TiO2–Fe3O4 Composite Systems—Preparation, Physicochemical Characterization, and an Attempt to Explain the Limitations That Arise in Catalytic Applications

Abstract

In this work, a composite material based on titanium(IV) oxide and iron(II,III) oxide was prepared using mechanothermal method. The obtained composite system was thoroughly characterized using techniques such as scanning electron microscopy, X-ray powder diffraction, thermogravimetric analysis, and nanoparticle tracking analysis. The acute toxicity of the composite material was evaluated with Microtox. In addition, the material’s photocatalytic potential was studied in photodegradation tests of ibuprofen. The composite system revealed magnetic properties of potential usage in its recovery after photocatalytic tests. However, the photocatalytic activity of TiO2–Fe3O4 was lower than that of bare TiO2. In the photocatalytic tests performed under UV (365 nm) light, a 44% reduction of initial ibuprofen concentration in the sample was noted for bare TiO2, while for TiO2–Fe3O4 composite, only a 19% reduction was observed. In visible light (525 nm), both materials achieved statistically insignificant photodegradation rates, which was contrary to the anticipated effect for TiO2–Fe3O4. The observation was explained by a side oxidation reaction of Fe3O4 to Fe2O3 by the generated reactive oxygen species (ROS) in the photocatalytic process, which significantly diminished the amount of available ROS for ibuprofen degradation. The oxidation process appearing within TiO2–Fe3O4 was evident and easily observed as the color of the material turned from gray to brown. Acute toxicity assay performed with the use of Microtox revealed reduced toxicity of TiO2–Fe3O4 (32% inhibition of the Aliivibrio fischeri bacteria cell viability according to bioluminescence emitted) when compared to bare Fe3O4 (56% inhibition), whereas bare TiO2 was non-toxic. In the study, the processes occurring during the photocatalytic reaction were analyzed and discussed in the context of the available literature data.