Polyacrylic acid pore-filled microporous membranes and their use in membrane-mediated synthesis of nanocrystalline ferrihydrite

A series of cation-exchange membranes were obtained by photoinitiated grafting of acrylic acid onto a polypropylene microporous support having 0.2 µm diameter pores. The poly(acrylic acid) was shown to be contained within the pores of the membrane. The ion-exchange capacities of these "pore-filled" membranes ranged from 65 to 80% of the theoretical values calculated on the basis of their measured graft yields, with water contents ranging from 72 to 77%. The membranes exhibited a chemical valve effect of flux as a function of pH. Treatment of a poly(acrylic acid) grafted membrane with a solution containing ferrous ions resulted in a large uptake of iron (>24% by weight of iron with a membrane containing 152% graft yield of poly(acrylic acid)). Subsequent alkaline (pH 14) oxidation at 70°C with either oxygen or hydrogen peroxide led to the formation of a superparamagnetic nanocrystalline form of ferrihydrite, 5Fe2O3 ·9H2O. The oxide was identified by temperature-dependent Mossbauer spectroscopy recorded fro...

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