Enhanced Adsorption of Ammonia on Metal-Organic Framework/Graphite Oxide Composites: Analysis of Surface Interactions

Composites of the metal-organic framework (MOF), MOF-5, and graphite oxide (GO) with different ratios of the two components are prepared and tested in ammonia removal under dry conditions. The parent and composite materials are characterized before and after exposure to ammonia by sorption of N-2, X-ray diffraction, thermal analyses, and FT-IR spectroscopy. The results show a synergetic effect resulting in an increase in the ammonia uptake compared to the parent materials. It is linked to enhanced dispersive forces in the pore space of the composites. Additionally, ammonia interacts with zinc oxide tetrahedra via hydrogen bonding and is intercalated between the layers of GO. Retention of a large quantity of ammonia eventually leads to a collapse of the MOF-5 structure in the composites. The effect resembles that observed when MOF-5 is exposed to water. Taking into account the similarity of ammonia and water molecules, it is hypothesized that ammonia causes a destruction of the MOF-5 and composite structure as a result of its hydrogen bonding with the zinc oxide clusters.