基于g-C3N4空间分离双助产氢光催化剂的构建及其作用机制研究

Photocatalytic H2 evolution from water utilizing solar energy is a promising strategy to solve the problems of declining fossil fuels and environmental pollution from fossil fuels combustion fundamentally, which has drawn much attention by domestic and foreign scholars. In this field, developing an efficient, stable and low-cost photocatalyst is one of the hot topics. Carbon nitride (g-C3N4) is a stable and low-cost photocatalytic material, but the photogenerated electron-hole pairs are easily recombined that greatly limits the photocatalytic H2 evolution efficiency. As a result, a new ideal is proposed to accelerate the separation of photogenerated charges of g-C3N4, in which spatial separation of noble-metal-free metal phosphide (reduction cocatalyst) and manganese or cobalt oxide (oxidation cocatalyst) will be loaded on the outer and the inner surfaces of g-C3N4 porous hollow sphere, respectively. In this case, the photogenerated electrons and holes of g-C3N4 will transfer to the outer surface and inner surface, respectively, leading to a significantly increase of electron-hole pairs separation. On the basis of this, the synergistic effect and the structure-activity relationship will be investigated by means of changing the loading mode of cocatalyst on the surface of g-C3N4 and controlling the structure of g-C3N4 and metal phosphides. In addition, the photocatalytic H2 stability will be discussed and analyzed as well through long-time and time-cycle experiments. This proposal will provide an important scientific support for the rapid development of photocatalytic H2 evolution from water.

利用太阳能光催化分解水产氢是从根本上解决化石能源日渐减少和环境污染问题的理想途径，受到国内外学者广泛关注，开发高效、稳定的廉价光催化剂是该领域研究热点之一。g-C3N4是一种结构稳定的廉价光催化材料，但光生电子-空穴对复合严重，极大地限制了光催化产氢效率。为此本课题创新性地提出空间分离负载非贵金属还原和氧化助催化剂加快g-C3N4光生电荷分离的新思路，即以金属磷化物为还原助催化剂，以锰或钴氧化物为氧化助催化剂，将其分别负载到g-C3N4孔状空心球的外表面和内表面，在其共同诱导下，g-C3N4光生电子和空穴分别加速转移至外表面和内表面，显著提高了电子-空穴对的分离。拟通过改变助催化剂在g-C3N4表面的负载方式及调控g-C3N4和金属磷化物的结构，开展协同效应和构效关系研究。在此基础上，通过长时间产氢和多次循环实验，拟开展光催化产氢稳定性研究。本课题的批准实施将为推动光催化分解水产氢的快速发展提供重要的科学支撑。

光催化分解水产氢是从根本上解决化石能源短缺和环境污染问题的理想途径之一，受到了广泛关注，开发高效、稳定的廉价光催化剂是该领域研究难点之一。g-C3N4是一种结构稳定的廉价光催化材料，但光生电子-空穴对复合严重，极大地限制了光催化产氢效率。针对这一瓶颈问题，本项目创新性地开发了在g-C3N4纳米片表面定点沉积过渡金属基氧化和还原助催化剂来构筑空间分离双助结构的新策略，获得了电荷分离迁移效率显著提升的非贵金属基g-C3N4/过渡金属氧化物/过渡金属硫化物产氢光催化剂。通过对g-C3N4表面助催化剂负载方式对产氢性能影响的研究，揭示出氧化物氧化助催化剂和硫化物还原助催化剂两者间的协同效应；通过对g-C3N4片层厚度和氧化物结晶度的调控，建立了g-C3N4片层厚度和氧化物结晶度，g-C3N4/过渡金属氧化物/过渡金属硫化物的结构及其光催化产氢性能三者间的构效关系；通过对光催化产氢稳定性研究，确定了g-C3N4/过渡金属氧化物/过渡金属硫化物具有高光催化产氢稳定性的原因。在此基础上，以超薄g-C3N4纳米片（片层厚度为2 nm左右）为光催化剂载体，在其表面引入结晶Co3O4和无定型MoS2纳米点，获得的g-C3N4/Co3O4-1.9/MoS2-0.9展现出最高的光催化产氢性能，在可见光激发下其产氢速率分别达到105 μmol h-1，约是g-C3N4的885倍，高于目前报道的绝大多数硫化物助催化剂修饰g-C3N4的光催化产氢活性，且在循环实验和不同水介质中保持优异的稳定性。这些研究结果将为高性能、低成本的产氢光催化剂的构建奠定了理论基础和方法指导。