Search

Membranes with zwitterionic surfaces are highly desired in water-based separations for their distinguished fouling resistance. Herein, a facile strategy for the preparation of zwitterion-functionalized membranes is developed by coupling the pore-making and zwitterion functionalization in one step. We soaked thin films of poly (2-dimethylaminoethyl methacrylate)- block -polystyrene (PDMAEMA- b -PS) in the mixture of ethanol and 1, 3-propanesultone (1, 3-PPST). In this mixture, PDMAEMA microdomains were selective swollen leading to nanoporous structures with PDMAEMA chains enriched on the surface. Simultaneously, the quaternization reaction between PDMAEMA and 1, 3-PPST took place. Unexpectedly, in addition to function as the zwitterionic agent, 1, 3-PPST also contributed to the selective swelling induced pore generation. It was found that the presence of 1, 3-PPST in ethanol slowed down the swelling process at the early stage, but evidently enhanced the swelling of PDMAEMA- b -PS films in longer duration. Thus-prepared zwitterion-functionalized membranes exhibited several times higher water permeance than non-zwitterionized counterparts, which should be attributed to increased pore size and strongly improved hydrophilicity as a result of zwitterion functionalization. Moreover, the membranes showed exceptional fouling resistance because of the presence of zwitterions. Image 1 • Selective swelling and zwitterion functionalization are coupled into one step. • 1, 3-PPST works as both one component of the swelling agent and modifying agent. • Zwitterionic membranes exhibit excellent anti-fouling performance. • Separation performance can be facilely regulated by swelling durations. [ABSTRACT FROM AUTHOR]

Inspired by biological membranes with charge-gated channels that allow the transport of water and ions but restrict the undesired substances, various regulated nanofiltration (NF) membranes containing charge-gated channels have been developed for water purification. However, most of these membranes are mono-charged (positively or negatively) that show high rejection only to the corresponding co-ions but low rejection to the counter-ions, which limits their wider applications. Herein, we report NF membranes with gas-tunable charge-gated channels and high rejection to different salts on demand. The membranes are prepared by assembling a CO 2 -responsive polymer, poly(N,N-dimethylaminoethyl methacrylate), on the surface of graphene oxide (GO). As a result of CO 2 -induced reversal of the charge sign, the membranes exhibit "self-regulation" of their surface charges. Upon bubbling CO 2 into water, the membranes are positively charged, which shows high rejection to MgCl 2. After bubbling Ar to remove CO 2 , the membranes gradually transform to negatively charged, and high rejection to Na 2 SO 4 is obtained. This study demonstrates the gas-tunable charge-gated ion transport behavior of the CO 2 -responsive NF membranes, and opens up new avenues for the design of on-demand NF membranes. New nanofiltration membranes exhibit on-demand switchable rejections toward cations and anions with the participation and departure of CO 2. Image 1 • New nanofiltration membrane was built with graphene oxide and CO 2 -responsive polymer. • The surface of nanopores can be reversibly switched between opposite charged state. • Charge sign can easily be reversed in a robust and contamination-free manner. • Ion transport behavior was dominated with the participation and departure of CO 2. [ABSTRACT FROM AUTHOR]