172 research outputs found
Pharmaceutical Applications of the Polarizable Amoeba Potential, Including Protein-Ligand Binding Affinity and Drug Solubility, using the Force Field X Software
First-principles-informed energy span and microkinetic analysis of ethanol catalytic conversion to 1,3-butadiene on MgO
Kinetic modeling of single-step catalytic conversion of ethanol to 1,3-butadiene is necessary to inform accurate process design. This paper uses first-principles-informed energy span and microkinetic analysis to explore the reaction free energy landscapes and kinetic limitations of competing reaction pathways on a MgO (100) step-edge. Previous studies suggested mechanisms proceeding via both dehydrogenation and dehydration of ethanol, and highlighted sensitivity to conditions and catalyst composition. Here, we use the energy span concept to characterize the theoretical maximum turnover and degree of turnover frequency control for states in each reaction pathway, finding the dehydration route to be less active for 1,3-butadiene, and suggesting rate-determining states in the dehydrogenation, dehydration, and condensation steps. The influence of temperature on the relative rate contribution of each state is quantified and explained through the varying temperature sensitivity of the free energy landscape. A microkinetic model is developed to explore competition between pathways, interaction with gas-phase species, and surface coverage limitations. This suggests that the turnover may be significantly lower than predicted solely based on energetics. Turnover frequency determining states found to have high surface coverage include adsorbed ethanol and two longer, oxygenated hydrocarbons. The combined energy span and microkinetic analysis permits investigation of a complex system from two perspectives and helps elucidate conflicting observations of rate determining steps and product distribution by considering both energetic and kinetic limitations. The impact of uncertainty in the energy landscape is quantified using a correlated error model. While the range of predictions is large, the average performance and trends are similar
Interactions of urea surfaces with water as relative humidity obtained from Dynamic Vapor Sorption experiments, in situ single particle Raman spectroscopy and ab initio calculation
Surface Analysis Insight Note: Observations relating to photoemission peak shapes, oxidation state, and chemistry of titanium oxide films
It is common practice to describe the coordination of metal atoms in a binding configuration with their nearest neighbors in terms of oxidation state, a measure by which the number of electrons redistributed between atoms forming chemical bonds. In XPS terms, change to an oxidation state is commonly inferred by correlating photoemission signal with binding energy. The assumption, when classifying photoemission signals into distinct spectral shapes, is that a distribution of intensities shifted to lower binding energy is evidence of a reduction in oxidation state. In this Insight note, we raise the prospect that changes in photoemission peak shape may occur without obvious changes, determined by XPS in stoichiometry for a material. It is well known that TiO2 measured by XPS yields reproducible Ti 2p photoemission peaks. However, on exposing TiO2 to ion beams, Ti 2p photoemission evolves to complex distributions in intensity, which are particularly difficult to analyze by traditional fitting of bellâshaped curves to these data. For these reasons, in this Insight note, a thin film of TiO2 deposited on a silicon substrate is chosen for analysis by XPS and linear algebraic techniques. Alterations in spectral shapes created from modified TiO2, which might be interpreted as the change in oxidation state, are assessed in terms of relative proportions of titanium to oxygen. It is found through detailed analysis of spectra that quantification by XPS, using procedures routinely used in practice, is not in accord with the typical interpretations of photoemission shapes. The data processing methods used and results presented in this work are of particular relevance to elucidating fundamental phenomena governing the surface evolution of materialsâenabled energy processes where cyclic/nonâsteady usage changes the nature of bonding, especially in the presence of contaminants
Definition of a new (Doniach-Sunjic-Shirley) peak shape for fitting asymmetric signals applied to reduced graphene oxide/graphene oxide XPS spectra
The existence of asymmetry in X-ray photoelectron spectroscopy (XPS) photoemission lines is widely accepted, but line shapes designed to accommodate asymmetry are generally lacking in theoretical justification. In this work, we present a new line shape for describing asymmetry in XPS signals that is based on two facts. First, the most widely known line shape for fitting asymmetric XPS signals that has a theoretical basis, referred to as the Doniach-Sunjic (DS) line shape, suffers from a mathematical inconvenience, which is that for asymmetric shapes the area beneath the curve (above the x-axis) is infinite. Second, it is common practice in XPS to remove the inelastically scattered background response of a peak in question with the Shirley algorithm. The new line shape described herein attempts to retain the theoretical virtues of the DS line shape, while allowing the use of a Shirley background, with the consequence that the resulting line shape has a finite area. To illustrate the use of this Doniach-Sunjic-Shirley (DSS) line shape, a set of spectra obtained from varying amounts of graphene oxide (GO) and reduced GO on a patterned, heterogeneous surface are fit and discussed
Effects of Eyjafjallajökull volcanic ash on innate immune system responses and bacterial growth in vitro.
To access publisher's full text version of this article click on the hyperlink at the bottom of the pageOn 20 March 2010, the Icelandic volcano Eyjafjallajökull erupted for the first time in 190 years. Despite many epidemiological reports showing effects of volcanic ash on the respiratory system, there are limited data evaluating cellular mechanisms involved in the response to ash. Epidemiological studies have observed an increase in respiratory infections in subjects and populations exposed to volcanic eruptions.We physicochemically characterized volcanic ash, finding various sizes of particles, as well as the presence of several transition metals, including iron. We examined the effect of Eyjafjallajökull ash on primary rat alveolar epithelial cells and human airway epithelial cells (20-100 ”g/cm(2)), primary rat and human alveolar macrophages (5-20 ”g/cm(2)), and Pseudomonas aeruginosa (PAO1) growth (3 ”g/104 bacteria).Volcanic ash had minimal effect on alveolar and airway epithelial cell integrity. In alveolar macrophages, volcanic ash disrupted pathogen-killing and inflammatory responses. In in vitro bacterial growth models, volcanic ash increased bacterial replication and decreased bacterial killing by antimicrobial peptides.These results provide potential biological plausibility for epidemiological data that show an association between air pollution exposure and the development of respiratory infections. These data suggest that volcanic ash exposure, while not seriously compromising lung cell function, may be able to impair innate immunity responses in exposed individuals.National Institutes of Health (NIH)
R01 HL079901
NIH RO1 HL096625
R21HL109589
National Science Foundation
NSF-EAR0821615
National Institute of Environmental Health Sciences (NIEHS) through the University of Iowa Environmental Health Sciences Research Center
NIEHS/NIH P30 ES005605
National Center for Research Resources, NI
Synthesis and properties of polyamideâAg2S composite based solar energy absorber surfaces
Silver sulfide (Ag2S), an efficient solar light absorber, was synthesized using a modified chemical bath deposition (CBD) method and polyamide 6 (PA) as a host material via solution phase reaction between AgNO3 and Na2S2O3. X-ray diffraction (XRD) data showed a single, α-Ag2S (acanthite), crystalline phase present while surface and bulk chemical analyses, performed using X-ray photoelectron (XPS) and energy dispersive (EDS) spectroscopies, showed 2:1 Ag:S ratio. Direct and indirect bandgaps obtained from Tauc plots were 1.3 and 2.3 eV, respectively. Detailed surface chemical analysis showed the presence of three distinct sulfur species with majority component due to the Ag2S chemical bonds and minority components due to two types of oxygenâsulfur bonds. Conductivity of the resulting composite material was shown to change with the reaction time thus enabling to obtain controlled conductivity composite material. The synthesis method presented is based on the low solubility of Ag2S and is potentially green, no by-product producing, as all Ag2S nucleated outside the host material can be recycled into the process via dissolving it in HNO3
Renewable energy based catalytic CH4 conversion to fuels
Natural gas is envisioned as a primary source of hydrocarbons in the foreseeable future. With the abundance of shale gas, the main concerns have shifted from the limited hydrocarbon availability to the sustainable methods of CH4 conversion to fuels. This is necessitated by high costs of natural gas transportation in its native gaseous form. Conventional gas-to-liquid conversion technologies are capital and scale intensive and can hardly be envisioned in their current form to be cost efficient in the remote locations of the natural gas extraction sites. Solar energy can be utilized at the gas extraction site to perform catalytic CH4 conversion using electrons obtained via photovoltaics or directly with photons. We provide broader insight into the catalytic CH4 conversion methods that utilize renewable energy via photo(electro)catalytic processes, with particular focus on the catalytic materials used, reaction conditions and intermediates, as well as their selectivity. Based on the currently available scientific literature, we propose several hybrid catalytic CH4 conversion processes based on both conventional and renewable â photo(electro)chemical â catalysis
Design of a Parabolic Trough Collector Solar Field for a Pilot CO2 Capture Plant from Natural Gas Combined Cycle Power Plant Flue Gas
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