Systematic Study on TiO₂ Crystallization via Hydrothermal Synthesis in the Presence of Different Ferrite Nanoparticles as Nucleation Seeds

In the present work, the crystallization of anatase TiO2 nanoparticles (NPs), using different ferrite nanoparticles with different chemical composition, dimensions and shape as nucleation seeds, was investigated. In particular, CoFe2O4, NiFe2O4 and Fe3O4 NPs with a volume ratio equal to 1:1000 with respect of TiO2 amount, were used in order to investigate the synthesis of nanocrys-talline tetragonal anatase TiO2 by a hydrothermal synthesis. In addition, Lu2O3 nanoparticles were also used to detect the effect of a non-magnetic nanoparticle on the synthesis and nanocrystal-lization of titania. For each sample, a deep physical characterization was performed by XRD (with a Rietveld refinement of the structural data), FE-SEM, STEM, HRTEM, DSC analysis and BET surface area measurement. Furthermore, for some samples, the photocatalytic activity was investigated by degradation of methylene blue in aqueous medium, in the framework of a standard ISO 10678:2010 protocol. The hydrothermal synthesis was performed with a 3 hours' thermal treatment, at a pressure of approximatively 9 bar and a temperature significantly lower (T-max = 150 degrees C) than the usual temperature necessary to obtain crystalline anatase TiO2 (T-cryst = 350 degrees C). The results give evidence that the mere presence of a nucleation seeds in the hydrothermal reactor, without any particular need for the composition and morphology, leads to crystalline anatase TiO2 nanoparticles with high photocatalytic performances.