TEMPLATE-CONTROLLED SYNTHESIS OF SUPERPARAMAGNETIC GOETHITE WITHIN MACROPOROUS POLYMERIC MICROSPHERES

A superparamagnetic form of goethite, alpha-[FeO(OH)], has been obtain ed within macroporous crosslinked poly(divinylbenzene) microspheres (a verage diameter 3.6 mu m and pore size 50-200 nm) by a chemical proces s involving (1) sulfonation of the internal and external surfaces of t he microspheres, (2) treatment of the sulfonated microspheres with aqu eous ferrous chloride solution, and (3) oxidation with hydrogen peroxi de, pH 14, 70 degrees C. Steps 2 and 3 were repeated four times, yield ing particles containing up to 19% Fe per total weight of material. TE M micrographs of sectioned microspheres revealed the presence of two f orms of goethite: disks 25 nm in diameter and needles 80 nm long and 2 5 nm wide. Temperature dependent magnetization and susceptibility data indicate that the materials are superparamagnetic above 50 K. The cal culated magnetic susceptibility for the particles is 3 orders of magni tude larger than that of bulk goethite. Aqueous solutions of ferrous c hloride were oxidized under the same conditions (H2O2, pH 14, 70 degre es C) (1) in the absence of microspheres and (2) in the presence of no nporous polystyrene latex particles carrying surface sulfate groups. N either situation yielded superparamagnetic goethite.