Magnetically doped multi stimuli-responsive hydrogel microspheres with IPN structure and application in dye removal

Interpenetrating polymer network (IPN) hydrogel microspheres composed of temperature-sensitive crosslinked poly(N-isopropylacrylamide) (PNIPAM) and pH-sensitive crosslinked poly(methacrylic acid) (PMAA) are prepared by sequential polymerization method. The IPN hydrogel microspheres are characterized for their temperature- and pH-responsive behaviors by measuring the variation of hydrodynamic diameters. The results showed that these hydrogel microspheres exhibited both temperature- and pH- sensitive volume phase transitions. The structure and properties are systematically characterized using FTIR, 1H-NMR, transmission electron microscope (TEM), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and thermo-gravimetric analyses (TGA). IPN hydrogel microspheres are then magnetically doped by in-situ formation of Fe3O4 nanoparticles. The adsorption/desorption of various dyes and subsequent separation of dye loaded magnetic hydrogel microspheres from the aqueous medium are studied under the influence of magnetic field.