Photo-swing extraction system for lanthanide separation by a thermosensitive polymer gel combined with carbon nanotubes

A novel photo-swing extraction system for lanthanide separation was developed using an acid phosphoxy ethyl methacrylate (Phosmer-M) copolymerized thermosensitive polymer gel and N-isopropylacrylamide (NIPAM) combined with single-walled carbon nanotubes (CNTs) as the extracting material. The swelling and shrinking phase transition of the Phosmer-M/NIPAM/CNT gel was successfully induced by photo-irradiation with a halogen lamp because of the heat generation by the CNTs, which occurred upon visible light absorption. The extraction ability of Eu(III) increased upon photo-irradiation because of changes in the volume and hydrophobicity of the composite gel. The ratio of the distribution coefficient with and without photo-irradiation (Kdphoto/Kd25) increased with an increase in the pH. The composite gel possessed sufficient loading and release capacities for Eu(III), La(III) and Lu(III) in repeated processes after photo-irradiation. The selectivity for Eu(III) over La(III) in binary metal systems increased due to photo-irradiation because the observed improvement in the extraction of Eu(III) was greater than that of La(III) during the phase transition of the gel.