One-step synthesis and deposition of ZnFe₂O₄ related composite films via SPPS route for photodegradation application

Binary spinel-type metal oxides (AB₂O₄) related materials, including ferrites (AFe₂O₄), are attractive photocatalysts thanks to their excellent visible light response for the photodegradation of organic pollutants. Currently, these materials are synthesized via conventional chemical routes suffering from long preparation duration and multistep. Moreover, the photocatalysts are obtained as nano-powders from conventional chemical routes would introduce another drawback for their recycling and reuse. From an industrial perspective, it is desirable to develop an efficient and facile synthesis process to produce photocatalysts in a non-dispersible form. Herein, we demonstrate that the solution precursor plasma spray (SPPS) process is a single-step method for depositing photocatalytically active zinc ferrite-based films within several minutes. The influence of the precursor ratio on the microstructures and phase compositions of the ZnFe₂O₄ films was investigated by XRD and Raman analyses. In addition, two optimized ZnFe₂O₄ films were prepared by increasing the ZnO loading and tailoring injection pattern of the precursor solution. The surface morphologies and optical bandgap were also determined by SEM and UV-visible spectroscopy. The photocatalytic activities of the ZnFe₂O₄ films were evaluated through the degradation of the Orange II dye and of tetracycline hydrochloride under UV or visible light irradiation. The results show that compositional ratios and composition distribution of the ZnFe₂O₄ films prepared via SPPS played a key role on the photocatalytic activity. The SPPS route was demonstrated to be a promising method for the synthesis and the deposition of metal oxide (i.e. perovskite type and spinel type) films within a single-step for functional applications.