A smart thermoresponsive adsorption system for efficient copper ion removal based on alginate-g-poly(N-isopropylacrylamide) graft copolymer.

In order to develop a smart Cu(II) ion adsorption and removal system for water purification, poly(N-isopropylacrylamide) (PNIPAAm) was grafted to alginate to give a thermoresponsive Alg-g-PNIPAAm graft copolymer. With low or high initial Cu(II) concentrations, the thermoresponsive Alg-g-PNIPAAm graft copolymer could precipitate at 50 °C, with which Cu(II) was efficiently adsorbed and removed from solutions. Alg gel beads crosslinked by calcium ion Ca(II) could adsorb and remove Cu(II), but the beads released significant amount of Ca(II). The adsorption isotherm study showed that thermoresponsive Alg-g-PNIPAAm and Alg gel beads followed the same Langmuir isotherm model for Cu(II) adsorption and removal, but Alg-g-PNIPAAm demonstrated much higher adsorption capacity than Alg gel beads, because the carboxyl groups in Alg-g-PNIPAAm were free, whereas those in Alg gel beads were complexed with Ca(II). In conclusion, the Alg-g-PNIPAAm copolymer formed a smart Cu(II) adsorption and removal system with superior performance.