Enhancing the Multifunctional Photocatalytic Activity of Sustainable Magnetic Nanoparticles

The development of efficient photocatalytic materials has intensified in response to increasing emphasis on sustainable energy conversion and environmental restoration. However, the excessive use and indiscriminate release of heavy metals from photocatalytic nanoparticles pose potential environmental risks. This study provides insights into optimizing visible-light-active photocatalysts to enhance their photocatalytic properties and stability. Specifically, cobalt doping and controlled pH modulation are employed on the modified Fe₃O₄, forming two distinct samples: Co@Fe₃O₄-B (base-treated) and Co@Fe₃O₄-A (acid-treated) nanoparticles. Microscopic characterization reveals that Co@Fe₃O₄-A undergoes a phase transition to hematite, whereas Co@Fe₃O₄-B retains its mixed-phase configuration. Spectroscopic analyses confirm that the cobalt dopants decorate the outskirts of each nanoparticle, forming a core–shell structure. However, Co@Fe₃O₄-B exhibit Co²⁺ states with a high oxygen vacancy content, whereas Co@Fe₃O₄-A contain mixed Co^2+/3+ states. The high density of defect states in the Co@Fe₃O₄-B results in superior photocatalytic efficiency, achieving near-complete oxidation of furfuraldehyde (97% conversion) and 5-hydroxymethylfurfural (94% conversion), as well as effective degradation of toluene (78% conversion). This study demonstrates that the combined approach of doping and pH treatment is promising for the surface-defect engineering of photocatalysts, enhancing their multifunctional performance and reusability for sustainable energy conversion.