The use of organic vapour preadsorption to understand water adsorption on activated carbons

Abstract In this work, n-octane preadsorption coupled with water vapour sorption has been assessed as a useful technique for the advanced characterization of porous carbon materials. First, two microporous activated carbons with different oxygen contents were gradually preloaded with the n-alkane and then characterized by different adsorbates. As the micropore system is being filled, a narrowing of the hysteresis loop and a decrease in the slope of the water isotherms at low and medium relative pressures was observed. The latter result indicates that the available surface oxygen content gradually decreased with the blockage of the micropores, thus suggesting that the primary water adsorption centers of activated carbons are located in the narrow pores. Moreover, correlations between the available surface oxygen content and the micropore volumes measured by N 2 and CO 2 adsorption were found. Then, the microporous system of two activated carbons with a mainly mesoporous structure was nearly completely blocked. The surface chemistry of these two carbons was modified in order to have a deeper analysis of the role played by the surface oxygen groups on the water adsorption mechanism. The obtained results showed that the water sorption in the mesopores is highly dependent on the available surface oxygen content.