Kinetic isotope quantum effects in the adsorption of H2O and D2O on porous carbons

This paper describes an investigation of the adsorption characteristics of H2O and D2O on two activated carbons, BAX950, containing a range of micro- and mesoporosity, and G209, a predominantly microporous material. Adsorption kinetics of H2O and D2O on activated carbon BAX950 were studied over temperature ranges of 293-313 K and 278-303 K, respectively. The adsorption/desorption of H2O and D2O were also studied on activated carbon G209 at 298 K. The adsorption isotherms for H2O and DO agree well while greater adsorption hysteresis was observed for H2O compared with D2O. Comparison of the adsorption kinetic behavior of H2O and D2O indicated a kinetic isotope effect. The trends in isotherm hysteresis, kinetic parameters, and activation energies are attributed to quantum effects, which are the source of differences in intermolecular hydrogen bonding in H2O and D2O adsorbates and bonding between these adsorbates and surface oxygen functional groups. The effects of confinement in pores on adsorbate structure are discussed.