Vincenzo Lordi

Bio: Vincenzo Lordi is an academic researcher from Lawrence Livermore National Laboratory. The author has contributed to research in topics: Band gap & Physics. The author has an hindex of 27, co-authored 109 publications receiving 3330 citations. Previous affiliations of Vincenzo Lordi include Princeton University & Stanford University.

Method for Supporting Platinum on Single-Walled Carbon Nanotubes for a Selective Hydrogenation Catalyst

Abstract: We have prepared a novel material, consisting of Pt particles supported on purified single-walled carbon nanotubes (SWNTs), representing the first reported metal-loaded SWNT material. The material contains 10 wt % Pt on entangled SWNT bundles consisting of 20−100 nanotubes each. The average Pt particle size is 1−2 nm. High-resolution transmission electron microscopy (HRTEM) observations combined with electron energy-loss spectroscopy (EELS) indicate chemical bonding between Pt and the SWNT surfaces. This bonding is accomplished presumably by ion exchange on carboxylic acid sites created on the nanotube surfaces by slow wet oxidation in dilute HNO3. In addition, a simple SWNT purification scheme requiring no filtration was developed for the preparation of this material. The purification results in a well-defined structure for the metal support useful for investigating the role of this material as a heterogeneous catalyst and the effects of metal−support interactions (MSI). Preliminary kinetics measurements...

Young’s modulus of single-walled carbon nanotubes

Abstract: We report in detail that unlike other materials, carbon nanotubes are so small that changes in structure can affect the Young’s modulus. The variation in modulus is attributed to differences in torsional strain, which is the dominant component of the total strain energy. Torsional strain, and correspondingly Young’s modulus, increases significantly with decreasing tube diameter and increases slightly with decreasing tube helicity.

Molecular mechanics of binding in carbon-nanotube–polymer composites

Abstract: Nanoscale composites have been a technological dream for many years. Recently, increased interest has arisen in using carbon nanotubes as a filler for polymer composites, owing to their very small diameters on the order of 1 nm, very high aspect ratios of 1000 or more, and exceptional strength with Young’s modulus of approximately 1 TPa. A key issue for realizing these composites is obtaining good interfacial adhesion between the phases. In this work, we used force-field based molecular mechanics calculations to determine binding energies and sliding frictional stresses between pristine carbon nanotubes and a range of polymer substrates, in an effort to understand the factors governing interfacial adhesion. The particular polymers studied were chosen to correspond to reported composites in the literature. We also examined polymer morphologies by performing energy-minimizations in a vacuum. Hydrogen bond interactions with the ∏-bond network of pristine carbon nanotubes were found to bond most strongly to the surface, in the absence of chemically altered nanotubes. Surprisingly, we found that binding energies and frictional forces play only a minor role in determining the strength of the interface, but that helical polymer conformations are essential.

Computational and Photoelectrochemical Study of Hydrogenated Bismuth Vanadate

Abstract: We demonstrate hydrogenation as a facile method to significantly enhance the performance of BiVO4 films for photoelectrochemical water oxidation. Hydrogenation was performed for BiVO4 films by annealing them in hydrogen atmosphere at elevated temperatures between 200 and 400 °C. Hydrogen gas can reduce BiVO4 to form oxygen vacancies as well as hydrogen impurities. DFT calculation predicted that both oxygen vacancies and hydrogen impurities are shallow donors for BiVO4 with low formation energies. These defects could increase the donor densities of BiVO4 without introducing deep trap states. Electrochemical impedance measurements showed that the donor densities of BiVO4 films were significantly enhanced upon hydrogenation. Hydrogen-treated BiVO4 (H-BiVO4) photoanodes achieved a maximum photocurrent density of 3.5 mA/cm2 at 1.0 V vs Ag/AgCl, which is 1 order of magnitude higher than that of air-annealed BiVO4 obtained at the same potential. The enhanced photoactivities were attributed to increased donor den...

Lithium Ion Solvation and Diffusion in Bulk Organic Electrolytes from First-Principles and Classical Reactive Molecular Dynamics

Abstract: Lithium-ion battery performance is strongly influenced by the ionic conductivity of the electrolyte, which depends on the speed at which Li ions migrate across the cell and relates to their solvation structure. The choice of solvent can greatly impact both the solvation and diffusivity of Li ions. In this work, we used first-principles molecular dynamics to examine the solvation and diffusion of Li ions in the bulk organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and a mixture of EC and EMC. We found that Li ions are solvated by either carbonyl or ether oxygen atoms of the solvents and sometimes by the PF6– anion. Li+ prefers a tetrahedrally coordinated first solvation shell regardless of which species are involved, with the specific preferred solvation structure dependent on the organic solvent. In addition, we calculated Li diffusion coefficients in each electrolyte, finding slightly larger diffusivities in the linear carbonate EMC compared to the cyclic carbonate EC. The magnitud...

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Polymer Nanocomposites Containing Carbon Nanotubes

Abstract: We review the present state of polymer nanocomposites research in which the fillers are single-wall or multiwall carbon nanotubes. By way of background we provide a brief synopsis about carbon nanotube materials and their suspensions. We summarize and critique various nanotube/polymer composite fabrication methods including solution mixing, melt mixing, and in situ polymerization with a particular emphasis on evaluating the dispersion state of the nanotubes. We discuss mechanical, electrical, rheological, thermal, and flammability properties separately and how these physical properties depend on the size, aspect ratio, loading, dispersion state, and alignment of nanotubes within polymer nanocomposites. Finally, we summarize the current challenges to and opportunities for efficiently translating the extraordinary properties of carbon nanotubes to polymer matrices in hopes of facilitating progress in this emerging area.

Electrostatic deflections and electromechanical resonances of carbon nanotubes

Abstract: Static and dynamic mechanical deflections were electrically induced in cantilevered, multiwalled carbon nanotubes in a transmission electron microscope. The nanotubes were resonantly excited at the fundamental frequency and higher harmonics as revealed by their deflected contours, which correspond closely to those determined for cantilevered elastic beams. The elastic bending modulus as a function of diameter was found to decrease sharply (from about 1 to 0.1 terapascals) with increasing diameter (from 8 to 40 nanometers), which indicates a crossover from a uniform elastic mode to an elastic mode that involves wavelike distortions in the nanotube. The quality factors of the resonances are on the order of 500. The methods developed here have been applied to a nanobalance for nanoscopic particles and also to a Kelvin probe based on nanotubes.