Combining Acid- And Base-Imprinted Nanoparticles in a Hydrogel Film for Temperature-Responsive Quick and Reversible Capture of Salt

Hydrogel films that reversibly absorb salt in response to thermal stimuli are prepared and evaluated. Co-immobilization of temperature responsive poly(N-isopropylacrylamide) (polyNIPAm) nanoparticles (NPs) in which carboxylic acids and amines are imprinted is crucial in the design of the film. At high temperatures, acids and bases are imprinted in the NPs in deionized form and thus NPs are not capable of capturing counterions. However, at low temperatures, the NPs swell and denature from the imprinted structures and are thus capable of absorbing salts by providing counterions. The absorbed salts are released upon heating owing to the regeneration of the imprinted acids and bases. The imprinted microenvironment around the acids and bases as well as the spatial distribution of the functional groups is crucial in the design of the films. The films showed quick phase transition behavior of which relaxation time is about 800 ms and can reversibly capture up to 468 μmol/g (27 mg/g) of NaCl in a heating and cooling cycle. It was demonstrated that the films can almost completely desalinate (>90%) a sugar solution and can be immediately regenerated by heating.