Enhanced adsorption of Methylene blue with walnut shell carbon chemically activated by K₂CO₃

In this study, walnut shell-based activated carbon (WSAC2-900) was prepared by pyrolysis-carbonization coupled with chemical activation of K₂CO₃ for the first time. The samples were characterized by XRD, nitrogen adsorption/desorption, SEM and FTIR. In addition, the zero-point potential pH_pzc was determined. The specific surface area of WSAC2-900 reached 1690 m²/g, and the total pore volume was 0.73 cm³/g, of which 87.7% was the micropore volume. The surface of WSAC2-900 is rich in many oxygen-containing functional groups, such as hydroxyl and aldehyde groups, and its zero-charge point pH_pzc is less than 2. The isotherms, kinetics and thermodynamics of MB adsorption by WSAC2-900 were investigated. The removal efficiency of WSAC2-900 for MB reached 99.6%, and the maximum adsorption capacity reached 557.5462 mg/g. At 283 K, 293 K, 303 K and 313 K, the maximum adsorption capacities of MB were 468.1695 mg/g, 506.3057 mg/g, 524.4298 mg/g and 548.2178 mg/g, respectively. In addition, the mechanism of MB adsorption by WSAC2-900 was discussed.