多重改性构建TiO2基光致阴极保护涂层和载流子迁移控制

Strong attention has been attracted to titania coatings in recent years for their ability to render a non-sacrificial cathodic protection to certain metals under ultraviolet illumination.The process is called photo-induced cathodic protection effect of TiO2 semiconductor. Up to now, no practical utilization of titania protective coatings has yet been developed. One issue of the utilization of TiO2 to be considered is how to guarantee the supply of electricity in the dark situation. Moreover, the corrosion invalidation of TiO2 coatings will limit its potential use in practice also. It is worthy of special mention that the corrosion of TiO2 coatings, which is caused by the accumulation of holes, is neglected in the study of TiO2 coatings. In view of the features above, the control of carrier transport in the photoelectric process of TiO2 coatings is first proposed in the project. Electron storage material doped TiO2 coatings are prepared on different metal substrates. Electrons generated by the photo-electric conversion function of TiO2 will be stored partially under illuminated situation and be discharged from the doped material to the metal substrate in the dark situation, enabling to sustain the cathodic protection function. Some transition metal oxides and compounds with electron storage effect can be proposed as the electron storage material. On the other hand, as the corrosion failure of TiO2 protective coatings is caused generally by the accumulation of holes, hole transporting material is prepared on the surface of TiO2 films. With this approach, the transfer impedance of the holes is reduced greatly. The rapid out-migration of holes accelerates the separation of electrons and holes and the corrosion of the coatings is avoided. These measures on the control of carrier transport will make a full-time photocatodic protection of TiO2 coatings become reality and provide the theoretical foundation for the practical application of TiO2 protective coatings.

纳米TiO2光致阴极保护涂层是近年来发展的非牺牲性阴极保护技术，克服了传统阴极保护的时效问题，具有广阔的应用前景。然而，光致阴极保护对光照条件的依赖以及涂层表面缺陷和失效已成为制约其实际应用的主要瓶颈。申请者在前期研究中发现TiO2涂层自身存在腐蚀引起失效，空穴累积是TiO2腐蚀产生的主要原因。结合当前对无光照条件下阴极保护的研究现状，本课题提出控制TiO2光致阴极保护过程的载流子迁移，采用空穴传输材料改性，降低空穴迁移阻抗，减少空穴积累和涂层腐蚀，同时结合储电子化合物改性，使电子在光照条件下存储，无光照时释放至金属基体，在金属表面构建均匀致密、附着力强并具有长效腐蚀保护效果的纳米TiO2光致阴极保护涂层；分析空穴和电子载流子在阴极保护过程中的迁移路径和传输机制，在光致阴极保护的实际应用方面寻求突破并提供理论基础。

纳米TiO2具有光致阴极保护效应。但是TiO2的禁带宽度过宽、电子和空穴复合率高。项目利用载流子传输材料和变价金属氧化物对氧化钛进行改性，并利用结构分析和光电化学性能分析技术，研究改性氧化钛载流子的迁移过程和光电性能表现。主要内容、结果及科学意义如下：.(1)利用一步水热技术制备石墨烯改性氧化钛复合半导体。适当改性条件下石墨烯导致介稳相板钛矿的形成，混晶效应、可见光吸收增强效应以及石墨烯与半导体费米能级的差别引起的费米能级偏移效应，减少了电子迁移势垒，提高复合半导体的光电性能和光致阴极保护特性。.(2) 利用一步水热和原位聚合技术制备聚苯胺和石墨烯共改性氧化钛。复合半导体组分间不同的电子势能，促使载流子在组分内自发迁移，减少电子－空穴的复合和由于空穴聚积形成的氧化钛失效。费米能级移动使半导体异质结界面内电场增强，提高复合半导体的光电化学性能和光致阴极保护能力。同时聚苯胺的氧化还原能力也使三元复合材料具有充放电能力，有望在无光照条件下为金属基体提供暗态阴极保护。.（3）利用硅烷偶联剂改性纳米TiO2，固化硅烷起连接TiO2颗粒的作用，可提高涂层的表面致密性和力学性能；复合涂层具有较好的疏水效果，有利于抑制水中腐蚀介质对涂层的侵蚀。但是疏水性不利于空穴的迁移，使硅烷复合涂层的长效阴极保护表现并不突出。.（4）采用溶胶-凝胶技术制备半导体氧化锡SnO2和WO3复合纳米TiO2粉体。改性改变氧化钛微观结构，同时能带耦合效应促进载流子的内部迁移，显著增强氧化钛的光电流响应。.（5）利用煅烧和二次水热技术制备g-C3N4和石墨钛改性复合纳米氧化钛。三元组分之间通过键合，促进光生载流子在组分间迁移，使半导体光吸收红移；同时半导体的费米能级偏移，提高促进电荷循环的内电场强度，提高半导体的光生电流强度和光致腐蚀电位。.