超薄LDHs纳米材料的构建与光催化还原CO2机理研究

The photocatalytic reduction of CO2 into hydrocarbon fuels by utilizing the abundant solar energy holds promise to address the current and future demand of energy supply. However, the low efficiency of the reaction is always a key factor to restrict the practical application of this technology. On the basis of significant enhancement on the separation of photogenerated charge carriers and the adsorption/activation of CO2, this project will carry out a fundamental research on the CO2 photoreduction over layered double hydroxides (LDHs).The ultrathin geometry of LDHs (thickness <10 nm) efficiently improves spatial separation of photogenerated electrons and holes, and promotes charge carriers to move rapidly from the interior to the surface to participate in the photoreduction reaction, due to the great decrease in the transport distance of photogenerated electrons and holes. Furthermore, by controlling co-catalyst (e.g., Pt, Au), surface defects (e.g., oxygen vacancies), functional group (e.g., -OH or -NH2) can be introduced that alter the ultrathin LDHs surface atomic structure and greatly enhance CO2 sorption ability and potential for CO2 activation. According to activation methods of C=O bond, a series of ultrathin LDH-based nanomaterials will be designed and fabricated to satisfy high catalytic activity and selectivity. To improve the efficiency of CO2 photoreduction, the relationship and synergistic effect among ultrathin nanostructure, surface modification, transfer and separation of photogenerated electrons and holes, adsorption/activation of CO2 will be carefully explored. Finally, the physichemical mechanism to enhance the CO2 photoreduction over ultrathin LDHs-based materials will be clarified. The investigations on ultrathin LDHs systems provide some scientific and experimental bases for research on novel, high efficient photocatalysts to photocatalytic reduction of CO2.

目前，太阳能光催化还原CO2为碳氢燃料具有广阔的应用前景，但转化效率低，未能达到实际应用的要求。本项目围绕提高转化效率的两个关键问题：光生电子空穴有效分离和CO2吸附与活化，开展超薄层状双金属氢氧化物(LDHs)还原CO2研究。通过调控超薄LDHs纳米材料的厚度(<10 nm)，大幅缩短光生载流子的迁移距离，提高光生电子空穴的分离效率，使其快速迁移至表面反应位点，增加参与光催化反应的光生载流子数量。通过调控助催化剂(Pt、Au等)、缺陷(氧空位)、碱性基团修饰超薄LDHs纳米材料的表面，构建有利于CO2 吸附与活化的表面化学组态，研究C=O键活化机理，设计高效CO2光催化还原路径及产物选择性。阐明LDHs材料的超薄化和表面修饰对光生载流子输运行为和CO2吸附与活化之间的影响规律和内在机理，为开发新型高效光催化还原CO2体系奠定一定的科学依据和实验基础。

人工光合成被认为是太阳能转换和存储的绿色化学方法之一，但转化效率低，未能达到实际应用的要求。本项目以提高转化效率为目标，开展层状双金属氢氧化物(LDHs) 人工光合成研究。本项目构建了全固态Z模型光催化体系CoZnAl-LDH/RGO/g-C3N4，以CoZnAl-LDH和g-C3N4作为半导体催化剂，RGO作为电子传输中介提供电荷转移高速通道。在光辐照下，CoZnAl-LDH和g-C3N4均被激发产生电子和空穴。通过RGO的传导，CoZnAl-LDH的CB上的电子转移到g-C3N4的VB，最后与g-C3N4的VB上的光生空穴结合，从而有效地增强了光生载流子的分离，同时电子和空穴在g-C3N4的CB和CoZnAl-LDH的VB上积累，提高了各自的氧化性和还原性。此外，CoZnAl-LDH/RGO/g-C3N4的刺状表面结构增加了比表面积，提供了更多的反应位点。与纯相CoZnAl-LDH和g-C3N4相比，Z模型CoZnAl-LDH/RGO/g-C3N4体系光催化效率得到显著提高，CO产率达到19.39μmolg-1，其选择性超过96％。. 通过两步原位溶剂热化学还原方法成功地在CoAl LDHs上原位生长出了均匀分布的非晶态MoSx纳米片，MoSx/CoAl-LDHs材料OER催化性能增强的机理可归纳如下：（1）非晶态MoSx的丰富缺陷位点作为促进OER过程的催化活性位点；（2）MoSx和CoAl LDHs之间的异质结促进了电子从MoSx传递到CoAl LDHs，形成相对较低的钴离子成为氧化态，有助于Co-O键的断裂和O2分子的释放；（3）原位生长方法有效地产生了均匀分布的MoSx，并与CoAl-LDHs材料紧密接触，加速了电子转移。. 本项目深入研究了CoAl-LDHs材料的光催化反应机理和影响因素，对设计新型高效光催化材料具有重要的借鉴意义。