Template-Controlled Synthesis of Superparamagnetic Goethite within Macroporous Polymeric Microspheres

Abstract

A superparamagnetic form of goethite, α-[FeO(OH)], has been obtained within macroporous crosslinked poly(divinylbenzene) microspheres (average diameter 3.6 μm and pore size 50-200 nm) by a chemical process involving (1) sulfonation of the internal and external surfaces of the microspheres, (2) treatment of the sulfonated microspheres with aqueous ferrous chloride solution, and (3) oxidation with hydrogen peroxide, pH 14, 70 °C. Steps 2 and 3 were repeated four times, yielding particles containing up to 19% Fe per total weight of material. TEM micrographs of sectioned microspheres revealed the presence of two forms of goethite : disks 25 nm in diameter and needles 80 nm long and 25 nm wide. Temperature dependent magnetization and susceptibility data indicate that the materials are superparamagnetic above 50 K. The calculated magnetic susceptibility for the particles is 3 orders of magnitude larger than that of bulk goethite. Aqueous solutions of ferrous chloride were oxidized under the same conditions (H 2 O 2 , pH 14, 70 °C) (1) in the absence of microspheres and (2) in the presence of nonporous polystyrene latex particles carrying surface sulfate groups. Neither situation yielded superparamagnetic goethite.