【作者】 王玉新；

【导师】 李新勇；

【作者基本信息】 大连理工大学 ， 环境科学， 2008， 博士

【摘要】 光催化氧化处理有机废水技术是一项耗能低、易操作、无二次污染,具有广阔应用前景的新技术。然而其实际应用仍然受光催化效率较低所限制,因此,发展高效光催化剂已经成为一项重要的研究课题。ZnO是一种高效、无毒性、价格低廉的重要光催化剂,在降解和完全矿化环境中污染物领域备受关注。众所周知,无机材料的形貌对其多样化的性能及其相应的应用有重要的影响,而ZnO是一种具有丰富多样形貌的宽禁带半导体材料。因此,制备特殊形貌的ZnO纳米材料,可以有效的改善其光学性质,提高其光催化性能。本文采用低温液相合成法制备了具有特殊形貌的纳米ZnO粉末和薄膜材料,并且对材料进行了系统的表征和光催化降解性能的研究。围绕以上内容,主要开展了以下几方面的工作:（1）应用简单低温水热法,无需加入表面活性剂,成功制备不同形貌的纳米ZnO。通过对影响ZnO样品的因素进行考察,发现通过调节溶液中的碱性,可以得到花状和棒状形貌的ZnO。X射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）和选取电子衍射（SAED）表征分析显示,花状形貌的ZnO是由许多根纳米棒辐射发散自组装形成的,ZnO纳米棒为六方纤锌矿单晶结构,沿[0001]方向生长。并且根据晶体成核和生长方向理论,对ZnO纳米花和ZnO纳米棒的可控生长机理进行了探讨。（2）通过紫外-可见漫反射光谱（DRS）、拉曼光谱（Raman）、光致发光光谱（PL）、X射线光电子能谱（XPS）和表面光电压谱（SPS）对不同形貌的纳米ZnO进行表征,分析了特殊形貌的ZnO具有的电子结构和表面组成。所制备的不同形貌的纳米ZnO在光催化氧化降解染料和有机物污染物中都有很好的性能。ZnO纳米花光催化降解染料和酚类化合物的能力强于ZnO纳米棒,是由于在PL、XPS和SPS表征中发现,ZnO纳米花的表面含有大量的氧空位,而氧空位可以作为光催化剂的活性中心,捕获光生电子,从而抑制光生电子和空穴的复合。（3）应用简单的低温液相合成法在锌片上制备了高度定向排列的ZnO纳米棒阵列薄膜,这里锌片不仅用作基底,同时也作为锌离子源,通过在甲酰胺水溶液中直接生长ZnO纳米棒阵列薄膜。这种自源生长方法简单、低耗,无需在基底上预先生长一层ZnO粒子作为生长阵列的种子层,也无需在溶液中加入锌离子溶液。XRD、高倍透射电镜（HRTEM）和SAED表征分析,表明ZnO纳米棒阵列是六方纤锌矿的单晶结构,沿c轴方向晶面择优取向生长。此外,对ZnO纳米棒阵列薄膜的形成机理进行了探讨。（4）通过DRS分析,估算ZnO纳米棒阵列薄膜的带隙能为3.24eV,相比体相ZnO（3.37eV）有所红移。ZnO纳米棒阵列薄膜的PL谱中出现一个位于383nm处强的紫外发光峰和两个位于450和468nm处弱的可见发光峰。拉曼光谱分析表明,位于437cm^-1处的E_2H强振动峰对应于六方纤锌矿ZnO特征振动,位于332、379、415和580cm^-1处的弱的振动峰分别对应于ZnO的3E_2H-E_2L、A₁（TO）、E₁（TO）和E₁（LO）振动。此外,将ZnO纳米棒阵列薄膜光催化降解4-氯酚的效果与生长于钛基底上ZnO纳米棒膜进行比较,发现ZnO纳米棒阵列薄膜表现出更好的光催化性能。更多还原

【Abstract】 Photocatalytic oxidation for organic wastewater treatment is a promising technology with low cost,easy operation and non-secondary pollution.However,it is limited to actual application due to the low photocatalytic efficiency.Therefore,the development of highly effective photocatalyst has become one of the most important research subjects.ZnO,as a well-known photocatalyst for its high efficiency,non-toxic nature and low cost,has been paid much attention in the degradation and complete mineralization of environmental pollutants. The morphologies of inorganic materials are demonstrated to have great effects on their widely varying properties and corresponding potential applications.It is well known that ZnO exhibits the richest range of morphologies among the wide band gap semiconductors. Therefore,the fabrication of ZnO nanomaterials with special morphologies could effectively improve their optical properties and photocatalytic activity.In the present work, nanostructured-ZnO powders and films with particular morphologies were prepared and characterized.Meanwhile,the optical properties and photocatalytic degradation activities were investigated.In this dissertation,our investigations are carried out as follows:（1） Nanostructured ZnO samples with different morphologies were successfully synthesized by simple low-temperature hydrothermal routes in the absence of surfactants. Systematic experiments were carried out to investigate the factors that affect the morphology. We demonstrate that ZnO with different morphologies such as flowers and rods can be controllably obtained by simply varying the basicity in the solution.The as-prepared samples were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）, transmission electron microscopy（TEM） and selected area electron diffraction（SAED）.We found that the ZnO nanoflowers contain many radial nanorods and these ZnO single-crystalline nanorods with the wurtzite structure grow along the[0001]direction.The formation mechanisms of ZnO nanoflowers and nanorods were initially interpreted in terms of the general theory of the crystal nucleation and crystal growth direction.（2） Nanostructured ZnO samples with different morphologies exhibit interesting optical properties.They were characterized by UV-vis diffuse reflectance（DRS）,Raman, Photoluminescence（PL）,X-ray photoelectron spectroscopy（XPS） and surface photovoltage spectroscopy（SPS）.The obtained samples with different morphologies have significant potentials in photocatalytic oxidation of dyes and organic pollutants.ZnO with flower-like morphology exhibited improved ability on the photocatalytic degradation of dye and phenolic compounds in aqueous solution under UV radiation compared with ZnO nanorods.The higher photocatalytic activity of the ZnO nanoflowers results from the larger content of oxygen vacancy on the surface of 1D nanomaterials as revealed by their Raman,PL,XPS and SPS spectra features.It is suggested that oxygen vacancy may act as the active centers of the catalyst,which could capture photo-induced electrons,whereas the recombination of photo-induced electrons and holes can be effectively inhibited.（3） Highly oriented and large-scale ZnO nanorod arrays film have been successfully synthesized on zinc foil by a simple,low temperature,solution-phase approach.Here,zinc foil was used as not only a substrate but also zinc-ion source for the growth of ZnO nanorod arrays film by direct oxidation of zinc foil in an aqueous solution of formamide.This is a simple,self-source and low-cost method without the need of pre-casting ZnO nanoparticles onto the substrates as a seed layer and adding materials such as Zn²⁺-contained salts.X-ray diffraction（XRD） analysis,high-resolution TEM（HRTEM） photographs and selected area electron diffraction（SAED） patterns indicated that the ZnO nanorod arrays on the zinc foil substrate was single crystalline and grown predominant crystal orientation along the c-axis direction with the wurtzite structure.In addition,the possible formation mechanism of ZnO nanorod arrays was discussed.（4） The band gap of ZnO nanorod arrays film is 3.24 eV estimated by DRS,which is red-shifted compared with bulk ZnO（3.37 eV）.The PL spectrum of ZnO nanorod arrays film appeared a dominant UV emission at 383nm and two weak visible emissions at 450 nm and 468 nm.Raman spectrum indicates that the remarkable E_2H mode of ZnO nanorod arrays film is located at 437 cm^-1,which corresponds to the characteristic band of hexagonal wurtzite phase,and the weaker peaks appear at 332,379,415 and 580 cm^-1,which can be assigned to the 3E_2H-E_2L,A₁（TO）,E₁（TO）and E₁（LO）mode of ZnO,respectively.Furthermore,the photocatalytic activity of ZnO nanorod arrays has been tested by degradation of 4-chlorophenol（4-CP） under UV light irradiation compared to that of the disordered ZnO nanorods film grown on the Ti substrate,indicating that the as-synthesized ZnO nanorod arrays exhibit excellent photocatalytic activity.更多还原