Predictive morphology, stoichiometry and structure of surface species in supported Ru nanoparticles under H2 and CO atmospheres from combined experimental and DFT studies.

Further understanding of the chemisorption properties towards CO and H2 on silica-supported Ru nanoparticles is crucial in order to rationalize their high activity towards methanation, Fischer Tropsch and Water Gas Shift reactions. Ru nanoparticles having the same chemisorption properties towards CO and H2 were synthesized on different silica-based supports in order to combine various analytical techniques and obtain complimentary detailed information on their structure; while silica spheres were used in order to obtain high-resolution TEM images of the Ru nanoparticles, high surface area silica-based material (SBA) allowed CO chemisorption to be monitored by (13)C NMR spectroscopy. In addition, a model of the hcp-based Ru nanoparticles observed by HR-TEM was used to predict by ab initio calculations the CO and H2 coverages on the Ru nanoparticle under different conditions of interest in catalysis. For both adsorbates we show and quantify how the adsorption properties of the nanoparticle differ from the commonly used slab models. For the case of CO we show how the top, bridge and hollow sites can be present on the Ru nanoparticle, providing a description at atomistic level in good agreement with the IR spectroscopy measurements.

Gas mixing system for imaging of nanomaterials under dynamic environments by environmental transmission electron microscopy.

A gas mixing manifold system that is capable of delivering a stable pressure stream of a desired composition of gases into an environmental transmission electron microscope has been developed. The system is designed to provide a stable imaging environment upon changes of either the composition of the gas mixture or upon switching from one gas to another. The design of the system is described and the response of the pressure inside the microscope, the sample temperature, and sample drift in response to flow and composition changes of the system are reported.

Understanding oligonucleotide-templated nanocrystals: growth mechanisms and surface properties.

We describe studies of nanoparticle synthesis using oligonucleotides as capping ligands. The oligonucleotides nucleate, grow, and stabilize near-infrared fluorescent, approximately uniform PbS nanocrystals in an aqueous environment. The properties of the resulting particles strongly depend upon the sequences as well as synthesis conditions. Fourier Transform infrared measurements suggest that functional groups on the nucleobases such as carbonyl and amine moieties are responsible for surface passivation, while the phosphate backbone is strained to accommodate nucleobase bonding, preventing irreversible aggregation and thereby stabilizing the colloids. Our theoretical model indicates that oligonucleotide-mediated particle growth relies on the chemical reactivity of the oligonucleotide ligands that saturate dangling bonds of growing clusters, and favorable sequences are those that have the highest surface reactivity with growing particles. The oligonucleotide template approach is facile and versatile, offering a route to produce a range of material compositions for other chalcogenide semiconductor quantum dots and metal oxide nanoparticles.