LaCoO3外延膜的取向、结构调控及可见光催化性质研究

Nowadays, photocatalytic materials have gained much attention due to their excellent performance for degradation of persistent organic pollutants. However, most widely-used photocatalysts, such as TiO2, can not effectively utilize the visible light. Therefore, in this program, LaCoO3 with ABO3-type perovskite structure is proposed due to its high visible-light-induced photocatalytic activity. A simple and cost-effective polymer assisted deposition method will be considered to prepare LaCoO3 epitaxial films. In order to control the crystal orientation of LaCoO3 epitaxial film, single-crystal substrates with different orientation will be used. Similarly, CoO6 octahedron distortion and crystal-field splitting characteristic of Co3+ will be changed by the control of lattice mismatch and epitaxial strain. Then the effects of film orientation and epitaxial strain on the structural distortion of LaCoO3 will be discussed for clarifying the control mechanism of film orientation, structural distortion and crystal-field splitting characteristic of Co3+. Based on characterization for spectral absorption property and organic pollutant degradation rate of the LaCoO3 epitaxial films under visible light irradiation, the effects of orientation control and structure modify on the energy band structure, electron transition and visible-light-induced photocatalytic property of LaCoO3 will also be investigated. The results may not only provide scientific guidance for expounding the structure and property control mechanism of visible-light-induced photocatalytic materials with perovskite structure, but also have an important practical significance for environmental protection and energy utilization.

针对当前广泛应用的TiO2等光催化材料不能利用太阳光谱中可见光的问题，以具有可见光催化活性的钙钛矿结构LaCoO3为研究对象，采用高分子辅助沉积法制备LaCoO3外延膜；借助单晶衬底的诱导和限制作用，通过改变衬底取向，实现对LaCoO3外延膜晶面的定向控制；通过调节LaCoO3外延膜的晶格失配度及应力大小，改变CoO6八面体畸变程度，实现对Co3+晶体场分裂属性的调控；通过研究不同取向及应力调控下LaCoO3的结构变化规律，阐明LaCoO3取向与结构畸变及Co3+晶体场分裂属性的调控机制；结合LaCoO3外延膜的光学吸收谱特征及对有机物进行可见光降解的特点，探明晶面取向、结构调控对LaCoO3能带结构变化、电子跃迁及可见光催化性质的影响机制。研究成果不仅为阐明钙钛矿结构光催化材料的结构与性能调控机制提供科学依据，而且所制备的LaCoO3外延膜对于环境保护和能源利用等也具有重要的实际意义。

项目针对当前广泛应用的TiO2等光催化材料不能有效利用可见光的问题，以具有可见光催化活性的钙钛矿结构LaCoO3（LCO）为研究对象，采用高分子辅助沉积（PAD）法制备LCO外延膜，查明了关键制备条件对薄膜外延质量的影响规律；研究了不同取向及应力调控状态下LCO的结构变化特征，阐明了LCO外延膜取向、Co3+晶体场分裂属性的调控机制；研究并揭示了晶面取向、结构畸变程度对LCO外延膜光学吸收特征、可见光催化性质的影响机制。结果表明，PAD外延技术核心是聚乙烯亚胺（PEI）的螯合作用，而-NH基团在PEI螯合阳离子过程中起关键作用，较高分子量PEI中存在较多-NH，有利于提高薄膜的外延质量；PEI分解并释放螯合离子后，较快的升温速率和较高的热处理温度可有效抑制薄膜多晶化。借助单晶衬底对薄膜生长的诱导和限制作用，可有效实现对LCO晶面的定向控制及其结构畸变的调控；不同取向LCO外延膜中CoO6八面体的受力方向与畸变模式不同：（100）LCO外延膜中主要存在类Jahn-Teller效应的CoO6畸变，（111）LCO外延膜中主要为CoO6的扭转；而（110）LCO外延膜中CoO6的变形则介于以上两者之间；在（100）LCO外延膜中，晶格失配的差异导致CoO6四角畸变程度不同；但外延膜中LCO的单胞体积、平均Co-O键长都比LCO块材要大。LCO外延膜对甲基橙、罗丹明均有明显的可见光催化降解性能，其催化活性与CoO6晶体场分裂能以及Co3+-O2-结合能密切相关；Co-O键长的增大有利于降低CoO6晶体场分裂能以及Co3+-O2-结合能，并增加Co3d-O2p电子轨道杂化程度，使材料禁带宽度（Eg）减小、光催化能力增强；而CoO6四方畸变程度的增大，则会使eg与t2g轨道进一步分裂，减小t2g-eg带隙、增加Co3d-O2p杂化程度，从而减小Eg并增强催化活性。研究成果不仅为阐明钙钛矿结构光催化材料的结构与性能调控机制提供科学依据，而且所制备的LCO外延膜对环境保护和能源利用等也具有重要的实际意义。