Vekeman Jelle, Faginas-Lago Noelia, Lombardi Andrea, Sánchez de Merás Alfredo, García Cuesta Inmaculada, Rosi Marzio
Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Perugia, Italy.
Instituto de Ciencia Molecular, Universidad de Valencia, Valencia, Spain.
Front Chem. 2019 Jun 3;7:386. doi: 10.3389/fchem.2019.00386. eCollection 2019.
We theoretically investigate graphene layers, proposing them as membranes of subnanometer size suitable for CH/N separation and gas uptake. The observed potential energy surfaces, representing the intermolecular interactions within the CH/N gaseous mixtures and between these and the graphene layers, have been formulated by adopting the so-called Improved Lennard-Jones (ILJ) potential, which is far more accurate than the traditional Lennard-Jones potential. Previously derived ILJ force fields are used to perform extensive molecular dynamics simulations on graphene's ability to separate and adsorb the CH/N mixture. Furthermore, the intramolecular interactions within graphene were explicitly considered since they are responsible for its flexibility and the consequent out-of-plane movements of the constituting carbon atoms. The effects on the adsorption capacity of graphene caused by introducing its flexibility in the simulations are assessed via comparison of different intramolecular force fields giving account of flexibility against a simplified less realistic model that considers graphene to be rigid. The accuracy of the potentials guarantees a quantitative description of the interactions and trustable results for the dynamics, as long as the appropriate set of intramolecular and intermolecular force fields is chosen. In particular it is shown that only if the flexibility of graphene is explicitly taken into account, a simple united-atom interaction potential can provide correct predictions. Conversely, when using an atomistic model, neglecting in the simulations the intrinsic flexibility of the graphene sheet has a minor effect. From a practical point of view, the global analysis of the whole set of results proves that these nanostructures are versatile materials competitive with other carbon-based adsorbing membranes suitable to cope with CH and N adsorption.
我们从理论上研究了石墨烯层，提出将其作为适用于CH/N分离和气体吸收的亚纳米尺寸的膜。通过采用所谓的改进的 Lennard-Jones（ILJ）势来构建观察到的势能面，该势能面代表了CH/N气态混合物内部以及这些混合物与石墨烯层之间的分子间相互作用，它比传统的Lennard-Jones势精确得多。先前推导的ILJ力场被用于对石墨烯分离和吸附CH/N混合物的能力进行广泛的分子动力学模拟。此外，明确考虑了石墨烯内部的分子内相互作用，因为它们决定了石墨烯的柔韧性以及构成碳原子随之产生的面外运动。通过比较考虑柔韧性的不同分子内力场与一个简化的、不太现实的将石墨烯视为刚性的模型，评估了在模拟中引入石墨烯柔韧性对其吸附能力的影响。只要选择了合适的分子内和分子间力场集，势的准确性就能保证对相互作用进行定量描述并获得可靠的动力学结果。特别值得注意的是，结果表明只有明确考虑石墨烯的柔韧性，一个简单的联合原子相互作用势才能提供正确的预测。相反，在使用原子模型时，在模拟中忽略石墨烯片的固有柔韧性影响较小。从实际角度来看，对整个结果集的综合分析证明，这些纳米结构是多功能材料，与其他适用于处理CH和N吸附的碳基吸附膜相比具有竞争力。
