Probing the Effect of Amine N-Oxide Zwitterionic Polymer Additives in Polysulfone Forward Osmosis Membranes

Abstract

Forward osmosis (FO) is a passive liquid separation process where a hypertonic solution drives water across a semipermeable membrane. Compared to other membrane-based water purification processes, FO has the potential of producing clean water with minimal energy consumption. To achieve its potential, membranes with enhanced properties, such as high fouling resistance and solute rejection, high hydrophilicity and water permeability, and a wide pH and temperature tolerance, must be developed. In this work, we studied the effect of amine N-oxide zwitterionic polymer additives in the properties and morphology of polysulfone (PSf) based membranes. These additives were synthesized via a three-step reaction in which analogues of trimethylamine oxide (TMAO) were covalently incorporated into PSf. TMAO is a well-known organic osmolyte and its antifouling properties offer an interesting avenue to explore its potential use in water purification applications such as FO. Moreover, we studied three analogues which varied in their alkyl chain length: diethyl, dibutyl, and dihexyl. Our interest in these three alkyl groups was to systematically increase the carbon chain and study their effect in the overall membrane formation and performance. The successful synthesis of the amine N-oxide zwitterionic polymer additives was confirmed by FT-IR, NMR, and XPS. Then, we fabricated the membranes through the nonsolvent induced phase separation (NIPS) process. The morphology of the membranes was evaluated with SEM, while the hydrophilicity was monitored with contact angle measurements. Our results showed that the addition of these TMAO analogues significantly affects the PSf membrane formation and properties. Moreover, the PSf–DEAO membrane with the shortest carbon chain improve the membrane surface hydrophilicity and enhanced the water flux by a 4-fold increase. Altogether, our results suggest that longer alkyl groups could compromise the antifouling properties of the amine oxide.

Zwitterionic and Photocatalytic Janus Membrane Based on Diethylamine N-Oxide Group and WS2 Nanosheets for Dye Removal in Forward Osmosis

“…Also, the reduction of the A 1g peak in the Raman spectra concerning the bulk’s Raman spectra indicates the layered tungsten disulfide, as reported by Kashya, D. et al It suggests the dispersion of the T01 phonon at the edge of the Brillion zone. Therefore, the frequency difference in the exfoliated material and the decrease of the peak A 1g in the nanosheets Raman spectra can corroborate that the WS 2 nanosheets were obtained and layered in 4 monolayers thick. ,− …”

“…The first step to fabricate the Janus membrane was modification of the PSF backbone with the DEAO zwitterionic group. Our group previously reported this type of modification in 2021 . Briefly, methyl chloride is added to the PSF’s structure (PSF-Cl) as a reactive site.…”

“…Trimethylamine N-oxide (TMAO), a small molecule found in various marine organism tissues, has gained interest because there are no carbons between the charged nitrogen (+) and oxygen (−) bonds and it facilitates more hydrogen bonds. When TMAO is incorporated into the membrane, it can improve the selectivity, hydrophilicity, water flux, and antifouling properties …”

Recent Advances in Antifouling Surface Polymer Brushes

“… This sets PTMAO apart from other conventional zwitterionic polymers, the surface hydration and antifouling properties of which can be significantly compromised when in contact with concentrated salt solutions. Since their emergence, PTMAO are increasingly used to develop antifouling surface polymer brushes especially in the application of membrane modification for water purification. ,,, For instance, Feng et al used surface-initiated ATRP to prepare PTMAO brushes from polyamide thin-film-composite (TFC) reverse osmosis membranes. The grafting of the superhydrophilic PTMAO brushes improved the antifouling performance of the TFC membrane without compromising its transport properties such as water permeability and water–salt selectivity …”

Forum: Polymer Membranes for Precision Separations

“…Forward osmosis is a separation process that is well-suited for treating complex, highly concentrated sources of saline water. Eduardo Nicolau from the University of Puerto Rico probes the effect of amine N -oxide zwitterionic polymer additives on the formation of membranes for forward osmosis. Three zwitterionic polymers functionalized with analogues of trimethylamine oxide (TMAO) were synthesized and used in the fabrication of membranes.…”