Hafnium-Based Magnetic UiO-66 Metal-Organic Framework Nanocomposites; Microwave-Assisted Synthesis and Comprehensive Characterization

Abstract

This study describes the synthesis and characterization of hafnium-based magnetic metal-organic frameworks (Hf-MMOFs) that combine superparamagnetic behavior with tunable surface functionality. Magnetic Fe₃O₄ nanoparticles were synthesized via microwave-assisted co-precipitation, followed by silica encapsulation and solvothermal growth of functionalized Hf-UiO-66 shells to form Fe₃O₄@SiO₂@Hf-UiO-66 core-shell nanocomposites. Surface modification with carboxylic acid, was achieved through a controlled layer-by-layer approach. Structural, morphological, and magnetic properties were evaluated using XRD, FTIR, SEM, TEM, EDS, and VSM analyses, confirming successful MOF coating, retained crystallinity, and strong magnetic responsiveness. The nanocomposites exhibited saturation magnetization values of 23-41 emu/g, enabling rapid magnetic separation within 30 seconds. Optimal synthesis conditions were identified at 700 W microwave power and 8-9 minutes reaction time, yielding 85-88% conversion. The high stability of Hf-O bonds provides enhanced resistance to hydrolysis and thermal degradation, highlighting their potential for catalytic and environmental applications.