A sustainable, low-cost carbonaceous hydrochar adsorbent for methylene blue adsorption derived from corncobs

In this study, activated carbon from corncobs was successfully synthesized by hydrothermal carbonization and hydrochemical activation at low temperatures, followed by pyrolysis. A developed method of hydrochemical activation of hydrochar that uses only small amounts of chemicals is a promising approach. After activation, the activator residues in the hydrothermal product can constantly act as a chemical activator during pyrolysis to form corncob-activated carbon (AHC-KOH), which had specific surface area of 965.028 m2/g and oxygenated functional groups of 0.3780 mmol/g, 31.67 and 4 times, respectively, of those of the inactivated sample. AHC-KOH was used to study the adsorption characteristics of methylene blue (MB). The MB adsorption efficiency of AHC-KOH was the highest at 489.560 mg/g, which was considerably higher than that of activated carbons produced from other biomasses. The isotherm equilibrium and adsorbent kinetics parameters of MB adsorption on AHC-KOH were also determined using the Langmuir isotherm model (R2 = 0.99) and pseudo-second-order kinetic model (R2 > 0.99). Thus, the results indicate that an inexpensive adsorbent produced from corncobs using the above method is a promising material for wastewater treatment. [Display omitted] •AHC-KOH prepared by hydrothermal carbonization of corncob biomass.•The specific surface area of AHC-KOH was approximately 965.028 m2/g.•Methylene blue adsorption on AHC-KOH was high at 489.560 mg/g.•The Langmuir isotherm model suited methylene blue adsorption on AHC-KOH.•Methylene blue adsorption on AHC-KOH followed pseudo-second-order kinetic model.