Ultralight TETA-Functionalized Cellulose Aerogels for Ultrahigh Synchronous Indigo and Congo Red Adsorption: Combined Experimental and Detailed DFT Mechanistic Insights

The rapid expansion of the textile dyeing industry has created an urgent need for high-performance dye wastewater treatment materials due to the limitations of traditional adsorbents in efficiency and separability. Herein, we report the synthesis of ultralight, cost-effective aerogel adsorbents by introducing triethylenetetramine (TETA) into α-cellulose (CU). The resulting CU/TETA-0.25 aerogel displays outstanding adsorption capacities for Congo Red and indigo dyes, reaching 575.7±20   mg/g and 516.4±20   mg/g, respectively. Remarkably, less than 1   g of this aerogel continuously filters over 35   L (50   mg/L) of deeply colored red–blue dye wastewater to near transparency. Its high adsorption efficiency remains stable even under simultaneous exposure to multiple ions, organic compounds, and pH fluctuations. Mechanistic insights, derived from SEM, EDX, and XPS analyses and first-principles calculations (including molecular structure optimization, frontier molecular orbital distribution, weak interaction, and charge density difference), confirm that the –OH and –NH₂ groups on CU/TETA-0.25 drive dye adsorption through hydrogen bonding, supplemented by electrostatic and van der Waals interactions. Owing to its mass-producibility, lightweight nature, and low cost, CU/TETA-0.25 holds great promise for large-scale applications in mitigating water pollution caused by mixed dyes.