【作者】 刘大锐；

【导师】 蒋引珊； 魏存弟；

【作者基本信息】 吉林大学 ， 材料学， 2011， 博士

【摘要】 近年来光催化已发展成为一门新兴的备受关注的前沿学科,许多半导体材料具有光催化作用,可被用于污染控制。但是大多数光催化剂的光响应范围都在紫外光区,而太阳光中紫外光含量仅占3-4%,对太阳光的利用率较低。因此,研制光响应范围更广的、结构稳定的、易回收、可重复使用的新型光催化剂势在必行。钙钛矿型化合物的结构和组成具有多样性,可以在保持其结构的条件下通过改变组成来提高光催化活性,是一类极有潜力的光催化剂。目前,对于钙钛矿型光催化剂的研究还较少。因此,进一步加强对钙钛矿型化合物的合成及催化性能的研究,对于发展和完善光催化技术具有重要意义。光催化性能优异的钙钛矿型NaTaO3,只能在紫外光下受激发,严重限制了光催化技术的推广应用。为了进一步提高NaTaO3的光催化性能,本文研究了非金属元素N、S离子掺杂对纳米NaTaO3的晶体结构、粒子形貌及光催化性能的影响,并对其掺杂改性机理进行研究。采用改进的固相法和水热法合成了N掺杂NaTaO3(NaTaO3-xNx)光催化剂,并对其光催化性能进行对比研究。实验结果表明改进固相法能够在700℃下得到结晶度高、粒径大小均一的N掺杂的NaTaO3,而且实验过程中不需要二次研磨。虽然固相法制备的N掺杂的NaTaO3不具有可见光活性,但是N的掺杂增加了NaTaO3在紫外光下的吸收。水热法制备的N掺杂的NaTaO3结晶度高,具有立方形貌,平均粒径在200-500nm之间,而且在可见光下具有较好的活性。这充分证明光催化剂的制备方法对提高光催化活性过程中的重要性。N元素的掺入成功的提高了NaTaO3的光催化活性,可能与N元素掺入后在NaTaO3晶体内形成O空位有关。相关研究表明,光催化剂中掺入的非金属离子能够在样品内形成一个接近导带的新的浅势能级,这个浅势能级可以作为光生电子或空穴的捕获陷阱,有利于光生电子和空穴的分离,从而使光催化剂表面产生更多的OH·和·O2-,这种活性自由基一方面可以进一步促进光生电子和空穴的分离；另一方面,可以参加反应的具有强氧化性活性自由基越多,光催化氧化反应的效率更高,即光催化剂的活性更高。钙钛矿型SrFeO3是一种具有多种独特理化性能的新型无机非金属材料,但对其光催化活性的研究却相对较少。论文采用两种技术路线合成了钙钛矿型SrFeO3光催化剂,并对其光催化行为进行深入研究。实验结果表明,聚乙二醇的加入对纯相SrFeO3的形成有一定的影响。当体系中不加入聚乙二醇时,无论怎样改变反应条件,最终产物中仍含有SrCO3杂质,可能是由于样品在烧结后的冷却过程中与周围环境中的CO2相互作用而产生了部分SrCO3；当体系中加入聚乙二醇时,能够得到纯相SrFeO3,这可能是由于在溶胶-凝胶的过程中柠檬酸与乙二醇可以通过聚合反应形成有机网络,这种有机网络具有优异的热稳定性,煅烧时不容易发生偏析,所以能够得到纯相的SrFeO3。甲基橙光降解实验结果表明,与纯相的SrFeO3相比,杂相的SrFeO3在可见光下具有较高的活性,这可能是因为纯相的SrFeO3其表面氧空位相对含量远小于杂相SeFeO3,所以光催化活性较低。光催化稳定性研究表明,含有杂相的SrFeO3光催化实验后其自身结构发生晶格坍塌,而纯相SrFeO3光催化测试后样品的结构没有明显变化,由此可以推出SrFeO3所显示的光催化活性有可能来自于其晶格内的Fe4+离子和表面氧空位的共同作用。综上所述,论文首次系统的研究了非金属元素N、S离子掺杂对纳米NaTaO3的晶体结构、粒子形貌及光催化性能的影响和铁酸锶在光降解过程中的稳定性。该项研究对于新型半导体光催化剂的开发,科研以及将来的实际应用有着重要的意义。更多还原

【Abstract】 In the last decades, the semiconductor photocatalysis has attracted extensive attention due to its wide potential application in the treatment of all kinds of contaminants, especially for the removal of organic contaminants. However, most photocatalysts can only be excited by UV or near-UV radiation (only 5% of the natural solar light), which hinders its practical applications. So, it is of great significance to develop the photocatalysts that can be used in visible light, structural stability, easy recovery and reusable catalyst. Perovskites compounds with the diversity of structure and composition can be improved the photocatalytic activity by changing the composition, which is a promising kind of photocatalyst. But there are very few investigations about the perovskite photocatalysts. So, further strengthening the study on the systhesis and catalytic properties is of great significance for the development and improvement of photocatalytic technologyAmong these semiconductors, NaTaO3 with a perovskite structure show high activity for photocatalytic water splitting only under UV light irradiation, which hinders its practical applications. Due to this fact, NaTaO3 is not active under visible-light irradiation, which hinders its practical applications. To further improve the photocatalytic properties of NaTaO3, the effect of N, S elements doped on crystal structure, particle morphology, photocatalytic properties, and the doping mechanism were investigated. N-doped NaTaO3 (NaTaO3-xNx) was synthesized by the improved solid phase and one-step hydrothermal method, respectively. The results showed that the improved solid stated method requires low calcination temperature (only 700℃), which is obviously lower than 1000℃and avoidance of intermittent grinding. Although as prepared photocatalyst do not have visible light response, N doping can increased its photocatalytic activity under UV-light irradiation. The NaTaO3-xNx synthesized by hydrothermal method showed cubic morphology with the edge length of 200-500 nm. Moreover, this photocatalyst has good activity under visible light. All these results prove that the preparation method of photocatalyst is important for the photocatalytic activity increased.N elements doping can improve NaTaO3 photocatalytic activity, which may be related to the formation of O vacancies in crystal lattice after N doping. Researches indicate that in the case of the right nitrogen, the newly formed intra-band gap states can serve as a capture trap of photo-electron or cavity, which is conducive to photo-electron and cavity separation. The surface of photocatalyts can produce more OH·and·O2-, which can further promote separation of photo-electron and cavity. Moreover, the more strong oxidizing activity of radical, the higher photocatalytic activity.Perovskite SrFeO3 is a new material, but its photocatalytic activity is very few investigations. In this paper, SrFeO3 was prepared through two lines and its photocatalytic behavior was investigated in details. The experimental results showed that the addition of polyethylene glycol on the formation of pure phase SrFeO3 has a certain impact. When polyethylene glycol was not added, the final product contains SrCO3 impurities, which may be due to the samples reacted with CO2 in surrounding environment after cooling process. When polyethylene glycol was added, the pure phase SrFeO3 can be obtained. The possible reason is that during the sol-gel process, citric acid and ethylene glycol can form organic network which has excellent organic thermal stability and not prone to segregation during calcination, so the pure phase SrFeO3 can be prepared. The photodegradation results showed that compared with the pure phase SrFeO3, miscellaneous phase SrFeO3 has much higher photocatalytic activity, which may be due to the oxygen vacancies in the surface of pure phase SrFeO3 was much fewer than of impurity SeFeO3. Photocatalytic stability studies displayed that the lattice structure of impurity SrFeO3 collapsed and the pure phase SrFeO3 did not change after photocatalytic experiment, which indicate that SrFeO3 photocatalytic activity possibly come from Fe4+ ions in the lattice reacted with the surface oxygen vacancies.In summary, the effect of the nonmetallic element N, S doping on the crystal structure, morphology and photocatalytic properties and the stability of strontium ferrate during the degradation process were investigated. This study has important significance for the new semiconductor catalyst development, scientific research and practical applications.更多还原