Facile green synthesis of core–shell magnetic MOF composites (Fe₃O₄@SiO₂@HKUST-1) for enhanced adsorption capacity of methylene blue

In general, the synthesis of magnetic composites by in-situ, ex-situ, layer-by-layer and self-template methods provide desired properties, such as magnetic properties. However, syntheses using these methods still have the difficulty of controlling and avoiding aggregation of magnetic particles in the matrix. In this research, the magnetic MOF composite Fe₃O₄@SiO₂@HKUST-1 with a core–shell form has been successfully synthesized through a facile green route using a pre-grinding method and less solvent. The morphology and structure of the core–shell, as confirmed by TEM and SEM, showed that the magnetic composite was spherical and not agglomerated. The incorporation of Fe₃O₄@SiO₂ magnetic particles with mass variations of 50 and 100% to HKUST-1 was able to increase the pore size and resulted in the formation of mesopores. The composite when used as an adsorbent for synthetic dyes showed an adsorption capacity of 2.3 times higher (434.78 mg/g) than pure HKUST-1 (188.7 mg/g). The kinetic and isotherm study of the adsorption process followed a pseudo-second-order model and the Langmuir isotherm model. In addition, the feature of Fe₃O₄@SiO₂ magnetic on the composite gave a stability enhancement of the adsorbent when used in aqueous media, being evidenced by the high adsorption capacity of the composite (71.95%) after being recycled five times.