Magnetically Separable Photocatalyst Fe3O4/SiO2/N-TiO2 Hybrid Nanostructures

Magnetically separable photocatalysts composed of Fe₃O₄@SiO₂ nanoparticles coated with nitrogen-doped TiO₂(Fe₃O₄/SiO₂/N-TiO₂) are analyzed in this paper. First, Fe₃O₄@SiO₂ nanoparticles were synthesized using an autocombustion sol-gel method, with ferric nitrate and tetraethyl orthosilicate (approximately 23 wt% of SiO₂). In the second step, once the TiO₂ gel was formed from the alkoxide precursor, titanium tetraisopropoxide, magnetite Fe₃O₄@SiO₂ nanoparticles were mechanically dispersed and urea was mechanically added to the mixture. The final Fe₃O₄/SiO₂/N-TiO₂ calcined nanostructure was analyzed using X-ray diffraction, and Rietveld refinement was employed for the estimation of the relative percentage of each component: 10.5% ± 0.5% of Fe₃O₄@SiO₂ and 90% ± 1% of TiO₂ (anatase). With respect to the magnetic properties (SQUID magnetometry), the TiO₂ coating does not introduce remarkable changes in the room temperature behavior (i.e., anhysteretic superparamagentic behavior). On the other hand, diffuse reflectance UV-Vis (DRUV) shows a clear enhancement of the absorption in the visible region (between 400 and 550 nm), a characteristic feature of the nitrogen-doped TiO₂ materials. Finally, the photocatalytic activity was evaluated employing methyl orange as substrate and UV (monochromatic light 365 nm) and visible light (Xe lamp). The most interesting feature of the developed hybrid photocatalytic nanostructure is the possibility to extract the photocatalyst with an external magnetic field once the organic substrate is degraded.