Preparation and adsorption properties of green cellulose-based composite aerogel with selective adsorption of methylene blue

Four green aerogels were prepared to remove the cationic dye methylene blue (MB), using the method of solution mixing and freeze-drying. Polyethylene glycol diglycidyl ether (PEGDE) was employed as a crosslinker. The structure and performance of the adsorbents were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), zeta potential measurement and mechanic testing. The results identified that PEGDE efficiently assisted in forming network structure of the porous aerogels, and the removal rates of four aerogels were all higher than 90%. The aerogel composed of sodium carboxymethyl cellulose (CMC) and carboxylated cellulose nanofibers (CNF–C) performed best with adsorbance of 579.50 mg/g, which had a strong electrostatic attraction with MB, exhibited selective adsorption, and did not collapse after ten cycles of underwater compression tests. The adsorption process of CMC/CNF–C aerogel was compatible with the pseudo-second-order kinetic model and Langmuir isothermal model, and the maximal adsorption capacity was 917.43 mg/g. According to the calculation of thermodynamic parameters, the adsorption process was spontaneous and benefited from temperature rise in 20–40 °C. After five regenerations, the adsorption capacity of CMC/CNF–C aerogel decreased from 579.5 mg/g to 513.2 mg/g, indicating a reusable adsorbent in wastewater treatment.