Design of highly microporous activated carbons based on walnut shell biomass for H2 and CO2 storage

Abstract

Low-cost walnut shell-based carbons with high microporosity were prepared by simple one-step carbonization with chemical activation using KOH, exhibiting the promising potential to be a very good CO2 and H2 adsorbent. The physicochemical properties of the obtained carbons were characterized by N2 and CO2 adsorption isotherms, X-ray powder diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and elemental analysis. The activated carbon AC-800 was characterized by a highly developed specific surface area of 1868 cm2/g and a high micropore content of 0.94 cm3/g. It highly exhibited CO2 uptake in 1 bar was up to 9.54, 5.17, 4.33 mmol/g for 0, 25 and 40 °C, respectively. In addition, the H2 storage capacity was 3.15 mmol/g at 40 bars. Significantly, confirmed an exceptionally high dependency of CO2 and H2 uptake vs micropores structure of activated carbon. AC-800 also shows good selectivity for CO2/N2 and fast adsorption kinetics that be easily regenerated with superior cyclic stability after multiple cycles The experimental isotherm data of activated carbon produced from walnut shells were analyzed using Langmuir, Freundlich, Temkin, Sips, and Toth isotherm equations. The fitting details showed that the multitemperature Toth equation is a powerful tool to mathematically represent CO2 and H2 isotherms on activated carbon. The easy way of preparation and high capture abilities endow this kind of activated carbon attractive as a promising adsorbent for CO2 and H2 storage.