Sand mulch-aided ambient-air fabrication of microporous cocoa waste derived-activated carbon for methylene blue adsorption

Porous carbon materials for adsorption applications are regarded as one of the most viable water cleaning strategies. Cocoa pod husk (CPH) was treated with two-step catalytic pyrolysis employing hydroxides and carbonates of sodium and potassium to synthesise activated carbon for methylene blue (MB) decolourisation. Dye adsorption assessment of activated carbon prepared with various activators (NaOH, KOH, Na2CO3 and K2CO3) established KOH-derived activated carbon as a superior absorbent. Upon impregnation ratio optimisation with KOH, CPHAC-3K (CPH: KOH of 3) prepared at 800°C acquired a BET surface area, pore volume and pore size of 1688.4 m2/g, 0.76 cm3/g and 1.25 nm, respectively. The maximum MB adsorption capacity of CPHAC-3K was 445 mg/g, demonstrating an impressive adsorption property compared with literature. The dye adsorption of CPHAC-3K was mainly attributed to its excellent textural property (microporous) and numerous oxygen-containing functional groups on the surface, as shown by BET and FTIR studies, respectively. Adsorption investigations demonstrated that the Langmuir adsorption isotherm and pseudo-second-order kinetic model effectively represented the adsorption process, with a considerable contribution from electrostatic and π-π interactions, pore filling and hydrogen bonding. This work established that CPHAC-3K generated through an optimised preparation process and conditions may be used as an efficient adsorbent compared to some previously reported biomass-based activated carbon to remove cationic dyes from wastewater.