A new approach to convert rice husk waste in a quick and efficient adsorbent to remove cationic dye from water

Abstract In this work, a new approach was used to convert rice husk waste in a quick and efficient adsorbent for cationic dye (methylene blue). The waste recovery was obtained by the delignification process followed by an oxidative treatment to produce a natural adsorbent based on cellulose and lignin modified from rice husk waste (RHW). RHW was characterized and used to remove methylene blue from aqueous media. The adsorbent presented good thermal stability and functional groups of lignin were still present in the sample after delignification and oxidative treatments were identified. Parameters as pH, thermodynamics, kinetic and equilibrium were also studied. The adsorption increased with pH increase and showed the best result at 10, whereas in the kinetics tests the satisfactory model was the pseudo-first order to represent the behavior with a R2 = 0.99. Freundlich and Sips models presented better results to fit the equilibrium data in the isotherm curves with R2adj = 0.99, and the negative results of ΔG (between -24.20 and -24.00 kJ mol-1) indicated that the process was spontaneous in all tested temperatures. The RHW presented a good potential to remove the methylene blue from aqueous media quickly with only 30 s to reach equilibrium and showed, from isotherm experiments, strong adsorption capacity with maximum of 1350 mg g-1.