Enhancing Polyvalent Cation Rejection Using Perfluorophenylazide-Grafted-Copolymer Membrane Coatings

Abstract

Surface modification offers a straightforward means to alter and enhance the properties and performance of materials, such as nanofiltration membranes for water softening. Herein, we demonstrate how a membrane's surface charge can be altered by grafting different electrostatically varying copolymers onto commercial membrane surfaces using perfluorophenylazide (PFPA) photochemistry for enhanced ion separation performance. The native membrane's performancei.e., in terms of divalent cation separationwith copolymer coatings containing a positively charged quaternary ammonium (−N(Me) 3 + ), a negatively charged sulfonate (−SO 3 − ), and an essentially neutral zwitterion (sulfobetaine, −N(Me) 2 R 2 + , and −SO 3 − ), respectively, indicates that: (a) the sulfonated polymer induces robust Coulombic exclusion of divalent anions as compared to the negatively charged native membrane surface on account of its higher negative charge; (b) the positively charged ammonium coating induces exclusion of cations more effectively than the native membrane; and significantly, (c) the zwitterion polymer coating, which reduces the surface roughness and improves wettability, in spite of its near-neutral charge enhances exclusion of both divalent cations and anions on account of aperture sieving by the compact zwitterion polymer that arises from its ability to limit the size of ions that transport through the polymer along with dielectric exclusion. The outcomes thereby inform new pathways to achieve size-and charge-based exclusion of ionic, molecular, and other species contained in liquid streams.

Saline Water-Based Mineralization Pathway for Gigatonne-Scale CO2Management

“…86 On the other hand, 47 Gt of wastewater are processed annually 87 in more than 14,700 treatment plants in the U.S. 88 If a single CO 2 abatement facility were to process 2000 Mt (i.e., the size of a large wastewater treatment plant) 89 of seawater per year, then 1760 such plants would need to be built globally, with each plant being supplied with 10 Mt NaOH per year. Because the carbonate yield is limited by the content of divalent cations in the feed, enriching the Ca and Mg concentrations in the feed stream (e.g., using membranes that can selectively separate divalent cations, see Aguilar et al 90 ) would allow for the processing of a smaller quantity of water. Such pretreatment can obviously only be fulfilled while incurring a substantial energy penalty which appears unviable, in spite of the increase in the carbonate yields that would result.…”

Ultrapermeable nanofiltration membranes with tunable selectivity fabricated with polyaniline nanofibers

“…Reacting diamines with acyl chlorides enables the formation of a highly crosslinked aromatic polyamide (PA) film at the interface of two immiscible solvents. The thickness, 19 nanoscale morphology, 20 charge, 21,22 and microporosity 23–26 of the interfacially polymerized PA layers can greatly affect the NF performance. Extensive efforts have been made to develop next-generation NF membranes that possess excellent separation performance and high application feasibility.…”

Polyamide Nanofiltration Membrane from Surfactant-assembly Regulated Interfacial Polymerization of 2-Methylpiperazine for Divalent Cations Removal

“…Alternatively, positively charged NF membrane with an appropriate pore size is more powerful. Till now, positively charged NF membranes are always prepared by means of surface grafting [22,23] , layer-by-layer(LBL) assembly [24,25] and IP [26,27] . Through surface grafting and LBL assembly, amine-rich polymers, such as polyethylene imine (PEI) [17] , dendrimers [28] or quaternized compounds [29] were modified on the surface, resulting a positively charged NF membrane.…”