Synthesis of Gd2O3 Nanoparticles and Gd2O3@SiO2 Core–Shell Particles with Variable Morphology

Various methods to produce Gd-containing nanoparticles (precursors of Gd2O3) were assessed. Their size and morphology are shown to strongly depend on the synthesis technique and composition. The reaction of highly diluted solutions of gadolinium nitrate with ammonium oxalate led to formation of Gd2(C2O4)3 oxalate sol particles with a size of ~8 nm in presence of surfactant and ~26 nm particles when it was absent. During storage of these sols, the particle size increases to 180–200 nm. Gd(OH)3 particles and Gd2(C2O4)3 particles were synthesized by the sol–gel method. Hydroxide Gd(OH)3 had the morphology of extended broken planes, while oxalate Gd2(C2O4) had the structure of micrometer-sized polyhedra. Subsequent application of SiO2 shells to their surface by the hydrolytic decomposition of tetraethoxysilane led to formation of core–shell particles Gd(OH)3@SiO2 and Gd2(C2O4)3@SiO2, morphologically identical to the Gd(OH)3 and Gd2(C2O4)3 nuclei. Thermal decomposition of Gd(OH)3 and Gd2(C2O4)3 or gadolinium citrate resulted in formation of cubic Gd2O3 particles whose morphology does not depend on that of the precursors.