Isotope effect on water adsorption on hydrophobic carbons of different nanoporosities

The adsorption isotherms of H2O and D2O on pitch-based activated carbon fibers (ACFs) of different pore widths from 0.6 to 1.5 nm were measured at 298 K. Briefly speaking, the D2O adsorption isotherms are close to the H2O adsorption isotherms. However, we observed an evident difference in the rising and desorption relative pressures for the H2O and D2O adsorption isotherms. The D2O adsorption rises at a higher relative pressure than the H2O adsorption. Correspondingly the D2O desorption occurs at a higher relative pressure than the H2O desorption. Detailed comparison of the H2O and D2O adsorption isotherms confirmed a reproducible difference over the whole relative pressure range. The different adsorption behavior of H2O and D2O in the hydrophobic micropores is discussed with the relevance to the difference in the hydrogen bonding of H2O and D2O.

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