Macroporous Polyacrylamide γ-Fe<sub>2</sub>O<sub>3</sub> Nanoparticle Composites as Methylene Blue Dye Adsorbents
María T. Vallejo-Macías, Carolina L. Recio-Colmenares, José B. Pelayo-Vázquez, Sergio Gómez‐Salazar, Francisco Carvajal‐Ramos, J. F. A. Soltero, Milton Vázquez‐Lepe, Josué D. Mota‐Morales, María G. Pérez‐García
Abstract
In this work, we have explored the use of hydrophobic deep eutectic systems (DESs) composed of d,l-menthol and different naturally occurring acids (acetic acid, lauric acid, lactic acid, and pyruvic acid) as an alternative green internal (dispersed) phase in the formulation of high internal phase emulsions (HIPEs). DES-in-water (DES/W) HIPEs were formulated using the hydrophilic monomer acrylamide and the cross-linker N,N′-methylenebis(acrylamide) with water as the continuous phase and stabilized with a nonionic triblock copolymer surfactant (Pluronic F127). Furthermore, HIPEs formulated with tetradecane as the dispersed phase were comparatively studied. Surprisingly, stable DES/W HIPEs were obtained with the d,l-menthol/acetic acid (M:AA) DES and used as templates to obtain polyacrylamide macroporous materials (polyHIPEs) within a sustainable framework. The materials were coated with maghemite nanoparticles (γ-Fe2O3 Nps; synthesized in situ onto the porous structure by a coprecipitation method), allowing the formation of hydrophilic polyHIPEs with magnetic and electrostatic properties, which were satisfactorily used as methylene blue (MB) dye adsorbents. The use of the M:AA DES as the internal phase in HIPE formulation allowed the synthesis of macroporous materials with higher surface area (SBET) and γ-Fe2O3 Nps amount than those formulated with tetradecane because of the different porous structures obtained. Therefore, the magnetic polyHIPEs obtained with the M:AA DES presented higher MB dye maximum adsorption capacity (359.71 mg g–1) than those with tetradecane (264.55 mg g–1) in the same synthesis conditions, even higher than some commercial MB adsorbents. The materials were reused for more than six adsorption/desorption cycles without losing their adsorption capacity. Thus, the M:AA DES represents a green tool for the preparation of magnetic macroporous materials composed of polyacrylamide γ-Fe2O3 Nps with a promising and competitive performance as MB dye adsorbents.