Fabrication of Citric-Acid-Modified Cellulose Adsorbent for Remediation of Methylene Blue Dye from Aqueous Solutions: Equilibrium, Kinetic, and Thermodynamic Studies

In this study, we report a simple method for producing citric-acid-modified cellulose adsorbent from coir waste for the remediation of cationic methylene blue dyes. The modification of cellulose nanofibers with citric acid increased the surface area and porosity of the adsorbent, thereby enhancing its adsorption capacity. The morphology and chemical structure of the modified adsorbent were examined using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) techniques. The adsorption of methylene blue (MB) onto the adsorbent was studied at different pH, MB concentrations, adsorbent dosages, temperatures, contact times, and in the presence of other salts. The adsorbent demonstrated a remarkable removal efficiency of 99% at dye concentration of 10 mg/L. The maximum adsorption capacity of the adsorbent was 156.25 mg/g at an initial dye concentration of 15 mg/L, adsorbent dosage of 0.15 g/L, pH of 9, and temperature of 303 K after 240 min of duration. The adsorption kinetics and equilibrium adsorption isotherms were consistent with pseudo-second-order kinetic and Langmuir isotherm models, respectively. The thermodynamic parameters indicated that the removal of methylene blue dye by the modified adsorbent was endothermic, and spontaneous in nature. Furthermore, reusability experiments revealed that the adsorbent exhibited 93% efficiency, even after five cycles of adsorption and desorption.