Synthesis of mesoporous spherical aluminum phosphate particles using metal ions

Influences of various kinds of divalent and trivalent metal ions on the formation, sizes, and pore structures of spherical aluminum phosphate particles were investigated. The addition of metal ions dramatically decreased the size of the spherical particles. A remarkable particle size reduction was observed in the systems doped with trivalent Fe3+ ions compared with those doped with divalent Co2+, Zn2+, and Mn2+ ions. Incorporation of Fe3+ ions into the crystal lattice to give solid solutions with a chemical composition of Al(1-x)Fe(x)PO4 . nH(2)O was observed in the systems doped with trivalent Fe3+ ions, though no substitution to yield particles with a chemical composition of AlPO4 . nH(2)O occurred for divalent ions. The divalent metal ions were adsorbed onto primary fine particles to interfere with particle growth. The divalent metal ions residing among the primary particles in secondary spherical aluminum phosphate particles were eliminated by rinsing and produced highly mesoporous materials without altering the particle morphology. A similar mechanism was depicted for particle formation in the presence of Fe3+ ions and incorporation into the crystal structure. The spherical aluminum phosphate particles produced with Co2+ ions exhibited an electrically neutral surface in the aqueous medium, while those formed with Fe3+ ions manifested an acidic surface due to phosphate ions exposed on particle surfaces. (C) 1998 Academic Press.