Production and Characterization of Porous Carbon from Date Palm Seeds by Chemical Activation with H₃PO₄: Process Optimization for Maximizing Adsorption of Methylene Blue

The potential of date palm pits to be a suitable precursor for preparation of porous carbon was explored in the present work, utilizing phosphoric acid as the activating agent. Experimental methods reported in the literature were chosen with certain modifications in order to simplify the process. Process optimization was performed using the popular response surface methodology (RSM) adopting a Box-Behnken design. Process optimization was intended to maximize the porous carbon yield and the methylene blue (MB) adsorption capacity, with the process variables being the activation temperature, impregnation ratio (IR), and activation time. The structural characteristics were assessed based on nitrogen adsorption isotherms, SEM, and FT-IR, while the adsorption capacity was estimated using MB adsorption. The optimized experimental conditions were identified to be an activation temperature of 400°C, IR of 3, and activation time of 58 min, with the resultant porous carbon having a yield of 44% and MB adsorption capacity of 345 mg/g. The structural characteristics of the porous carbon reveal the BET surface area to be 725 m²/g, with pore volume of 1.26 cc/g, an average pore diameter of 2.91 nm, and total micropore volume of 0.391 cc/g. The popular Langmuir and Freundlich adsorption isotherm models were tested, and a maximum monolayer adsorption capacity of MB was estimated to be 455 mg/g, which compares with the highest for MB reported in literature, evidencing the suitability of porous carbon for adsorption of macromolecular compounds. The low activation temperature and activation time with highest yield render the process technically and economically attractive for commercial use.