Temperature-Swing Solid-Phase Extraction of Heavy Metals on a Poly(N-isopropylacrylamide) Hydrogel

Abstract

The feasibility of temperature-swing adsorption of heavy metals on a thermosensitive N-isopropylacrylamide (NIPA) hydrogel was examined. We have proposed a novel temperature-swing solid-phase extraction (TS-SPE) technique. First, a metal ion in an aqueous solution is complexed with an extractant. Subsequently, the metal-extractant complexes (or micelles) are adsorbed onto the NIPA hydrogel through a hydrophobic interaction above the lower critical solution temperature (LCST). Finally, the metal-extractant complexes are desorbed from the NIPA hydrogel after it is cooled below the LCST. In a model system consisting of Cu(II) ions, sodium n-dodecylbenzenesulfonate (SDBS), and NIPA hydrogel, the proposed TS-SPE technique has been successfully conducted. The following observations can be made: the amount of adsorbed Cu(II) ions increases with the increase in temperature, the maximum adsorption is attained at a temperature above the LCST, and the hydrogel adsorbs and desorbs Cu(II) ions reversibly due to the temperature-swing between 10 and 40 degrees C. The LCSTs of poly(NIPA) in aqueous SDBS solutions with/without CuCl2 and the surface tensions of their solutions suggest that the hydrophobicity of the complex Cu(DBS)2 is greater than the hydrophobicities of SDBS and DBS. In addition to the separation of heavy metals, TS-SPE is potentially applicable to cases such as the separation of biological molecules by means of metal-ion affinity.

Quartz crystal microbalance electrode modified with thermoresponsive crosslinked and non-crosslinked N-isopropylacrylamide polymers. Response to changes in temperature

“…Because of their environmental sensitivity and unique structure, these polymeric hydrogels have been employed in a variety of fields, e.g., in controlled drug release systems, artificial muscles, sensors, molecular recognition systems, and as specific sorbents. Their attachment to the surface of an electrode improves their usefulness in, e.g., surface patterning, construction of switchable sensors/biosensors and more [8][9][10][11][12][13][14][15][16].…”

Removal of heavy metal ions and humic acid from aqueous solutions by co-adsorption onto thermosensitive polymers

“…The NIPA polymer is hydrophilic and soluble in water below the LCST and is hydrophobic and insoluble above the LCST. In our earlier studies, adsorbents using poly(NIPA) as a matrix [11,12] and a separation technique using both poly(NIPA) and extractants [13,14] were developed; those permit temperature-swing adsorption, i.e., the controlling the adsorption and desorption of heavy metal ions in a solution by changing the temperature. In addition, a thermosensitive flocculation using poly(NIPA) has been developed for the removal of suspended substances such as activated sludge [15], TiO 2 [16], and In(III)-organophosphorus extractant complexes [14].…”

Temperature-swing adsorption of precious metal ions onto poly(2-(dimethylamino)ethyl methacrylate) gel

“…Studies have been conducted on the adsorption of metal ions from solutions onto poly(DMAEMA); however, in our literature survey, we did not find any study that reported on temperature-swing adsorption (TSA), i.e., the control of the adsorption and desorption behavior of metal ions by changing the temperature. In our earlier studies, we prepared the adsorbents using thermosensitive poly(N-isopropylacrylamide), poly(NIPA), as a matrix [28][29][30] and developed separation technique using both poly(NIPA) and extractants [31,32]; the use of these adsorbents facilitates TSA, and this separation technique can be used for TSA. Moreover, we successfully enrich Au(III) ions in a diluted solution by means of TSA [28].…”