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

• Published in: Inorganic chemistry 2018-08, Vol.57 (16), p.10072-10080
• Main Authors: Tayal, Akhil, Chen, Yanna, Song, Chulho, Hiroi, Satoshi, Kumara, L. S. R, Palina, Natalia, Seo, Okkyun, Mukoyoshi, Megumi, Kobayashi, Hirokazu, Kitagawa, Hiroshi, Sakata, Osami
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b01230

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 addition, the Ni lattice was found to be slightly compressed as a result of surface stresses in the nanosized particles or surface ligand environment. Electronic structure investigation using hard X-ray photoelectron spectroscopy shows a significant narrowing of the valence band and a decrease in the d-band center (toward the Fermi level) when the heating temperature is increased, thus suggesting promising catalytic properties for NiNP@MOF composite.