TiO2纳米薄膜电极对染料溶液的降解行为

论文摘要

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。

论文目录

• 摘要
• Abstract
• Table of contents
• Chapter 1:General introduction
• 1.1.Generalities
• 1.2.General statement of water treatment problem
• 1.3.Statement of the hypotheses and solution
• 1.3.1 Generalities on Advanced Oxidation Process
• 1.3.2 Basic principles of heterogeneous photocatalysis
• 1.3.3 Crystal structure and photocatalytic activity of titanium dioxide
• 1.3.4 Band structure of semiconductor and band gap energy
• 1.3.5 Enhancement of Titanium dioxide photocatalytic activity
• 1.3.6.Applications of Titanium dioxide
• 1.4.Research objectives and methodology
• 1.5.Conclusion
• 1.6.References
• Chapter 2:Literature review
• 2.1 Introduction
• 2'>2.2.Influence of some fundamental parameters on the photodegradation kinetics of an organic pollutant in UV-irradiated TiO₂
• 2.2.1.Effect of Initial organic pollutant concentration
• 2.2.2.Temperature and pH
• 2.2.3.Inorganic ions
• 2.2.4.Light intensity
• 2.2.5.Influence of oxygen and inorganic oxidizing agents
• 2.2.6.Wavelength
• 2.2.7.Effect of external applied potential bias
• 2 thin films by anodic oxidation'>2.3.Influence of anodizing parameters on the preparation of multi-porous TiO₂ thin films by anodic oxidation
• 2.3.1.Introduction
• 2.3.2.Effect of the nature of the electrolyte
• 2.3.3.Effect of the electrolyte concentration
• 2.3.4.Effect of the electrolyte bath agitation and temperature
• 2.3.5.Effect of the current density and the anodization time
• 2.3.6.Effect of the anodization voltage
• 2.4.Other methods for producing titanium dioxide thin films
• 2.4.1.Chemical Vapor Deposition
• 2.4.2.Sol-gel method
• 2.4.3.Hydrothermal method
• 2.4.4.Electrodeposition method
• 2.5.Conclusion
• 2.6.References
• Chapter 3:Experimental:Materials and Analytical Methods
• 3.1.Introduction
• 3.2.Materials
• 3.2.1.Glassware
• 3.2.2.Chemical reagents
• 3.2.3.Ultraviolet Lamps and Reactors characteristics
• 3.3.Analytical Methods
• 3.3.1.Scanning electron microscopy and energy dispersive x-ray
• 3.3.2.Transmission electron microscopy and Electron Diffraction
• 3.3.3.X-ray diffraction
• 3.3.4.Roman spectroscopy
• 3.3.5.UV-visible optical absorption spectroscopy
• 3.3.6.Linear Voltammetry
• 3.3.7.Electrochemical polarization theory
• 3.3.8.Chemical oxygen demand
• 3.3.9.The pH-value measurement
• 3.4.Conclusion
• 3.5.References
• Chapter 4:Preparation of titanium dioxide electrodes by anodic oxidation
• 4.1.Introduction
• 4.2.Experimental Details
• 2 thin films in H₂SO₄ solution'>4.2.1.Preparation of TiO₂ thin films in H₂SO₄solution
• 2 thin films in NaOH solution'>4.2.2.Preparation of TiO₂ thin films in NaOH solution
• 4.3.Results and discussion
• 2 thin films prepared in H₂SO₄'>4.3.1.Electrochemical properties of TiO₂ thin films prepared in H₂SO₄
• 2 films prepared in H₂SO₄ 0.5mol/l by adjusting the anodization voltage'>4.3.2.Morphology of TiO₂ films prepared in H₂SO₄ 0.5mol/l by adjusting the anodization voltage
• 2 films prepared in H₂SO₄ 0.5mol/l by adjusting the anodization voltage'>4.3.3.XRD of TiO₂ films prepared in H₂SO₄ 0.5mol/l by adjusting the anodization voltage
• 2SO₄ concentration on the preparation of TiO₂ films'>4.3.4.Effect of H₂SO₄ concentration on the preparation of TiO₂films
• 2 th in films'>4.3.5.Effect of the anodization time on the preparation of TiO₂ th in films
• 2'>4.3.6.Effect of the application of low voltage on the preparation of TiO₂
• 2 thin films electrodes prepared in NaOH'>4.3.7.Morphology of TiO₂ thin films electrodes prepared in NaOH
• 2 films prepared at 130V by varying the H₂SO₄ concentration'>4.3.8.Morphology of TiO₂ films prepared at 130V by varying the H₂SO₄concentration
• 2 thin films'>4.3.9.Electrochemical properties of the prepared TiO₂ thin films
• 4.4.Conclusion
• 4.5.References
• Chapter 5:Preparation of transition metals-doped dioxide electrodes
• 5.1.Introduction
• 5.2.Experimental Details
• 5.3.Results and discussions
• 5.3.1.Electrodes morphology
• 5.3.2.Electrodes composition
• 2 electrode'>5.3.3.Effects of applied anodic bias and the transition metal dopant concentration on the photocatalytic activity of TiO₂electrode
• 2 electrode'>5.3.4.Effect of electrodeposition time on the photocatalytic activity of TiO₂electrode
• 2 electrode on the photocatalytic activity of TiO₂ electrode'>5.3.5.Effect of the nature of transition metal doping TiO₂ electrode on the photocatalytic activity of TiO₂electrode
• 2 electrodes'>5.3.6.Optical properties of transition metals-doped TiO₂electrodes
• 5.4.Conclusion
• 5.5.References
• 2'>Chapter 6:Photo-degradation of acid red G by transition metals-doped TiO₂
• 6.1.Introduction
• 6.2.Experimental Details
• 6.3.Results and discussions
• 6.3.1.Effect of pH on the degradation of acid red G
• 2 electrodes'>6.3.2.The photoelectrochemical properties of transition metals-doped TiO₂electrodes
• 6.3.3.Effect of initial concentration on the degradation of acid red G
• 6.3.4.Effect of the nature of metal dopant on the degradation of acid red G
• 2 on the degradation of acid red G'>6.3.5.Influence of the concentration of metal-doped TiO₂ on the degradation of acid red G
• 2 electrode'>6.3.6.Reduction of COD upon illumination of acid red G by UV /Mn-TiO₂electrode
• 6.3.7.Qualitative photocatalytic degradation kinetics of acid red G
• 6.3.8.Electrodes composition after photodegradation of acid red G
• 6.3.9 The electrode lifetime
• 6.4 Conclusion
• 6.5 References
• 2'>Chapter 7:Periodate ion photo-assisted the degradation of acid orange 7 in the presence of Fe-TiO₂
• 7.1.Introduction
• 7.2.Experimental details
• 7.2.1.Materials
• 7.2.2.Photoreactor
• 7.3 Results and discussions
• 7.3.1.Influence of pH on the degradation of acid red G
• 2 on the degradation of AO7'>7.3.2.Influence of the concentration of Fe metal-doped TiO₂ on the degradation of AO7
• 2 electrodes'>7.3.3.Photocurrent response of TiO₂electrodes
• 7.3.4.Effect of 2-propanol addition on the degradation of AO7
• 7.3.5.Effect of oxidizing agents on the photodegradation of acid orange 7
• 7.3.6.Effect of initial concentration on the degradation of acid red G
• 7.3.7.Qualitative photocatalytic degradation kinetics of acid orange 7
• 7.3.8.COD reduction
• 7.4.Conclusion
• 7.5.References
• General Conclusions and perspectives
• Papers published
• Acknowledgments