Hydrothermally Synthesized Spinel Nanoferrites as Magnetically Separable and Recyclable Visible-Light Photocatalysts for Degradation of Hydrophilic Organic Pollutant

The objective of this study is to develop a nanosized, visible-light-responsive photocatalyst with magnetic separability and recyclability for repeated use. Spinel ferrite nanoparticles, which are environmentally friendly, are promising candidates for achieving this goal. Spinel ferrite nanoparticles were synthesized via a low-temperature hydrothermal method to investigate their microstructural characteristics, magnetic properties, and photocatalytic performance. Initially, four ternary spinel ferrite (MFe2O4, where M = Mg, Mn, Co, and Zn) nanoparticles were compared in terms of their physical properties and photodegradation efficiencies of organic dye methylene blue (MB). Among them, the MgFe2O4 and ZnFe2O4 samples exhibited superior photocatalytic activity compared to the MnFe2O4 and CoFe2O4 samples. Subsequently, a systematic investigation of the Zn–Mg ferrite system (Zn1−xMgxFe2O4, x = 0 to 0.8 in increments of 0.2) was carried out. The results revealed that the x = 0.8 samples achieved the highest photodegradation efficiency of 99 for a 10 MB aqueous solution under visible-light irradiation for 90 min. This improved performance is attributed to formation of a heterojunction of Zn–Mg nanoferrite/Fe2O3, which promotes light harvesting and prevents photogenerated charge recommendation, thus significantly improving photocatalytic activity.