CO₂ uptake by activated hydrochar derived from orange peel (Citrus reticulata): Influence of carbonization temperature

In this study, activated hydrochar was prepared from orange peel (OP) waste using KOH for the first time for potential environmental applications. The influence of hydrothermal carbonization temperature (180 °C, 200 °C, and 220 °C) on the CO₂ adsorption capacity of OP-derived activated hydrochar (OP-180, OP-200, and OP-220) was investigated. Scanning electron microscope (SEM) images revealed that the activated OP hydrochar has high microporosity, a desired attribute for effective adsorption. The yield and the oxygen content of the hydrochar decreased with the increasing process temperature whereas the carbon content showed an increase. Fourier-transform infrared spectroscopy showed the presence of various functional groups including ketone, aldehydes, esters, and carboxyl in the hydrochar. CO₂ adsorption isotherm was determined for all hydrochar samples. At 25 °C and 1 bar, OP-220 showed the highest CO₂ uptake at 3.045 mmol/g. The use of OP waste for CO₂ adsorption applications contributes to carbon neutrality and a circular economy.