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Biomedical subjects

Dean C Sayle

Publications and source records attributed to Dean C Sayle.

6 recordsLinked to original sources
PubMed2005

Generating MnO2 nanoparticles using simulated amorphization and recrystallization.

Models of MnO2 nanoparticles, with full atomistic detail, have been generated using a simulated amorphization and recrystallization strategy. In particular, a 25,000-atom "cube" of MnO2 was amorphized (tension-induced) under molecular dynamics (MD). Long-duration MD, applied to this system, results in the sudden evolution of a small crystalline region of pyrolusite-structured MnO2, which acts as a nucleating "seed" and facilitates the recrystallization of all the surrounding (amorphous) MnO2. The resulting MnO2 nanoparticle is about 8 nm in diameter, conforms to the pyrolusite structure (isostructural with rutile TiO2, comprising 1 x 1 octahedra) is heavily twinned and comprises a wealth of isolated and clustered point defects such as cation vacancies. In addition, we suggest the presence of ramsdellite (2 x 1 octahedra) intergrowths. Molecular graphical snapshots of the crystallization process are presented.

Crystallization↗
PubMed2005

Oxidising CO to CO2 using ceria nanoparticles.

We calculate, using simulated amorphisation and recrystallisation (A&R), that ceria (CeO2) nanoparticles, about 8 nm in diameter, comprise a high concentration of labile surface oxygen species, which we suggest will help promote the oxidation of CO to CO2. In particular, the ceria nanoparticle contains a high proportion of reactive {100} surfaces, surface steps and corner sites. When reduced to CeO1.95, the associated Ce3+ species and oxygen vacancies decorate step, corner and {100} sites in addition to plateau positions on {111}. The energetics of CO oxidation to CO2, catalysed by a ceria nanoparticle, is calculated to be lower compared with CO oxidation associated with the lowest energy surface (i.e. CeO2(111)) of the corresponding 'bulk' material. Our calculated morphologies for the ceria nanoparticles are in accord with experiment.

Carbon Dioxide↗
PubMed2003

Encapsulated oxide nanoparticles: the influence of the microstructure on associated impurities within a material.

Simulation techniques have been used to explore how the microstructure of a material influences the nature of associated impurities embedded therein. We illustrate this by exploring four systems: BaO and CaO nanoparticles encapsulated within a ("perfect") MgO host lattice and SrO and MgO nanoparticles encapsulated within a ("microstructural") BaO lattice, which comprises a network of screw-edge dislocations. This study uses annealing techniques to generate energetically feasible nanoparticle structures and morphologies, dislocation networks, interfacial boundaries, and strain profiles. Specifically, the different encapsulated nanoparticles exhibit a range of morphologies, expose a variety of facets at the nanoparticle/host lattice interface, and are observed to rotate within the cavity they occupy inside the host lattice. The structure and nature of the nanoparticles reflect the lattice misfit between the nanoparticle and the host lattice. The study suggests also that there exists a "critical nanoparticle size", above which dislocations evolve.

Journal Article↗
PubMed2002

Atomistic models for CeO(2)(111), (110), and (100) nanoparticles, supported on yttrium-stabilized zirconia.

Ceria is an important component in three-way catalysts for the treatment of automobile exhaust gases owing to its ability to store and release oxygen, a property known as the oxygen storage capacity. Much effort has been focused on increasing the OSC of ceria, and one avenue of exploration is the ability to fabricate CeO(2)-based catalysts, which expose reactive surfaces. Here we show how models for a polycrystalline CeO(2) thin film, which expose the (111), (110), and dipolar (100) surfaces, can be synthesized. This is achieved by supporting the CeO(2) thin film on an yttrium-stabilized zirconia substrate using a simulated amorphization and recrystallization strategy. In particular, the methodology generates models which reveal the atomistic structures present on the surface of the reactive faces and provides details of the grain-boundary structures, defects (vacancies, substitutionals, and clustering), and epitaxial relationships. Such models are an important first step in understanding the active sites at the surface of a catalytic material.

Journal Article↗