高结晶氮化碳的熔盐法合成及其化学结构和光催化活性增强机制的核磁共振研究

Polymeric carbon nitride has received wide attention in photocatalysis owing to its low-cost and metal-free properties. However, the intrinsic drawback of low crystallinity of carbon nitride greatly reduces the charge separation efficiency during photocatalytic reaction and also makes its chemical structure analysis difficult. Based on previous research and preliminary exploration, the proposed project aims to develop a highly crystalline carbon nitride photocatalyst that is synthesized via a novel molten salt method coupled with thermal polycondensation route. The engineering of crystallinity and structure of carbon nitride will be attempted through facile tailoring of the condensation conditions in a molten salt medium, which results in improved photocatalytic activity in hydrogen evolution from water splitting and environmental pollutant removal. By using carbon nitride synthesized from 13C- and 15N-labeled precursors, the advanced NMR techniques with enhanced sensitivity will be employed to elucidate the chemical structure of carbon nitride at a molecular level. Combined with theoretical calculations, electron spin resonance, and other characterization methods, the various in situ and ex situ NMR techniques will be developed to investigate the surface adsorbed species on the photocatalyst, the reactive intermediate species, as well as the products during the photocatalytic reaction to give deep insight into the reaction mechanism. The influences of molten salt conditions on the structure, crystallinity, charge separation, and photocatalytic activity of carbon nitride will be clarified in this study, which would offer important references for developing highly efficient carbon nitride photocatalytic system.

氮化碳作为一种廉价的、不含金属组分的光催化剂受到研究者的广泛关注。然而，氮化碳固有的低结晶性不仅严重影响光生电荷的有效分离，而且为化学结构解析带来诸多挑战。基于以往研究积累和前期探索，本项目以可控合成高结晶氮化碳为出发点，基于离子热熔盐-热聚合法，通过系统调变熔盐合成条件原位调控氮化碳的结构和结晶性，从而提高其可见光分解水产氢和环境污染物消除性能；采用先进的NMR技术为研究手段，利用13C、15N同位素标记提高NMR灵敏度，建立和发展氮化碳光催化体系的原位和非原位NMR研究方法，并结合理论计算、ESR和其它实验技术，从分子水平上全面解析氮化碳的化学结构，并对光催化剂表面吸附物种、反应中间物种和反应产物进行分析辨认，阐明熔盐合成条件对氮化碳结构、结晶性、光生电荷分离以及光催化活性的影响规律，促进多角度深刻认识和理解其光催化反应机理和增强机制，为开发、设计高效的氮化碳光催化体系提供新的思路。

氮化碳作为一种廉价的、不含金属组分的光催化剂受到研究者的广泛关注。然而，氮化碳固有的低结晶性严重影响了光生电荷的有效分离，限制了其光催化应用。针对以上问题，本项目围绕高结晶氮化碳的可控合成和光催化活性增强机制进行研究。我们利用离子热熔盐热聚合法，通过系统调变熔盐合成条件如前驱体、合成温度和熔盐/前驱体摩尔比等，获得了高结晶的氮化碳，并灵活调控了氮化碳的能带结构，显著提高了氮化碳的可见光分解水产氢和Cr(VI)/有机污染物的协同消除性能。通过NMR、ESR、时间分辨光谱和光电化学等表征技术，揭示了氮化碳的结构、结晶性和光生电荷分离、光催化性能之间的构效关系。此外，在具有高结晶性和较高光催化活性的基础上，我们进一步对氮化碳进行了缺陷工程调控，构建了一种同时提升体相与表面光生载流子分离效率的体系，分别通过两种方法即离子热熔盐-碱处理两步法和超分子聚合物预组装的熔盐缩聚耦合快速热处理法，在高结晶氮化碳的表面引入了丰富的缺陷并调控缺陷的种类和含量，进而协同提高了氮化碳的载流子分离效率和可见光光催化产氢活性，并利用NMR等多种手段深入研究了光催化活性增强机制。项目研究结果为高效氮化碳光催化体系的开发设计提供了新的研究思路和理论基础。