Ionic liquid decorated MXene/Poly (N-isopropylacrylamide) composite hydrogel with high strength, chemical stability and strong adsorption

Organic phenolic pollutants in industrial wastewater cause severe environmental pollution and physiological damage. Poly (N-isopropylacrylamide) (PNIPAM) hydrogels generally have poor mechanical strength and are also intrinsically frangible, limiting their widespread applications in wastewater treatment. Combining them with 2-dimensional materials can also only improve the mechanical properties of hydrogels. Here, we report a high-strength, chemical stability and strong adsorption MXene/poly (N-isopropylacrylamide) (PNIPAM) thermosensitive composite hydrogel for efficient removal of phenolic pollutants from industrial wastewater. Ionic liquids (ILs) were grafted onto the surface of MXenes and introduced into NIPAM monomer solution to obtain composite hydrogels by in-situ polymerization for improved mechanical strength and adsorption capacity of the composite hydrogel. Compared with the MXene/PNIPAM composite hydrogel, the introduction of ILs simultaneously improves the mechanical and adsorption properties of the composite hydrogel. The ILs bind to the surface of MXene flakes through electrostatic interactions, which improved the thermal stability and oxidation resistance of MXenes while maintaining its good dispersion. Using 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) modified MXene (MXene-EMIMBF4) did not change significantly were observed after aging for 45 days. As-prepared composite hydrogels demonstrated excellent mechanical properties, reusability, and high adsorption capacity for p-Nitrophenol (4-NP). The MXene-EMIMBF4/PNIPAM hydrogel could recover after ten 95% strain compression cycles under the synergistic effect of chemical bonding and electrostatic attraction. Its maximum adsorption capacity for 4-NP was 200.29 mg g-1 at room temperature, and the adsorption capacity maintained at ∼90% of its initial value after five adsorption cycles, which was related to the introduction of EMIMBF4 to form a denser network structure. The adsorption data followed the pseudo-second-order kinetics and Freundlich models.