Facile synthesis of micro-mesoporous activated carbon in ambient air via one and two-stage activation of palm kernel shell waste for methylene blue adsorption

The primary objective of this study was to discover the effects of one - and two-stage activation process on the synthesis and methylene blue (MB) adsorption performance of palm kernel shell-derived activated carbon using KOH as activator in ambient air. The two-stage process can produce a higher yield of porous carbon materials (PKSAC) in contrast to the one-stage process (RPKSAC). Significant differences in morphology, textural properties, organic structure and crystallinity of prepared activated carbons were observed. BET findings show that PKSAC had a higher specific surface area (1298 m(2)/g) and pore volume (0.58 cm(3)/g) with numerous micropores compared to RPKSAC (surface area: 1160 m(2)/g and Pore volume: 0.48 cm(3)/g), this may be attributed to reaction nature between activator and precursor as temperature increases, which determines the pore-forming path way. Moreover, PKSAC (MB adsorption capacity = 417 mg/g) absorbs 62 mg/g more than RPKSAC (MB adsorption capacity = 355 mg/g) due to its excellent surface textural property and oxygen-containing functional groups on the surface. Furthermore, Langmuir model fits the adsorption behaviour of PKSAC/MB adsorption system. The dye adsorption mechanism was dominated with physical, electrostatic, pi-pi and hydrogen bonding interactions. Thermodynamic parameters indicated that, the MB adsorption on the prepared activated carbon was spontaneous and endothermic. In conclusion, these results demonstrate that two-stage activation process enhances the adsorption ability of activated carbon, proving palm kernel shells as viable for activated carbon production.