Effect of immobilization method and particle size on heavy metal ion recovery of thermoresponsive polymer/magnetic particle composites

•Thermoresponsive polymer/magnetic particle was prepared for heavy metal recovery.•Various immobilization methods and magnetic particles were used.•Smaller particle size resulted in higher polymer immobilized amount.•In situ immobilization method resulted in better heavy metal recovery property. To examine the effect of the immobilization method and particle size on the Cu(II) recovery performance of the thermoresponsive polymer, poly(NIPAM-co-AA), and on its immobilization onto magnetic support, we compare the "grafting to" and the "in situ" methods, and use two different supports, such as magnetite nanoparticles and ferrite particles with primary particle sizes of approximately 21 nm and 12 μm, respectively. The results show that although the magnetite nanoparticle forms aggregates and the surface area of the primary particle cannot be fully utilized for immobilization; the immobilized copolymer amounts on the magnetite nanoparticles are about 10–42 times higher than that on the ferrite particle. For Cu(II) adsorption, poly(NIPAM-co-AA) immobilized on the magnetite nanoparticles show adsorption amounts approximately 13–20 times higher than that on the ferrite particle. The effect of the immobilization method is also examined by comparing the "grafting to" and the "in situ" methods. Between the two methods, the "in situ" method shows a higher immobilized copolymer amount and better Cu(II) adsorption property. These results show that a combination of the "in situ" method, as the immobilization method, and magnetite nanoparticle, as support, can be a very effective approach to synthesize the thermoresponsive adsorbent of poly(NIPAM-co-AA) immobilized on magnetic particles.