Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Molecular dynamics simulation of water-ethanol separation through monolayer graphene oxide membranes: Significant role of O/C ratio and pore size Quan Liu a , Yuanyan Wu b , Xian Wang b , Gongping Liu a , Yudan Zhu a , Yusong Tu b, ⁎ , Xiaohua Lu a , Wanqin Jin a, ⁎ a State Key Laboratory of Materials-Oriented Chemical Engineering, Jiangsu National Synergetic Innovation Center for Advanced Materials, College of Chemical Engineering, Nanjing Tech University, 5 Xinmofan Road, Nanjing 210009, China b College of Physics Science and Technology, Yangzhou University, Jiangsu 225009, China ARTICLE INFO Keywords: Graphene oxide membrane Molecular simulation Water-ethanol separation ABSTRACT Molecular dynamics (MD) simulations were employed to investigate water-ethanol separation through mono- layer graphene oxide (GO) membranes with different pore sizes and O/C ratios. The ultrahigh water flux and infinite water separation factors were achieved. The separation properties under 50/50 w/w water-ethanol mixtures reveal that higher O/C ratios favor water selectivity, and water flux is enhanced with O/C ratio and pore size. With the help of highest oxidization, water largely sorption amount governs permeation process. On the contrary, with low oxidization degree of GO membrane, water diffusion effect becomes dominant factor of permeation. We screen an optimal microstructure of GO membrane which equipped with an adequately sized pore (D = 2.4 Å) and a highest O/C ratio (R = 0.49). This optimal one D2.4Å_R0.49 achieves the highest water flux and fully ethanol rejection in the mimicked experimental system. This simulation study elucidates the role of O/C ratio and pore diameter in water-ethanol separation through porous GO membranes on the microscopic level and uncovers the governing effects for water permeation and also suggests a potential candidate as a water- ethanol separation membrane. 1. Introduction The emerging excellent separation performances of graphene oxide (GO) membranes in desalination, [1] water treatment [2] and gas se- paration [3] are arising many concerns about its inside microstructures and separation mechanism. Together with interlayer spacing, [4] in- trinsic defect, [5] lateral size, [6] preferential adsorption [7] and ratio of O/C, [8] pore size in GO membranes determines the molecular se- paration properties. Small sized pore increased the energy barrier for molecule passing over the graphene membrane [9]. Large one can fa- cilitate molecules permeating whereas impairs its separation selectivity. For this reason, a critical sized pore is far more important. With a well tunable pore size in monolayer graphene membranes, CO 2 /CH 4 can be effectively separated through ion-gated porous graphene membrane [10], and water permeance with 2–3 orders of magnitude higher than conventional reverse osmosis membranes can be achieved in water desalination process [11]. A nearly 100% salt rejection rate was ob- tained by porous graphene membranes equipped with a 0.5–1.0 nm sized pore by oxygen plasma etching [12]. In addition, the appropriate shape of pore (asymmetric hourglass-shaped) in multilayer graphene was examined by Kim [13] and water permeation can be improved significantly through this shaped pores. Another important factor, the oxidization degree of GO membrane characterized by O/C ratio, has a decisive role in selectively adsorbing molecules in the feed and then enhancing their permeation. Oxidized by the hydroxyl groups, the pores of graphene can double the water flux owing to the reinforced hydrophilic character [11]. Lu et al. [9] also found that hydroxyl-functionalized pores contribute to Cl - transport while hydrogen-modified ones prefer to facilitate Na + diffusion. In particular, the oxygen-functional groups decorated around the defect or pores increase the affinity between water and GO membranes during solvent dehydration process, while Galvao et al. [14] just simulated two kind of oxidization degrees of GO membranes and the water separation factors are far below than the experimental values [15]. Although oxidized and non-oxidized pores have been compared in these relevant simulations, and. A series of oxidization degree is not clear so far. And it https://doi.org/10.1016/j.seppur.2019.05.030 Received 8 January 2019; Received in revised form 7 May 2019; Accepted 7 May 2019 ⁎ Corresponding authors. E-mail addresses: ystu@yzu.edu.cn (Y. Tu), wqjin@njtech.edu.cn (W. Jin). Separation and Purification Technology 224 (2019) 219–226 Available online 08 May 2019 1383-5866/ © 2019 Elsevier B.V. All rights reserved. T