Abstract
The pH-responsive membrane is a new wastewater treatment technology developed in recent years. In this paper, a novel film with intelligent pH-responsiveness was first prepared by blending functional gates comprised of hydrolyzed aramid nanofibers (HANFs) into aramid nanofiber (ANF) membranes via a vacuum filtration method. Those as-prepared membranes exhibited dual pH-responsive characteristics, which were featured with a negative pH-responsiveness in an acidic environment and a positive pH-responsiveness in basic media. These dual pH-responsive membranes also exhibited a high tensile strength which could still reach 55.74 MPa (even when the HANFs content was as high as 50 wt%), a high decomposition temperature at ~363 °C, and good solvent resistance. The membranes described herein may be promising candidates for a myriad of applications, such as the controlled release of drugs, sensors, sewage treatment, etc.
Highlights
As one of the environmental responsiveness of “smart” membranes, pH-responsive membranes can adjust their flux and separation performance with the change of environmental pH value [1,2,3]
Polymers 2021, 13, 621 orange system was washed with distilled water, the volume of which was equivalent to five times that of that colloid-like orange system by means of filtration, until the KTB, methanol, and DMSO were thoroughly removed from the aramid nanofiber (ANF) system and the pH of the above system returned to neutral
In a polar solvent such as DMSO that could be saturated with a strong Lewis base, the H atoms could be removed from the N-H groups in the macromolecule chains and the whole chain could be converted into a polyanion, which can weaken and eliminate the interchain interactions and the homogenizing dispersions is achieved (Figure S1) [14]
Summary
As one of the environmental responsiveness of “smart” membranes, pH-responsive membranes can adjust their flux and separation performance with the change of environmental pH value [1,2,3]. On account of the lack of polar functional groups, high crystallinity, and the tendency of hydrogen bonds to form between molecules, aramid fibers are chemically inert and their surfaces are extremely smooth. Their interfacial bonding strength with other substrates is poor, which greatly limits the applicability of aramid fibers [22,23,24]. The pH-responsive membranes prepared in this study can overcome the poor binding energy between ANF and matrix interfaces, and retain much of the excellent performance of ANFs. Interestingly, we found that the obtained films have excellent distinctive properties such as smart dual pH-responsive characteristics, desirable mechanical behavior, as well as excellent physical and chemical stability.
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