Effect of graphite features on the properties of metal-organic framework/graphite hybrid materials prepared using an in situ process.

ABSTRACT

Metal-organic framework (MOF)/graphite hybrid materials were prepared using an in situ process. Graphites with various chemical and physical features were used, and HKUST-1 was selected as the MOF component. The samples (parent materials and hybrid materials) were characterized by X-ray diffraction, nitrogen sorption, scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Then they were tested as ammonia adsorbents in dynamic conditions. The results indicate that the functionalization of graphite is important to build the hybrid materials with synergistic properties. The lack of functional groups on graphite results in the formation of a simple physical mixture. Besides the surface chemistry of the graphitic component, the physical parameters (porosity and size of flakes) also seem to influence the formation of the hybrid materials. It is observed that the graphite particles disturb the formation of HKUST-1 and induce a different crystal morphology (more defects and increased surface roughness) than the one observed when MOF is formed in the absence of a substrate. The latter behavior causes less ammonia to be adsorbed on the hybrid materials than is expected for the simple physical mixture of HKUST-1 and graphite. The MOF structure collapses (in HKUST-1 and the hybrid materials) upon ammonia adsorption and leads to the formation of new species.