Qin Lanlan, Zhou Jian
School of Chemistry and Chemical Engineering, Guangdong Provincial Key Lab for Green Chemical Product Technology, South China University of Technology Guangzhou 510640 P. R. China
RSC Adv. 2024 Apr 2;14(15):10560-10573. doi: 10.1039/d4ra01217h. eCollection 2024 Mar 26.
Molecular dynamics simulations were performed to tune the transport of water molecules in nanostructured membrane in a desalination process. Four armchair-type (7,7), (8,8), (9,9) and (10,10) carbon nanotubes (CNTs) with pore diameters around 1 nm were chosen, their interior surfaces were modified with -OH, -CH and -F groups. Simulation results show that water transport in nanochannel depends on confined water structures which could be regulated by precisely controlled channel diameter and chemical functionalization. Increasing CNT diameter changes water structures from single-file-like to be square and hexagonal-like, then into a disordered pattern, resulting in a concave-shaped trend of water permeance. The -OH functional groups promote structural ordering of water molecules in (7,7) CNT, but disrupt water structures in (8,8) and (9,9) CNTs, and reduce the order degree of water molecules in (10,10) CNT, moreover, exert an attraction to enhance surface friction inside channel. The -CH groups induce more strictly single-file movement of water molecules in (7,7) CNT, turning water structures in (8,8) and (9,9) CNTs into two and triangular column arrangements, improving water transport, however, causing again square-like water structure in (10,10) CNT. Fluorinations of CNT make water structure more disordered in (7,7), (9,9) and (10,10) CNTs, while enhance the square water structure in (8,8) CNT with a lower water permeance. Through changing channel diameter and functionalization, the low tetrahedral order corresponds to a more single-file-like water structure, associated with rapid water diffusion and high permeability; an increase in tetrahedrality results in more ice-like water structures, lower water diffusion coefficients, and permeability. The results of this study demonstrate that water transport could be finely regulated a functionalized CNT membrane.
进行了分子动力学模拟，以调节脱盐过程中纳米结构膜内水分子的传输。选择了四种孔径约为1nm的扶手椅型（7,7）、（8,8）、（9,9）和（10,10）碳纳米管（CNT），其内壁用-OH、-CH和-F基团进行了修饰。模拟结果表明，纳米通道中的水传输取决于受限水结构，而这种结构可通过精确控制通道直径和化学功能化来调节。增加碳纳米管直径会使水结构从单链状变为方形和六边形，然后变为无序模式，导致水渗透率呈凹形趋势。-OH官能团促进了（7,7）碳纳米管中水分子的结构有序性，但破坏了（8,8）和（9,9）碳纳米管中的水结构，并降低了（10,10）碳纳米管中水分子的有序度，此外，还产生吸引力以增强通道内的表面摩擦力。-CH基团促使（7,7）碳纳米管中的水分子更严格地单链移动，使（8,8）和（9,9）碳纳米管中的水结构变为两层和三角形柱状排列，改善了水传输，然而，在（10,10）碳纳米管中又导致了方形水结构。碳纳米管的氟化使（7,7）、（9,9）和（10,10）碳纳米管中的水结构更加无序，而增强了（8,8）碳纳米管中的方形水结构，其水渗透率较低。通过改变通道直径和功能化，低四面体有序度对应于更单链状的水结构，与快速的水扩散和高渗透率相关；四面体度的增加导致更多冰状水结构、更低的水扩散系数和渗透率。本研究结果表明，在功能化碳纳米管膜中，水传输可以得到精细调节。
