Micro/nanostructure and directional channel of recyclable carboxylated aerogels from waste cotton for wastewater treatment

Developing high value-added utilization of waste cotton provides a promising approach for the sustainable development. Herein, the carboxylated cellulose aerogels (CCAs) featuring in micro/nanostructure and directional channel are fabricated from cotton fabrics via the ingenious combination of selective oxidation, high-speed cutting, and freeze-drying. The as-prepared 2.0-CCA demonstrates not only excellent adsorption capacity for cationic dyes in water but also recyclability due to the abundant carboxyl groups (3.20 mmol/g) and the robust porous structure. And it shows a static maximum adsorption capacity (q_m) of 751 mg/g and a dynamic breakthrough amount more than 700 mg/g for methylene blue (MB), more efficient than most reported cellulose-based adsorbents. In addition, the 2.0-CCA shows a high equilibrium adsorption capacity (q_e) about 680 mg/g for MB at pH = 6 and keeps q_e above 600 mg/g even in a broad pH range of 3‒10, indicating a high tolerance to the solution pH value. At an ion concentration lower than 0.25 mol/L, the additional cations such as Na⁺ and K⁺ or anions such as Cl^‒, SO₄^2‒, and NO₃^‒ show a little effect on the q_e (higher than 500 mg/g) of 2.0-CCA for MB. The treated dye wastewater can be recycled for fabric dyeing, and there is no significant color difference (∆E) between fabrics dyed with dye liquors prepared with fresh or recycled water. The theoretical study confirms the importance of the electrostatic attraction between carboxyl groups of 2.0-CCA and dye molecules for the efficient adsorption.