The escalating global population, coupled with an acute water scarcity crisis, underscores a pressing challenge in managing our planet's finite freshwater reserves. This challenge is compounded as diverse sources of potable water around the world become increasingly contaminated with various emerging pollutants, many of which are small, uncharged molecules that conventional separation methods struggle to effectively address. In this context, the study of water separation processes not only becomes crucial but urgent, as it directly addresses the imperative to secure our water future through technological advancements. Among the array of solutions explored, polymeric membranes have emerged as a promising candidate for these types of separations, demonstrating significant potential in purifying water from small molecules, such as urea. Urea’s relatively low molecular weight, strong polarity, and its propensity to form hydrogen bonds with water make this a challenging separation. This work explores different ionic polymers such as sulfonated poly(styrene-isobutylene-styrene) (SIBS), cellulose triacetate (CTA), poly(m-phenylene isophthalamide) (PMIA), and polysulfone (PSF) in the separation of urea, dimethyl urea, and diethyl urea. Membranes were prepared by a non-solvent induced phase separation (NIPS) at room temperature and characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis (TGA), atomic force microscopy (AFM) and small angle x-ray scattering (SAXS), pure water permeability was measured using a reverse osmosis (RO) setup. Solutes permeability data were collected using a forward osmosis (FO) setup and calculated by the time-lag methodology. Preliminary findings reveal a hierarchy of ureas permeability: SIBS shows the highest value, followed by CTA, PMIA, and finally PSF, which demonstrated negligible permeability. These results are directly associated with membrane hydrophilicity, as expected PSF membrane presented the lowest water permeability with a value of 1.59 Lm
-2h
-1bar
-1. CTA membrane showed a water permeability of 13 Lm
-2h
-1bar
-1. PMIA membrane presented the highest permeability with a value of 57.3 Lm
-2h
-1bar
-1.
The outcomes of this study underscore the critical role of ionic polymer membranes in advancing the separation processes for small, polar molecules like urea and its derivatives from water. The distinct permeability profiles of SIBS, CTA, PMIA, and PSF membranes, as revealed through our comprehensive characterization and performance testing, highlight the potential of tailoring membrane materials to specific separation challenges. Notably, the high urea permeability of SIBS, followed by CTA and PMIA, with PSF showing the least, delineates a clear correlation between membrane hydrophilicity, chemical composition, and separation efficiency. These findings significantly contribute to the field of water treatment, providing a foundational understanding of how specific ionic polymers perform for the selective separation of challenging solutes like urea. By addressing one of the critical challenges in water purification as it is the effective removal of small, uncharged molecules, this work covers the way for developing more efficient and sustainable water purification technologies.
