Adsorption of ammonia on graphite oxide/aluminium polycation and graphite oxide/zirconium–aluminium polyoxycation composites

Graphite oxide (GO) synthesized from commercial graphite was modified with aluminium or zirconium–aluminium polyoxycations and then calcined at 350 °C. On the samples obtained adsorption of ammonia from moist air was investigated. The surface of materials before and after exposure to ammonia was characterized using adsorption of nitrogen, XRD, SEM, FTIR, TA, CHN analysis, and potentiometric titration. The results showed that in spite of the fact that graphite composites/pillared graphites (PG) have Keggin-like ions located between the layers, that space blocked for nitrogen molecules used to determine the specific surface area. During calcinations, the deflagration of layers occurred as a result of decomposition of epoxy groups. This results in formation of disordered graphitic carbons with some mesoporosity. Even though these materials were not porous, the significant amount of ammonia was retained on the surface. Since ammonia molecule is able to specifically interact with oxygen groups of graphite oxide and Brønsted centers of inorganic pillars, it is likely intercalated between the composite layers. While the best performance was found for GO modified with aluminium–zirconium species, after calcinations the samples containing Keggin Al13 like cations revealed the high capacity which is linked to the high acidity of incorporated inorganic compounds.

Graphical abstractThe significant amount of ammonia was retained on the surface of modified graphite oxides via acid–base interactions with inorganic oxides and carboxylic groups and via intercalation between layers.Figure optionsDownload full-size imageDownload as PowerPoint slide