Coumarin-modified cellulose as an efficient adsorbent for cationic dye removal from aqueous environments: synthesis, characterization, and adsorption performance.

In this study, a novel cellulose-based adsorbent was developed through a two-step chemical modification process involving commercially available cellulose, sodium periodate as an oxidizing agent, and a coumarin-thiazole derivative as the functionalizing agent. The modified cellulose was successfully prepared and characterized using FTIR analysis confirmed the formation of C = N stretching vibrations with a new peak at 1729 cm⁻¹. FESEM images showed a rougher and more irregular in texture and the EDX confirmed nitrogen and sulfur peaks corroborates the presence of the coumarin-thiazole compound on the cellulosic fiber, but BET analysis determined that COMC exhibited a surface area of 7.933 m²/g, a total pore volume of 0.05976 cm³/g, and an average pore diameter of 25.207 nm. The performance of the modified cellulose was assessed for its efficiency in adsorbing and separating cationic dyes. The resulting material exhibited significant adsorption capabilities, with maximum capacities reaching 142.24 mg/g for methylene blue (MB) and 68.49 mg/g for rhodamine B (RhB). To gain insights into the adsorption behaviour, several operational parameters were systematically investigated, including pH, initial dye concentration, contact time, temperature, and adsorbent dosage. An optimal adsorbent mass of 0.05 g was identified for the effective removal of 80 mg/L MB and 25 mg/L RhB. Adsorption equilibrium data conformed closely to the Langmuir isotherm model (R > 0.985) and followed the pseudo-second-order kinetic model, suggesting monolayer adsorption and chemisorption mechanisms. Thermodynamic analyses indicated that the dye adsorption was both spontaneous and exothermic, as evidenced by negative Gibbs free energy (ΔG) and enthalpy (ΔH) values. Furthermore, the modified cellulose demonstrated strong applicability in treating real wastewater samples, achieving dye removal efficiencies exceeding 91%. The inherent functional versatility of regenerated cellulose thus presents a promising strategy for the efficient removal of a wide array of cationic dyes from aqueous environments.