The role of surface ionisation in the hydration-induced swelling of graphene oxide membranes
The role of surface ionisation in the hydration-induced swelling of graphene oxide membranes
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DOI：
10.1016/j.memsci.2022.120489
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发表时间：
2022-04-08
影响因子：
9.5
通讯作者：
Carbone, Paola
中科院分区：
文献类型：
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作者：
Bin Shaharudin, Mohd Rafie;Williams, Christopher D.;Carbone, Paola
氧化石墨烯（GO）膜是亲水性材料，其在潮湿环境中或当与液态水接触时在水存在下溶胀，并且溶胀的幅度和机制取决于GO薄片表面上存在的官能团的电离程度。在这项工作中，使用大正则Monte Carlo和分子动力学模拟，我们调查的效果，表面电荷，电离过程中产生的，在各种湿度条件下的膜中吸附的水的量和膨胀的膜与液态水接触。使用了表面电荷从-63 mC/m2增加到-177 mC/m2的三种模型和中性模型。我们表明，通过掺入电离的官能团，吸附的开始被转移到一个较低的化学势和内部的膜压力增加，由于石墨烯片之间的排斥相互作用。我们认为，对于一个相当有序的膜，如在这里建模的表面电荷为-120 mC/m2的上限膜脱层之前。我们的模拟还表明，在通道中的离子的存在下，由于屏蔽效应，减少了溶胀，但也增加了水的吸附量时，膜浸没在液态水中。相反，在低化学势下，吸附的水量由电离基团的数量决定。荷电模型能够定性地再现实验数据，展示了在GO模型中包括表面电荷以预测水化和溶胀机制的重要性。这些研究结果是至关重要的支撑GO膜在模拟和实验研究的水分离的未来发展，因为水化诱导的溶胀是众所周知的，导致显着恶化的性能。
Graphene oxide (GO) membranes are hydrophilic materials that swell in the presence of water either in a humid environment or when in contact with liquid water and the magnitude and mechanism of the swelling is dependent on the degree of ionisation of the functional groups present on the surface of the GO flakes. In this work, using Grand Canonical Monte Carlo and Molecular Dynamics simulations we investigate the effect that the surface charge, resulting from the ionisation process, has on both the amount of water adsorbed in the membranes at various humidity conditions and the swelling of the membranes in contact with liquid water. Three models with increasing surface charge from -63 mC/m2 to -177 mC/m2 and a neutral one are used. We show that by incorporating ionised functional groups, the onset of adsorption is shifted to a lower chemical potential and the internal membrane pressure increases due to the repulsive interactions between the graphene flakes. We suggest that for a fairly ordered membrane as the ones modelled here a surface charge of -120 mC/m2 is the upper limit before membrane delaminate. Our simulations also show that the presence of ions in the channels reduced the swelling due to screening effect but also increases the amount of water adsorbed when the membrane is immersed in liquid water. At low chemical potential, instead, the amount of water adsorbed is determined by the number of ionised groups. The charged model is able to qualitatively reproduce experimental data showcasing the importance of including surface charge in GO model to predict hydration and swelling mechanism. These findings are crucial in underpinning the future development of GO membranes in simulation and experimental study for aqueous separations since hydration-induced swelling is widely known to lead to significant deterioration in performances.