Triple Stimuli-Responsive N‑Isopropylacrylamide Copolymer toward Metal Ion Recognition and Adsorption via a Thermally Induced Sol–Gel Transition

• Published in: Industrial & engineering chemistry research 2017-02, Vol.56 (5), p.1223-1232
• Main Authors: Cheng, Jinjin, Shan, Guorong, Pan, Pengju
• Format: Article
• Language: English
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/acs.iecr.6b03626

Poly­(N-isopropylacrylamide-co-maleic acid-co-1-vinylimidazole), P­(NIPAM-MA-VI), has been prepared in water by free radical polymerization. The aqueous solution of low-molecular-weight P­(NIPAM-MA-VI) has four distinct phases above a critical concentration. Effects of monomer ratio, copolymer concentration, and pH on the phase transition temperatures of P­(NIPAM-MA-VI) were studied. The addition of divalent metal ions promoted the gelation process of P­(NIPAM-MA-VI). Therefore, the adsorption behavior of P­(NIPAM-MA-VI) to Cu2+ ions was further investigated; this adsorption behavior was pH-dependent, and the adsorption isotherm could be well fitted by the Freundlich model. The maximum adsorption capacity reaches 21.1 mg g–1 dried copolymer at 60 °C and pH 5. The adsorbed P­(NIPAM-MA-VI) can be regenerated by the treatment of hydrochloric acid and reused in the following adsorption process. X-ray photoelectron spectroscopy (XPS) and synchrotron radiation small-angle X-ray scattering (SAXS) were used to investigate the effect of Cu2+ ions on the phase transition behavior of P­(NIPAM-MA-VI). O 1s and N 1s XPS spectra and SAXS results analyzed by the Ornstein–Zernike and generalized Ornstein–Zernike models are in agreement with the proposed mechanisms and adsorption behavior. As a thermo-, pH-, and metal ion-responsive copolymer, P­(NIPAM-MA-VI) could be used for the ion recognition, water purification, and enrichment of heavy metal ions.