【作者】 云虹；

【导师】 林昌健；

【作者基本信息】 厦门大学 ， 物理化学， 2008， 博士

【摘要】 纳米TiO₂薄膜独特的光电化学性质,已受到广泛的关注,并成功应用于光催化处理污染物、超双亲自清洁、太阳能转换和储存等高科技领域。TiO₂的光电特性在金属腐蚀防护方面表现出诱人的应用前景,正日益受到人们的重视。然而,TiO₂是宽禁带半导体化合物,只吸收λ＜387nm的紫外光,太阳能利用率仅为3-4%,而且光生电子—空穴对快速复合,光转化效率还很低,通常在暗态下难以对金属基体起到有效的光生阴极保护作用。本论文侧重发展多种纳米TiO₂复合膜及表面改性技术,探索纳米涂覆层表面均一化、消除各种物理缺陷的有效技术,以期在TiO₂纳米覆盖膜材料的制备和改性方面有所突破。发展环境友好的水热法制备特殊纳米结构的TiO₂薄膜,研究在金属防护中可能的应用,考察相关的影响因素和规律性,揭示TiO₂表面结构和光电性质的相关性。结合掺杂和半导体复合技术有效地延长TiO₂光生电子-空穴对的寿命,强化暗态下的光生阴极保护作用,并探索纳米TiO₂复合膜光生阴极保护的作用机理。主要的研究进展及成果如下:1.发展了溶胶.凝胶法和浸渍一提拉技术,在316L SS表面分别构筑N、S和Cl改性的纳米TiO₂复合膜。经不同的无机离子改性的TiO₂纳米膜的表面形貌、微结构和结晶度存在明显差异。N改性的纳米TiO₂膜结晶度良好,膜表面更均一和致密,平均的晶粒尺寸为25 nm。在相同的测试条件下,N改性的TiO₂纳米膜具有较高的光电响应。2.N改性的TiO₂纳米膜在0.5 mol/L NaCl溶液中具有较好的表面阻挡层作用。在白光的照射下,N-TiO₂复合膜可为金属基体提供有效的阴极保护,而在暗态下,阻挡层发挥主要作用,可有效地保护金属免遭腐蚀.纳米N-TiO₂薄膜对金属基体有双重的保护作用。3.采用溶胶-凝胶法制备非金属B掺杂的CeO₂,B原子固溶于CeO₂晶隙中,形成了B-Ce-O键。结合半导体复合技术,在不锈钢表面构筑（外）TiO₂|（内）B-CeO₂纳米复合膜。光电化学测试结果表明,在白光照射下,TiO₂|B-CeO₂复合膜可使金属基体处于阴极保护状态,而且当停止光照后,纳米TiO₂ | B-CeO₂复合膜可实现持续的光生阴极保护作用,即暗态下TiO₂| B-CeO₂ | 316L SS电极的电位可稳定在-0.10V_SCE附近（低于316L SS的自然腐蚀电位）,并保持一段较长的时间（～7h）。另一方面,TiO₂ | B-CeO₂复合膜作为阻挡层也有较好的保护性能,复合膜光生阴极保护和阻挡层双重作用的有机结合可更好地实现对金属的有效防护。4.发展环境友好、成本低廉、操作简便的水热合成法,并结合简单的后处理技术,在Ti基底表面制备了锐钛矿型纳米TiO₂薄膜。对水热反应的温度和时间工艺参数的调节可实现对纳米TiO₂薄膜的表面结构和厚度的可控。不同表面结构和厚度的纳米TiO₂薄膜具有不同的光电响应行为。在膜厚一致的条件下,在白光照射下,水热合成的网络状结构的TiO₂纳米膜和电化学阳极氧化制备的TiO₂纳米管阵列膜均可提供有效的光生阴极保护作用。5.发展低温水热法制备特定晶型纳米TiO₂薄膜。与常规高温煅烧（450℃,2h）制备锐钛矿型TiO₂的方法相比,环境友好的水热法可在低温（170℃）下制得结晶度良好的锐钛矿型TiO₂。通过改变水热工艺参数,可控制TiO₂的结晶程度和表面形貌。在模拟海水介质中,与常规450℃热处理2h所制备的TiO₂纳米膜相比,170℃水热反应4h获得的结晶度高、结构致密的TiO₂纳米膜对金属基体具有更好的防护性能。更多还原

【Abstract】 Nano TiO₂ thin films,due to their unique photoelectrochemical properties,have been world-wide attractive,and extensively applied in many hi-tech fields,such as photocatalysis,surper-hydrophilic self-cleaning,solar cells and so on.The investigation of TiO₂ for photogenerated cathode protection of metals has received great attention.However,due to the wide band gap of TiO₂ semiconductor,it is only excited by ultraviolet light（λ＜387nm）,and only 3-4%solar energy can be utilized. And the recombination rate of photogenerated electron-hole pairs in TiO₂ is high and the quantum efficiency is low,it is usually impossible to offer a distinctly photogenerated cathode protection for metal substrates under dark conditions.In this dissertation,the various techniques have been developed to prepare nano TiO₂ composite films combining with the surface modifications in order to achieve an optimal barrier resistance and efficient photo-generated cathodic protection to corrosion of metals.An environmentally friendly hydrothermal method has been developed to synthesize special nanostructured TiO₂ thin films and their dual functions of barrier resistance and photo-generated cathode protection to corrosion of metals have been investigated.The results have been discussed in terms of the structure of TiO₂ film and its performance of photogenerated cathode protection.The emphases have been made to efficiently last the life of electron-hole pairs in nano TiO₂ composite films by doping and coupling to another semiconductor,and enhance the photogenerated cathode protection for metals in dark.The mechanism of nano TiO₂ composite films for photogenerated cathode protection has been further examined as well.The main results and progresses of this work are outlined as following:1.A sol-gel and dip-coating technique has been developed to prepare nano TiO₂ films modified with anions of nitrogen,sulfur and chlorine supplied on the surface of 316L stainless steel,respectively.When modified with the different anions,the surface morphology,structure and the degree of crystallization of TiO₂ films are remarkably different.The N-modified TiO₂ nano-coatings show higher photocurrent under the same measurement conditions.2.N-modified TiO₂ nano-films are able to act as an optimal barrier layer to metallic substrates in 0.5 M NaCl solution.And N-modified TiO₂ nano-films provide a distinctly photogenerated cathode protection for 316L SS under the white light illumination.When the illumination is stopped,the N-modified TiO₂ nano-films still exhibit a protective barrier layer for metals,showing a dual function in corrosion protection of metals.3.A sol-gel technique is used to prepare CeO₂ doped by B element,which is found to exist in the interstitial space of CeO₂ crystal lattice by forming B-Ce-O bond. Bilayer coatings consisting of a B-doped CeO₂ inner layer and a TiO₂ outer layer are made on 316L SS substrate（316L SS｜B-CeO₂｜TiO₂） by coupling.Based on the photoelectrochemical measurements,the TiO₂｜B-CeO₂ films provide a distinctly photogenerated cathode protection for 316L SS under the white light illumination,and sustain the photoeffect for nearly 7 hours when the illumination is stopped,indicating that TiO₂｜B-CeO₂ films are able to continue photogenerated cathode protection for a long period of time in dark.On the other hand,the TiO₂｜B-CeO₂ films still exhibit a good barrier layer for metals, both protective performances of TiO₂｜B-CeO₂ films can offer better protection for metals in a corrosive environment.4.A simple,low-cost and environmentally friendly hydrothermal method followed by a facile post-treatment has been developed to prepare anatase TiO₂ thin film on the Ti substrate.The morphology and thickness of the as-attained TiO₂ film can be successfully controlled by varying the hydrothermal reaction temperature and time.The TiO₂ films with different surface morphology or thickness show different photocurrent maximum.When the thickness of TiO₂ films is comparable,the net-like structured TiO₂ film obtained with a low-temperature hydrothermal process and the TiO₂ nanotube（TN） array film prepared by electrochemical anodization both offer a distinctly photogenerated cathode protection for 316L SS under the white light illumination.5.A low-temperature hydrothermal method has been developed to prepare TiO₂ thin films with certain crystallization.Different from the common method, namely,calcination at 450℃for 2h,it is facile for a hydrothermal method to attain anatase TiO₂ with high crystallization at a low temperature of 170℃.The surface morphology and the degree of crystallization of the as-attained TiO₂ film can be successfully controlled by varying the temperature and time of hydrothermal reaction.Compared with TiO₂ film derived by calcined at 450℃for 2h,the TiO₂ film derived by hydrothermal reaction at 170℃for 4h exhibits better barrier resistance to corrosion in simulated seawater.更多还原