Role of graphite precursor in the performance of graphite oxides as ammonia adsorbents

Graphite oxide was synthesized from three commercial graphites. The samples were used as adsorbents of ammonia at dry and wet conditions. Exceptionally high capacities reaching 10 wt% were measured. The initial and exhausted materials were characterized using adsorption of nitrogen, XRD, FTIR, TA, and potentiometric titration. The results showed differences in the texture and chemistry of adsorbents depending on the type of graphite precursor whose features determine the mechanism of ammonia adsorption. The strongly adsorbed species are either interacting with carboxylic groups to form salts, or with epoxy groups to form amines. A small amount of ammonia is weakly adsorbed via dispersive interactions or dissolved in the film of adsorbed water. As the concentration of amorphous carbon in the initial graphite increases, the ammonia removal capacity on the derived graphite oxide is improved.