Self-organizing blends of an amphiphilic comb polymer having a poly(methyl methacrylate) (PMMA) backbone and poly(ethylene oxide) (PEO) side chains in poly(vinylidene fluoride) (PVDF) have been examined as a means to create foul-resistant, self-healing surfaces on polymer membranes. X-ray photoelectron spectroscopy (XPS) analysis of phase inversion membranes prepared from these blends indicates substantial surface segregation of the amphiphilic component, which occurs both during the coagulation step of the phase inversion process and in subsequent annealing of the membranes in water. With annealing, a near-surface coverage of nearly 45 vol % comb polymer is produced on a membrane with a bulk comb concentration of only 3 vol %. Surface enrichment of the hydrophilic comb polymer is shown to impart significant resistance to the adsorption of bovine serum albumin (BSA). XPS analysis of membranes treated with concentrated acid shows that hydrophilic surface layers removed by acid exposure may be regenerated b...

Preparation of Protein-Resistant Surfaces on Poly(vinylidene fluoride) Membranes via Surface Segregation

The clustering phenomenon has been observed in many macromolecular systems. Poly(ethylene oxide) solutions are characterized by a clustering effect that has been extensively discussed in the literature. Its origin has remained elusive. Using small-angle neutron scattering from PEO solutions in various deuterated solvents, the possible causes of clustering that have been given in the literature are analyzed here. These include impurities in water, possible PEO crystallization, a subtle phase transition whereby a concentrated phase coexists with free polymer coils, hydrogen-bond physical cross-linking, and finally chain ends effect. We have shown that under the experimental conditions considered here (4% PEO weight fraction) the mostly forgotten chain ends effect is at the origin of clustering in poly(ethylene oxide) solutions.

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Insight into Clustering in Poly(ethylene oxide) Solutions

In this study, we investigated the removal of Fe, Pb, Cd, and Zn from synthetic mine waters by a natural zeolite. The emphasis was given to the zeolite's behavior toward a few cations in competition with each other. Pb was removed efficiently from neutral as well as from acidic solutions, whereas the uptake of Zn and Cd decreased with low pH and high iron concentrations. With increasing Ca concentrations in solution, elimination of Zn and Cd became poorer while removal of Pb remained virtually unchanged. The zeolite was stable in acidic solutions. Disintegration was only observed below pH 2.0. Forward- and back-titration of synthetic acidic mine water were carried out in the presence and absence of zeolite to simulate the effects of a pH increase by addition of neutralizing agents and a re-acidification which can be caused by subsequent mixing with acidic water. The pH increase during neutralization causes precipitation of hydrous ferric oxides and decreased dissolved metal concentrations. Zeolite addition further diminished Pb concentrations but did not have an effect on Zn and Cd concentrations in solution. During re-acidification of the solution, remobilization of Pb was weaker in the presence than in the absence of zeolite. No substantial differences were observed for Fe, Cd, and Zn immobilization. The immobilization of the metals during pH increase and the subsequent remobilization caused by re-acidification can be well described by a geochemical equilibrium speciation model that accounts for metal complexation at hydrous ferric oxides, for ion exchange on the zeolite surfaces, as well as for dissolution and precipitation processes.

Removal of Heavy Metals from Mine Waters by Natural Zeolites

Permeable reactive barrier for groundwater remediation

WATER CHEMISTRY AND MINERAL SOLUBILITY. Physical Chemistry of Water and Some of Its Constituents. Solution/Mineral-Salt Chemistry. SOIL MINERALS AND SURFACE CHEMICAL PROPERTIES. Soil Minerals and Their Surface Properties. Sorption and Exchange Reactions. ELECTROCHEMISTRY AND KINETICS. Redox Chemistry. Pyrite Oxidation Chemistry. Reaction Kinetics in Soil-Water Systems. SOIL DYNAMICS AND AGRICULTURAL-ORGANIC CHEMICALS. Organic Matter, Nitrogen, Phosphorus and Synthetic Organics. COLLOIDS AND TRANSPORT PROCESSES IN SOILS. Soil Colloids and Water-Suspended Solids. Water and Solute Transport Processes. The Chemistry and Management of Salt-Affected Soils and Brackish Waters. LAND-DISTURBANCE POLLUTION AND ITS CONTROL. Acid Drainage Prevention and Heavy Metal Removal Technologies. SOIL AND WATER: QUALITY AND TREATMENT TECHNOLOGIES. Water Quality. Soil and Water Decontamination Technologies. Appendix. Suggested and Cited References. Index.

Environmental Soil and Water Chemistry: Principles and Applications

Ion exchange of Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ in ammonium mordenite has been studied in aqueous solution over a pH range of 4–7 at 25°C. Values of the thermodynamic equilibrium constant Ka and the standard free energy of exchange ΔG⊖ were calculated for reversible systems. In no case at 25°C did the degree of exchange of metal ions exceed 50%, and pH and anion were found to have no significant effect on the equilibria. A thermodynamic affinity sequence of Mn2+ > Cu2+ > Co2+∼ Zn2+ > Ni2+ was established and thermodynamic affinities of the zeolite for pairs of metal ions were calculated using the triangle rule. Selectivity quotients indicated that mordenite would preferentially remove manganese(II) or copper(II) from a binary solution mixture of one of these ions with cobalt(II), nickel(II) or zinc(II).

Transition metal ion exchange in zeolites. Part 1.—Thermodynamics of exchange of hydrated Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ ions in ammonium mordenite

Ion exchange properties of natural clinoptilolite, ferrierite and mordenite: 1. Sodium—ammonium equilibria

Ion-exchange properties of natural clinoptilolite, ferrierite and mordenite: Part 2. Lead—sodium and lead—ammonium equilibria

Zeolites find relatively few direct applications as ion exchangers and it is perhaps for this reason that the study of their ion exchange behaviour is somewhat neglected in comparison to their other properties. Nevertheless, ion exchange is an essential part of preparative procedures for the manufacture of zeolitic sorbents and catalysts, and there is now increasing recognition of the importance of using strictly controlled conditions during ion exchange in order to avoid hydrolysis and crystal damage. Some practical points concerning ion exchange are therefore considered, and in addition two aspects of the theory of ion exchange are reviewed. Firstly, some recent discussions regarding the propriety of using the Gaines and Thomas thermodynamic formulation to evaluate activity coefficients within the exchanger phase are considered. Secondly, recent progress in the prediction of multicomponent exchange equilibria is discussed. Finally, some suggestions are made regarding possible fruitful future areas of research.

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Ion Exchange in Zeolites: Some Recent Developments in Theory and Practice

As part of a general study of the theory of ternary ion exchange in zeolites, a simple model is developed for the evaluation of the required activity-coefficient ratios in dilute solutions containing three salts. The application of this model is discussed with particular reference to ternary or multicomponent exchange in zeolites.

Rodney P. Townsend

Papers

Transition metal ion exchange in zeolites. Part 1.—Thermodynamics of exchange of hydrated Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ ions in ammonium mordenite

Ion exchange properties of natural clinoptilolite, ferrierite and mordenite: 1. Sodium—ammonium equilibria

Ion-exchange properties of natural clinoptilolite, ferrierite and mordenite: Part 2. Lead—sodium and lead—ammonium equilibria

Ion Exchange in Zeolites: Some Recent Developments in Theory and Practice

Ternary ion exchange in zeolites. Part 3.—Activity coefficients in multicomponent electrolyte solutions