Dual-responsive copolymer hydrogel as broad-spectrum adsorbents for metal ions

A copolymeric hydrogel (PEGMA) with poly(ethylene glycol) methyl ether acrylate (PEGA), 2-methoxyethyl acrylate (MEA) and acrylic acid (AA) was synthesized in this study. The obtained PEGMA hydrogel exhibited sensitive response to pH and temperature and showed excellent adsorption properties for many metal ions, such as Fe(Ⅲ), Pb(Ⅱ), Zn(II), Ni(II), Mn(II) and Co(II), etc. Fe(Ⅲ) and Pb(Ⅱ) were selected to study thermodynamics and kinetics. The adsorption process followed pseudo-second-order kinetics equation. The adsorption isotherms could be described by Freundlich isotherm models. The maximum adsorption amount was calculated to be 195.43 (Fe³⁺) and 176.06 (Pb²⁺) mg/g. Besides, using the thermal and pH responsiveness, the PEGMA hydrogels can quickly release the adsorbed molecules with control. The heavy metal ions loaded PEGMA hydrogels could also be easily regenerated by diluted hydrochloric acid and still keep a major adsorption capacity. After five cycles, the adsorption ability remained more than 90% of the original PEGMA. Thus, the PEGMA hydrogels may be new high-performance and environment friendly material for metal pollution treatment with promising developmental potential.