Partially carboxymethylated cellulose fibres as high-performance bioadsorbents for efficient cationic dye removal

This study reports the synthesis of partially carboxymethylated cellulose fibres (CMFs), obtained from commercial dissolving pulps, as efficient and sustainable bioadsorbents for the removal of methylene blue (MB) from aqueous solutions. Carboxymethyl groups were introduced onto the cellulose framework through a simple, two-step heterogeneous reaction, enhancing surface charge and reactivity while preserving the native fibrous structure. This modification resulted in a significant increase in carboxyl content and negative zeta potential, improving dye adsorption via electrostatic interactions and π-π stacking. CMFs exhibited excellent adsorption performance, achieving adsorption capacities up to 120.5 mg/g and over 94 % MB removal within 10 min, clearly superior to unmodified cellulose. The adsorption process followed pseudo-second-order kinetics and was best described by the Temkin isotherm, indicating chemisorption on a heterogeneous surface. Structural and chemical changes after carboxymethylation were confirmed by ATR-FTIR, XPS, SEM, and XRD analyses. Furthermore, CMFs demonstrated high regeneration potential, maintaining over 90 % desorption efficiency in the first reuse cycle. These findings highlight the potential of chemically modified cellulose fibres as low-cost, scalable, and eco-friendly adsorbents, bridging renewable materials design with practical water remediation applications.