Sustainable Synthesis of Magnetic PolyHIPE Nanocomposites Using a Menthol-Based Deep Eutectic Solvent for Efficient Fenton Catalytic Dye Degradation

This work presents a sustainable approach for synthesizing magnetic macroporous nanocomposites (NCs) via Pickering-type high-internal phase emulsions (HIPEs) using a deep eutectic solvent (DES) composed of d,l-menthol/acetic acid (MA, 1:1 molar ratio) as a green alternative to traditional organic solvents for the internal phase. The DES-in-water HIPEs were formulated with acrylamide/<i>N</i>,<i>N</i>'-methylenebis(acrylamide) (AAm:BAAm, 10:1 molar ratio) as the continuous phase and stabilized by a synergistic combination of the Pluronic F127 surfactant and magnetite nanoparticles (MNPs). HIPEs formulated with tetradecane as the internal phase were comparatively studied. The resulting materials exhibited an interconnected macroporous structure with embedded MNPs, enhancing their performance as heterogeneous Fenton catalysts. Magnetic polyHIPE NCs synthesized using MA DES demonstrated outstanding dye degradation efficiency within an 8 h reaction time, achieving removal rates of approximately 98.2% for methyl orange, 97.1% for neutral red, 98.5% for gentian violet, and 92.3% for a complex dye mixture. These materials demonstrated successful reuse across 10 cycles, with performance directly correlated to their specific surface area (<i>S</i>_BET) and MNP content. In contrast, materials synthesized with tetradecane displayed significantly lower dye degradation efficiency (ca. 80.7% for gentian violet) due to a substantial reduction in <i>S</i>_BET (19.84 and 7.14 m²/g for polyHIPEs synthesized using MA DES and tetradecane, respectively). These findings underscore the potential of hydrophobic DESs as sustainable media for developing advanced macroporous nanocomposites for environmental remediation, particularly in degrading organic pollutants from wastewater.