Local Geometry and Electronic Properties of Nickel Nanoparticles Prepared via Thermal Decomposition of Ni-MOF-74

Metal–organic frameworks (MOFs) provide highly selective catalytic activity because of their porous crystalline structure. There is particular interest in metal nanoparticle-MOF composites (MNP@MOF) that could take advantage of synergistic effects for enhanced catalytic properties. We present an investigation into the local geometry and electronic properties of thermally decomposed Ni-MOF-74 calcined at different temperatures and time durations. Pair distribution function analysis using high-energy X-ray diffraction reveals the formation of fcc-Ni nanoparticles with a mixture of MOF phase in samples heated at 623 K for 12 h. Elevating the calcination temperature and lengthening the time duration assisted complete precipitation of Ni nanoparticles in the MOF matrix. Local structures and valence states were investigated using X-ray absorption fine structure spectroscopy. Evidence of ligand-to-metal charge transfer and gradual reduction of Ni2+ is apparent for those samples heated above 623 K for 12 h. In ad...