稀土掺杂金属有机骨架材料限域单原子催化剂的可控制备及光还原CO2机制研究

Photocatalytic conversion of CO2 into clean carbonaceous fuels driven by solar energy is one of the most promising technologies to alleviate the energy crisis and global warming. This project is aimed at solving the problems of conventional photocatalytic materials, such as low quantum efficiency, narrow light-response range, and easy recombination of photogenerated carriers. Based on the upconversion properties of rare-earth ions, the controllable preparation of rare-earth doped MOFs with high quantum efficiency can be realized by in-situ doping and post-synthesis exchange methods. Furthermore, utilizing the confinement effect of molecular cage and the strong coordination interaction of functional groups, single metal atoms can be directionally and quantitatively introduced into the rare-earth doped MOFs via the strategy combining two-solvent method and stepwise optical deposition. Thus, the single-atoms/rare-earth doped MOFs composite materials can be constructed to achieve the rapid adsorption, efficient activation and in-situ photoreduction of CO2. With the help of isotope tracer technique, in-situ characterization technique, and density functional theory, the influences of synergistic effects between the upconversion of rare earth ions, multi-active sites of MOFs, and the schottky barrier generated from single-atoms and MOFs on the photocatalysis performance of CO2 reduction will be studied. Meanwhile, the mechanism of CO2 adsorption and catalysis conversion on the composite materials will also be clarified. The implementation of this project will provide a new idea for the resource utilization of industrial waste gases and the efficient control of greenhouse effect.

利用光催化技术在太阳能驱动下将CO2还原为清洁的碳基燃料是缓解能源危机和全球变暖最具前景的方法之一。针对传统光催化材料存在的量子效率低、光响应范围窄、光生载流子易复合等问题，本项目利用稀土离子的上转换效应，采用原位掺杂和后合成交换法，可控制备高量子效率的稀土掺杂MOFs材料；基于其分子笼的限域效应和功能基团的强配位作用，通过双溶剂法和分步光沉积相结合的策略，实现金属单原子的定向、定量引入和分散稳定，制备单原子/稀土掺杂MOFs复合材料，实现温和条件下CO2在表界面上的快速吸附、高效活化以及原位光还原过程的一体化。借助同位素示踪技术、原位表征技术和密度泛函理论，揭示稀土离子的上转换效应、MOFs的多活性位点及其与单原子形成的肖特基势垒之间的协同效应对光还原CO2性能的影响规律，明确该材料对CO2吸附-催化转化的作用机制。本项目的实施为工业废气的资源化利用和温室效应的高效控制提供了新思路。

CO2的吸附捕集与高值化转化是实现“碳达峰、碳中和”国家战略目标的重要途径，其瓶颈在于高吸附量、高选择性的催化材料的开发。剖析CO2吸附、活化、催化转化的确切活性位点，明确CO2在不同位点上的还原机制，是突破上述瓶颈的关键。基于此，本项目从载体结构优化与活性组分调控角度出发，制备出多种改性MOFs材料，系统开展了构效关系及吸附、催化机理相关方面的研究，取得的主要研究结果如下：(1) 采用原位自组装和配体预改性等策略制备了微介孔HKUST-1复合材料、交联孔道UiO-66-NH2材料，通过提高微孔含量、缩短扩散路径、引入功能基团等方式，提升了吸附量、选择性及吸附速率，实现了多活性吸附位点的可控构筑；(2) 采用后修饰合成法制备了Er2O3/UiO-66-NH2、CeO2/g-C3N4等稀土改性光催化材料，通过构建异质结、形成内置电场等方式提高了光生载流子的分离效率，提升了光催化性能，明晰了CO2的活化方式以及还原路径；(3) 采用辐射还原法制备了CuNi SAs/UiO-66催化材料，通过Ni位点的引入加速了中间物种的电子转移和加氢转化，促进了CO2高选择性转化为CH3OH产物，同时结合同位素示踪、DFT理论计算剖析了CO2在双金属单原子催化剂上的还原反应历程。本项目的成功实施为高性能光催化还原CO2材料的创制提供了相关的理论依据和可实用化的路径。