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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,459 records · Page 81
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DOE OSTI2015

Mesoscopic Constructs of Ordered and Oriented Metal–Organic Frameworks on Plasmonic Silver Nanocrystals

We enclose octahedral silver nanocrystals (Ag NCs) in metal-organic frameworks (MOFs) to make mesoscopic constructs O h -nano-Ag$\subset$MOF in which the interface between the Ag and the MOF is pristine and the MOF is ordered (crystalline) and oriented on the Ag NCs. This is achieved by atomic layer deposition of aluminum oxide on Ag NCs and addition of a tetra-topic porphyrin-based linker, 4,4',4'',4''-(porphyrin-5,10,15,20-tetrayl)tetrabenzoic acid (H 4 TCPP), to react with alumina and make MOF [Al 2 (OH) 2 TCPP] enclosures around Ag NCs. Alumina thickness is precisely controlled from 0.1 to 3 nm, thus allowing control of the MOF thickness from 10 to 50 nm. Electron microscopy and grazing angle X-ray diffraction confirm the order and orientation of the MOF by virtue of the porphyrin units being perpendicular to the planes of the Ag. We use surface-enhanced Raman spectroscopy to directly track the metalation process on the porphyrin and map the distribution of the metalated and unmetalated linkers on a single-nanoparticle level.

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DOE OSTI2016

Plasmon-Enhanced Photocatalytic CO 2 Conversion within Metal–Organic Frameworks under Visible Light

Materials development for artificial photosynthesis, in particular, CO 2 reduction, has been under extensive efforts, ranging from inorganic semiconductors to molecular complexes. In this report, we demonstrate a metal-organic framework (MOF)-coated nanoparticle photocatalyst with enhanced CO 2 reduction activity and stability, which stems from having two different functional units for activity enhancement and catalytic stability combined together as a single construct. Covalently attaching a CO 2 -to-CO conversion photocatalyst Re I (CO) 3 (BPYDC)Cl, BPYDC = 2,2'-bipyridine-5,5'-dicarboxylate, to a zirconium MOF, UiO-67 (Re n -MOF), prevents dimerization leading to deactivation. By systematically controlling its density in the framework (n = 0, 1, 2, 3, 5, 11, 16, and 24 complexes per unit cell), the highest photocatalytic activity was found for Re 3 -MOF. Structural analysis of Re n -MOFs suggests that a fine balance of proximity between photoactive centers is needed for cooperatively enhanced photocatalytic activity, where an optimum number of Re complexes per unit cell should reach the highest activity. Here, based on the structure-activity correlation of Re n -MOFs, Re 3 -MOF was coated onto Ag nanocubes (Ag$\subset$Re 3 -MOF), which spatially confined photoactive Re centers to the intensified near-surface electric fields at the surface of Ag nanocubes, resulting in a 7-fold enhancement of CO 2 -to-CO conversion under visible light with long-term stability maintained up to 48 h.

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