【作者】 鲁娜；

【导师】 全燮；

【作者基本信息】 大连理工大学 ， 环境工程， 2008， 博士

【摘要】 纳米TiO₂是光降解有机物的催化剂中性质好、光催化活性高、研究最广泛深入的一种半导体。阳极氧化法制备的TiO₂纳米管阵列具有比表面积大、光吸收效率高、与钛基体结合牢固等优点,表现出比TiO₂纳米膜更高的光催化性能和光电转化效率。因此,通过对TiO₂纳米管阵列进行合理的改性和修饰而进一步提高其光催化活性,为TiO₂纳米管阵列能够被实际推广使用具有重要意义。非会属元素掺杂是改善TiO₂光催化活性的一种有效方法。光电催化氧化方法可阻止光生电子和空穴发生简单复合,能够有效提高TiO₂纳米管的光催化反应效率。为此,制备了氮掺杂和硼掺杂TiO₂纳米管阵列电极,并对材料进行了系统表征和光电催化性能的研究。另外,增强TiO₂纳米管对目标物的吸附是提高光电催化效果的关键。分子印迹聚合物对特定的目标分子具有特异选择性。所以,在TiO₂纳米管阵列电极上修饰一薄层分子印迹聚合物,以期改善TiO₂吸附污染物的能力,提高光电催化活性。本论文围绕以上内容,主要开展了以下几个方面的工作:（1）应用加热法在氮气气氛中焙烧阳极氧化TiO₂纳米管制备了氮掺杂TiO₂纳米管电极。电极为致密的阵列结构,平均孔径为80 nm,平均管长为250 nm。X射线光电子能谱（XPS）、X射线衍射（XRD）和紫外-可见漫反射光谱（DRS）分析显示,500℃和600℃制得的电极的氮掺杂量分别为0.6 at.%和0.9 at.%;在500℃制备的氮掺杂电极为锐钛矿相,600℃制备的电极为锐钛矿相和金红石相混合晶相;氮掺杂提高了TiO₂纳米管对可见光的吸收。可见光照下,反应6小时,两种氮掺杂TiO₂纳米管电极对五氯酚的光电催化降解率均比相同温度下焙烧的TiO₂电极提高了28%左右,并且五氯酚的光催化和电化学作用间存在显著的协同作用。对氮掺杂TiO₂纳米管电极具有可见光活性的机理进行了简要探讨。（2）以阳极氧化TiO₂纳米管阵列为基底,应用化学气相沉积法制备了硼掺杂TiO₂纳米管电极。通过扫描电镜（SEM）、XPS、XRD和DRS对电极进行表征,显示高度有序的纳米管阵列沿垂直钛基体方向生长,平均管长为800 nm,纳米管管壁呈齿纹状;硼原子掺杂到TiO₂晶格中,形成Ti-B-O键;XRD谱图中观察到锐钛矿相的（101）晶面和金红石相的（110）晶面的衍射峰,同时TiO₂纳米管的平均粒径增大了10 nm;DRS谱图表明TiO₂纳米管在紫外区的吸收强度也明显增强,并且吸收边带红移了20 nm。光电化学性能测试中,硼掺杂TiO₂纳米管电极的紫外和可见光电流密度均明显高于TiO₂纳米管电极,并且紫外光转化效率达到31.5%。光电催化实验表明,硼掺杂电极对五氯酚的紫外和可见光电催化降解速率的提升幅度高于对降解率的提升幅度。此外,应用电化学方法制备了不同硼掺杂量的TiO₂纳米管阵列电极。该方法能够一步完成纳米管形成和硼掺杂,简化了制备过程,降低了实验成本。SEM结果显示纳米管底部氧化层的厚度为30nm,氟硼化钠加到阳极氧化电解液中不会影响TiO₂纳米管阵列的形貌。XPS、XRD和DRS分析表明,硼原子在低硼掺杂量（1.5 at.%）样品中以Ti-B-O态存在,而在较高硼掺杂量（3.1 at.%和3.8 at.%）样品中硼的化学环境与B₂O₃相似;硼掺杂电极的晶相以锐钛矿相为主,混合少量金红石相;不同含量的硼掺杂均使TiO₂纳米管的吸收延伸至可见光区,同时提高了在紫外光区的吸收,当硼掺杂量为3.1 at.%时,对提高TiO₂纳米管的可见和紫外光吸收贡献最大。在相同实验条件下,三种硼掺杂电极的光电流密度和对阿特拉津的光电催化降解效率均高于TiO₂纳米管电极,其中硼掺杂量为3.1at.%的电极效果最好。（3）以TiO₂纳米管阵列为基底,采用自由基聚合的方法合成四环素分子印迹聚合物（MIP）,制备了MIP修饰的TiO₂纳米管电极。电极表面仍然为紧密的纳米孔状结构,平均管径为50 nm。DRS分析表明,MIP的修饰提高了TiO₂纳米管电极的可见光吸收。吸附实验中,MIP修饰的TiO₂纳米管电极对四环素的最大吸附量为34.88 ng,是TiO₂纳米管电极的1.5倍。在模拟太阳光照下,电极迅速产生光响应,光电流密度随外加偏压的增加而依次增大。由于MIP具有特异的选择吸附性能,因此MIP修饰的TiO₂电极对四环素的光电催化降解能力和矿化能力优于TiO₂电极。另外,无分子印迹的聚合物选择性差,厚的分子印迹聚合物对光的衰减程度更深,因而都不利于光电催化反应的讲行。更多还原

【Abstract】 Nano titanium dioxide（TiO₂） has long been regarded as the most promising photocatalyst because of its outstanding photocatalytic（PC） activity and finds its wide applications in breaking down many kinds of organic pollutants.TiO₂ nanotube arrays prepared by anodization method possess great specific surface area,prominent light absorption ability and strong mechanical strength,and thus exhibit better PC performance and higher photoelectron conversion efficiency than TiO₂ nano film.Therefore,it is important to further improve its photocatalytic activity by reasonable doping or modification to realize practical application of TiO₂ nanotube arrays.It has been proved that nonmetal doping would be a viable way to improve the photocatalytic activity of TiO₂.Photoelectrocatalytic（PEC） oxidation can prevent the simple combination of photogenerated electrons and holes, consequently improving the PC efficiency of TiO₂ nanotube arrays.Considering what mentioned above,in the present work,nitrogen doping and boron doping TiO₂ nanotube array electrodes were prepared and characterized.Meanwhile,the PEC capabilities of these electrodes were investigated.Additionally,increasing the adsorption of the organic pollutants over TiO₂ nanotube is considered to be an important parameter in enhancing the degradation rates of PEC oxidation.Molecular imprinted polymer（MIP） has unique property of specific affinity for target compound.Therefore,the MIP-modified TiO₂ nanotube array electrode was prepared.Higher PEC activity might be obtained with improved adsorption capability of the electrode.In this dissertation,some works were carried out as follows:（1） The N-doped TiO₂ nanotube array electrodes were prepared by forming nanotube-like TiO₂ film in anodization process on Ti sheets and afterward being annealed under N₂ flow at 500 and 600℃.The electrodes presented compact array configuration with an average pore diameter of approximately 80 nm and the nanotube length of approximately 250 nm.The total nitrogen concentrations for electrodes prepared at 500 and 600℃analyzed by X-ray photoelectron spectroscopy（XPS） were 0.6 at.%and 0.9 at.%,respectively.X-ray diffraction（XRD） indicated that the crystal structure of N-doped electrode prepared at 500℃was pure anatase phase and the other N-doped one was a mixture of anatase and rutile phases. UV-vis absorption spectra（DRS） showed noticeable increase of visible light absorption for TiO₂ nanotube array electrodes due to nitrogen doping.Under visible light irradiation,the PEC degradations of PCP in 6 h on N-doped electrodes were both 8%higher than those on TiO₂ electrodes annealed under 500 and 600℃,respectively,and there was a synergetic effect between PC and electrochemical processes.At last,the possible visible PEC mechanism was discussed.（2） The boron-doped TiO₂ nanotube array electrode was prepared by forming a nanotube-like TiO₂ film in an anodization process on a Ti sheet,followed by chemical vapor deposition treatment,and was characterized by scanning electron microscope（SEM）,XPS, XRD and DRS.The highly ordered vertically oriented nanotube arrays were obtained with the length of approximately 800 nm and there were ripples present in the side-walls of the tubes. Analysis by XPS indicated that the introduced boron was probably incorporated into TiO₂ and the chemical environment surrounding boron might be Ti-B-O.The anatase（101） and rutile （110） diffraction peaks were observed in the B-doped electrode and the CVD process led to an increase in crystal size of 10 nm.DRS showed stronger absorption intensity in UV region and the absorption edge shifted 20 nm to a lower energy.The B-doped electrode exhibited higher UV and visible photocurrent densities than TiO₂ electrode,and a notable photoconversion efficiency of 31.5%was achieved under UV light irradiation.Furthermore, the B-doped TiO₂ nanotube electrode exhibited higher PEC activity than non-doped one and contributed more to the UV and visible PEC degradation rate of PCP than PCP degradation efficiency.The boron-doped TiO₂ nanotube arrays were fabricated by potentiostatic anodization of titanium in an aqueous electrolyte containing fluoride ion and sodium fluoroborate（NaBF₄）.This electrochemical method provides a one-step way to prepare B-doped electrode,which not only predigests the preparation procedure but also reduces the experimental cost.SEM images showed a barrier layer of approximately 30 nm at the end of the nanotubes and the addition of NaBF₄ had no effect on the morphology of TiO₂ nanotube arrays.XPS data indicated that the boron atoms were successfully incorporated into the TiO₂ matrix,forming Ti-B-O bond in the sample with small amount of boron（1.5 at.%）,and the chemical environment surrounding boron was more similar to that in B₂O₃ in the samples with larger amounts of boron（3.1 at.%and 3.8 at.%）.The B-doped TiO₂ nanotube arrays with a mixture of anatase phase and very little rutile phase were identified by XRD.Red shifts and enhanced absorption intensities in both UV and visible light regions were observed in the spectra of UV-vis absorption of B-doped samples,especially the B-doped electrode with 3.1 at.%of boron.Under the same experimental conditions,B-doped nanotube array electrodes showed improved photocurrent densities and visible PEC degradation of atrazine.By comparison,the sample with 3.1 at.%of boron exhibited the best PEC performance.（3） The modified TiO₂ nanotube array electrode was prepared by coating a thin layer of molecular imprinted polymer（MIP）.Its surface was well structured with compact voids and the average pore diameter decreased from approximately 80 nm to 50 nm.A distinguishable red shift in the absorption spectrum was observed.The maximum of adsorption capacity at equilibrium condition was about 34.88 ng for the MIP-modified sample,which was nearly 1.5-fold of that for the TiO₂ nanotube arrays.Photocurrent was generated on the MIP-modified photoanode and increased with the increase of positive bias potential under simulated solar light irradiation.Due to the better adsorption capability of MIP-modified TiO₂ nanotube array electrode,it increased not only the TC removal efficiency but also the mineralization of TC in the PEC process.In addition,the TC removal on nonimprinted-modified electrode was lower due to its poor adsorption of the target compound, and the thick MIP layer would weaken the light more deeply,which was unfavorable to PEC degradation.更多还原