摘要
光催化技术可以实现太阳能至化学能的有效转化，应用在有机污染物处理领域，可以将水体中的有机物污染物分解为无毒的无机产物，有助于解决世界性的环境问题。制备具有合适带隙的可见光响应半导体光催化剂、促进光生电子-空穴对的有效分离是光催化技术实际应用的关键。
铁基氧化物以及铁基复合氧化物（铁酸盐）具有合适的禁带宽度，化学和光化学稳定性良好。特定的结构对铁基氧化物以及铁基复合氧化物的光催化性能有着重要的影响，特殊的空心结构或者分级结构有利于提高可见光的吸收和载流子的分离。
本文选择热解金属有机配位聚合物前驱体制备铁基氧化物光催化剂。与其他常见模板或者前驱体相比，金属有机配位聚合物具有独特的结构和孔隙率，这种独特的优势有助于开发一系列具有特定可控形貌的纳米材料。通过选择具有特殊形貌的金属有机配位聚合物并且在合适的实验环境进行转化，可以获得具有期望形貌的铁基氧化物以及铁基复合氧化物。
通过简单的溶剂热法结合后续热处理制备了磁性可分级ZnFe2O4/g-C3N4复合光催化剂。前驱体微球由纳米粒子组成，由于g-C3N4纳米片的空间限制效应，金属配位聚合物前驱体纳米粒子直径受到限制。热解之后次级结构得到很好的保留。在降解过程中，g-C3N4表面产生的光生电子迁移到ZnFe2O4表面，促使光生电子-空穴对的有效分离。ZnFe2O4/CN-150光催化剂降解动力学常数比纯ZnFe2O4的动力学常数提高10倍以上。此外，复合光催化剂具有抗光腐蚀的化学稳定性，其铁磁性使其可磁性回收并方便地重复使用。
通过微波溶剂热法制备了Fe-MIL材料，通过调节溶剂种类获得了具有分级结构的中心棒状形貌前驱体。空气气氛下，在不同温度条件下进行热处理，可以获得不同物相的氧化铁材料。在可见光条件下，使用相应材料降解有机污染物，研究了物相对氧化铁光催化剂性能的影响。发现500摄氏度热解前驱体制得的γ相α相两相复合的Fe2O3光催化剂性能较好，这是因为具有匹配能带结构的两种物相紧密结合，构建有效的同质异相结，使得光生电子与空穴有效分离。
氧化铁除了可以作为光催化剂，还可以用作锂电负极材料。使用微波溶剂热法制备的Fe-MIL材料作为前驱体，通过两次烧结的方式，制得了γ-Fe2O3材料。γ-Fe2O3锂电负极材料表现出了优秀的比容量和良好的循环稳定性。
关键词：氧化铁；铁酸锌；光催化剂；配位聚合物；分级结构
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Abstract
Photocatalytic technology can realize the effective conversion from solar energy to chemical energy. It can be applied for the treatment of organic pollutants, and it can decompose organic pollutants in water into non-toxic inorganic products. The preparation of visible light-responsive semiconductor photocatalysts with a suitable bandgap and the promotion of effective separation of photogenerated electron-hole pairs are the key to the practical application of photocatalytic technology.
Iron-based oxides have suitable bandgaps and chemical stability. The structure has an important influence on the photocatalytic performance of iron-based oxides and composite oxides, and a hollow structure or a hierarchical structure is beneficial to visible light absorption and carrier separation.
The unique structure and porosity of metal organic coordination polymers help to develop a series of nanomaterials with specific controllable morphology. Transformed from a metal organic coordination polymer with a particular morphology, an iron-based oxide or an iron-based composite oxide with the desired morphology can be obtained.
A magnetically ZnFe2O4/g-C3N4 composite photocatalyst is prepared by a simple solvothermal method combined with subsequent heat treatment. Precursor microspheres are composed of nanoparticles, whose diameter is limited due to the space-constrained effect of g-C3N4 nanosheets. After the pyrolysis the secondary structure is well preserved. The structure of ZnFe2O4/g-C3N4 heterojunction greatly improves the photodegradation efficiency of methylene blue and Rhodamine
B under visible light. In addition, the composite photocatalyst is chemically resistant to photo-corrosion and its ferromagnetic properties make it magnetically recyclable and reusable.
Fe-MIL materials are prepared by microwave solvothermal method. A hollow rod-like morphology precursor with a hierarchical structure is obtained. Different heat treatment temperature conditions bring about different phases of iron oxide materials. It is found that the γ-phase and α-phase composite Fe2O3 photocatalyst obtained from the 500 °C pyrolysis of the precursor has better performance because the two species with the matching energy band structure are tightly combined to construct an effective phase junction. Photogenerated electrons and holes are effectively separated.
Iron oxide can be used as a lithium negative electrode material. With Fe-MIL material prepared by the microwave solvothermal method as a precursor, γ-Fe2O3 material is obtained. When used as a negative electrode material, the obtained γ-Fe2O3 material exhibits excellent specific capacity and good cycle stability.
Keywords: Fe2O3, ZnFe2O4, Photocatalyst, Coordination Polymer, Hierarchical Structure
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