Gas phase synthesis of encapsulated iron oxide–titanium dioxide composite nanoparticles by spray pyrolysis

Composite nanoparticles are of a great interest due to the possibility of combining properties of several different materials. In this study, a spray pyrolysis process utilizing flame-synthesized nanopowder was used to generate iron oxide–titanium dioxide (γ-Fe2O3–TiO2) composite nanoparticles. Iron oxide and titanium dioxide were selected because they are known to have magnetic and photocatalytic properties, respectively. First, dry γ-Fe2O3 nanopowder was prepared with the liquid flame spray technique. After that, the flame-synthesized nanoparticles were mixed with liquid titanium(IV) isopropoxide (TTIP) and isopropyl alcohol. This mixed-phase precursor was sprayed into a tube furnace where TTIP thermally decomposed to form solid TiO2, encapsulating the γ-Fe2O3 powder particles. The synthesized nanoparticles were characterized with aerosol measurements, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The size distributions of the composite nanoparticles were broad, and the mode diameters were 80–130 nm. The particles consisted of a γ-Fe2O3 agglomerate that was either partially or fully encapsulated by a spherical TiO2 particle, depending on the concentration of TTIP in the mixed-phase precursor. The flame-synthesized iron oxide powder was crystalline maghemite, whereas, spray pyrolyzed titanium dioxide had amorphous phase. The as-synthesized composite nanoparticles were calcinated to attain crystalline anatase TiO2. The crystal structures as well as demonstrated photoactivity and magnetic response suggest that the composite nanoparticles could find use as magnetically separable photocatalyst.