title: Separation of fluoride from other monovalent anions using multilayer polyelectrolyte nanofiltration membranes.
abstract: Nanofiltration (NF) is an attractive technique for reducing F- concentrations to acceptable levels in drinking water, but commercial NF membranes such as NF 270 and NF 90 show minimal Cl-/F- selectivity. In contrast, simple layer-by-layer deposition of 4.5-bilayer poly(styrene sulfonate) (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) films on porous alumina supports yields NF membranes that exhibit Cl-/F- and Br-/F- selectivities>3 along with solution fluxes that are >3-fold higher than those of the commercial membranes. Fluoride rejection by (PSS/PDADMAC)4PSS membranes, which is >70%, is independent of pressure over a range of 3.6 to 6.0 bar, suggesting that the primary transport mechanism in these films is convection. Moreover, the fact that Br-/F- selectivity is 12% higher than Cl-/F- selectivity suggests that discrimination among the monovalent ions is based on size (Stokes radius). Chloride/fluoride selectivities are essentially constant over Cl-/F- feed ratios from 1 to 60, so these separations will be viable over a range of conditions. Interestingly, PSS/protonated poly(allylamine) films show little Cl-/F- selectivity, and the selectivity of PSS/PDADMAC membranes is a strong function of the number of deposited layers, indicating that NF properties are very sensitive to film structure.
authors.affiliation: Department of Chemical Engineering, Hanbat National University, Daejeon 305-719, South Korea.
authors.forename: Seong Uk
authors.initials: SU
authors.lastname: Hong
authors.forename: Ramamoorthy
authors.initials: R
authors.lastname: Malaisamy
authors.forename: Merlin L
authors.initials: ML
authors.lastname: Bruening
mesh_terms: D000838:Anions / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry*; D005374:Filtration; D005459:Fluorides / Q000737:chemistry* / Q000302:isolation & purification*; D049329:Nanostructures / Q000737:chemistry*; D011312:Pressure
chemical_list: D000838:Anions; D004573:Electrolytes; D005459:Fluorides