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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Magnetic and EPR Spectroscopic Studies of Thiolate Bridged Divalent Ni, Pd, and Pt Ions Capped with VO(N 2 S 2 ) Metalloligands

Reactions of the metallodithiolate complex VO(bme-dach) (hereafter abbreviated as V, where bme-dach = N,N ′-bis(2-mercaptoethyl)-1,4-diazacycloheptane) with [Pd II (CH 3 CN) 4 ](BF 4 ) 2 and [Pt II (CH 3 CN) 4 ](BF 4 ) 2 yield the V–M–V trimetallic compounds [VPdV](BF 4 ) 2 (2) and [VPtV](BF 4 ) 2 (3). Reaction of a similar metalloligand, VO(bme-daco) (hereafter abbreviated as V′ where bme-daco = N,N′-bis(2-mercaptoethyl)-1,5-diazacyclooctane) with [Ni II (CH 3 CN) 6 ](BF 4 ) 2 afforded the related salt [V′NiV′](BF 4 ) 2 (1). X-ray structural analyses revealed that cations in 1, 2, and 3 adopt a stairstep C 2h structure consisting of two terminal VO(N 2 S 2 ) moieties bridged via thiolate sulfur to the group 10 metal ions. Weak ferromagnetic superexchange coupling (J = 0.282 cm –1 for 1, 0.954 cm –1 for 2, and 1.372 cm –1 for 3) was observed between the two S = 1/2 V IV centers separated by distances in the range of 5.9–6.3 Å, with J values varying following the order Ni < Pd < Pt. Frozen-solution EPR spectra measured on the more soluble [BArF 24 ] − (BArF 24 – = tetrakis((3,5-trifluoromethyl)phenyl)borate) analogues revealed that the [VPtV] 2+ cation exhibits a 15-line hyperfine splitting of 225 MHz at g = 4 in parallel mode, confirming exchange coupling between the two 51 V, I = 7/2 nuclei. Density-functional theory (DFT) calculations indicate an S = 1 ground state for 1–3. These results demonstrate that the choice of paramagnetic metallodithiolate ligand and diamagnetic bridge in such trimetallic species influences the sign and magnitude of magnetic interactions.

anions↗
DOE OSTI2018

Improved Chemical and Colloidal Stability of Gold Nanoparticles through Dendron Capping

Nanoparticle (NP) stability is imperative for commercialization of nanotechnology. In this study, we compare the stability of Au NPs with surfaces functionalized with oleylamine, dodecanethiol, and two dendritic ligands of different generations. Dendrimer ligands provide a significant increase in the chemical stability of Au NPs when analyzed by cyanide-induced NP decomposition as well as an investigation into their colloidal stability at ambient conditions. These results were supported by absorption measurements, transmission electron microscopy, thermogravimetric analysis, nuclear magnetic resonance, and small-angle transmission X-ray scattering and show that dendrimers play a key role in improving the chemical and colloidal stability of NPs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Biomimetic Control over Bimetallic Nanoparticle Structure and Activity via Peptide Capping Ligand Sequence

Here, the controlled design of bimetallic nanoparticles (BNPs) is a key goal in tailoring their catalytic properties. Recently, biomimetic pathways demonstrated potent control over the distribution of different metals within BNPs, but a direct understanding of the peptide effect on the compositional distribution at the interparticle and intraparticle levels remains lacking. We synthesized two sets of PtAu systems with two peptides and correlated their structure, composition, and distributions with the catalytic activity. Structural and compositional analyses were performed by a combined machine learning-assisted refinement of X-ray absorption spectra and Z-contrast measurements by scanning transmission electron microscopy. The difference in the catalytic activities between nanoparticles synthesized with different peptides was attributed to the details of interparticle distribution of Pt and Au across these markedly heterogeneous systems, comprising Pt-rich, Au-rich, and Au core/Pt shell nanoparticles. The total amount of Pt in the shells of the BNPs was proposed to be the key catalytic activity descriptor. This approach can be extended to other systems of metals and peptides to facilitate the targeted design of catalysts with the desired activity.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Direct Observation of Morphological and Chemical Changes during the Oxidation of Model Inorganic Ligand-Capped Particles

Functionalization and volatilization are competing reactions during the oxidation of carbonaceous materials and are important processes in many different areas of science and technology. Here, we present a combined ambient pressure X-ray photoelectron spectroscopy (APXPS) and grazing incidence X-ray scattering (GIXS) investigation of the oxidation of oleic acid ligands surrounding NaYF 4 nanoparticles (NPs) deposited onto SiO x /Si substrates. While APXPS monitors the evolution of the oxidation products, GIXS provides insight into the morphology of the ligands and particles before and after the oxidation. Our investigation shows that the oxidation of the oleic acid ligands proceeds at O 2 partial pressures of below 1 mbar in the presence of X-rays, with the oxidation eventually reaching a steady state in which mainly CH x and –COOH functional groups are observed. The scattering data reveal that the oxidation and volatilization reaction proceeds preferentially on the side of the particle facing the gas phase, leading to the formation of a chemically and morphologically asymmetric ligand layer. This comprehensive picture of the oxidation process could be obtained only by combining the X-ray scattering and APXPS data. The investigation presented here lays the foundation for further studies of the stability of NP layers in the presence of reactive trace gases and ionizing radiation and for other nanoscale systems where chemical and morphological changes happen simultaneously and cannot be understood in isolation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗