Adsorption properties of poly(NIPAM-co-AA) immobilized on silica-coated magnetite nanoparticles prepared with different acrylic acid content for various heavy metal ions

Recyclable thermoresponsive heavy metal adsorbents, poly(NIPAM-co-AA) immobilized on silica-coated magnetite nanoparticle (MNP) were prepared by changing the weight ratio between N-isopropylacrylamide (NIPAM) and acrylic acid (AA) monomer and employed for heavy metal ion recovery. The results showed that the adsorbent with the smallest AA amount of 28 mol% in the copolymer exhibited both the highest immobilized copolymer amount of 0.489 g-copolymer/g-MNP and Cu(II) adsorption capacity of 0.511 mol/g-MNP. The result of competitive adsorption using Cu(II), Co(II), Mn(II) and Ni(II) showed that the adsorbent had significant selectivity for Cu(II). Cu(II) recovery from the saturated adsorbent was achieved by merely changing the solution temperature from 50 to 10 degrees C without using acidic solution, and no deterioration of Cu(II) recovery performance was observed in several cycles. The adsorbent achieved a comparable maximum adsorbed amount with a higher desorption ratio by temperature swing with shorter operation time compared to the other thermoresponsive hydrogel adsorbents. In addition to an isothermal bath heating, induction heating of MNP was applied to control the solution temperature for Cu(II) recovery. The results showed that essentially the same Cu(II) recovery property with shorter recovery time was obtained using the induction heating compared to the isothermal bath heating. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.