Incorporation of nanomaterials such as nanoparticles into nanoporous materials such as metal organic frameworks (MOFs) is attractive to broaden their applications. However, it is challenging to control the synthesis in this nanoconfined environment without fundamental understanding of molecular local chemistry, in particulare the role of functional groups. This work illlustrates how functional groups can both catalyze the initial nucleation reactions and control the size of nanoparticles by combining in situ spectroscopic, physical, and imaging measurements, with ab initio calculations for two distinct conditions, vapor and liquid phase processing. Firstly, the synthesis of Al2O3 by atomic layer deposition (ALD) is considered. For this vapor phase method, the reactivity of ALD precursors in Zr-based MOFs is shown to critically depend on the presence of internal functional groups such as –NH2, which act as catalyst to foster hydrolysis. First principles calculations reveal that the –NH2 group anchors the precursor molecule in close proximity to the MOF bridge OH. In the absence of –NH2, the precursor resides in the middle of the pore too far from the µ3-OH to react. The understanding derived from this work explains previous experimental observations of nanoclusters growth in UiO-66-NH2 template [ACS Catal., 2014, 4, 1340]. Secondly, we demonstrate that isolated, ligand-free Au NPs (~1nm) can be synthesized by photo-reduction of HAuCl4 inside thiol-functionalized MOFs, including MOF-808-SH and MIL-101 (Cr) in an alcoholic MOF suspension without the need for additional reducing or stabilizing agents. A combination of physical, imaging, spectroscopic measurements, and ab initio calculations confirms that the Au NPs are dispersed inside the bulk of the MOFs and demonstrate that the thiol group is critical to stabilize the Au NPs inside individual pores. The thiol-functionalized MOFs thus fulfill a dual purpose: they foster the nucleation of the Au NP and also provide confinement and a framework that keeps the NPs separate.

Role of functional groups for the synthesis of nanomaterials within metal organic frameworks materials

2019 Fall National Meeting

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