Towards a better understanding of water adsorption hysteresis in activated carbons by scanning isotherms

The occurrence of water sorption hysteresis associated with the filling of micro and narrow mesopores (particularly for pores of widths smaller than ca. 3 nm, where nitrogen and argon isotherms at their boiling temperatures, i.e. 77 K and 87 K, respectively, are known to be reversible) provides additional opportunities for textural characterization. In this work systematic water scanning desorption isotherms within the hysteresis loop were carried out on well-characterized activated carbons with varied textural features and surface chemistry. Accurate micro-mesopore analysis was obtained by means of nitrogen, argon and carbon dioxide adsorption experiments coupled with advanced density functional theory methods (i.e., NLDFT, QSDFT). The obtained results indicated that water adsorption/desorption phenomena for pores of different sizes take place independently from each other. This investigation constitutes a starting point for the interpretation of water adsorption hysteresis by means of scanning desorption measurements.