离子热控制合成新型石墨相氮化碳及其光催化产氢构效关系研究

Graphite carbon nitride as a novel polymer semiconductor material is of importance in the field of new energy photocatalysis. Carbon nitride is usual prepared through high-temperature thermal polymerization process which limits the optimization and modification of its structure. Based on our previous research conclusions that carbon nitride material with visible-light photocatalytic activity for hydrogen evolution could be prepared through one-pot method at low temperature in liquid media. This project intends to synthesize new carbon nitride material performed high hydrogen evolution activity using room temperature ionic liquids as medium under relatively mild conditions, while achieving optimized molecular structure and controlled morphology at the same time. We will carry out systematically study of the effects of different reaction conditions on the composition, morphology, structure etc. of the catalysts. The nature of molecular self-assembly polymerization process will be discussed, and a polymerization mechanism model will be proposed. The energy band structure, surface states and photoelectric response of the catalyst is determined by detailed characterization. Combined with the photocatalytic performance on hydrogen evolution under visible light irradiation of the catalyst, the relationship between the structure and photocatalytic properties of catalysts will be clarified. The main factors that affect the photocatalytic activity and stability of the catalysts will be determined. Thus, carbon nitride with high photocatalytic hydrogen evolution activity will be developed through new ionothermal route at low temperature. This project enriches research methods to synthesize and modify polymer semiconductors. Therefore, it has important implications to develop the application of non-metallic materials in the field of photocatalysis.

石墨相氮化碳作为新型的聚合物半导体材料，在新能源光催化领域具有重要研究价值。针对高温热聚合的制备方法限制了对其进行结构优化改性的难题，依据低温液相法可一步制备出具有可见光催化产氢催化活性氮化碳材料的前期研究结论，本项目拟选用室温离子液体为反应介质，较温和条件下控制合成新型高效产氢氮化碳材料，同时实现分子结构优化及形貌控制。系统考察制备条件对材料组成、形貌、结构等的影响，揭示反应过程中分子聚合自组装的本质过程，提出聚合机理模型。对催化剂的能带结构、表面态、光电响应等性质进行系统表征分析，结合催化剂可见光催化分解水产氢性能评价，阐明催化剂的结构与光催化性能之间的关系，确定影响其光催化活性及稳定性的主要因素，提出低温离子热合成具有较高光催化产氢活性氮化碳材料的新途径。本项目丰富了聚合物半导体的合成及改性研究方法，对发展非金属材料在光催化领域的研究及应用具有重要意义。

以聚合物半导体为光催化剂，通过分解水制氢是一条理想的新能源获取途径。石墨相氮化碳(CN)作为新兴光催化剂，通过结构改性提高其光催化效率对推动太阳能制氢具有重要的实践意义。离子热合成可在宽温度范围内实现“液相”介质中分子组装调控，对CN微结构调节优化和形貌控制，提高CN的聚合度和结构有序度，来提高其光解水产氢效率。. 本项目研究包含以离子液体为掺杂源制备非金属掺杂CN和熔盐离子热制备高聚合度掺杂型CN以促进其产氢性能。（1）以四氟硼酸盐和碘化离子液为掺杂源直接聚合得到B/F共掺杂CN和C-I共掺杂CN，后热处理得到掺杂型多孔纳米片。不同电负性B、F分别掺杂在CN骨架内部和表面，电荷离域性和共轭芳环聚合结构的优化共同促进了光生电荷的分离和传输。C-I共掺杂使得光诱导电子密度增加，负向移动的导带位置提供了更强的热力学还原动力，产物产氢速率均提高9倍左右。对不同掺杂途径对产物性能的影响进行进一步研究发现，原位掺杂更有利于杂原子在分子骨架中的分布，表面-骨架共修饰更有利于提高催化剂的光电子产生、分离和转移效率，产氢活性比仅表面修饰提高5倍。（2）熔盐离子热处理可显著提高CN的聚合度，500 oC为最佳后热处理温度，可显著扩展催化剂的可见光吸收，增大孔隙率和比表面积。将C-I共掺杂CN进行熔盐离子热后热处理，共轭结构的重构减少了缺陷态，同时聚合结晶度的提高优化了长程有序结构。离子掺杂和离子热后热处理共同作用能够更有效改善催化剂结构提高制氢性能，比纯后热处理CN提高了5倍。在惰性气体氮气中优化后热处理过程，改善了介孔均一性，降低了缺陷，增强了面内聚合单元的共轭性，进一步扩展了可见光的吸收，同时增强了电荷传输和转移效率，大幅度提高了可见光解水制氢活性，且保持长时间的活性稳定性。本项目为进一步通过微结构调控优化聚合物半导体光催化性能提供了一定的实验指导。