Saraswat Vivek, Jacobberger Robert M, Ostrander Joshua S, Hummell Courtney L, Way Austin J, Wang Jialiang, Zanni Martin T, Arnold Michael S
Department of Materials Science & Engineering , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States.
Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States.
ACS Nano. 2018 Aug 28;12(8):7855-7865. doi: 10.1021/acsnano.8b02015. Epub 2018 Jul 18.
Laminates made of graphene oxide nanosheets have been shown to exhibit high water permeance and salt rejection and, therefore, have generated immense interest from the scientific community due to their potential in separation applications. However, there is no clear consensus on the water-transport pathways through such laminates. In this study, we synthesized chemically identical graphene oxide nanosheets with 2 orders of magnitude difference in lateral sizes and measured water permeance through laminates of different thicknesses fabricated by pressure-assisted deposition of these nanosheets. Our results reveal that water permeance through these laminates is nearly the same despite such massive difference in lateral sheet size. Furthermore, we simulated fluid flow through laminates using an interconnected nanochannel network model for comparison with experiments. The simulations in combination with the experimental data show that it is unlikely that the dominant fluid transport pathway is a circuitous, lateral pathway around individual sheets, as has been proposed in some studies. Rather, nonideal factors including trans-sheet flow through pinhole defects in sheet interiors and/or flow-through regions arising from imperfect stacking in the laminates can significantly affect the fluid transport pathways. The presence of such nonidealities is also supported by thickness- and time-dependent measurements of permeance and by infrared spectroscopy, which indicates that water predominantly adopts a bulk-like structure in the laminates. These analyses are significant steps toward understanding water transport through graphene oxide laminates and provide further insight toward the structure of water inside these materials, which could have immense potential in next-generation separation applications.
由氧化石墨烯纳米片制成的层压板已被证明具有高透水性和拒盐性，因此，由于其在分离应用中的潜力，引起了科学界的极大兴趣。然而，对于通过此类层压板的水传输途径尚无明确共识。在本研究中，我们合成了横向尺寸相差2个数量级的化学性质相同的氧化石墨烯纳米片，并测量了通过压力辅助沉积这些纳米片制成的不同厚度层压板的水渗透率。我们的结果表明，尽管横向片尺寸存在如此巨大的差异，但通过这些层压板的水渗透率几乎相同。此外，我们使用相互连接的纳米通道网络模型模拟了层压板中的流体流动，以便与实验进行比较。模拟结果与实验数据相结合表明，主导流体传输途径不太可能是如一些研究中所提出的围绕单个片的迂回横向途径。相反，包括通过片内部针孔缺陷的跨片流动和/或层压板中不完全堆叠产生的流通区域等非理想因素会显著影响流体传输途径。渗透率的厚度和时间依赖性测量以及红外光谱也支持了这种非理想性的存在，红外光谱表明水在层压板中主要采用类似本体的结构。这些分析是理解水通过氧化石墨烯层压板传输的重要步骤，并为深入了解这些材料内部的水结构提供了进一步的见解，这在下一代分离应用中可能具有巨大潜力。
