Synthesis of ZnCl₂-activated carbon from macadamia nut endocarp (Macadamia integrifolia) by microwave-assisted pyrolysis: Optimization using RSM and methylene blue adsorption

We report the synthesis of activated carbon from macadamia nut endocarp using ZnCl₂ as activating reagent by microwave-assisted pyrolysis. The effects of synthesis conditions and variables were evaluated using the response surface methodology (RSM), which allowed us to obtain an optimized activated carbon (AC_op) for efficient adsorption of methylene blue dye (MB). The chemical and textural characteristics of AC_op were investigated by using N₂ adsorption-desorption measurements, SEM, FT-IR spectroscopy, XPS and the Boehm and pH_drift methodologies. The AC_op was obtained with impregnation ratio of 3:1 (ZnCl ₂:char), microwave heating time of 20 min, and microwave power of 720 W. The AC_op possessed microporous structure, with BET surface area (S_BET) of ca. 600 m² g^-1, and it had mainly acid functional groups on its surfaces. The adsorption kinetic data exhibited by the material for MB were all well-fitted to the pseudo-second-order model, indicating chemisorption. The adsorption isotherms for MB were well-described by Redlich-Peterson model, and the AC_op monolayer adsorption capacity for MB was found to be 194.7 mg g^-1, which is comparable to other values reported in the literature.