Holst James R, Gillan Edward G
Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, USA.
J Am Chem Soc. 2008 Jun 11;130(23):7373-9. doi: 10.1021/ja709992s. Epub 2008 May 20.
Nitrogen-rich carbon nitride (CN x , x >/= 1) network materials have been produced as disordered structures by a variety of precursor-based methods, many that involve solid-state thermolysis at or above 500 degrees C. One popular precursor building block is the triazine unit (C 3N 3), and most postulated amorphous CN x network structures are based on cross-linked triazine units. Since hydrogen is most often observed in the product, these materials are usually more appropriately described as CN x H y materials. Results from recent carbon nitride studies using larger conjugated heptazine (C 6N 7) precursors and from rigorous structural investigations of triazine to heptazine thermal conversion processes have prompted a reexamination of likely local structures present in amorphous carbon nitride networks formed by triazine thermolysis reactions. In the present study, the formation and local structure of a CN x H y material formed via the rapid and exothermic decomposition of a reactive triazine precursor, C 3N 3(NHCl) 3, was examined by byproduct gas mass spectrometry, NMR and IR spectroscopy, base hydrolysis, and crystallographic analysis. The combined results clearly indicate that the moderate-temperature ( approximately 400 degrees C) self-sustaining decomposition of trichloromelamine results in ring fragmentation and reorganization into a CN x H y product that contains predominantly larger heptazine-like structural building blocks. These results may have applicability to many other disordered carbon nitride materials that are formed via triazine thermolysis. It also provides clearer and more accurate structural guidance in the use of these carbon nitrides as photoactive materials or coordination supports for metal and nonmetal species.
富含氮的碳氮化物（CNx，x≥1）网络材料已通过多种基于前驱体的方法制备成无序结构，其中许多方法涉及在500℃或更高温度下的固态热解。一种常见的前驱体结构单元是三嗪单元（C3N3），大多数假定的非晶态CNx网络结构基于交联的三嗪单元。由于在产物中最常观察到氢，这些材料通常更恰当地描述为CNxHy材料。最近使用更大的共轭庚嗪（C6N7）前驱体进行的碳氮化物研究结果以及对三嗪到庚嗪热转化过程的严格结构研究，促使人们重新审视由三嗪热解反应形成的非晶态碳氮化物网络中可能存在的局部结构。在本研究中，通过副产物气体质谱、核磁共振和红外光谱、碱水解以及晶体学分析，研究了由活性三嗪前驱体C3N3(NHCl)3快速放热分解形成的CNxHy材料的形成和局部结构。综合结果清楚地表明，三聚氯氰在中等温度（约400℃）下的自持分解导致环断裂并重新组织成主要包含较大庚嗪类结构单元的CNxHy产物。这些结果可能适用于许多其他通过三嗪热解形成的无序碳氮化物材料。它还为将这些碳氮化物用作光活性材料或金属和非金属物种的配位载体提供了更清晰、更准确的结构指导。
