Removal of dye AG25 by a hybrid process of plasma-activated water and cobalt nanoferrite photocatalysis: part I

Cobalt nanoferrite CoFe 2 O 4 (NFCo) was synthesized using the sol–gel auto-combustion method. The structural, morphology, and magnetic properties were characterized. X-ray diffraction analysis revealed the formation of a pure phase with an inverse spinel structure, featuring an average crystallite size of 67 nm. Scanning electron microscopy observations revealed the existence of particle agglomerates and a porous morphology. The spinel structure was confirmed by Raman spectroscopy, with the identification of the five characteristic modes (A 1g (1) , E g , T 2g (3) , T 2g (2) , T 2g (1) ), as well as by FTIR spectroscopy, where the two vibrational modes in the tetrahedral and octahedral sites (576.8 and 412.12 cm −1 ) were observed. Magnetic analysis revealed that the coercive field increased resistance to demagnetization. Various oxidation processes, including UV, plasma-activated water (PAW) by gliding arc discharge (GAD), and NFCo, as well as hybrid systems UV, PAW/UV, NFCo/UV, PAW/NFCo, and PAW/NFCo/UV, were employed to assess the elimination of AG25 dye. Decolorization processes, mechanisms, and photocatalysis were studied. The effect of experimental parameters as a function of time, pH, and UV exposure showed that the maximum decolorization rate was 56.1% with PAW alone, 73.1% with PAW/UV, 72.4% with PAW/NFCo, and 99.1% with PAW/NFCo/UV after 360 min. The effect of pH demonstrated that the treatment is more effective under acidic conditions (pH = 2), achieving a decolorization rate of 75.6% in just 60 min, compared to neutral and alkaline conditions. This study underscores the potential of NFCo combined with plasma-activated water and UV as magnetic nanophotocatalysts to replace classical heterogeneous catalysts in water treatment, offering new perspectives for more effective methods of degrading organic pollutants in water treatment applications.