Scientific Publications 2005
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2005. "A Combined Vacuum Ultraviolet Laser and Synchrotron Pulsed Field Ionization Study of BCl₃." Physical Chemistry Chemical Physics. PCCP 7(7):1518-1526. doi:10.1039/b417083k Abstract No abstract is available for this journal article at this time.
2005. "Thermal Growth and Performance of Manganese Cobaltite Spinel Protection Layers on Ferritic Stainless Steel SOFC Interconnects." Journal of the Electrochemical Society 152(9):A1896-A1901. Abstract To protect solid oxide fuel cells (SOFCs) from chromium poisoning and improve metallic interconnect stability, manganese cobaltite spinel protection layers with a nominal composition of Mn1.5Co1.5O4 were thermally grown on Crofer22 APU, a ferritic stainless steel. Thermal, electrical and electrochemical investigations indicated that the spinel protection layers not only significantly decreased the contact area specific resistance (ASR) between a LSF cathode and the stainless steel interconnect, but also inhibited the sub-scale growth on the stainless steel by acting as a barrier to the inward diffusion of oxygen. A long-term thermal cycling test demonstrated excellent structural and thermomechanical stability of these spinel protection layers, which also acted as a barrier to outward chromium cation diffusion to the interconnect surface. The reduction in the contact ASR and prevention of Cr migration achieved by application of the spinel protection layers on ferritic stainless steel resulted in improved stability and electrochemical performance of SOFCs.
2005. "Automated portable analyzer for lead(II) based on sequential flow injection and nanostructured electrochemical sensors ." Talanta 68(2):256-261. Abstract A fully-automated portable analyzer for toxic metal ion detection based on a combination of a nanostructured electrochemical sensor and a sequential flow injection system has been developed in this work. The sensor was fabricated from a carbon paste electrode modified with acetamide phosphonic acid self-assembled monolayer on mesoporous support (Ac-Phos SAMMS) which was embedded in a very small wall-jet (flow-onto) electrochemical cell. The electrode was solid-state and mercury-free. Samples and reagents were injected into the system and flowed through the electrochemical cell by a programmatic sequential flow technique which required minimal volume of samples and reagents and allowed the automation of the analyzer operation. The portable analyzer was evaluated for lead (Pb) detection due to the excellent binding affinity between lead and the functional groups of Ac-Phos SAMMS as well as the great concern for lead toxicity. Linear calibration curve was obtained in a low concentration range (1 to 25 ppb of Pb(II)). The reproducibility was excellent; the percent relative standard deviation was 2.5 for seven consecutive measurements of 10 ppb of Pb(II) solution. Excess concentrations of Ca, Ni, Co, Zn, and Mn ions in the solutions did not interfere with detection of lead, due to the specificity and the large number of the functional groups on the electrode surface. The electrode was reliable for at least 90 measurements over 5 days. This work is an important milestone in the development of the next-generation metal ion analyzers that are portable, fully-automated, and remotely-controllable.
2005. "Optimization of A Portable Microanalytical System to Reduce Electrode Fouling from Proteins Associated with Biomonitoring of Lead (Pb) in Saliva." Talanta 67(3):617-624. Abstract There is a need to develop reliable portable analytical systems for on-site and real-time biomonitoring of lead (Pb) from both occupational and environmental exposures. Saliva is an appealing matrix since it is easily obtainable, and therefore a potential substitute for blood since there is a reasonably good correlation between Pb levels in both blood and saliva. The microanalytical system is based on stripping voltammetry of Pb at the microelectrochemical cell having a flow injection/flow-onto design. Samples that contain as little as 1% saliva can cause electrode fouling, resulting in significantly reduced responsiveness, irreproducible quantitations, and the need for frequent electrode regeneration. In addition, incomplete Pb release from salivary protein can also yield a lower Pb response than expected. This paper evaluates the extent of in vitro Pb-protein binding and the optimal pre-treatment for releasing Pb from the saliva samples. Even in 50% by volume of rat saliva, the electrode fouling was not observed, due to the appropriate sample pretreatment (with 1.0 M acid, followed by centrifugation at the RCF of 15200×g) and the constant flow of the sample and acidic carrier that prevented passivation by the protein. The system offered a linear response over a low Pb range (1-10 ppb), low detection limit (1 ppb), excellent reproducibility (5% RSD), and reliability. It also yielded the same Pb concentrations in unknown samples as did the ICP-MS. These encouraging results suggest that the microanalytical system represents an important analytical advancement for real-time non-invasive (i.e., saliva) biomonitoring of Pb.
2005. "Nanostructured Electrochemical Sensors Based on Functionalized Nanoporous Silica for Voltammetric Analysis of Lead, Mercury and Copper." Journal of Nanoscience and Nanotechnology 5(9):1537-1540. Abstract We have successfully developed electrochemical sensors based on functionalized nanostructured materials for voltammetric analysis of toxic metal ions. Glycinyl-urea self-assembled monolayers on mesoporous silica (Gly-UR SAMMS) was incorporated in carbon paste electrodes for the detection of toxic metal ions such as lead, copper, and mercury based on adsorptive stripping voltammetry (AdSV). The electrochemical sensor yields a linear response at low ppb level of Pb2+ (i.e., 2.5 to 50 ppb) after a 2 minute preconcentration period, with reproducible measurements (%RSD = 3.5, N = 6), and excellent detection limits (at few ppb). By exploiting the interfacial functionality of Gly-UR SAMMS, the sensor is selective for the target species, does not require the use of a mercury film, and can be easily regenerated in dilute acid solution. The rigid, open, parallel pore structure, combined with suitable interfacial chemistry of SAMMS, also results in fast analysis times (2-3 minutes). The nanostructured SAMMS materials enable the development of miniature sensing devices that are compact and low-cost, have low-energy-consumption, and are easily integrated into field-deployable units. Keywords: electrochemical sensor, glycinyl-urea, self-assembled monolayer, mesoporous silica, lead, mercury, copper, adsorptive stripping voltammetry.
2005. "Hydroxypyridinone (HOPO) Functionalized Self-Assembled Monolayers on Nanoporous Silica for Sequestering Lanthanide Cations." Journal of Nanoscience and Nanotechnology 5(4):527-535(9). doi:10.1166/jnn.2005.096 Abstract 1,2-Hydroxypyridinone (1,2-HOPO) ligands were installed as self-assembled monolayers on nanoporous silica (MCM-41) to create a superior class of sorbent materials for lanthanide cations. Lanthanides were used as a model system for the radioactive, expensive and highly hazardous actinides in the preliminary screening studies. The ligand properties of the 1,2-HOPO ligand field and the extremely large surface area of the MCM-41, coupled with the dense monolayer coating contribute to extremely high lanthanide binding capacity of the 1,2-HOPO nanoporous sorbent. At pH 4-5.9, the mass-weighted partition coefficients (Kd) for La, Nd, Eu, Lu were 354,000, 344,000, 210,800, 419,800, respectively. The rigid, open pore structure of the silica also allows for very rapid sorption. Being silica-based, the sorbent is compatible with vitrification processing into a final glasseous waste form, for subsequent disposition in a deep geological repository.
2005. "Screen-Printed Electrodes Modified with Functionalized Mesoporous Silica for Voltammetric Analysis of Toxic Metal Ions." Electrochemistry Communications 7(11):1170-1176. doi:10.1016/j.elecom.2005.08.018 Abstract Mercury-free sensors for lead (Pb2+) assay based on chemical modification of screen-printed carbon electrodes (SPCEs) with acetamide phosphonic acid self-assembled monoloyer on mesoporous support (Ac-Phos SAMMS) have been developed. The preconcentration of Pb2+ at SAMMS-based sensors utilize the binding affinity of the acetamide phosphonic acid and Pb2+, which can be accomplished at open circuit potential without electrolyte and solution degassing. Due to the strong covalent bonding of the functional groups on SAMMS, the SAMMS based sensors with a built-in 3 electrode system can be reused for tens of measurements with minimal degradation, enabling the establishment of the calibration curve and lowering the costs. Linear calibration curve was found in the range of 0 to at least 100 ppb Pb2+ after 5 minutes of preconcentration. The detection limit was calculated from 3S/N to be 1 ppb of Pb2+. Reproducibilty (%RSD) was found to be 5% for a single sensor (6 measurements) and 10% for 5 sensors. The reproducibility can be improved through the precision of manufacturing of the sensors, in which SAMMS modification can be done in-situ, increasing the user-friendliness of the sensors. Cadmium, lead, and copper can also be detected simultaneously at the SAMMS screen-printed sensors.
2005. "Supercritical Fluid Immersion Deposition: A New Process for Selective Deposition of Metal Films on Silicon Substrates." Surface & Coatings Technology 190(1):25-31. Abstract Supercritical CO2 is used as a new solvent for immersion deposition, a galvanic displacement process traditionally carried out in aqueous HF solutions containing metal ions, to selectively develop metal films on featured or non-featured silicon substrates. Components of supercritical fluid immersion deposition (SFID) solutions for fabricating Cu and Pd films on silicon substrates are described along with the corresponding experimental setup and procedure. Only silicon substrates exposed and reactive to SFID solutions can be coated. The highly pressurized and gas-like supercritical CO2, combined with the galvanic displacement property of immersion deposition, enables the SFID technique to selectively deposit metal films in small features. SFID may also provide a new method to fabricate palladium silicide in small features or to metallize porous silicon.
2005. "Supercritical Fluid Attachment of Palladium Nanoparticles on Aligned Carbon Nanotubes." Journal of Nanoscience and Nanotechnology 5(6):964-969. doi:10.1166/jnn.2005.133 Abstract Nanocomposite materials consisting of Pd nanoparticles deposited on aligned multi-walled carbon nanotubes have been fabricated through hydrogen reduction of palladium precursor in supercritical carbon dioxide. The supercritical fluid processing allowed deposition of high-density Pd nanoparticles (~5-10 nm) on both as-grown (unfunctionalized) and functionalized (using HNO3 oxidation) nanotubes. However, the wet processing for functionalization results in pre-agglomerated, bundle-shaped nanotubes thus significantly reducing the effective surface area for Pd particle deposition, although the bundling provides more secure, lock-in-place positioning of nanotubes and Pd catalyst particles. The nanotube bundling is substantially mitigated by Pd nanoparticle deposition on the unfunctionalized and geometrically separated nanotubes, which provides much higher catalyst surface area. Such nanocomposite materials utilizing geometrically secured and aligned nanotubes can be useful for providing much enhanced catalytic activities to chemical and electrochemical reactions (e.g. fuel cell reactions), and eliminate the need for tedious catalyst recovery process after the reaction is completed.
2005. "Deposition of Platinum Nanoparticles on Carbon Nanotubes by Supercritical Fluid Method." Journal of Nanoscience and Nanotechnology 5(11):1852-1857. doi:10.1166/jnn.2005.421 Abstract Carbon nanotube-supported platinum nanoparticles with a 5-15 nm diameter size range can be synthesized by hydrogen reduction of platinum(II) acetylacetonate in methanol modified supercritical carbon dioxide. XPS and XRD spectra indicate that the carbon nanotubes contain zero-valent platinum metal and high-resolution TEM images show that the visible lattice fringes of the Pt particles are crystallites. Carbon nanotubes synthesized with 25% by weight of Pt nanoparticles exhibit a higher activity for hydrogenation of benzene compared with a commercial carbon black platinum catalyst. The carbon nanotube-supported Pt nanocatalyst can be reused at least six times for the hydrogenation reaction without losing activity. The carbon nanotube-supported Pt nanoparticles are also highly active for electrochemical oxidation of methanol and for reduction of oxygen suggesting their potential use as a new electrocatalyst for polymer electrode fuel cell applications.
2005. "Differential Kinetic Analysis of Diesel Particulate Matter (Soot) Oxidation by Oxygen Using a Step-Response Technique." Applied Catalysis. B, Environmental 61(1-2):120-129. Abstract A novel step-response technique was developed for the kinetic study of diesel soot oxidation. Using this technique, various aspects of the oxidation process can be probed while consuming only differential amounts of carbon, and the impact of the reaction heat on the measured rates can be minimized. Due to its high throughput, the technique allows broad parametric studies to be performed rapidly and in a kinetically rigorous manner. The technique was applied to soot oxidation by O2, one of the major regeneration mechanisms for the catalytic soot filter systems. It was found that, after decoupling effects due to the sample history, carbon oxidation by O2 in the absence of H2O can be well described by an unmodified Arhenius equation, with similar activation energy values for diesel and model soot samples (137±8.7 and 132±5.1 kJ/mol, respectively). The reaction order in O2 for these samples was found to be 0.61±0.03 and 0.71±0.03, respectively, and was remarkably independent of the temperature, suggesting that the fractional order is not due to mixed kinetic control. The reaction mechanism was also found to be independent of carbon conversion. The density of the reaction sites, however, appeared to increase with oxidation. This increase could not be accounted for by the changes in the specific surface area, either directly measured, or derived from such simplified models as the shrinking core formalism. The entire set of obtained experimental results can be described using a kinetically uncomplicated model in a broad range of temperatures, partial pressures of oxygen and degrees of soot oxidation.
2005. "Chemical Bonding in Si52- and NaSi5- via Photoelectron Spectroscopy and Ab Initio Calculations." Journal of Physical Chemistry A 109(50):11385-11394. Abstract Photoelectron spectroscopy and ab initio calculations are used to investigate the electronic structure and chemical bonding of Si5 - and Si5 2- in NaSi5 -. Photoelectron spectra of Si5 - and NaSi5 - are obtained at several photon energies and are compared with theoretical calculations at four different levels of theory, TD-B3LYP, R(U)OVGF, UCCSD(T), and EOM-CCSD(T), all with 6-311+G(2df) basis sets. Excellent agreement is observed between experiment and theory, confirming the obtained ground-state structures for Si5 - and Si5 2-, which are both found to be trigonal bipyramid with D3h symmetry at several levels of theory. Chemical bonding in Si5, Si5 -, and Si5 2- is analyzed using NPA, molecular orbitals, ELF, and NICS indices. The bonding in Si5 2- is compared with that in the isoelectronic and isostructural B5H5 2- species, but they are found to differ due to the involvement of electron densities, which are supposed to be lone pairs in the skeletal bonding in Si5 2-.
