Effect of metal ions adsorption on the efficiency of methylene blue degradation onto MgFe ₂ O ₄ as Fenton-like catalysts

Magnesium ferrite (MgFe ₂ O ₄ ) and metal-loaded (Mn ²⁺ , Co ²⁺ , Ni ²⁺ , and Cu ²⁺ ) MgFe ₂ O ₄ nanoparticles were used as Fenton-like catalysts for methylene blue (MB) degradation in aqueous solutions under visible light. Primarily investigated here were the effects of metal ions adsorbed onto MgFe ₂ O ₄ and the conditions of catalytic MB degradation. The results of catalytic tests indicated that in the optimal conditions (catalyst dose of 0.5 g/L, pH 6.0, and H ₂ O ₂ concentration of 20 mmol/L), the mineralization rate of MB reached approximately 98% in 30 min under visible light. There were no significant changes of crystal structure, morphology, particle size, and textural properties of studied catalysts after the adsorption and MB degradation tests. The kinetic studies indicated that the pseudo-first order model fitted well to the experimental data. The catalytic activity of metal-loaded samples rose with increasing Fe ³⁺ and M ²⁺ mobility and this activity ranged from approximately 91 to 97% after 4 consecutive cycles. The main role of ^[rad] OH radicals and holes h _ВC ⁺ in the MB degradation was established. Magnesium ferrite can serve as an effective material for catalytic and adsorption treatment of multi-component aqueous solutions containing organic pollutants and toxic metal ions. High efficiency of MgFe ₂ O ₄ Fenton-like catalyst for MB mineralization under visible light was indicated. A catalytic mechanism in metal-loaded MgFe ₂ O ₄ / H ₂ O ₂ systems was proposed.