High-resolution 2H solid-state NMR of 2H2O adsorbed onto activated carbon

Abstract

Adsorption of deuteriated water onto activated carbon has been studied using magic-angle spinning (MAS)²H NMR. At ²H₂O vapour concentrations below 80% relative humidity a single line of moderate width is observed. The peak is chemically shifted by 6–8 ppm to low frequency of the signal for bulk ²H₂O. At high relative humidities ( > 80%) a further, sharper, ²H NMR signal was observed close to the chemical shift of bulk ²H₂O. The observed chemical shifts and line widths are discussed in terms of the adsorption of the ²H₂O into the porous carbon substrate.

Signal intensities were measured relative to a standard sample and an adsorption isotherm plotted. The results are consistent with the standard gravimetric isotherm method for the sample. However, NMR offers the advantage of the direct observation of the chemical species present in various locations within the sample.