Fe3O4/TiO2/Graphene磁性复合吸附剂的制备及其去除水体中的重金属离子机制研究

Due to non-easily degradation, high chemical toxicity and cumulative effect in the future, the heavy metal pollution has become a major environmental concerned issues. The heavy metal ions contamination of Jiaozhou Bay, which is a semi-closed bay, has bring serious threats to the human health and marine life. In this study, the adsorption and photocatalytic methods will be combined to improved the efficiency of heavy metal ions removal in wastewater. The Fe3O4/TiO2/Graphene magnetic semiconductor nanocomposites will be prepared by using hydrothermal method in our work. The synthesis conditions, such as reagents proportion, reaction temperature, ultrasonic time and etc., will be optimized to obtain the high adsorptive and high catalytic performance products. Combined with experimental method, the first-principles based on density functional theory (DFT) will be used to explore the structure and properties of the composite and its mechanism of metal ions removal. The hetero-structure mixed phase model of the composite can be obtained by the atomic cluster model and the layered structure model, respectively. And it will be verified which model is favorable and reliable in our theoretical study. The bulk electronic and interface structure, charge distribution, surface and interface properties, charge mobility between the interface of two mixed-phases, and the catalytic activities of the composite are all involved in our work. The metal ions containing wastewater was treated by the obtained nanocomposites as absorbent, the factors such as, the content of the adsorbent, absorption time, the adsorptive form, pH value, ionic strength are investigated during the adsorption process. The metal ions form combined on the surface, such as physical adsorption, chemical adsorption, or complex form, and physic-chemical reactions on the surface will be explored in the metal ions removal process. The mechanism of “physi-chemcial adsorption and oxidation-reduction” is proposed in this work to illustrate the reaction of metal ions on the surface of absorbent. The results will provide the scientific basis to the heavy metal pollution treatment and the application of magnetic nanomaterials in purification of wastewater containing metal ions.

因其在水中难降解、毒性强、具有积累效应等特征，重金属污染已成为备受关注的重大环保课题。胶州湾是一个半封闭型海湾，其重金属污染对人类健康和海洋生物带来了严重的威胁。本课题拟将吸附法与光催化方法相结合提高废水中重金属离子的去除效率。通过优化反应条件和工艺，合成高吸附性、具有高催化性能的Fe3O4/TiO2/Graphene 磁性复合吸附剂。构建异质结构复合物混合相模型，采用第一性原理计算并与实验相结合，研究催化剂界面结构与电荷布居对复合物电子结构和属性、表面性质、电荷迁移率和光催化性能的影响，探究重金属离子在吸附剂表面的作用形式及表面氧化还原反应机理，初步提出重金属在吸附剂表面的“物理化学双吸附-氧化还原”反应机制，为水体中重金属污染的修复以及利用磁性纳米材料处理重金属废水污染提供科学依据。

环境水体中的重金属等污染物对人类健康和社会发展带来了严重危害。设计合成TiO2和Fe3O4为基质的复合材料，采用光催化和吸附的方法联合用于去除水体中的污染物。设计TiO2/graphene、TiO2(001)/graphene、WO3/graphene、Fe3O4(111)以及(WO3)x/(TiO2)y复合材料，采用第一性原理方法研究复合材料的几何结构和电子属性，探讨其表面和界面性质。由界面电荷分布和密度的变化，讨论其电荷布局、电子迁移效率、方向及其氧化还原性质。研究了石墨烯复合对改善材料的能带结构、界面电荷迁移、光生电子-空穴复合率以及氧化还原电位的影响。制备了TiO2(100)/graphene、WO3/Graphene、TiO2/WO3/石墨烯、多孔结构Fe3O4、Fe3O4/TiO2、Fe3O4/生物质、Fe3O4/TiO2/Graphene复合纳米材料，对其结构和性能进行了表征，讨论了石墨烯以及氧化物的复合对材料氧化还原和吸附性能的影响，并用于废水中重金属离子Cr(VI)、Cu(II)以及染料罗丹明B的去除，探索其去除机制研究。.研究发现：催化和吸附均在表面发生，晶体表面具有一定的生长机制，合成特定活性表面的氧化物基质较为重要。氧化物的复合对光催化和吸附行为具有显著影响，光生电子-空穴的复合率大大降低，光催化活性增强，表面氧化还原能力提高。(WO3)x/(TiO2)y层状结构模型可有效解释实验结果。石墨烯的复合对材料性能有显著提升，石墨烯的复合拓展了氧化物的表面，使其表面吸附能力增强，另一方面，石墨烯的复合导致氧化物/石墨烯的界面电荷由石墨烯向氧化物转移，改变了电子迁移途径，促进光生电子-空穴的分离，提高了复合材料的氧化还原性质。Fe3O4基吸附剂(Fe3O4、Fe3O4/TiO2/GO、Fe3O4/生物质)具有较高的吸附性能，将其用于去除水中的Cr(VI)、Cu(II)和罗丹明B，其最大吸附量为97.08 mg.g-1。Fe3O4基吸附剂去除金属离子污染物可分为表面扩散、颗粒内部扩散和吸附平衡三个反应阶段，其中表面扩散为主要过程。球形Fe3O4对Cr(VI)的去除为单层化学吸附， Fe3O4表面复合石墨烯或者氧化物后，与重金属离子在复合表面的作用形式发生了变化，Cu(II)、Cr(VI)在复合物表面为物理吸附，其吸附动力学仍然符合伪二级反应动力学。