Fabrication of bifunctional cellulose fibers via phosphorylation and carboxymethylation for enhanced dye adsorption and filtration

Cellulose-based adsorbents offer sustainable alternatives to petroleum-derived ion-exchange fibers for dye wastewater treatment. However, existing cellulose derivatives face an inherent trade-off: introducing sufficient cationic groups to achieve high adsorption capacity inevitably causes excessive swelling and structural deformation, compromising filtration performance. Here, we report a bifunctional cellulose fiber (BCF) that overcomes this limitation through integrated phosphate esterification and carboxymethylation. The phosphate groups serve a dual role—providing additional cation-exchange sites (2.09 mmol·g⁻¹) while forming an internal crosslinked scaffold (confirmed by ³¹P NMR) that suppresses swelling and preserves fiber integrity. The resulting BCF exhibits exceptional methylene blue adsorption capacity (1243.96 mg·g⁻¹), exceeding its theoretical ion-exchange capacity. The molar ratio of adsorbed dye to anionic sites (1.095 > 1.0) and Sips heterogeneity parameters (1/nₛ = 0.7268–0.8324) confirm synergistic adsorption mechanisms involving electrostatic interactions, hydrogen bonding, and dipole-dipole forces. Crucially, the crosslinked scaffold enables the BCF nonwoven filter to achieve a rapid filtration rate (31.85 m³·m⁻²·h⁻¹) and maintain > 98% removal efficiency after four regeneration cycles without requiring glass fiber blending. This work establishes a molecular design paradigm resolving the capacity-stability conflict in cellulose adsorbents, advancing sustainable biomass for practical wastewater treatment. • Cellulose fibers were upgraded via phosphate esterification and carboxymethylation. • The generated material was comprehensively characterized. • The adsorption and filtration fundamentals of the material were evaluated. • The product showed excellent dye adsorption capacity and filtration affinity. • The fabricated material could be used as a renewable filter for dye decontamination.