【作者】 张彤；

【导师】 洪樟连；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2010， 硕士

【摘要】 近年来,半导体光催化技术在空气/水体净化清洁、有害污染物治理等方面的重大应用价值受到极大关注和广泛研究,被认为是解决工业化发展所致全球环境污染问题的一种重要的污染治理技术。其中,开发高效半导体光催化剂是技术关键之一。目前,主要有两大类的半导体光催化剂:一类是以TiO₂为代表的传统半导体材料及其掺杂体系;另一类是全新组成的窄带隙半导体材料。与传统的TiO₂宽带隙材料相比较,窄带隙半导体材料因其能够有效吸收利用可见波段的太阳光能量的特性,可用来在可见光条件下进行有机物降解及光解水制氢等优异特性,成为新型半导体材料的研发热点。本文在综述了窄带隙半导体制备和研究进展的基础上,提出围绕铁基半导体材料的制备、结构物相表征和特性研究开展研究工作,分别采用水热法、固相法和溶胶凝胶法制备了钙钛矿结构的BiFeO₃,SiO₂/YFeO₃复合物和Aurivillius相化合物Bi₅Ti₃FeO₁₅;重点开展原料配比,反应温度,保温时间,包覆次数等工艺条件对合成样品的物相合成规律、物相结构和种类,以及合成产物可见光条件下光催化降解甲基橙（MO）特性的影响作用;此外,对纳米尺寸Bi₅Ti₃FeO₁₅的水热合成路线、半导体特性以及磁学性能进行了分析和表征。论文第一部分,是以Bi₂O₃,Fe₂O₃,硝酸盐为原料,采用固相法和水热法制备BiFeO₃的研究工作。固相合成工艺中,重点开展了原料配比,原料种类和烧结温度对合成纯相BiFeO₃的影响规律,以及产物的可见光催化性能。同时,在矿化剂的辅助作用下利用水热条件合成了BiFeO₃;并对固相法和水热法合成BiFeO₃的物相形成条件,以及产物在可见光催化性能方面的差异进行了对比分析。结果表明,采用固相法合成BiFeO₃时,增加原料的铋/铁比,较容易产生Bi₂₅FeO₄₀杂相;固定铋/铁比为1时,反应温度对产物纯度有重要影响,提高反应温度容易产生Bi₂Fe₄O₉杂相。此外,采用纳米Fe₂O₃颗粒作为原料,经分析这与固相反应中纳米Fe₂O₃容易和Bi₂O₃混合,原料颗粒表面能、固相反应扩散速率增加等因素有关。在此基础上,获得了固相法合成杂质较少的的单相BiFeO₃的适宜工艺条件:原料铋/铁比为1:1,在830℃温度下保温3h。在水热法制备BiFeO₃工艺中,在一定的保温时间条件下提高反应温度,或者在一定的反应温度下增加保温时间,都有利于促进BiFeO₃的生成。光催化效率测试结果表明,固相法合成的含有杂相的BiFeO₃产物,可见光催化效率要好于水热合成纯相BiFeO₃的光催化效率。这种差异的原因可能与杂相辅助BiFeO₃降解MO的机制有关,此外,光催化性能高低与BiFeO₃的产物颗粒自形发育状态及晶格缺陷有关。论文第二部分工作,是采用Pechini溶胶-凝胶法,在非晶SiO₂微球上复合YFeO₃。通过将YFeO₃前驱液沉淀涂覆,制备不同包覆次数的SiO₂/YFeO₃复合物,研究了不同包覆次数对SiO₂/YFeO₃复合物的形貌、可见光催化性能的影响规律,以及不同包覆次数产物降解MO过程和降解动力学规律。结果发现,增加包覆次数,产物可见光催化降解MO的效率提高。论文第三部分工作,通过水热法和固相法制备Aurivillius相化合物Bi₅Ti₃FeO₁₅。在水热法工艺中,探明了增加保温时间条件下,产物Bi₅Ti₃FeO₁₅相的生成过程和结构演化规律。在固相法工艺中,通过改变烧结温度获得了合成单相Bi₅Ti₃FeO₁₅的最佳烧结条件。研究发现,水热法工艺中200℃保温48h,固相法900℃保温5小时,可制备出单相的Bi₅Ti₃FeO₁₅。产物Bi₅Ti₃FeO₁₅除了具有半导体特性之外,在室温下表现出顺磁特性。更多还原

【Abstract】 In recent years, the environment pollution is becoming more and more seriousall over the world with the development of the global economics and industry.Semiconductor photocatalysts with high photocatalytic activity have received moreand more attention because of their important role on environmental applicationssuch as air purication, water disinfection, hazardous waste remediation and waterpurification. In genereal, there have two main categories for semiconductorphotocatalysts: one is the titania dioxide and its modification by doping method, theother is the novel narrow bandgap semiconductor materials. The latter, narrowbandgap semiconductor semiconductor materials with characters of absorbing thevisible light, can degrade the organic pollutants and split the water under visible light,thus became the focus in the research in recent years.In this thesis, the related research progress and preparation method on narrowbandgap semiconductor were summarized. The focus of present study is about thepreparation and characterization of iron related compounds such as BiFeO₃ with theperovskite structure, SiO₂/YFeO₃ comporiste, and the aurivillius phase layeredBi₅Ti₃FeO₁₅. Hydrothermal method and solid-state reaction method were adopted toprepare the BiFeO₃ and Bi₅Ti₃FeO₁₅, respectively. And the SiO₂/YFeO₃ compositephotocatalyst was synthesized via sol-gel method. Among various preparationparameters, the ratio of raw material, synthesis temperature, the reaction time and thenumber of the reaction times are taken into account to obtain the targer products,together with the measurement of phase rype, morphology, photocatalytic properties.In addition, beside its semiconductor characters, the magnetic property ofBi₅Ti₃FeO₁₅ product was studied in present study.BiFeO₃, a semiconductor with visible-light response and photocatalyticdegradation ability, was synthesized via hydrothermal and solid-state reactionmethod using Bi₂O₃, Fe₂O₃ and nitrate salts as starting materials. Th effect of rawmateriald ratio, reaction temperature and different kinds of Fe₂O₃ raw materials onvisible-light degradation efficiency of MO was investigated. Furthermore, thesignificant difference of visible-light degradation efficiency between products prepared via solid-state method and those prepared by hydrothermal method wasrevealed and clarified from the point view of particle morphology and lattice defects.It is revealed that the impurities of Bi₂₅FeO₄₀ co-exists with increase of Bi₂O₃/Fe₂O₃ ratio, also the impurities of Bi₂Fe₄O₉ is readily to exist with increase ofreaction temperature with fixed Bi₂O₃/Fe₂O₃ ratio of 1. Also, using nano sized Fe₂O₃raw material provides high surface energy and promotes the solid-reaction rate,therefore benefits the BiFeO₃ product. It was found that the optimal solid-reactionconditions for relatively pure BiFeO₃ product are: the Bi₂O₃/Fe₂O₃ ratio of 1,sintered temperature of 830℃, and sintering time of 3 hours.As for the hydrothermal method route, the target phase BiFeO₃ is easily toobtain with increase of the temperature under fixed reaction time, or with increase ofthe reaction time under the fixed reaction temperature. Photocatalytic degradationtests showed that the BiFeO₃ with small amount of impurities prepared in thesolid-state method exhibits better photocatalytic degradation efficiency on MO thanthat of pure BiFeO₃ prepared by hydrothermal under visible light irradiation. It isbelieved that, besides the structure defects and the particle morphology, theimpurities played an assist-role on degradation process.Second, SiO₂/YFeO₃ composite was synthesized via Pechini sol-gel method.The relationship amony the morphology, the number of the preparation cycles, andthe photocatalysis efficiency of SiO₂/YFeO₃ was investigated. It was demonstratedthat increase the prepation cycles could improve the photocatalytic degradationefficiency of products.Finally, the aurivillius phase layered Bi₅Ti₃FeO₁₅ were prepared byhydrothermal and solid-state reaction method respectively. The growth of theBi₅Ti₃FeO₁₅ prepared by hydrothermal method under the different reaction time wasinvestigated. The results revelaed that pure phase of the Bi₅Ti₃FeO₁₅ could beobtained through 48h reaction under hydrothermal condition or sintered for 5 hoursat 900℃via solid-state method. Besides its semiconductor characters, weakferromagnetism at room temperature was also detected for the pure phase ofBi₅Ti₃FeO₁₅ product.更多还原