Mi Baoxia, Zheng Sunxiang, Tu Qingsong
Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA.
Faraday Discuss. 2018 Sep 28;209(0):329-340. doi: 10.1039/c8fd00026c.
Layer-stacked graphene oxide (GO) membranes, in which unique two-dimensional (2D) water channels are formed between two neighboring GO nanosheets, have demonstrated great potential for aqueous phase separation. Subjects of crucial importance are to fundamentally understand the interlayer spacing (i.e. channel height) of GO membranes in an aqueous environment, elucidate the mechanisms for water transport within such 2D channels, and precisely control the interlayer spacing to tune the membrane separation capability for targeted applications. In this investigation, we used an integrated quartz crystal mass balance (QCM-D) and ellipsometry to experimentally monitor the interlayer spacing of GO, reduced GO and crosslinked GO in aqueous solution and found that crosslinking can effectively prevent GO from swelling and precisely control the interlayer spacing. We then used molecular dynamics simulations to study the mass transport inside the 2D channels and proved that the chemical functional groups on the GO plane dramatically slow down water transport in the channels. Our findings on GO structure and water transport provide a necessary basis for further tailoring and optimizing the design and fabrication of GO membranes in various separation applications.
层状堆叠的氧化石墨烯（GO）膜在相邻的GO纳米片之间形成了独特的二维（2D）水通道，已展示出在水相分离方面的巨大潜力。至关重要的课题是从根本上了解GO膜在水环境中的层间距（即通道高度），阐明水在这种二维通道内传输的机制，并精确控制层间距以调节膜的分离能力，用于特定应用。在本研究中，我们使用集成石英晶体微天平（QCM-D）和椭偏仪实验监测了水溶液中GO、还原型GO和交联型GO的层间距，发现交联可以有效防止GO膨胀并精确控制层间距。然后，我们使用分子动力学模拟研究二维通道内的质量传输，并证明GO平面上的化学官能团显著减缓了通道内的水传输。我们关于GO结构和水传输的研究结果为进一步定制和优化各种分离应用中GO膜的设计与制造提供了必要依据。
