Thermal and pH dual-responsive cellulose microfilament spheres for dye removal in single and binary systems

Cellulose microfilaments/poly(N-Isopropylacrylamide-co-acrylic acid) spheres (MPNAA) were prepared via the in-situ synthesis of semi-interpenetrating networks (semi-IPN). The free radical copolymerization of acrylic acid (AA) (for pH-sensitive chain segments) and N-isopropylacrylamide (NIPAM) (for temperature-sensitive chain segments) was conducted in a microwave-reactor in the presence of porous cellulose/microfilament composite spherical beads pre-prepared. The surface morphology and adsorption properties of the as-prepared spheres were systematically characterized. The adsorption behaviors of resulting MPNAA towards dyes, methylene blue (MB) and methyl violet (MV), were pH sensitive; and the optimal adsorption occurred at pH 9. The dynamic adsorption processes could be well fitted with pseudo-second-order kinetic, Elovich and simplified intraparticle diffusion models. Meanwhile, Langmuir, Temkin, Freundlich, and Dubinin-Raduskevich models were used to fit the adsorption isotherms at 25, 40, and 55 °C, respectively. The results indicated that the adsorption capacities of MPNAA towards MB and MV could reach as high as 497.5 and 840.3 mg g^-1, respectively, in single systems; and high adsorption capacity was maintain in binary systems with the favorable adsorption of MV. Overall, the semi-IPN MPNAA spheres are promising as novel pH- and temperature-responsive adsorbents, facilitating the controllable adsorption/desorption processes.