【作者】 俞娇仙；

【导师】 黄柏标；

【作者基本信息】 山东大学 ， 材料学， 2011， 博士

【摘要】 材料是人类生存和生活必不可少的部分,是人类文明的物质基础和先导。半导体材料的发现与利用,使人类进入了一个全新的发展阶段。利用半导体材料制成的各种器件已经被广泛的应用于我们的日常生活中,例如手机、电脑等。半导体材料由于具有发光性质、气敏性质、光催化性质、光电转换性质等特性而被广泛应用于发光二极管、气敏传感器、空气净化系统以及太阳能电池等方面。继续开发和研究具有更好性能的半导体材料成为现在科学发展的重点。20世纪80年代以来,随着纳米技术与纳米材料的出现与应用,人们发现材料的性能不仅与材料本身的化学组分有关,还与其微观结构有着密切关系。通过微结构调控,不仅可以控制其微观形态,而且可以改变其物理、化学性质。而微结构又受到制备工艺、生长过程等因素的影响。因此,研究材料的制备方法、生长过程等因素对材料形貌等微结构以及微结构与性能之间的关系,从而进一步改善材料的物理化学性能有着重要的意义。在本文中,我们对半导体光催化材料进行了微结构调控,并研究了其对气敏性能、光催化活性、光电化学性质等不同性质的影响,主要分为以下几个方面。在第一章中,简单介绍了半导体材料及其分类,化合物半导体,特别是二氧化钛、氧化锌、铟酸镉、卤氧铋。并简单介绍了纳米半导体材料的几种重要的物理性质。介绍了微结构对半导体材料性能的影响。在第二章中,我们以硝酸镉和硝酸铟为原材料用自模板法制备了CdIn₂O₄空心球。利用X射线粉末衍射仪和扫描电子显微镜对制备样品的结构与形貌进行了表征。系统研究了初始Cd/In的比例对组分、形貌和可见光光催化性能的影响,研究了煅烧温度对样品结构与形貌的影响。确定了合成纯相CdIn₂O₄空心球的最佳初始Cd/In的比例以及最佳煅烧温度。通过EDS测试表征了合成样品的实际Cd/In比例。通过一系列测试表征,对CdIn₂O₄空心球的可行性形成机理进行了探究。通过对亚甲基蓝的降解评价了合成样品的光催化活性。气敏元件作为检测环境控制与安全的一种器件,需求日益增加。以半导体为基础的气敏材料被广泛的应用于空气中有害、有毒气体的检测。半导体金属氧化物在过去的几年里由于对不同气体种类的敏感性得到了广泛的关注。CdIn2O4是众所周知的n型半导体,作为气敏材料被广泛的研究,但是在大多数研究中含有氧化镉、氧化铟等杂相,较难获得纯相CdIn2O4。我们研究了纯相CdIn2O4对含碳氧化物的气敏特性以及形貌对气敏特性的影响。研究了CdIn2O4气敏元件的气体灵敏度随C2H5OH浓度的变化以及其光响应特性、恢复特性。结果表明,由CdIn2O4空心球制备的气敏元件的气体灵敏度普遍高于由研磨后样品制备的元件的气体灵敏度。对于50 ppm乙醇,前者的灵敏度是后者的2.5倍。根据响应恢复特性,我们探索了CdIn2O4气敏元件的瞬态响应机理。三维分等级结构的整体尺寸较大,而其组成基元仍保持纳米尺度,这样既有利于催化剂的回收利用,又能保持纳米尺度带来的催化效率的提高。因此,制备分等级结构特别是三维分等级结构的光催化材料具有现实意义。而铋系化合物半导体（BiOX （X=Cl, Br, I））由于价格低廉、环境友好、并且具有独特的电子结构,良好的光性能和催化性能,而逐渐成为光催化研究领域的一颗新星。在第三章中,我们用简单的水热法制备了分等级结构的BiOCOOH。在不改变其三维花状结构的基础上用离子交换法制备了BiOCl、BiOBr和BiOI等铋系化合物半导体。利用X射线衍射仪和扫描电子显微镜对样品的结构和形貌进行表征,发现样品均为纯相,没有其他的杂相出现,显示了三维分等级的花状结构。研究了样品的发光性能、吸光特性。通过对罗丹明B以及重铬酸钾溶液的降解评价了体系的光催化活性。样品BiOCl、BiOBr在20分钟内对罗丹明B的降解率可以达到90%,BiOI在20分钟内对罗丹明B的降解率为70%。BiOCl、BiOBr、BiOI在可见光照射下,半小时对Cr （Ⅵ）的去除能力分别为9.29毫克／克,13.98毫克／克,16.93毫克／克。第四章中,我们以球形Si02为模板采用简单的水热法合成了具有{001}面的类球形TiO2。系统的研究了反应时间对结构、形貌的影响。样品的结构与形貌通过X射线粉末衍射仪和扫描电子显微镜进行表征。利用能量色散谱来确定样品的最终化学计量比。结果发现随着反应时间的增加,样品的结晶性能逐渐增加,{001)面逐渐明显。类球形TiO2为锐钛矿相,微球的直径约为1.5μm是由{001}面边的长度<1μm的TiO2组成的。根据研究结果提出了一种可行性生长机理。通过对罗丹明B溶液的降解评价了样品的光催化活性,通过刮涂法将样品涂覆在导电玻璃上制备了Ti02电极,并测试了体系的光电流。为了使TiO2便于回收利用,我们进一步采用阳极氧化法在钛基片上直接制备了TiO2纳米管。通过X射线衍射（XRD）和扫描电子显微镜（SEM）对样品结构和形貌进行了表征。结果表明在500℃空气气氛下退火2h得到的TiO2纳米管为锐钛矿和金红石的混合相,TiO2纳米管直径约40 nm,壁厚约5 nm。以TiO2纳米管阵列为阳极, Pt片为辅助电极研究了光电化学特性。同时研究了电压对光电流的影响。将长有TiO2纳米管的钛片浸渍于氯金酸中,光还原制备了金负载TiO2纳米管。测试了金负载TiO2纳米管的光电流密度,并与未负载的做了比较。发现负载后的光电流密度比负载前的约高20μA/Cm2.在第五章中,以F掺杂SnO2玻璃为基底生长了不同的ZnO薄膜,包括ZnO纳米棒薄膜、纳米线薄膜、纳米片薄膜。利用X射线粉末衍射仪和扫描电子显微镜对样品的结构与形貌进行了表征。研究了不同氧化锌薄膜的光致发光性能以及光电化学性能,并通过对亚甲基蓝的降解表征了光催化活性。结果表明,一维纳米材料更有利于电子、空穴的分离,ZnO纳米棒优先沿C轴取向生长,取向性越好,光电流越高,其最高光电流密度可以达到60μA/cm2。氧化锌纳米棒薄膜的光催化活性最高,这与其光电流密度最大相一致。由于氧化锌薄膜是生长在基片上的,基片的存在起到了固定催化剂的骨架作用,因此有利于催化剂的回收和循环使用。这种薄膜有望成为潜在的、可回收循环使用的光催化材料,在太阳能电池方面亦具有潜在的应用。更多还原

【Abstract】 Material plays an important role in human life and the development of material science is a symbol of human civilization. Now we have entered a new stage based on the discovery and use of semiconductor materials. Devices made of semiconductor materials have been widely used in our daily life, such as mobile phones, computers and so on. Semiconductor materials have also been widely used in light-emitting diodes, gas sensors, air purification system and solar cells due to their physical properties of luminescence properties, gas properties, photocatalytic activities and photoelectric conversion characteristics. It is very important to explore and study new materials with superior properties.With the emergence and application of nanotechnology and nano-materials, people began to realize that the properties of materials are not only determined by the chemical compositions, but also have close relationship with the microstructure. Through the control of microstructure, we can not only control its morphology, but also change its physical and chemical properties. The micro-structure was influenced by preparation craft, growth procedure and so on. Morphology control of nanomaterials has become one of the most active aspects in research field. It is significant to investigate the influences of synthetic method, growth procedure on the intrinsic structures to improve the physical and chemical properties of materials.In this thesis, we controlled the mcrostructure of the semicinductor photocatalysts, studied various properties including photoluminescent properties, photocatalytic activities, photoelectrochemical properties and so on. The investigations were focused on the following aspects.In chapter one, we briefly introduced the semiconductor materials and its categories, especially TiO₂, ZnO, CdIn₂O₄ and BiOX （X=Cl, Br, I）. We also discussed important physical properties of semiconductor and the effects of microstructure modulation.In chapter two, CdIn₂O₄ hollow spheres were synthesized by a self-template method. Cadmium nitrate （Cd（NO₃）2-4H₂O） and Indium nitrate （In（NO₃）3-4.5H₂O） were used as raw materials. XRD and SEM were employed to characterize the structures and morphologies of as-grown samples. The effects of Cd/In ratios on the compositions, morphologies and photocatalytic activities have been systematically investigated. The effects of annealing temperature on the structure and morphologies were also investigated. The optimal initial Cd/In ratio and calcination temperature were determined for the synthesis of pure phase of CdIn₂O₄ hollow spheres. The actual Cd/In ratio of the synthesized samples were measured by EDS. A self-template growth mechanism of CdIn₂O₄ hollow spheres was proposed based on our experimental data. The photocatalytic activities of the samples were evaluated through the degradation of Methylene Blue solution.There has been an increasing demand of gas sensors for better environmental control and safety. Gas-sensing materials based on semiconductor have been widely used to detect combustible and noxious gases in air. Semiconductor metal oxides have attracted much attention due to their sensitivities on different gaseous species in the past few years. CdIn₂O₄ is a well-known n-type semiconductor, which has been extensively studied as gas sensor materials. However, the impurity phases, such as CdO and In₂O₃ phases, could easily appear, which is regarded as the main problem on the synthesis of CdIn₂O₄ materials. The gas sensitivity of pure CdIn₂O₄ hollow spheres for hydrocarbons was measured and the effects of morphologies on gas sensing had been investigated. The sensitivities of CdIn₂O₄ gas sensors on the concentration of C₂H₅OH as well as the response and recovery properties were investigated. The results indicated that the sensor fabricated by CdIn₂O₄ hollow spheres had higher gas sensitivity than that fabricated by the sample after grinding. The gas sensitivity of CdIn₂O₄ hollow spheres on exposure to 50 ppm of C₂H₅OH was measured to be 2.5 times that of the material obtained by grinding the spheres. Moreover, a plausible transient responding mechanism on CdIn₂O₄ hollow spheres was proposed.Generally speaking, the three-dimensional hierarchical structure is of large size, and its composition remains in nanometer scale, which is not only beneficial for the catalyst recycling, but also exhibits high efficiency due to its nano-scale. Therefore, the preparation of photocatalytic materials with hierarchical structures is of practical significance. Bismuth oxyhalides （BiOX （X=Cl, Br, I）） semiconductors have attracted extensive attention and offered a new family of promising photocatalysts due to their low cost, environmentally friendly, unique electronic sructure, excellent photocatalytic activities and so on. In chapter three, we synthesized hierarchical BiOCOOH by a simple hydrothermal method. BiOX （X=Cl, Br, I） were synthesized by simply ion exchange method based on 3D-flower like BiOCOOH. The structures and morphologies were characterized by XRD and SEM. The samples are of pure phase and there is no other impure peaks appear. The luminescence properties of the samples, and the absorption properties were investigated. The photocatalytic activities were evaluated by degradation of RhB and K₂Cr₂O₇ solution. The degradation rate of BiOCl and BiOBr on RhB under visible light in 20 min can reach up to 90%,70% RhB was degradated by BiOI in 20 min. In the visible light irradiation of 30 min, Cr （VI） removal capacity of BiOCl, BiOBr and BiOI are 9.29 mg/g,13.98 mg/g and 16.93 mg/kg, respectively.In chapter four, we synthesized spherical TiO₂ made up of crystallites with high percentage of{001} facets by a simple one-step hydrothermal process. The spherical SiO₂ were used as templates. The effect of the reaction time on the structures and morphologies were systematically investigated. The structures and morphologies of the as-synthesized samples were characterized by X-ray diffractometer （XRD） and scanning electron microscopy （SEM）. Energy-dispersive spectroscopy （EDS） was employed to determine the final stoichiometry of the samples. The results showed that the crystallinity increased with the increase of reaction time. The spherical TiO₂ were of anatase phase, the spheres were about 1.5μm in diameter and the composed TiO₂ {001} facets were of<1μm in length. According to the investigation, we proposed a plausible growth mechanism. The photocatalytic activities were investigated through the degradation of RhB solution. For further investigation, we formulated TiO₂ electrode as working electrode using the above TiO₂ microspheres and measured its photocurrent.TiO₂ nanotubes were fabricated by anodic oxidation of Ti plate. The structures and morphologies were characterized by X-ray diffractometer （XRD） and scanning electron microscopy （SEM）. The results showed that mixture phase of anatase and rutile was obtained by annealing the samples at 500℃for 2 h in air atmosphere. The diameter of TiO₂ nanotubes is about 40 nm and the thickness of the tube wall is about 5nm. The photoelectrochemical properties were investigated by using TiO₂ nanotubes as anodes and Pt as counter electrode. The effects of bias voltage to photocurrent were also investigated. Ti plates with TiO₂ nanotubes were immersed in HAuC14, and Au-TiO₂ nanotubes were obtained through photoreduction methood. For comparation, the photocurrent density of Au-TiO₂ was measured. The photocurrent density of Au-TiO₂ nanotubes was found to be 20μA/cm2 higher than that of TiO₂ nanotubes.In chapter five, ZnO films with morphology of nanorods, nanowires and nanosheets were grown on F-doped SnO₂ glass substrate. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were employed to characterize the structures and morphologies of the as-synthesized samples. The photoluminescence （PL） and the photoelectrochemical properties of ZnO films were also measured. The photocatalytic activities were evaluated by degradation of MB solution. The results showed that one-dimensional nanomaterials are beneficial for the separation of electrons and holes. ZnO nanorods preferentially oriented along the c-axis and had the largest photocurrent density which is as high as 60μA/cm2. The photocatalytic activity of ZnO nanorods films is the best, which is consistent with the results of photocurrent density. It is beneficial for the recovery and recycling of catalyst as it has been fixed on the substrate, which may have potential application in solar cells.更多还原