Green self-activating synthesis system for porous carbons: Celery biomass wastes as a typical case for CO2 uptake with kinetic, equilibrium and thermodynamic studies

Abstract

Due to its rich porous structure, high specific surface area, and stable chemical characteristics, hierarchically biomass-derived porous carbon is considered to be the most potentially effective material for CO2 capture. Herein, a green self-activating synthesis system (SASS) has been introduced for the synthesis of porous carbons. In this system, there is no external reagent for the activation process, and the activating agents are the circulating gases such as CO2, CO, and H2O released during the pyrolysis treatment. As a typical case, this system was used for the synthesis of hierarchical porous carbons from celery wastes in hydroponic greenhouses. Based on the adsorption-desorption results, the optimal porous carbon was synthesized at 700 °C, providing a surface area as high as 1126 m2g−1 and a micropore volume of approximately 0.7 cm3g−1. The existence of graphitic-pyridinic nitrogen in the synthesized porous carbon structure was confirmed by X-ray photoelectron spectroscopy. The synthesized porous carbons were applied as an adsorbent for CO2 uptake. Under low pressures (0–1 bar), the synthesized carbons adsorbed 5 mmolg−1 at 0 °C and 2.03 mmolg−1 at 25 °C. The sorption capacity of the synthesized carbon at 25 °C and relatively high pressure of 9.5 bar was 9.57 mmolg−1. Based on the thermodynamic and kinetic models, it was clarified that the sorption process can be regarded as physisorption with an adsorption enthalpy of 23.2 kJmol−1. The fractional-order kinetic model was also shown to be the best fit in the kinetic curves. The presented synthesis system is a promising strategy for manufacturing green porous carbon from various waste organic precursors.