离子化氨基酸对氧化石墨烯膜渗透汽化过程中水选择性渗透的影响

Effect of Ionized Amino Acid on the Water-selective Permeation through Graphene Oxide Membrane in Pervaporation Process

在氧化石墨烯(GO)膜通道内引入离子化基团,可通过静电作用吸附更多的水分子,有望实现更高效的水分子渗透。研究采用真空抽滤方法将离子化的碱性氨基酸赖氨酸(Lys)引入GO膜内,通过共价交联制备出Lys(Na^(+))-GO复合膜。赖氨酸分子两端的氨基与GO可交联形成C–N共价键,从而对膜结构进行调控使其更加规整有序,并将离子化羧酸根引入氧化石墨烯通道中。相比于未离子化的赖氨酸,离子化的赖氨酸中荷负电的羧酸根通过静电作用提高了与水分子的作用力,增强了膜的亲水性。通过物理结构和化学结构调控的协同作用,面向不同的水/醇分离体系, Lys(Na^(+))-GO复合膜的渗透通量和分离因子得到同时提升。在40℃下,对质量分数90%的乙醇/水、正丁醇/水以及异丙醇/水体系进行渗透汽化测试, Lys(Na^(+))(10)-GO膜(抽滤溶液中Lys(Na^(+))与GO的质量比为10)的渗透通量分别达到882、2461和1127 g/(m^(2)·h),渗透侧水的质量分数分别达到95.38%、99.11%和99.42%。

Introduction of ionized groups into the channels of graphene oxide(GO) membrane can adsorb more water molecules through electrostatic interaction, which is expected to achieve more efficient water-selective permeation. In this work, a vacuum filtration method was adopted to introduce the ionized basic amino acid lysine(Lys) into the GO membrane to obtain the Lys(Na^(+))-GO composite membrane through covalent crosslinking. The terminal amino groups in Lys covalently crosslink GO through forming C–N covalent bond, thus regulating the membrane structure to make it more orderly. Meanwhile, the ionized carboxylate groups are introduced into GO channels. Compared with unionized lysine, the negatively charged carboxylate in ionized lysine increases the interaction with water molecules,and improves the membrane hydrophilicity. Through synergistic effect of tuning physical structure and chemical structure of GO channels, Lys(Na^(+))-GO composite membranes achieve the simultaneous enhancement of permeation flux and separation factor for the separation of different water/alcohol mixtures. For the pervaporation separation of ethanol/water, n-butanol/water and i-propanol/water mixtures at 40 ℃ with alcohol concentrations of 90%, the Lys(Na^(+))(10)-GO membrane(mass ratio of Lys(Na^(+)) to GO in the extract solution at 10) shows permeation flux of 882, 2461 and 1127 g/(m^(2)·h) with water content reaching 95.38%, 99.11% and 99.42%, respectively.