Control on size and adsorptive properties of spherical ferric phosphate particles

Abstract

Ferric phosphate particles were prepared by aging a solution dissolving Fe(ClO 4) 3 and H 3PO 4 at 40–80 °C for 16 h in a Teflon-lined screw-capped Pyrex test tube. The spherical or agglomerated fine particles were only precipitated with an extremely fast rate of reaction. The spherical particles were only produced at a very narrow region in fairly low pH solutions. TEM observation revealed that these particles grew in spherical structure by aggregation of primary small particles. The size of spherical particles was decreased by increase in the solute concentration or raising the aging temperature. Therefore, the formation of spherical particles was explained by a polynuclear layer mechanism proposed by Nielsen. The uniform spherical particles produced are amorphous, but they were crystallized to FePO 4 after calcining above 600 °C. It was suggested that the voids between the primary particles within the secondary agglomerated particles constitute mesopores. The Fe/P molar ratio determined and weight loss in TG curves gave the chemical formulas of the particles as Fe(PO 4) x (H 2PO 4) y ⋅ nH 2O ( x: 0.93–1.00, y: 0–0.22, n: 2.4–2.7). The amorphous spherical ferric phosphate particles showed a high selective adsorption of H 2O by penetration of H 2O molecules into ultramicropores, produced after outgassing pretreatment, of that size is smaller than N 2 molecule. The more particles grew, the more adsorption selectivity of H 2O became remarkable.