Controlled synthesis of core-shell, yolk-shell and hollow spheres C@La2Zr2O7 via the combination of hard templating and co-precipitation method

Core-shell and yolk-shell architectures are attracting great attention owing to their unique structure and infusive applications in the nanotechnology field. In this research, core-shell structured C@La2Zr2O7 nanospheres were synthesized through a facile technique using carbon spheres as templates. Lanthanum nitrate (La(NO3)3·6H2O) and zirconium oxychloride (ZrOCl2·8H2O) co-precipitated homogeneously on the surface of modified carbon spheres by adding ammonia dropwise. The close-to perfect spherical La2Zr2O7 hollow spheres were obtained by a two-step calcination of the C@La2Zr2O7 core-shell components, which were calcined at a high temperature in argon atmosphere and followed by low temperature oxidization calcination. SEM, TEM, XRD, and FTIR were used to characterize the morphology, size, composition, and crystal structure of synthesized products. The results show that La2Zr2O7 nanoparticles were attached tightly on the surface of carbon spheres through the functional groups, such as -OH, and O˭C-O-. After modified by NaOH, the carbon spheres surface possessed more abundant oxygen containing groups, resulting in much more La3+ and Zr4+ co-precipitated uniformly on their surface. Ultimately, an average diameter of the La2Zr2O7 hollow spheres was about 220 nm and the shell thickness was about 40 nm. Through controlling the oxidation calcination time, the morphology of the powders exhibited core-shell structured, yolk-shell structured and hollow structured spheres. Further, the formation mechanism of the hollow La2Zr2O7 spheres was elucidated.