【作者】 刘进；

【导师】 张高科；

【作者基本信息】 武汉理工大学 ， 环境工程， 2012， 硕士

【摘要】 光催化技术用于环境污染物的处理具有节能、无二次污染等优点。光催化的关键是光催化剂,开发新型高效的催化剂是光催化领域的研究热点之一。Zn2GeO4具有特殊的晶体结构和更分散的能级结构,这使得导带上的光生电子具有很高的流动性,从而能有效地利用光生电子和空穴,且它具有良好的光稳定性,是一种具有研究价值的新型光催化剂。本文以GeO2、Zn(NO3)2·6H2O和尿素为原材料,采用水热法成功制备分等级Zn2GeO4微米球催化剂。利用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)、氮气吸附脱附法、紫外可见漫反射吸收(DRS)、和傅立叶红外(FTIR)等多种表征技术对所合成样晶的物相、尺寸形貌、表面结构、比表面积和孔径等进行研究。锗酸锌催化剂合成条件实验研究表明,水热温度为140℃有利于形成均匀分散的Zn2GeO4微米球,且水热法制备的Zn2GeO4纯度高、结晶度好,晶体粒径小于固相法合成的Zn2GeO4。SEM和FESEM结果表明水热法合成的Zn2GeO4球的直径为5-10μm,球体由长度为0.5-1μm纳米棒组成。TEM则表明组成微米球的纳米棒的宽度为200-500nm。UV-vis DRS分析结果表明Zn2GeO4微米球与普通Zn2GeO4相比,吸收带边发生了蓝移,这有助于提高其光催化活性。尿素投加量实验结果表明尿素的增加促进了Ge02的溶解和Zn2GeO4晶体的生长。通过温度条件实验对Zn2GeO4微米球的生长过程及相关机理进行了探讨,实验结果表明30min时就生成了由纳米束棒组成的Zn2GeO4微米球和Zn2GeO4微米片,随着水热时间的增加,早期形成的Zn2GeO4晶体通过溶解-结晶-自组装最终形成由纳米棒组成的实心微米球,同时部分结晶度不好的微米球在Ostwald熟化机制的作用下形成了空心微米球。光催化降解实验表明,在紫外光照射下,与固相法合成的普通Zn2GeO4催化剂相比,Zn2GeO4微米球催化剂对酸性红G、4-硝基酚溶液都具有较好的降解性能。另外,Zn2GeO4微米球催化剂对甲醛气体也具有良好的降解效果。降解循环实验进一步表明该催化剂具有良好的高效性和稳定性。化学荧光分析实验表明,羟基自由基是光催化反应的最主要活性基团,并在此基础上对该光催化体系可能的降解机理进行讨论。更多还原

【Abstract】 Photocatalysts have been a hot topic in environmental field due to its low energy consumption and no second pollution. The photocatalyst is the key factor of the photocatalytic technology, so the development of new and efficient photocatalyst is the hot topic in the photocatalytic field. Zn2GeO4has the special crystal structure and much dispersed band, thus the photo-generated electrons have high mobility in the CB, and can make full use of the electrons and holes. Besides, the Zn2GeO4photocatalysts is very stable under irradiation of the UV light. So it is a new and excellent photocatalysts. Hierarchical Zn2GeO4microspheres have been successfully synthesized via a simple hydrothermal route, using Zn(NO3)2and GeO2as Zn and Ge sources, respectively. The as-prepared samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherm, UV-vis diffuse reflectance spectrum (UV-vis DRS), and fourier transform infrared (FT-IR) spectroscopy.The temperature experiment results showed that it was better to form well-dispersed hierarchical Zn2GeO4microspheres at the140℃. Moreover, the obtained samples has no impurity and good crystallinity and the crystalline size of Zn2GeO4microsphere was smaller than that of bulk Zn2GeO4. SEM, FESEM and TEM results showed the hierarchical Zn2GeO4microspheres with diameters ranging from5-10μm were found to be constructed of randomly aggregated nanorods which had dimensions of about0.5-1μm in length and200-500nm in width. From the UV-vis DRS analyses, the obvious blue shift of the optical band gap of the hierarchical Zn2GeO4microspheres can been found, compared with the bulk Zn2GeO4. The experiment results showed the dissolution rate of GeO2will increase with the increasing of the urea dosage, which promoted the growth of the Zn2GeO4crystal. Finally, a formation mechanism of the hierarchical Zn2GeO4microspheres was researched by the time-dependent experiments. The results presented the formation of Zn2GeO4microsheets and microspheres constructed of nanorod bundles for30min. With increasing the time, Zn2GeO4solid microspheres were formed by dissolution-recrystallization-self-assembly. Meanwhile, the hollow Zn2GeO4microspheres were formed through the complicated Ostwald ripening process.The Zn2GeO4microspheres exhibited high photocatalytic properties and excellent stability for the degradation of ARG and4-NP as compared to the Zn2GeO4prepared by the solid-state reaction. Besides, the HCHO gas can be effective degradated by the microspheres. The hydroxyl radicals (·OH) were measured by TAPL for the photocatalysis. Based on the experimental results, we have discussed the possible mechanism of the photocatalysis over the Zn2GeO4更多还原