S. Belfer

TFC polyamide membranes modified by grafting of hydrophilic polymers: an FT-IR/AFM/TEM study

Abstract Surface modification using grafting of a hydrophilic polymer onto the membrane surface is a possible route to improving the fouling properties of polyamide thin-film composite membranes. The structure of nanofiltration (NF) and reverse osmosis (RO) membranes modified using graft polymerization of acrylic (AA) monomers was visualized and analyzed using attenuated total reflection–Fourier transform infrared spectroscopy, atomic force microscopy and transmission electron microscopy. The results show that a layer of AA polymer is indeed formed on the polyamide surface, which could be accompanied by a change of the surface morphology. It was observed that for the NF membranes studied polymerization could also take place inside the pores of the support as a result of penetration of the monomer through the active layer, particularly for high degrees of grafting. It suggests that the modification procedures should be optimized so that the latter effect is minimized.

Surface modification of commercial composite polyamide reverse osmosis membranes

Radical grafting of two monomers, methacrylic acid and polyethylene glycolmethacrylate, onto commercial composite polyamide reverse osmosis membranes was performed. A redox system was used for initiation, and grafting was performed in an aqueous medium at room temperature. Surface grafting was characterized by ATR-FTIR, ESCA and streaming potential measurements. It was found that the membranes were surface modified without damage to their transport properties.

Surface modification of commercial polyamide reverse osmosis membranes by radical grafting: An ATR‐FTIR study

A new grafting procedure was developed for surface modification of commercial polyamide reverse osmosis membranes. Acidic and neutral acrylic monomers and sulfo-containing vinyl monomers were successfully grafted from aqueous solutions under mild conditions. The modifications were monitored by ATR-FTIR spectra. The characteristic peaks of functional groups introduced by grafting were evaluated. The spectral findings correlated with physicochemical properties of the membranes.

Bacterial attachment to RO membranes surface-modified by concentration-polarization-enhanced graft polymerization.

Concentration polarization-enhanced radical graft polymerization, a facile surface modification technique, was examined as an approach to reduce bacterial deposition onto RO membranes and thus contribute to mitigation of biofouling. For this purpose an RO membrane ESPA-1 was surface-grafted with a zwitterionic and negatively and positively charged monomers. The low monomer concentrations and low degrees of grafting employed in modifications moderately reduced flux (by 20-40%) and did not affect salt rejection, yet produced substantial changes in surface chemistry, charge and hydrophilicity. The propensity to bacterial attachment of original and modified membranes was assessed using bacterial deposition tests carried out in a parallel plate flow setup using a fluorescent strain of Pseudomonas fluorescens. Compared to unmodified ESPA-1 the deposition (mass transfer) coefficient was significantly increased for modification with the positively charged monomer. On the other hand, a substantial reduction in bacterial deposition rates was observed for membranes modified with zwitterionic monomer and, still more, with very hydrophilic negatively charged monomers. This trend is well explained by the effects of surface charge (as measured by ζ-potential) and hydrophilicity (contact angle). It also well correlated with force distance measurements by AFM using surrogate spherical probes with a negative surface charge mimicking the bacterial surface. The positively charged surface showed a strong hysteresis with a large adhesion force, which was weaker for unmodified ESPA-1 and still weaker for zwitterionic surface, while negatively charged surface showed a long-range repulsion and negligible hysteresis. These results demonstrate the potential of using the proposed surface- modification approach for varying surface characteristics, charge and hydrophilicity, and thus minimizing bacterial deposition and potentially reducing propensity biofouling.

Effect of surface modification in preventing fouling of commercial SWRO membranes at the Eilat seawater desalination pilot plant

Abstract Flat sheet samples of SWRO membranes of the SWC2 type (Hydranautics) were surface modified with hydrophilic polymers formed by redox initiated grafting with vinyl monomers. These were mounted on specially designed stubs along with unmodified membranes and tested at the Mekorot seawater RO pilot plant located in Eilat. A spiral 2.5″ element of SWC2 was also modified and run at the pilot plant for 5 months. All samples were run at conditions designed to exacerbate fouling. In three different experiments of 1–3 months, the stubs with modification were shown to have less fouling as measured by relative flux decline. FTIR—ATR characterization showed that the modified membranes also had fewer organic deposits as compared to modified membranes. SEM and EDAX showed that on fouled deposits, iron and chromium were mixed with organic deposits. These are likely corrosion products from upstream in the test unit. The spiral wound element showed stable water flux for 3 months. When fouling did occur, it appeared to be bio-fouling and appeared to have developed in the dead space between the element and the stainless steel pressure housing and from there was carried into the element.

Surface modification of dense membranes using radical graft polymerization enhanced by monomer filtration.

Surface graft polymerization is a promising way to modify membranes for improved performance. Redox-initiated graft polymerization of vinyl monomers is a facile and inexpensive method carried out at room temperature in aqueous media; however, its use is often limited by slow kinetics, low surface specificity, and excessive consumption of chemicals on undesired homopolymerization. It is shown that in the case of RO or NF membranes these drawbacks may be eliminated by utilizing the selectivity of the membranes toward monomers and carrying out the polymerization while applying pressure, i.e., under filtration conditions. Concentration polarization that ensues raises the concentration of reagents near the membrane surface and thereby drastically increases the rate of reaction and preferentially directs it towards surface grafting. Grafting experiments using 2-hydroxyethyl methacrylate and other monomers and characterization of modified membranes using permeability measurements, ATR-FTIR, AFM, XPS, and contact angle demonstrate that the required monomer concentrations can be drastically reduced, particularly when a small fraction of a cross-linker is added. As an additional benefit, this approach enables broadening the spectrum of utilizable monomers to sparingly soluble hydrophobic, charged, and macro-monomers, as was demonstrated using sparingly soluble ethyl methacrylate and 2-ethoxyethyl methacrylate and other monomers. Even though the kinetics of the process is substantially complicated by evolution and concentration polarization of oligomeric and polymeric species, especially in the presence of a cross-linker, it is well offset by the benefits of higher rate, specificity, and reduced monomer consumption.

Characterization of commercial RO and UF modified and fouled membranes by means of ATR/FTIR

Abstract A simple grafting procedure was developed for surface modification of commercial polyamide reverse osmosis membranes. The modifications were monitored by spectral analysis. This technique was also used for study of membrane hydration. It was established that water interaction with surface functional groups of polyacrylonitrile (PAN) modified membrane produced very strong changes in the regions of CO and CO stretching vibrations. Adsorption and pressure experiments using Nahal Taninim feed water have been conducted on modified RO membranes. The membranes have been examined by ATR/FTIR for extent of adsorption of organic contaminants. Comparison with unmodified membranes shows that surface modification of the membranes resulted in drastic decrease in contaminant adsorption for some polymer grafts and increased ease in rinsing the contaminated surface.

Removal of heavy metals from tap water by a cation exchanger

Abstract Selective removal of heavy metals such as Cu, Ni, Co, Mn, Cd, and Pb from tap water that contains relatively high concentrations of calcium and magnesium was carried out with a cation-exchange resin possessing a chelating iminodiacetic acid group. When the concentration of each of these metals in tap water was of the order of a few ppm, their leakage fell below the permitted level in drinking water. Removal of the heavy metals from the resin was successfuly perfomed with 3 M HCl or HNO3.

Metal sorption properties of sulfur-chlorinated jojoba wax bound to polystyrene beads

A new solid extractant (designated PS-DETA-JS) in which sulfur-chlorinated jojoba wax is bound via an amine spacer group to polystyrene beads was synthesized. The absorption of mercury cations from acidic solutions and of chromate anions from saline solutions onto PS-DETA-JS was investigated. The sorption of mercury ions by the solid extractant was compared with that by liquid-sulfurized jojoba wax impregnated inside macroporous resins. The static and dynamic properties of dichromate sorption from 2-20 g/L NaCl solutions at pH 4.1 were studied. Selective sorption of Cr(VI) ) was obtained at low chromate concentrations ( 6 ppm) in saline aqueous solutions. Complete regeneration of the PS-DETA-JS resin was achieved after the reduction of Cr( VI ) to Cr ( III ) and the elution of the Cr(III) ) with 1N HCl.

Functionalization at the double-bond region of jojoba oil. 7. Chemical binding of jojoba liquid wax to polystyrene resins

Jojoba wax was chemically bonded to a polystyrene matrixvia a stable C-C covalent bond. This was achieved by binding allyl-brominated jojoba derivatives to lithiated crosslinked polystyrene-2% divinylbenzene or XAD-4 polymeric beads via a nucleophilic substitution reaction. The double-bond regions in the jojoba wax were preserved. A side reaction that accompanied the nucleophilic substitution was HBr elimination, which produced diene and triene systems in the bound jojoba. Phosphonation and sulfur chlorination at the double bonds of the jojoba wax, bonded to the polystyrene matrix, were also performed.