Theoretical study on Janus graphene oxide membrane for water transport
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RESEARCH ARTICLE
Theoretical study on Janus graphene oxide membrane for water transport Quan Liu1, Mingqiang Chen1, Yangyang Mao2, Gongping Liu (✉)2 1 Analytical and Testing Center, Anhui University of Science and Technology, Huainan 232001, China 2 State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing 211816, China
© Higher Education Press 2020
Abstract Graphene oxide (GO) membranes have received considerable attention owing to their outstanding water-permeation properties; however, the effect of the membrane’s microstructures (such as the distribution of oxidized and pristine regions) on the transport mechanism remains unclear. In this study, we performed molecular simulations to explore the permeation of a water–ethanol mixture using a new type of Janus GO membranes with different orientations of oxidized and pristine surfaces. The results indicate that the oxidized upper surface endows the GO membrane with considerable water-capture capability and the in-built oxidized interlayer promotes the effective vertical diffusion of water molecules. Consequently, using the optimized Janus GO membrane, infinite water selectivity and outstanding water flux (~40.9 kg⋅m–2⋅h–1) were achieved. This study contributes to explaining the role of oxidized regions in water permeation via GO membranes and suggests that Janus GO membranes could be used as potential candidates for water–ethanol separation. Keywords graphene oxide membrane, molecular dynamics simulation, water permeation, water-ethanol separation, oxidized and pristine regions
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Introduction
After Nair et al. demonstrated that graphene oxide (GO) membranes exhibit excellent water transfer properties [1], many researchers have been involved in studying their confined transport mechanism [2,3] and ultra-high water permeability [4,5]. Chen et al. reported that the water Received January 22, 2020; accepted April 27, 2020 E-mail: [email protected]
transport behavior through GO membranes was considerably affected by the thermophoretic [4] and rarefied effects [3] and that the flow rate could be tuned by varying the structural parameters of GO membranes [6]. In addition to the pore size [7,8], the interlayer distance [6,9], and the oxidized degree [10,11], the orientations of the oxidized and pristine regions in GO membranes play a vital role in the water–separation process [12], determining the number of empty spaces in the interlayer gallery and the wrinkles in GO nanosheets [13,14]. Both oxidized and pristine regions are highly interlaced in GO membranes [15]. Using molecular simulations, Willcox and Kim [16] and Ban [15] et al. demonstrated that the random locations of the oxidized and pristine zones blurred the water-transfer mechanism through GO membranes. Practically, it was found that the interlayer transport for water permeation was considered as plug flow in the pristine zone, whereas it was considered as Poiseuille flow in the oxidized zone [17]. Generally, the oxidized surface of GO mem
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