羟基石墨烯：氢键网络的动力学
Hydroxygraphene: dynamics of hydrogen bond networks
摘要：
采用分子动力学方法，模拟了羟基官能化过程中石墨烯表面氢键网络的动力学过程。它表明，两个OH基团形成一个积极的更有利的结构，当它们被共价连接在一侧的片形成相对顶点的一个六边形的价键的片的碳原子。OH基团与位于价键六边形相对顶点的碳原子的连接导致羟基石墨烯C $_4$（OH）的出现。在这种位于平坦基底上的片中，在其外表面上连接的氧原子形成六方晶格，并且羟基由于它们的转动可以以各种方式形成氢键链。从两侧对片进行改性导致在石墨烯片的两侧上形成具有HB网络的羟基石墨烯C $_2$（OH）。这些片的动力学模拟表明，它们在低温下的热容量$T<T_0$单调增加，当温度上升，达到最大值在$T=T_0$，然后单调下降。初始生长是由氢键晶格中的取向缺陷的积累引起的，而在$T>T_0$处的减少是由晶格的“熔化”解释的。对于连接到纳米颗粒外侧的一条OH基团链，熔融温度为$T_0=500$ K，而对于一侧改性的石墨烯片C4（OH）为$T_0=260$ K，对于两侧改性的石墨烯片C为$_2$（OH）为$T_0=485$ K。
英文摘要：
Using the molecular dynamics method, dynamics of hydrogen bond (HB) networks emerging on the surface of a graphene sheet during its functionalization with hydroxyl groups OH are simulated. It is demonstrated that two OH groups form an energetically more advantageous structure when they are covalently attached on one side of the sheet to carbon atoms forming opposite vertices of one hexagon of valence bonds of the sheet. Attaching of OH groups to carbon atoms located at the opposite vertices of hexagons of valence bonds leads to the emergence of hydroxygraphene C$_4$(OH). In such sheet lying on a flat substrate, attached oxygen atoms on its outer surface form a hexagonal lattice, and hydroxyl groups due to their turns can in various ways form chains of hydrogen bonds. The modification of the sheet from two sides results in forming of hydroxygraphene C$_2$(OH) with HB networks on both sides of the graphene sheet. Simulation of the dynamics of these sheets shows that their heat capacity at low temperatures $T<T_0$ increases monotonously when the temperature rises, reaches its maximum at $T=T_0$ and then decreases monotonically. The initial growth is caused by the accumulation of orientational defects in the lattice of hydrogen bonds whereas the decrease at $T>T_0$ is explained by the "melting" of the lattice. For one chain of OH groups connected to the outer side of a nanoribbon the melting temperature is $T_0=500$K, while for a graphene sheet C4(OH) modified on one side $T_0=260$K, and for a graphene sheet C$_2$(OH) modified on both sides $T_0=485$K.
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