Reactive adsorption of ammonia on Cu-based MOF/graphene composites

New composites based on HKUST-1 and graphene layers are tested for ammonia adsorption at room temperature in both dry and moist conditions. The materials are characterized by X-ray diffraction, FT-IR spectroscopy, adsorption of nitrogen, and thermal analyses. Unlike other MOF/GO composites reported in previous studies, these materials are water-stable. Ammonia adsorption capacities on the composites are higher than the ones calculated for the physical mixture of components, suggesting the presence of a synergetic effect between the MOF and graphene layers. The increased porosity and dispersive forces being the consequence of the presence of graphene layers are responsible for the enhanced adsorption. In addition to its retention via physical forces, ammonia is also adsorbed via binding to the copper sites in HKUST-1 and then, progressively, via reaction with the MOF component. This reactive adsorption is visible through two successive changes of the adsorbents' color during the breakthrough tests. More ammonia is adsorbed in moist conditions than in dry conditions owing to its dissolution in a water film present in the pore system.