Combined Role of Water and Surface Chemistry in Reactive Adsorption of Ammonia on Graphite Oxides

Abstract

Graphite oxide synthesized using the Brodie method was tested for ammonia adsorption after two different levels of drying in dynamic conditions at the ambient temperature. Surface characterization before and after exposure to ammonia was done using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and potentiometric titration. On the surface of the initial materials, besides epoxy, hydroxyl, and carboxylic groups, various amounts of water within the interlayer space are present. The results showed that ammonia is intercalated within the interlayer space of graphite oxides. Water enhances the amount of ammonia adsorbed via the dissolution and promotes the dissociation of surface functional groups. This enhances formation of ammonium ions. On the other hand, water screens the accessibility of epoxy and -COOH groups for reactions with ammonia and thus limits the amount adsorbed. The retention of ammonia on a partially dried graphite oxide is enhanced not only owing to those reactions but also because of the formation of new adsorption centers as a result of an incorporation of ammonia to the graphene layers.