Carbon molecular sieve membranes (CM) are typically synthesized through pyrolysis of polymers, and are suitable for gas separation under high pressure conditions due to their high selectivity and mechanical strength. There is a lack of knowledge of the mechanisms of membrane formation during pyrolysis, which would be of fundamental importance to a better understanding and precise control of the process. In this work, we investigate the process of CM formation upon pyrolysis of polyetherimide. A carbon membrane was synthesized on a ceramic support and characterized by different techniques, demonstrating the conversion of the polymeric precursor into a porous and predominantly amorphous carbon structure, containing embedded graphitic domains. The membrane showed effective molecular sieve performance as demonstrated in gas permeation tests. Reactive molecular dynamics simulations were carried out to explore the mechanisms of the polymer→CM transformation at the atomistic level. The simulations show that the continuous reaction among the reactive radicals formed upon polymer pyrolysis along with atomic rearrangements spontaneously led to the formation of a nanoporous amorphous carbon matrix, containing interconnected graphitic domains throughout the structure, as observed in the experiments. These results are expected to be of great help to the development of techniques for controllable synthesis of CMs.

中文翻译：

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聚醚酰亚胺热解过程中碳分子筛膜形成的实验和计算分析

碳分子筛膜（CM）通常是通过聚合物热解合成的，由于它们的高选择性和机械强度，适合在高压条件下进行气体分离。缺乏热解过程中膜形成机理的知识，这对于更好地理解和精确控制过程至关重要。在这项工作中，我们研究了聚醚酰亚胺热解过程中CM的形成过程。碳膜是在陶瓷载体上合成的，并通过不同的技术进行了表征，证明了聚合物前体已转变为包含嵌入式石墨域的多孔且主要为非晶态的碳结构。该膜表现出有效的分子筛性能，如气体渗透测试所示。进行了反应性分子动力学模拟，以探索在原子水平上聚合物→CM转变的机理。模拟表明，如在实验中观察到的，在聚合物热解后形成的反应性自由基之间的连续反应以及原子重排自发地导致了纳米多孔无定形碳基质的形成，该基质在整个结构中均包含相互连接的石墨域。预期这些结果对可控合成CM的技术的发展将有很大的帮助。模拟表明，如在实验中观察到的，在聚合物热解后形成的反应性自由基之间的连续反应以及原子重排自发地导致了纳米多孔无定形碳基质的形成，该基质在整个结构中均包含相互连接的石墨域。预期这些结果对可控合成CM的技术的发展将有很大的帮助。模拟表明，如在实验中观察到的，在聚合物热解后形成的反应性自由基之间的连续反应以及原子重排自发地导致了纳米多孔无定形碳基质的形成，该基质在整个结构中均包含相互连接的石墨域。预期这些结果对可控合成CM的技术的发展将有很大的帮助。