spectroscopy was applied to investigate the MFE on the degradation route. The results revealed that the employment of magnetic field may not change the mechanism of photocatalytic degradation of benzene, however, after a period of application time, the integration area of benzene peak was down to 0.57 from 0.82,while CO2 was up to 42.78 from 28.3. Furthermore, the relative intensity of the two peaks ascribed to two major intermediates (quinone to phenol) was up to 1.05 from 0.96. The results indicated that the superimposition of magnetic field not only favor the conversion of benzene, but also facilitate the conversion of phenol to quinone, resulting in the formation rate of quinone is faster than that of phenol, and increasing the amount of CO2. That is, it greatly altered the distribution of the intermediates and products, resulting in improvement of the performance of the photocatalytic degradation.This work introduced the magnetic field i nto the heterogeneous photocatalytic degradation domain for the first time, and opened a new door to improve the quantum efficiency of the degradation of the pollutant.更多还原