Near-infrared light-responsive hydrogels via peroxide-decorated MXene-initiated polymerization

Two-dimensional MXene Ti(3)C(2)T(x) nanosheets with peroxide decoration (p-Ti(3)C(2)T(x)) are synthesized by a sonication-assisted MILD etching method. The obtained MXenes can generate hydroxyl radical species and act as an initiator for free-radical polymerization of a series of acrylic monomers without the use of light illumination or co-initiators. The monomers analyzed include acrylamide, N-isopropylacrylamide (NIPAM), N,N-dimethylacrylamide, methyl methacrylate, and hydroxyethyl methacrylate. By simply mixing N-isopropylacrylamide monomers and p-Ti(3)C(2)T(x) nanosheets under deoxygenated conditions, PNIPAM-based nanocomposite hydrogels are synthesized using a high concentration of the monomer. The nanocomposite hydrogels have a photothermal conversion efficiency of 34.7% and photothermal stability superior to that of pristine Ti(3)C(2)T(x). Taking advantage of the thermal responsive behavior of PNIPAM, the nanocomposite hydrogels are successfully exploited as remotely near-infrared light controlled “smart” windows, fluidic valves and photodetectors.