Preparation, Characterization and Photocatalytic Activity of Fe₃O₄/γ-Fe₂O₃@MOFs Composites in the Photocatalytic Decomposition of the Congo Red Dye

In this work, a series of promising iron-containing composite materials Fe₃O₄/γ-Fe₂O₃@Fe-MOF based on unsaturated organic dicarboxylates (maleic, itaconic and muconic acids) were synthesized, which were used for photocatalytic decomposition of the organic dye—Congo Red. The composition of the obtained composites was analyzed using elemental analysis, IR spectroscopy and X-ray phase analysis. Magnetic properties, thermal stability and surface characteristics of the synthesized composites were studied by vibration magnetometry, thermogravimetric analysis, low-temperature nitrogen adsorption-desorption methods. The highest efficiency of Congo Red removal via the Fenton reaction was demonstrated by the Fe₃O₄/γ-Fe₂O₃@ita-MIL-88a(Fe)-1 composite with itaconic acid as bridging ligands. The effective rate constants of photocatalytic decomposition of Congo Red for the synthesized Fe₃O₄/γ-Fe₂O₃@Fe-MOF composites ranged from (0.22 ± 0.03) × 10^–3 min^–1 to (19.1 ± 1.2) × 10^–3 min^–1. When compared against homogeneous Fenton, Fe₃O₄/γ-Fe₂O₃@ita-MIL-88a(Fe)-1 composite’s rate constant was 4 times higher.