Temperature-sensitive poly(N-isopropylacrylamide)-reduced graphene oxide/polysulfone as smart separation membrane: structure and performance

N-Isopropylacrylamide (NIPAM) was successfully grafted on reduced graphene oxide (RGO) by free radical polymerization and characterized by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, transmission electron microscope (TEM) measurements, thermogravimetric analysis and ultraviolet-visible transmission spectroscopy. The synthesized poly(N-isopropylacrylamide)-reduced graphene oxide (PNIPAM-RGO) was used to improve the properties of polysulfone (PSF) membranes with different PNIPAM-RGO weight fractions. The structure and properties of PNIPAM-RGO/PSF membrane were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscope, contact angle and tensile testing. The water permeability, self-cleaning recovery rate and water flux decline factor were tested. The blend membrane with 0.4wt% PNIPAM-RGO possessed the optimal rejection and exhibited an impressive self-cleaning recovery rate and fracture strain of 98.6 and 72.2%, showing a 67.4 and 76.5% enhancement compared to that of pure PSF membrane (58.9 and 40.9%), respectively. Meanwhile, the water flux decline factor decreased from 21.0 to 7.8%. The drastic change of permeability to aqueous solution, observed around lower critical solution temperature of PNIPAM-RGO, proved the thermal sensitivity of the blend membrane. The NIPAM grafted onto RGO by free radical polymerization and utilizing the advantages of both PNIPAM and RGO, which was used as an additive in the membrane, and very hard to lose during the membrane formation and application. The resulting membrane exhibited a significant increase in self-cleaning recovery rate, hydrophilicity, mechanical strength and thermosensitivity.