Optimizing cellulose extraction from coconut coir pith via response surface methodology for improving methylene blue adsorption

Dye wastewater currently damages both human health and aquatic ecosystem, so to reduce its negative effects and promote sustainable development, this study optimizes cellulose extraction process from coconut coir pith via employing response surface methodology combined with Design Expert software (version 11.0.1.0, Copyright©2017, Stat-Ese Inc., USA). The recovered cellulose after alkalizing and decolorizing process is applied to assess its adsorption capability of methylene blue from water. Methylene blue adsorption capacity is evaluated based on operating factors: pH, contact time, methylene blue initial concentration and cellulose mass. The success of cellulose extraction process is established by Fourier-transform infrared spectroscopy, X-Ray Diffraction and Thermogravimetric analysis. The recovered cellulose particles have a high crystallinity index of 46.39% and high purity of 35.63% with an average diameter of 344 μm with a specific surface area of 3.303 m².g⁻¹, a porous structure with a pore diameter of 34.952Å and pH_pzc of 6.14. Under optimal adsorption conditions, methylene blue adsorption efficiency of 99.22% is achieved, and the process is favorable, reversible, and monolayer adsorption. The adsorption in this work is in good agreement with pseudo-second-order kinetic model and physical adsorption is the main adsorption mechanism. Importantly, the recovered cellulose has a significantly high adsorption capacity of 145.81 mg.g⁻¹ after seven continuous using times. These findings propose that cellulose can recover from coconut coir pith by-product and holds a highly potential on dye removal from aqueous solution.