【作者】 周曦；

【导师】 李远志；

【作者基本信息】 武汉理工大学 ， 材料学， 2009， 硕士

【摘要】 ZnO因价廉、无毒、来源广、光催化活性高而受到人们的广泛关注,但是,由于其带隙较宽,只能被紫外光激发,而太阳光谱中仅含有5%左右的紫外线,因而对太阳光的利用率低,而且ZnO由于易发生光腐蚀,光稳定性较差,从而大大降低了光催化活性,不利于其在环境治理中的应用。因此,通过对ZnO的掺杂改性从而获得既具有光稳定性,又具有较高可见光光催化活性的ZnO光催化剂成为极具挑战性的课题,也是当前国际研究的前沿。本论文研究了C掺杂及表面络合物形成对ZnO可见光光催化活性和光稳定性的影响。选择4-氯苯酚、2,4-二氯苯酚、苯酚和甲醛为目标降解物研究其可见光光催化活性和光稳定性能,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）、红外光谱、拉曼光谱、紫外-可见漫反射光谱、N₂吸附及荧光光谱（PL）等对其进行表征,探讨了其结构变化与光催化性能的关系。其主要研究结果如下:（1）以ZnCl₂与乙二醇合成反应生成有机含锌化合物,然后将该有机物煅烧制成C掺杂ZnO。该催化剂中的C取代了ZnO中的晶格氧,从而使其光响应范围从紫外光区拓展到可见光区。光催化性能测试表明其在室内日光灯照射下能有效地使甲醛矿化为CO₂,而且其光催化活性优于目前光催化活性最好的N掺杂TiO₂。（2）酚类化合物（PC）如:4-氯苯酚、2,4-二氯苯酚、苯酚都能与ZnO形成表面络合物。4-氯苯酚与ZnO形成的表面络合物通过酚Zn-O-Ph-Cl键与ZnO相结合,这个键强于4-氯苯酚与YiO₂形成的表面络合物上的酚Ti-O-Ph-Cl键。这些表面络合物在可见光激发下发生配位体向余属中心的电荷转移,使ZnO的光吸收响应范围从紫外区拓展到可见光区,从而使ZnO具有较高的可见光光催化降解酚类化合物的催化活性。在可见光照射下,ZnO光催化降解4-氯苯酚的光催化活性比TiO₂在同样条件下高3.7倍,ZnO比TiO₂可见光光催化活性高是因为PC/ZnO比PC/TiO₂具有更高的光电流,说明前者比后者有更多的电荷转移。而且,表面络合物的形成明显提高了ZnO的光稳定性,其主要原因是由于ZnO的表面缺陷大大降低,且在紫外-可见光照射下ZnO表面捕获的光生空穴优先与表面络合物发生反应,而没有与表面氧原子发生反应。更多还原

【Abstract】 ZnO has been attracting much attention due to cheap, non-toxic, widely source and high photocatalytic activity. However, it is activated only under UV light irradiation because of its large band gap. But solar spectra only contain 5% UV, thus ZnO has the low utilization of sunlight. Moreover, ZnO significantly decreases the photocatalytic activity of ZnO and blocks its practical application in environment purification because of its photocorrosion and photoinstability. Therefore, it is a great challenging issue to explore efficient visible-light-induced photocatalysts by the modification of ZnO, which is the forefront of current international research.In this paper, we have researched the effect of carbon-doped and surface complex formation on the visible photocatalytic activity and photostabilty of ZnO. We chose photodegradation formaldehyde, 4-chlorophenol, 2, 4-dichlorophenol and phenol with irradiation of visible light to evaluate the photocatalytic activity of the photocatalysts. The as-prepared samples were characterized by XRD, XPS, FTIR, Raman, DRUV-vis, BET, PL, and so on. The relationship between the changes of structure and photocatalytic property has been investigated. The main results and conlusions are as follows:（1） Carbon-doped ZnO was prepared by calcination of organic zinc compound synthesized by the reaction between ZnCl₂ and glycol. It was characterized by thermal analysis, XPS, XRD, DRUV-vis, and PL. The results show that the substitution of lattice oxygen by carbon in ZnO results in significantly extending for its optical response from UV to visible region. The photocatalytic test shows that it efficiently photomineralize formaldehyde to CO₂ under the irradiation of indoor fluorescent lamp and its photocatalytic activity is much better than nitrogen-doped TiO₂.（2） Phenolic compound （PC） such as 4-chlorophenol, 2, 4-dichloropehol and phenol, can form a surface complex with ZnO. The surface 4-CP/ZnO complex binds to ZnO through phenolate Zn-O-Ph-Cl linkage, which is much stronger than the phenolate Ti-O-Ph-Cl linkage of the surface 4-CP/TiO₂ complex. The formation of the surface complex shifts the absorption response of ZnO from UV to visible region through ligand-to-metal charge transfer with excitation of visible photon, and induces efficient visible photocatalytic activity. ZnO exhibits 3.7 times higher photocatalytic activity for the photodegradation of 4-CP than TiO₂ under visible irradiation. The much higher visible photocataltyic activity of ZnO than TiO₂ is attributed to the higher efficiency of the charge transfer in the former than in the latter evidenced by the much larger photocurrent of PC/ZnO than PC/TiO₂ Moreover, the formation of the surface complex results in the substantial improvement of the photostability of ZnO as it leads to a considerable decrease of the surface defect sites of ZnO, and the photogenerated holes trapped on the surface of ZnO probably prefer reacting with the surface complex to reacting with surface oxygen atom under UV-visible irradiation.更多还原