Adsorption Characteristics of Porous Carbons prepared using CO_2 and H_3PO_4 Activation from Date Palm Pits

摘要

Porous carbons are excellent adsorbents owing to their large adsorption capacity. The present work attempts to compare the textural as well as the adsorption capacity of porous carbon prepared from date palm pits using CO_2 and phosphoric acid activation. The process of activation, the process conditions were known to influence the physicochemical properties and hence were chosen based on the optimized process parameters reported in literature. The textural characteristics were assessed based on nitrogen adsorption isotherms, SEM, FT-IR, while the adsorption capacity was estimated using the methylene blue (MB) adsorption. The CO_2 activation resulted in a micro porous carbon with yield of 44%, BET surface area of 666 m~2/g, while the phosphoric acid activation resulted in a mesoporous carbon with yield of 14.8%, BET surface area of 725 m~2/g respectively. The average pore diameter was estimated to be 1.51 nm for CO_2 activation, while it was 2.91 nm for the phosphoric acid activation. The equilibrium adsorption isotherms of MB, were tested with the popular Langmuir and Freundlich isotherm models and the monolayer adsorption capacity of CO_2 and phosphoric acid porous carbons were estimated to be 110 and 345 mg/g respectively for the optimized process conditions. However, a highest MB of 455 mg/g was estimated for the phosphoric acid activation, for the process condition that resulted in highest BET surface area.