Synthesis and characterization of porous activated carbons derived from lotus nut and their performance for CO₂ adsorption

The purpose of the current work is to transform the lotus nut, as a new precursor, into a low-cost, high-performance, porous activated carbon through a one-step chemical activation method using two different activating chemicals, Potassium hydroxide (KOH) and Zinc chloride (ZnCl₂) with the objective of the largest surface area, hence the maximum CO₂ adsorption capacity. Response Surface Methodology (RSM) was used to optimize critical production conditions, including the chemical to precursor ratio, activation time, and activation temperature. The largest specific surface area of the Activated Carbon prepared from KOH (ACK) was 1115.32 m²/g, which was obtained at the activation temperature of 726 °C, activation time of 134 min, and the chemical reagent ratio of 2.78. While, the specific surface area of the Activated Carbon prepared from ZnCl₂ (ACZ) was 912.51 m²/g, which was achieved at 70 min, 653 °C, and 1.74. The maximum CO₂ adsorption capacity of prepared activated carbons at 5 bar under optimal conditions was found to be 4.4 mmol/g for activated carbon prepared using KOH. The Scanning Electron Microscopy (SEM) images indicated that the use of KOH results in deeper and narrower pores, while larger pores were visible for the activated carbon prepared by ZnCl₂. The surface of activated carbons includes functional groups that contain nitrogen, according to the Fourier Transform Infrared Spectroscopy (FTIR) analysis.