金属态低维无机固体在光催化制氢中的增强机制

Design and preparation of the metallic compounds "grafting" photocatalytic system by simple and practical synthesis methods have very important scientific significance and application prospects. In our preliminary experiment，metallic molybdenum compounds significantly enhanced the efficiency of photocatalytic H2 evolution over ZnxCd1-xS solid solution. Metallic compounds may be loaded evenly on the surface of the photocatalyst to enhance photocatalytic H2 evolution in order to control the synthesis of photocatalysis - electrocatalysis system. The compostion and structure of "grafting" photocatalytic system can be controlled by varying the metallic low dimensional inorganic solids and the synthetic routes. The mechanism of enhancing photocatalytic activity will be systematic studied, the underlying connectivity between photocatalysis and electrocatalysis also will be illustrated, and then novel and high efficient photocatalystic hydrogen production nanomaterials would be obtained. Furthermore, the regulatory role of metallic compounds’ types, structures and loading amounts will also be studied in details, and then the "grafting" forming mechanism will be concluded. We will explore the potential relationships between photocatalysis - electrocatalysis from the viewpoint of electrochemistry by theory simulation, and sum up its basic principles. These researchs will provide theoretical guide for design improved synthetic strategies for the preparation other new function-oriented catalysts.

通过简单实用易操作的合成途径，合理设计并制备出金属态化合物“嫁接”的光催化体系具有非常重要的科学意义和应用前景。申请人前期研究发现，金属态钼化物能有效增强ZnxCd1-xS固溶体光解水制氢性能。因此，该项目拟借助金属态低维磷化物（氮化物）均匀“嫁接”负载在光催化剂表面，实现光催化-电催化体系的可控合成。系统研究金属态化合物提高光催化体系制氢活性的机理，阐明电催化和光催化的内在关联性，理清金属态低维电催化剂的作用机制，获得新型高效的光催化制氢纳米材料。研究金属态化合物的种类、结构、负载量等对光电催化实验性能的调控作用，总结低维无机固体负载到可见光驱动光催化体系的“嫁接”生成机理，通过理论模拟，从电化学的角度探索电催化和光催化的内在联系，总结出普遍规律，为功能导向的新型催化剂的设计和合成提供理论依据和实验方法。

将过渡金属体系电催化剂作为助催化剂负载在光催化剂表面合成优异的可见光光催化制氢异质结材料，有利于加速光生电子-空穴对的分离，降低其复合机率实现高效光催化制氢。首先，不使用有机溶剂溶液一步水热合成Cu3P纳米片，Z机制的Cu3P/TiO2异质结实现高效的光催化制氢效率。利用XPS光谱和UV-Vis光谱分析Cu3P和TiO2表面价态分布和能带结构，借助PL光谱、光电流和交流阻抗分析Cu3P和Cu3P/TiO2的产氢机理。实验结果表明Cu3P作为助催化剂能有效抑制光生电子空穴对的再复合和增强TiO2的活性表面积，从而增强TiO2的光催化活性。其次，将具有优异电催化活性的Co2P作为助催化剂对TiO2进行修饰。Co2P(3 wt%)/TiO2产氢率(409.5 μmol h-1g-1)是TiO2的17倍(23.6 μmol h-1g-1)。结果表明，Co2P的独特性质能有效增强光生电荷对的空间分离效率，使TiO2的光催化析氢性能得到了很好的提高。以上两项结果表明采用简单易行的方法合成磷化物作为助催化剂是合理的，为制备廉价、地球含量丰富的磷化物提供设计思路。.再次，采用一种简单的静电自组装的方法合成了Fe3N/BiVO4纳米复合材料。在可见光照射下，9 wt% Fe3N/BiVO4纳米复合材料的平均产氢效率达到1420.7 μmol h-1 g-1，约为纯BiVO4的4倍。Fe3N纳米颗粒作为助催化剂，可以大大提高电荷载体的分离效率，从而显著提高材料的光催化性能，光致发光、瞬态光电流响应和电化学阻抗谱也证明了这一结论。我们认为Fe3N纳米颗粒负载在了BiVO4的表面，形成了Z-scheme异质结构。最后，通过煅烧法实现了Ni3FeN和g-C3N4之间构建Z-scheme异质结构，在可见光照射下，改进后的Ni3FeN/g-C3N4异质结材料具有较高的光催化活性。其中，5 wt% Ni3FeN/g-C3N4复合材料的平均产氢速率达到528.7 μmol h-1 g-1，其原因可能是Ni3FeN和g-C3N4之间形成了异质结，促进了光生e-/h+的分离。另外，通过光致发光、瞬态光电流响应和电化学阻抗谱证明了Ni3FeN/g-C3N4异质结提高了光生载流子的分离效率。同时结果也表明，双金属氮化物作为助催化剂，更有利于提高光生e-/h+的分离速率，增强光催化剂的催化活性。