Hydrochar-derived activated carbon from chenopodium botrys for dual applications in dye removal and energy storage

This study reports the synthesis of activated carbon from Chenopodium botrys biomass through two approaches: direct chemical activation (Cb-AC) and a two-step route involving hydrothermal pretreatment followed by chemical activation (Cb-HC-AC). Structural characterization confirmed that hydrothermal pretreatment introduced abundant oxygen functional groups and facilitated mesopore development. In methylene blue (MB) adsorption experiments, Cb-HC-AC exhibited a maximum capacity of 140.83 mg/g, significantly higher than that of Cb-AC (77.15 mg/g). Adsorption kinetics followed a pseudo-second-order model, while isotherm and thermodynamic analyses revealed that adsorption on Cb-HC-AC was endothermic and entropy-driven, in contrast to the exothermic behavior of Cb-AC. Furthermore, Cb-HC-AC demonstrated excellent electrochemical performance as a supercapacitor electrode, achieving a specific capacitance of 441 F/g at 0.2 A/g, 93 % retention after 5000 cycles, and an energy density of 16.94 Wh/kg. These results introduce C. botrys as a novel, sustainable precursor for multifunctional activated carbon and highlight the critical role of hydrothermal pretreatment followed by chemical activation in enhancing both adsorption and energy storage applications.