【作者】 张华；

【导师】 韩建军； 李远志；

【作者基本信息】 武汉理工大学 ， 材料学， 2008， 硕士

【摘要】 在过去的二十多年,由于纳米TiO₂价格便宜、无毒,具有高效的降解有毒气体和污水的能力,因此得到了广泛的研究。但是由于它的禁带宽度较大（锐钛矿3.2eV,金红石3.0eV）只能被紫外光辐射激发。然而紫外光只占太阳光谱的5%,95%的太阳光对TiO₂光催化剂都是无用的,这一点大大地限制了TiO₂在治理环境污染中的应用。所以,目前关键的也最具挑战的任务就是通过TiO₂修饰获得对可见光敏感的光催化剂,这在光催化领域也是一个世界性的热点问题。本论文中,制备了两种复合光催化剂:具有核/壳/壳纳米结构的AgI/Ag-I₂/TiO₂复合光催化剂;具有核/壳纳米结构的三维有序的含染料的聚合物（YG）/TiO₂复合光催化剂。选择结晶紫和对氯苯酚为目标降解物研究其可见光光催化活性。运用各种现代分析测试手段,如:X射线衍射（XRD）、X射线光电子能谱（XPS）、扫描电镜（SEM）、透射电镜（TEM）、高倍透射电镜（HRTEM）、Raman光谱、红外光谱、N₂吸附及飞秒瞬态荧光光谱等对其进行表征。具体在以下几个方面取得了一定的结果:（1）以AgNO₃,LiI-3H₂O和Ti（OBu）₄为原料通过液相沉淀的方法制备了纳米AgI/TiO₂复合光催化剂。该催化剂具有一种新型的核/壳/壳AgI/Ag-I₂/TiO₂结构,与AgI/P25相比,这一特殊的纳米结构使得AgI的吸收边带发生显著的红移,同时也提高了AgI的吸收强度。光催化性能测试表明:该催化剂具有高效的可见光光催化活性,结晶紫和对氯苯酚的降解效率分别是AgI/P25的4倍和6倍。由于AgI/TiO₂复合光催化剂内部AgI,Ag,I₂和TiO₂之间的协同效应使得在可见光区域有强吸收和低的光生电子-空穴复合率,从而具有高效的可见光光催化活性。（2）通过表面溶胶-凝胶方法制备了具有核/壳结构的三维有序的含染料聚合物（YG）/TiO₂复合光催化剂。该复合催化剂中所含敏化染料为异硫氰酸荧光素,在400～500nm的可见光区具有强吸收,且在光照下稳定存在,显示出较好的可见光光催化活性。其可见光光催化作用机理如下:YG球中所含的染料起敏化TiO₂的作用,它吸收的可见光光子激发YG产生光生电子和空穴（YG⁺）,所产生的光生电子在TiO₂和YG球的界面处从激发态染料转移到TiO₂的导带,并与氧分子作用产生活性氧物种,最终降解结晶紫;而YG⁺可以和结晶紫反应,从而实现光敏剂的再生。实验结果表明,TiO₂-YG降解结晶紫经历两个竞争机制:脱甲基化和共轭结构破坏,在光照的初期,脱甲基化过程占主导地位,接着共轭结构破裂占主导地位。更多还原

【Abstract】 Nanostructured titania as a cheap,nontoxic,efficient photocatalyst for the detoxification of air and water pollutants has received much research attention during the past two decades.However,it is activated only under UV light irradiation because of its large band gap（3.2 eV for anatase and 3.0 eV for rutile）.However,solar spectra only contain 5%UV.A total of 95%of the solar photons are useless for TiO₂,which greatly limits its practical application in environmental decontamination.Therefore,it is crucial and of great challenge to explore efficient visible-light-induced photocatalysts by the modification of titania,which is an international hot topic in the field of photocatalysis.In this paper,we have synthesized nanostructured AgI/Ag-I₂/TiO₂ with a novel core/shell/shell structure and 3D-ordered titania hybrid photocatalyst with the core/shell structure of dey-containing polymer/titania,we chose photodegradation crystal violet and 4-chlorophenol with irradiation of visible light to evaluate the photocatalytic activity of the photocatalysts.The as-prepared samples were characterized by XRD,XPS,SEM,TEM,HRTEM,Raman,FTIR,BET,and Time-resolved Fluorescence.The main contents of this dissertation are listed as follows:（1） Nanostructured AgI/TiO₂ photocatalyst was synthesized by a feasible approach with AgNO₃,LiI-3H₂O,and Ti（OBu）₄.The results of characterization reveal that the nanostructured AgI/TiO₂ has a novel core/shell/shell nanostructure of AgI/Ag-I₂/TiO₂. Compared with TiO₂（P25） supported AgI,the formation of the nanostructure results in substantial shifting of the absorption edge of AgI to red,enhancement of the absorption intensity,and the appearance of a strong tail absorption above 490 nm, which is assigned to the absorption of I₂ and Ag.Photocatalytic tests show that the nanostructured AgI/TiO₂ photocatalyst exhibited very high visible-light-induced photocatalytic activity for the photodegradation of crystal violet and 4-chlorophenol, which is 4 and 6 times higher than that of P25 titania supported AgI,respectively.The highly efficient visible-light-induced photocatalytic activity of the nanostructured AgI/TiO₂ is attributed to its strong absorption in the visible region and low recombination rate of the electron-hole pair due to the synergetic effect among the components of AgI,Ag,I₂,and TiO₂ in the nanostructured AgI/TiO₂.（2） Photostable 3D-ordered titania hybrid photocatalyst with the core/shell structure of dye-containing polymer/titania was prepared by layer-by-layer coating of adsorption and hydrolysis of Ti（OBu）₄ on fluorescent polystyrene microspheres（YG）, in which a sensitized dye of fluorescein isothiocyanate with a strong absorption in the visible light region of 400～500 nm is fixed.Photocatalytic tests show that the nanostructured titania hybrid photocatalyst exhibited efficient and stable photocatalytic activity for the photodegradation of crystal violet（CV） under visible light irradiation.The characterization results show that the dye in YG spheres acts as a sensitizer for titania.By absorbing a visible photon it is promoted to an excited electronic state YG^*,from which an electron can be injected into the conduction band of titania on the interface of YG spheres and titania shell.The electron subsequently induces the generation of active oxygen species,which result in the degradation of CV.The produced YG⁺ radical cation can react with CV to realize the recycling of the photosensitized dye.The photodegradation of CV on TiO₂-YG undergoes two competitive mechanisms:N-demethylation and destruction of the conjugated structure. The N-demethylation process predominates during the initial irradiation period.Later, the process of ring rupture is significant.It is evidenced that the N-didemethylated intermediate and the N-tridemethylated intermediate of CV undergo a direct cleavage of their conjugated structures.更多还原