Abstract
Hollow fibre RO membranes would be desired for many applications, but are notoriously difficult to fabricate. Here we demonstrate that combining layer-by-layer and interfacial polymerization (IP) allows straightforeward production of defect-free hollow fiber RO membranes. A polyelectrolyte multilayer (PEM) is used to fill the pores of a support membrane, to provide a controlled and smooth surface that can nevertheless act as an IP monomer reservoir. This approach is first demonstrated on a model surface, with IP layers being successfully applied on both poly(diallyldimethylammonium chloride) (PDADMAC)/poly(4-styrene sulfonate) (PSS) and poly(ethyleneimine) (PEI)/PSS PEMs. On plain hollow fiber support membranes, IP coating was found to have a success rate as low as 40%. However, by application of a PEM interlayer the success rate increases to 72% for PDADMAC/PSS and 90% for PEI/PSS. Also the separation performance of the successfully prepared IP membranes was significantly better when a PEM interlayer was applied, with higher NaCl retentions (from 94% to 97%), and better removal of organic micro-pollutants (from 96% to 98%), with just a small decrease in permeability (from 0.9 L/m2hbar to 0.7 L/m2hbar). Combining layer-by-layer and IP approaches can thus lead to the fabrication of defect free RO membranes with improved separation performance.
Highlights
Water scarcity is one of the major problems to be faced by today’s society
To demonstrate that interfacial polymerization (IP) layers can be successfully prepared on polyelectrolyte multilayer (PEM) layers, we initially studied layer deposition on silicon oxide model surfaces (SiO2)
We propose that a PEM can act as an interlayer for the IP layer that acts to prevent the formation of defects, especially pinholes
Summary
Water scarcity is one of the major problems to be faced by today’s society. Global water usage has increased by as much as six times over the past 100 years [1], and the demand for fresh water is only expected to further increase due to increases in population, economic develop ment and consumption [2]. Micropollutants found in drinking water sources origi nate from industrial, medicinal, and agricultural activities, and, they can be toxic to the environment and to humans [5,6,7,8] Because of their small size (between 100 and 1000 Da.), they are difficult to remove using conventional water purification approaches. Due to the fast reaction rate and reasonable solu bility of MPD in organic phase, interfacial polymerization (IP) occurs in the organic phase and proceeds by MPD diffusion from aqueous phase to the organic phase This leads to the growth of a defect free thin film that limits additional monomer diffusion [11]. This multi-staged IP process typically results in the formation of a relatively rough (ridge and valley structure) nonhomogeneous surface [12], with excellent selectivities [9]
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