Size and shape tailored sol-gel synthesis and characterization of lanthanum phosphate (LaPO4) nanoparticles

Size and shape tailored stoichiometric lanthanum phosphate (LaPO4) nanoparticles were synthesized through an aqueous sol-gel technique. The effect of reactant concentration on the shape and size of nanoparticles was investigated. Shape evolution of nanoparticles was explained by the spherical diffusion growth mechanism. It was observed that by reducing the reactant concentration from high (100 mol/m(3)) to very low (0.125 mol/m(3)), the morphology of nanoparticles gradually changed from long nanorods to nanospheres. X-Ray diffraction (XRD) results indicate that hexagonal-to-monoclinic phase transformation initiated at lower temperatures in nanospheres compared to the nanorods. Nitrogen-adsorption measurements showed that although all samples are mesoporous, the nanorods synthesized at high concentrated solution had a markedly more specific surface area (e.g. at 100 mol/m(3) reactant concentration, surface area was 114 m(2)/g). The dispersion stability of LaPO4 nanoparticles in aqueous solutions in a wide range of pH (1-12) was evaluated. Dynamic light scattering (DLS) analysis indicated that the sols with pH similar to 2 and pH similar to 10.3 with the corresponding zeta potentials of +40 and -32 mv, provided the highest stability. Zeta-potential measurements of the suspensions revealed an isoelectric point (IEP) at pH similar to 7.5. (C) 2019 Published by Elsevier Ltd.