【作者】 爱可可；

【导师】 沈嘉年；

【作者基本信息】 上海大学 ， 材料学， 2008， 博士

【摘要】 TiO₂光催化纳米半导体是近几十年开发出来的新型功能材料之一,以其廉价、无毒、光化学性能活泼、抗光腐蚀性能强等优势,成为理想光催化剂的首选材料。TiO₂光催化纳米薄膜具备比表面大、光催化活性与粉末相当、应用便捷、易于回收等特点,而且二氧化钛具有很好的光敏性,尤其是紫外光,因此被广泛地应用到环境治理方面,特别在污水处理、空气净化、室内杀菌、除臭等多个领域。但目前TiO₂光催化技术存在光量子产率低（≤5%）、光能利用率小、光生电子和空穴易于复合、薄膜与基体结合不稳定等问题,制约了它在环境治理方面的应用。本论文系统的研究了电化学阳极氧化法在TiO₂纳米薄膜制备中的应用,成功地在Ti基体上得到TiO₂光催化纳米薄膜,研究了各项工艺参数,包括:电解质溶液组成、氧化电压、氧化温度、氧化时间等对二氧化钛薄膜的结构、形貌及其光催化活性等的影响,以及薄膜结构与性能的内在关系。结果表明阳极氧化工艺对制备条件要求宽松,电解质溶液的可选种类多、可用浓度范围较大,氧化电压、温度、时间都可适当变化,有一个相当宽的选择范围。其中,以1.0 mol/L H₂SO₄为电解质溶液、氧化电压为130V、氧化温度为室温28℃、氧化时间5min的制备条件下得到的TiO₂薄膜光催化活性最高。其晶体结构是纳米晶锐钛矿掺杂少量金红石,显示出相当高的光催化活性。本文研究了电化学阳极氧化法在TiO₂薄膜中掺杂过渡族金属离子对薄膜光催化活性的影响。作者还首次将外加偏压增强电极极化的方法引入TiO₂光催化体系。外加偏压可以推动半导体产生的电子空穴反向运动,加快电子与空穴的分离,抑制二者复合,进而提高薄膜的有效量子产率。检测结果表明:加偏压后的TiO₂薄膜光电流最大可比原来增大三个数量级。但薄膜的光催化性并不是随偏压的增长而不断提高,偏压过高可能导致薄膜被击穿而无法使用。光电流随着阳极偏压的增大而增大,当偏压增大到3.5V时,光电流的增大速率减小,在这个偏压下光电流从μA量级提高到mA量级。光电流随外加阳极偏压的变化趋势符合抛物线规律变化。电化学阳极氧化技术中,一种被称为三步电化学法的技术被应用于过渡金属元素掺杂到TiO₂薄膜中,过渡族金属元素一般是指原子的电子层结构中d轨道仅部分填充的元素,如Pt,Ir,Ag,Fe,Mn,Cr,Co,Ni等。实验结果显示,掺杂了过渡金属的二氧化钛光催化特性很大程度上取决于作为掺杂剂的过渡金属的属性。本研究显示常用的含氮合成纺织品染料如:酸性红G和酸性橙7能够有效的被采用阳极氧化法制备的掺杂过渡金属的二氧化钛电极所褪色。通过过渡金属的掺杂可以显著提高二氧化钛降解有机废水率,但是掺杂过渡金属镍对二氧化钛的降解效率有影响。同时,本文研究了过渡族金属的浓度对酸性红G降解的影响,结果显示光催化活性随着过渡金属掺杂浓度的增加而增加,最佳浓度是1.0 at%,当浓度＞1.0 at%时,光催化活性随着过渡金属掺杂浓度的增加而降低。吸收光谱显示由于Pt的沉积,显著增强了Pt-TiO₂薄膜电极对可见光的吸收,这个结果大大提高了二氧化钛的光响应范围。酸性红G或酸性橙7（阴离子染料）的光降解在酸性溶液（pH2.1）中变快,而在碱性溶液（pH12.2）中变慢。在酸性红G或酸性橙7溶液中,二氧化钛催化剂表面带正电而且酸性红G分子与催化剂表面结合,从而提升了降解率。在前期工作的基础上,作者设计了TiO₂光催化纳米薄膜实验室污水净化反应器,可旋转的并施加了偏压的TiO₂薄膜作为工作电极。检测结果表明:反应器具备普遍适用性,对常见的有机溶剂如酸性红G、酸性橙7等都具有良好的降解效果。实验结果显示,600ml浓度为7.5ppm的酸性红G溶液与酸性橙7溶液在反应器中处理三小时后,其光催化降解率达到95%以上,化学需氧量去除率大约86.3%。化学需氧量去除随着反应时间的增加而降低,化学需氧量去除率比褪色率低得多。这可能是由于在酸性红G降解过程中,越来越少的未着色物质产生,这促进了溶液的化学需氧量。为了使更小的有机化合物降解,则需要更长的紫外线照射时间。通过使用电化学阳极氧化方法制备的铁掺杂多孔二氧化钛,来研究无机氧化物例如IO₄^-和H₂O₂的添加对酸性橙7溶液光降解的影响,研究表明IO₄^-在紫外光照射前加入溶液中,可以显著促进酸性橙7的降解。而且,如果将丙醇加入到酸性橙7的溶液中,它的光降解并没有显著变化,这表明酸性橙7的光降解是由于孔的作用而不是OH°的作用。二氧化钛的光催化活性在掺杂铁的样品中发生了很大的变化。光催化活性达到最大值的时候,铁掺杂的浓度为1.0 at%。当把丙醇加到酸性橙7溶液中时,光电流会增大。光电流的增加是由于丙醇在二氧化钛电极表面通过孔洞发生感光氧化作用。丙醇在光催化体系中的添加对于酸性橙7的降解率没有明显的影响,而在KIO₄/紫外光体系中丙醇的添加对酸性橙7的降解率有显著的影响。这表明酸性橙7的光催化降解在pH=2.4酸性溶液中是通过光生电子对有机物直接进行氧化的,然而在KIO₄溶液中,OH°可能是引起酸性橙7发生光降解的一种主要氧化物。催化剂的有效期是光催化过程中的一个重要参数,因为它的使用期越长,反应的成本就会明显降低。结果表明过渡金属掺杂二氧化钛电极是一种具有很好的光催化特性的催化剂,从经济学的角度上来讲,更加适用于废水处理。含氮染料的处理需达到一定的条件,对于第一阶不均匀反应动力学模式,Langmuir-Hinshelwood速率公式用于研究酸性红G通过紫外/二氧化钛电极体系降解的动力学。吸附平衡常数、速度常数和初始降解率由不同的电极所决定。更多还原

【Abstract】 The most recent researches in water purification concern the oxidation of organic substrates dissolved in water. As one of the new functional materials, titanium dioxide nano-semiconductor has been proven to be the most suitable for widespread environmental applications. Titanium dioxide is biologically and chemically inert; it is stable to photo and chemical corrosion, inexpensive and non-toxic. Furthermore, TiO₂ is photoactive, sensitive to UV or near visible light.The photocatalytic activity of TiO₂ has been widely studied and applied in wastewater treatment, air purification, deodorization and room sterilization. However the use of TiO₂ is limited due to the low quantum efficiency （< 5%） because of the recombination of the generated electrons and holes, which become the main barrier in the development of the photocatalytic technology.The electrochemical anodic oxidation method was used into preparation of TiO₂ photocatalytic nanoporous film in our laboratory by our team in recent years. In this paper, the experimental preparation parameters including the nature of electrolyte, the oxidation voltage, the oxidation temperature and the oxidation time were carefully controlled. Their influence on the structure, morphology and photocatalytic activity of the TiO₂ film was systematically evaluated. The internal relationship between the structure and property of the TiO₂ film was analyzed. The result showed that there is a relatively wide range in the selection of the preparation condition.The experimental results revealed that the optimum preparing conditions are that the concentration of electrolyte solution is 1.0 mol/l H₂SO₄, the oxidation voltage is 130V, the oxidation temperature is at room temperature, and the oxidation time is at about 5min. The film prepared under such condition has multi-porous morphology and it is constituted of a mixture anatase and trace rutile. It showed a high photocatalytic activity. The effects of doping metal ions into TiO₂ film by anodic oxidation method on photocatalysis are also studied. In this work, the bias was firstly applied to improve the performance of TiO₂ photocatalysis. The bias can accelerate the move of the photogenerated electron and hole. Their recombination is restrained and then the quantum yield of the semiconductor is increased. The result indicated that by varying the potential bias, the photocurrent density increased from micro-scale （μA） to milli-scale （mA） and when the applied anodic bias reached the value of 3.5V, the rate of increasing of the photocurrent density began to decrease. The change of photocurrent density with the applied bias follows the parabolic laws.A three steps electrochemical method called in the present work re-anodization technique was designed to incorporate transition metals with unfilled d-levels （Pt, Ir, and Ag） and （Fe, Mn, Cr, Co and Ni） into TiO₂ film. The experimental results showed that the photocatalytic properties of transition metal doped-TiO₂ greatly depend on the nature of the transition metal used as dopant.This work demonstrates that a common textile synthetic azo-dye, acid red G and acid orange 7 could be decolorized efficiently using transition metals doped- multi-porous TiO₂ electrodes produced by a re-anodization method. The rate of degradation was remarkably enhanced by the incorporation of transition metals into titanium dioxide but the doping with nickel was detrimental.The effect of transition metals concentration on the degradation of acid red G was also investigated and the results showed that the photocatalytic efficiency increases with the increase in the metal dopant concentration up to an optimum level （about 1.0 at %）. Above the optimum metal doping concentration （about 1.0 at %）, the photocatalytic activity of metal-doped TiO₂ was lower.The experimental absorption spectra demonstrated that the Pt-TiO₂ film electrodes have a significant increase of absorbance in visible light due to Pt deposition, which indicates a new possibility for improving TiO₂ photoresponse. The photodegradation of acid red G or acid orange7 （anionic dyes） was faster in acidic condition （pH 2.1） while in alkaline solution the degradation was lower （pH 12.2）. At pH 7.1 an intermediate degradation was observed. At acidic pH, the TiO₂ catalyst surface is positively charged and acid red G molecules are bound on the catalyst surface enhancing then the photodegradation rate.Basing on the pervious work, a waste-water decontamination reactor is designed. It is composed of TiO₂ as working electrode, graphite as counter electrode, external power source to generate the applied bias, ammeter to monitor the direct current, transparent container and ultraviolet light. The experimental results showed that, after 3.0 h of illumination of acid red G 7.5 ppm （pH 2.1, using Pt-TiO₂ electrode）, the decolorization was about 95% and the COD removal was about 86.3 %. The reduction of COD removal increased with increasing reaction time. The rate of COD removal was much lower than that of decolorization. This is due probably to the formation of smaller uncolored products during the degradation of acid red G, which continue to contribute to the COD of the solution. To achieve complete degradation of smaller organic compounds, longer irradiation time is required.The effect of the addition of the inorganic oxidants such as IO₄^- and H₂O₂ on the photodegradation of acid orange 7 by using Fe-doped TiO₂ multi-nanoporous prepared by the re-anodization method was also investigated. This work demonstrated that the addition of IO4" prior to UV irradiation significantly increases the degradation of acid orange 7. Moreover, the addition of propanol, CH₃-CHOH-CH₃ to remove OH°in acid orange 7 solution demonstrated that the photodegradation of AO7 was not significantly affected by the addition of propanol. This observation showed that the photodegradation of AO7 is due to the holes reaction and not due to OH°reaction. The photocatalytic activity of the TiO₂ was greatly modified in samples doped with Fe. The maximum increase of photocatalytic activity was found at an optimum concentration of approximately 1.0 at % for Fe.The photocurrent increased when 2-propanol was added to AO7 solution. The increase of the photocurrent is due to the photo-oxidation of 2-propanol on the surface of TiO₂ electrode by holes. The degradation rate of AO7 was not significantly affected by the addition of an excess of 2-propanol in the photocatalysis system while the rate was strongly affected in the system KIO₄/ UV. This indicates that the photocatalytic degradation of AO7 in acidic solution （pH= 2.4） proceeds via a direct oxidation of the organics by the photogenerated valence band holes while the OH°radical could be one of the major oxygenating species responsible for the photodegradation of AO7 in the photolysis of KIO₄.The catalyst’s lifetime is an important parameter of the photocatalytic process, due to the fact that its use for a longer period of time leads to a significant cost reduction of the treatment. The results demonstrated that the transition metals-TiO₂ electrode represent a catalyst with good photocatalytic properties, probably suitable to use in a real wastewater applications for an economic point of view.The elimination of these azo dyes fulfils the conditions established for a first-order heterogeneous reaction kinetic model. Langmuir- Hinshelwood rate expression was employed to study the kinetic of the degradation of acid red G by UV / TiO₂ electrodes system. The adsorption equilibrium constant, the rate constant, and the initial degradation rates were determined for different electrodes.更多还原