Rodríguez Antonio M, Muñoz-García Ana B, Crescenzi Orlando, Vázquez Ester, Pavone Michele
Dipartimento di Scienze Chimiche, Università di Napoli Federico II, Comp. Univ. Monte Sant'Angelo Via Cintia 21, 80126 Naples, Italy.
Departamento de Química Orgánica, Facultad de Ciencias y Tecnologías Químicas-IRICA, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
Phys Chem Chem Phys. 2016 Aug 10;18(32):22203-9. doi: 10.1039/c6cp04213a.
In recent experiments, melamine (1,3,5-triazine-2,4,6-triamine) has been proposed as an effective exfoliating agent to obtain high quality graphene from graphite. After washing out the melamine in excess, small amounts (ppm) are still needed to stabilize the dispersion of graphene flakes in aqueous media. To understand the origin of this behaviour, we investigated the melamine-graphene-water system and the fundamental interactions that determine its structure and energetics. To disentangle the subtle interplay of hydrogen-bonding and dispersive forces we used state-of-the-art ab initio calculations based on density functional theory. First, we focused on the case of water molecules interacting with melamine-graphene assemblies at different melamine coverages. We found that water-melamine interactions provide the driving force for washing off the melamine from graphene. Then, we addressed the interaction of single and double layers of water molecules with the graphene surface in the presence of an adsorbed melamine molecule. We found that this melamine acts as a non-covalent anchor for keeping a number of water molecules conveniently close to the graphene surface, thus helping its stabilization in aqueous media. Our analysis helps understanding how competing weak forces can lead to a stable graphene water suspension thanks to small amounts of adsorbed melamine. From our results, we derive simple indications on how the water-graphene interfacial properties can be tuned via non-covalent adsorption of small functional molecules with H-bond donor/acceptor groups. These new hints can be helpful to prepare stable graphene dispersions in water and so to unlock graphene potential in aqueous environments.
在最近的实验中，三聚氰胺（1,3,5-三嗪-2,4,6-三胺）被提议作为一种有效的剥离剂，用于从石墨中获得高质量的石墨烯。在洗去过量的三聚氰胺后，仍需要少量（ppm级）三聚氰胺来稳定石墨烯薄片在水性介质中的分散。为了理解这种行为的起源，我们研究了三聚氰胺-石墨烯-水体系以及决定其结构和能量的基本相互作用。为了厘清氢键和色散力之间微妙的相互作用，我们使用了基于密度泛函理论的最先进的从头算计算方法。首先，我们聚焦于水分子在不同三聚氰胺覆盖度下与三聚氰胺-石墨烯组装体相互作用的情况。我们发现水分子与三聚氰胺之间的相互作用为从石墨烯上洗去三聚氰胺提供了驱动力。然后，我们研究了在存在吸附的三聚氰胺分子的情况下，单层和双层水分子与石墨烯表面的相互作用。我们发现这种三聚氰胺起到了非共价锚的作用，使一些水分子方便地靠近石墨烯表面，从而有助于其在水性介质中的稳定。我们的分析有助于理解由于少量吸附的三聚氰胺，相互竞争的弱力如何导致稳定的石墨烯水悬浮液。从我们的结果中，我们得出了关于如何通过具有氢键供体/受体基团的小功能分子的非共价吸附来调节水-石墨烯界面性质的简单指示。这些新线索有助于制备稳定的石墨烯水悬浮液，从而释放石墨烯在水性环境中的潜力。
