Sustainable transformation of waste cotton into quaternized carboxy cellulose nanocrystals enables chain-enhanced adsorption for industrial textile wastewater purification

The generation of dyeing wastewater in textile production, along with persistent cost and technological barriers, has concentrated manufacturing in regions prioritizing growth over regulation, threatening ecological integrity and industry sustainability. Here, we introduce a nanofiltration platform inspired by sand filters, using quaternized carboxy cellulose nanocrystals (FCNCs) synthesized from textile waste cotton via a rapid (60 min), high-yield (88.5 %) one-step functionalization. Combining Fe 3+ -mediated proton flux with temperature-programmed epoxy–amine chemistry enables regioselective grafting of carboxyl (–COO − ) and quaternary ammonium (–N + (CH₃)₃) groups, advancing efficiency and precision in FCNC production. Spectroscopy and DFT reveal a chain-enhanced adsorption mechanism, where cation coordination at –COO − promotes electron delocalization toward –N + (CH₃)₃, boosting anion affinity by 142 % and enabling equilibrium within 30 min. Integrated into a biomimetic sandwich-type matrix, FCNCs remove >97 % of dyes and metals with ultralow hydraulic resistance (62.2 % of conventional) and high throughput (3.5 ton·kg −1 ·h −1 ) without sludge, enabling a scalable “waste-to-treatment” process for sustainable water purification.