Development of eco-friendly CO₂-responsive cellulose nanofibril aerogels as "green" adsorbents for anionic dyes...

A novel CO₂-responsive cellulose nanofibril aerogel as a "green" adsorbent derived from poly(methacrylic acid-co-2-(dimethylamino) ethyl methacrylate) and carboxylated cellulose nanofibrils was successfully prepared via stepwise cation-induced gelation and freeze drying method. This aerogel exhibited CO₂-triggered adsorption behavior towards anionic dyes with a rapid adsorption rate and a high adsorption capacity, as well as satisfactory mechanical properties. Upon CO₂ stimulation, the charged aerogel can selectively adsorb anionic dyes from aqueous solutions based on an electrostatic interaction. The maximum adsorption capacities of this aerogel towards methyl blue (MB), naphthol green B (NGB), and methyl orange (MO) were 598.8, 621.1 and 892.9 mg g^-1, respectively, accompanied by fast adsorption equilibriums towards MB and NGB within 7 min, and MO within 12 min. Meanwhile, the adsorption isotherms and the kinetics of the CO₂-responsive adsorbents followed the Freundlich isotherm and the pseudo-second-order model, respectively. Furthermore, the resulting CO₂-responsive adsorbent exhibited outstanding recyclability, as its adsorption performance can still be maintained even after twenty cycles. Accordingly, the resultant CO₂-responsive cellulose nanofibril aerogel could be a promising adsorbent material for the removal of anionic dyes in wastewater remediation.