Adsorption competition onto activated carbon, studied by magic-angle spinning NMR
Abstract
The competition between water and two phosphorus-containing compounds for adsorption sites on two activated carbon materials has been studied by 2H and 31P magic-angle spinning (MAS) NMR as a function of time after addition of the second adsorbate. Both 2H and 31P spectra show two bands, one close to the resonance of the relevant liquid compound and the other (assigned to molecules in micro- and meso-pores) shifted by 6–9 ppm to low frequency. Addition of the phosphorus-containing compounds to carbons with pre-adsorbed water rapidly causes displacement of most of the water from the strong adsorption sites. Other changes occur over a period of up to 24 h. Addition of water to carbons with pre-adsorbed phosphate causes some transfer of phosphate from the macropore/surface sites to the micro/mesopores although these were already heavily occupied by phosphate.