Showing papers by "Environmental Molecular Sciences Laboratory published in 2015"
TL;DR: This study sequenced DNA from complex sediment and planktonic consortia from an aquifer adjacent to the Colorado River and reconstructed the first complete genomes for Archaea using cultivation-independent methods, which dramatically expand genomic sampling of the domain Archaea and clarify taxonomic designations within a major superphylum.
463 citations
TL;DR: This study presents ab initio molecular dynamics simulations of an unprecedented dynamic single-atom catalytic mechanism for the oxidation of carbon monoxide by ceria-supported gold clusters and highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in catalysis.
Abstract: Computational investigation of heterogeneous catalytic systems is fundamentally important. Here, the authors show that, under reaction conditions, reactant-induced structural changes in ceria-supported gold nanoparticle catalysts lead to the dynamic formation of single-atom catalytic sites at the interface.
362 citations
TL;DR: In this paper, three types of nitrogen-doped hollow carbon spheres with different pore sized porous shells were used to investigate the performance of sulfur confinement and it was successfully demonstrated that the sulfur/polysulfide will overflow the porous carbon during the lithiation process.
Abstract: Three types of nitrogen-doped hollow carbon spheres with different pore sized porous shells are prepared to investigate the performance of sulfur confinement. The reason that why no sulfur is observed in previous research is determined and it is successfully demonstrated that the sulfur/polysulfide will overflow the porous carbon during the lithiation process.
259 citations
TL;DR: By correlating images showing the sequence of Li electro Deposition and the evolution of the SEI layer with simultaneously acquired and calibrated cyclic voltammograms, electrodeposition, and electrolyte breakdown processes can be quantified directly on the nanoscale.
Abstract: An operando electrochemical stage for the transmission electron microscope has been configured to form a "Li battery" that is used to quantify the electrochemical processes that occur at the anode during charge/discharge cycling. Of particular importance for these observations is the identification of an image contrast reversal that originates from solid Li being less dense than the surrounding liquid electrolyte and electrode surface. This contrast allows Li to be identified from Li-containing compounds that make up the solid-electrolyte interphase (SEI) layer. By correlating images showing the sequence of Li electrodeposition and the evolution of the SEI layer with simultaneously acquired and calibrated cyclic voltammograms, electrodeposition, and electrolyte breakdown processes can be quantified directly on the nanoscale. This approach opens up intriguing new possibilities to rapidly visualize and test the electrochemical performance of a wide range of electrode/electrolyte combinations for next generation battery systems.
244 citations
TL;DR: A novel fabrication method for hierarchically porous Si nanospheres (hp-SiNSs), which consist of a porous shell and a hollow core, which exhibit high capacity, high power and long cycle life, which is superior to the current commercial Si-based anode materials.
Abstract: Silicon has been identified as a highly promising anode for next-generation lithium-ion batteries (LIBs). The key challenge for Si anodes is large volume change during the lithiation/delithiation cycle that results in chemomechanical degradation and subsequent rapid capacity fading. Here we report a novel fabrication method for hierarchically porous Si nanospheres (hp-SiNSs), which consist of a porous shell and a hollow core. On charge/discharge cycling, the hp-SiNSs accommodate the volume change through reversible inward Li breathing with negligible particle-level outward expansion. Our mechanics analysis revealed that such inward expansion is enabled by the much stiffer lithiated layer than the unlithiated porous layer. LIBs assembled with the hp-SiNSs exhibit high capacity, high power and long cycle life, which is superior to the current commercial Si-based anode materials. The low-cost synthesis approach provides a new avenue for the rational design of hierarchically porous structures with unique materials properties.
213 citations
TL;DR: In this paper, the progress towards tailoring of Si as anode for lithium ion battery is reviewed, including the fundamentals, the promises offered by nanoscale designs, and the challenges that remained to be addressed to allow the application of Si based materials as high capacity anode.
210 citations
TL;DR: Fifteen compounds, most of which are nitrophenols, are identified as major BrC chromophores responsible for the enhanced light absorption of Tol-SOA material produced in the presence of NOx.
Abstract: Atmospheric brown carbon (BrC) is a significant contributor to light absorption and climate forcing. However, little is known about a fundamental relationship between the chemical composition of BrC and its optical properties. In this work, light-absorbing secondary organic aerosol (SOA) was generated in the PNNL chamber from toluene photo-oxidation in the presence of NOx (Tol-SOA). Molecular structures of BrC components were examined using nanospray desorption electrospray ionization (nano-DESI) and liquid chromatography (LC) combined with UV/Vis spectroscopy and electrospray ionization (ESI) high-resolution mass spectrometry (HRMS). The chemical composition of BrC chromophores and the light absorption properties of toluene SOA (Tol-SOA) depend strongly on the initial NOx concentration. Specifically, Tol-SOA generated under high-NOx conditions (defined here as initial NOx/toluene of 5/1) appears yellow and mass absorption coefficient of the bulk sample (MACbulk@365 nm = 0.78 m(2) g(-1)) is nearly 80 fold higher than that measured for the Tol-SOA sample generated under low-NOx conditions (NOx/toluene < 1/300). Fifteen compounds, most of which are nitrophenols, are identified as major BrC chromophores responsible for the enhanced light absorption of Tol-SOA material produced in the presence of NOx. The integrated absorbance of these fifteen chromophores accounts for 40-60% of the total light absorbance by Tol-SOA at wavelengths between 300 nm and 500 nm. The combination of tandem LC-UV/Vis-ESI/HRMS measurements provides an analytical platform for predictive understanding of light absorption properties by BrC and their relationship to the structure of individual chromophores. General trends in the UV/Vis absorption by plausible isomers of the BrC chromophores were evaluated using theoretical chemistry calculations. The molecular-level understanding of BrC chemistry is helpful for better understanding the evolution and behavior of light absorbing aerosols in the atmosphere.
199 citations
University of Colorado Boulder1, Université de Montréal2, Cooperative Institute for Research in Environmental Sciences3, Peking University4, Harvard University5, Nanyang Technological University6, University of North Carolina at Chapel Hill7, California Institute of Technology8, University of Maryland, Baltimore County9, Goddard Space Flight Center10, University of California, Berkeley11, University of São Paulo12, Earth System Research Laboratory13, University of Oslo14, University of Innsbruck15, National Center for Atmospheric Research16, Alion Science and Technology17, Environmental Molecular Sciences Laboratory18, Met Office19, University of Manchester20, Princeton University21, Geophysical Fluid Dynamics Laboratory22
TL;DR: In this article, the authors applied positive matrix factorization (PMF) to aerosol mass spectrometer (AMS) measurements to identify secondary organic aerosol (SOA) formed from isoprene epoxydiols (IEPOX).
Abstract: . Substantial amounts of secondary organic aerosol (SOA) can be formed from isoprene epoxydiols (IEPOX), which are oxidation products of isoprene mainly under low-NO conditions. Total IEPOX-SOA, which may include SOA formed from other parallel isoprene oxidation pathways, was quantified by applying positive matrix factorization (PMF) to aerosol mass spectrometer (AMS) measurements. The IEPOX-SOA fractions of organic aerosol (OA) in multiple field studies across several continents are summarized here and show consistent patterns with the concentration of gas-phase IEPOX simulated by the GEOS-Chem chemical transport model. During the Southern Oxidant and Aerosol Study (SOAS), 78 % of PMF-resolved IEPOX-SOA is accounted by the measured IEPOX-SOA molecular tracers (2-methyltetrols, C5-Triols, and IEPOX-derived organosulfate and its dimers), making it the highest level of molecular identification of an ambient SOA component to our knowledge. An enhanced signal at C5H6O+ (m/z 82) is found in PMF-resolved IEPOX-SOA spectra. To investigate the suitability of this ion as a tracer for IEPOX-SOA, we examine fC5H6O (fC5H6O= C5H6O+/OA) across multiple field, chamber, and source data sets. A background of ~ 1.7 ± 0.1 ‰ (‰ = parts per thousand) is observed in studies strongly influenced by urban, biomass-burning, and other anthropogenic primary organic aerosol (POA). Higher background values of 3.1 ± 0.6 ‰ are found in studies strongly influenced by monoterpene emissions. The average laboratory monoterpene SOA value (5.5 ± 2.0 ‰) is 4 times lower than the average for IEPOX-SOA (22 ± 7 ‰), which leaves some room to separate both contributions to OA. Locations strongly influenced by isoprene emissions under low-NO levels had higher fC5H6O (~ 6.5 ± 2.2 ‰ on average) than other sites, consistent with the expected IEPOX-SOA formation in those studies. fC5H6O in IEPOX-SOA is always elevated (12–40 ‰) but varies substantially between locations, which is shown to reflect large variations in its detailed molecular composition. The low fC5H6O (
189 citations
TL;DR: The focus of this review is to present a coherent description of SFG-VS and discuss the main concepts and issues that can help advance this technique as a quantitative analytical research tool for revealing the chemistry and physics of complex molecular surfaces and interfaces.
Abstract: Sum-frequency generation vibrational spectroscopy (SFG-VS) can provide detailed information and understanding of the molecular composition, interactions, and orientational and conformational structure of surfaces and interfaces through quantitative measurement and analysis. In this review, we present the current status of and discuss important recent developments in the measurement of intrinsic SFG spectral lineshapes and formulations for polarization measurements and orientational analysis of SFG-VS spectra. The focus of this review is to present a coherent description of SFG-VS and discuss the main concepts and issues that can help advance this technique as a quantitative analytical research tool for revealing the chemistry and physics of complex molecular surfaces and interfaces.
180 citations
TL;DR: The study indicates a "lepidocrocite favoring effect" by OM and suggests that Fe(II)-catalyzed transformation of ferrihydrite may decrease OM stability in natural environments under moderately reducing conditions.
Abstract: Aqueous Fe(II) is known to catalyze the abiotic transformation of ferrihydrite to more stable Fe minerals. However, little is known about the impacts of coprecipitated OM on Fe(II)-catalyzed ferrihydrite transformation and its consequences for C dynamics. Accordingly, we investigated the extent and pathway of Fe(II)-induced transformation of OM-ferrihydrite coprecipitates as a function of C/Fe ratios and aqueous Fe(II) concentrations, and its implications for subsequent C dynamics. The coprecipitated OM resulted in a linear decrease in ferrihydrite transformation with increasing C/Fe ratios. The secondary mineral profiles upon Fe(II) reaction with OM-ferrihydrite coprecipitates depend on Fe(II) concentrations At 0.2 mM Fe(II), OM completely inhibited goethite formation and stimulated lepidocrocite formation. At 2 mM Fe(II), whereas goethite was formed in the presence of OM, OM reduced the amount of goethite and magnetite formation and increased the formation of lepidocrocite. The solid-phase C content rem...
174 citations
TL;DR: In this paper, International Simple Glass (ISG) was altered at 90°C in a solution initially saturated with respect to amorphous 29SiO2, and the pH was raised to 11.5 after 209d by the addition of KOH.
TL;DR: The study of SOM molecules by ESI FTICR MS revealed new insight into the molecular-level complexity of organics contained in soils, and presented the first comparative study of the molecular composition of SOM from different ecosystems using ultra high-resolution mass spectrometry.
Abstract: Soil organic matter (SOM), a complex, heterogeneous mixture of above and belowground plant litter and animal and microbial residues at various degrees of decomposition, is a key reservoir for carbon (C) and nutrient biogeochemical cycling in soil based ecosystems. A limited understanding of the molecular composition of SOM limits the ability to routinely decipher chemical processes within soil and accurately predict how terrestrial carbon fluxes will respond to changing climatic conditions and land use. To elucidate the molecular-level structure of SOM, we selectively extracted a broad range of intact SOM compounds by a combination of different organic solvents from soils with a wide range of C content. Our use of electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and a suite of solvents with varying polarity significantly expands the inventory of the types of organic molecules present in soils. Specifically, we found that hexane is selective ...
TL;DR: Epitaxial La1-x Srx CrO3 deposited on SrTiO3 (001) is shown to be a p-type transparent conducting oxide with competitive figures of merit and a cubic perovskite structure, facilitating integration into oxide electronics.
Abstract: Epitaxial La1-x Srx CrO3 deposited on SrTiO3 (001) is shown to be a p-type transparent conducting oxide with competitive figures of merit and a cubic perovskite structure, facilitating integration into oxide electronics. Holes in the Cr 3d t2g bands play a critical role in enhancing p-type conductivity, while transparency to visible light is maintained because low-lying d-d transitions arising from hole doping are dipole forbidden.
TL;DR: In this article, the Si-C yolk-shell nanocomposite electrode exhibits excellent capacity retention and high cycle effi ciency in situ transmission electron microscopy and finite element simulations consistently reveals that the dramatically enhanced performance is associated with the regulated breathing of the Si in the new composite, therefore the suppression of the overall electrode expansion.
Abstract: Si is an attractive negative electrode material for lithium ion batteries due to its high specifi c capacity (≈3600 mAh g –1 ) However, the huge volume swelling and shrinking during cycling, which mimics a breathing effect at the material/electrode/cell level, leads to several coupled issues including fracture of Si particles, unstable solid electrolyte interphase, and low Coulombic effi ciency In this work, the regulation of the breathing effect is reported by using Si–C yolk–shell nanocomposite which has been well-developed by other researchers The focus is on understanding how the nanoscaled materials design impacts the mechanical and electrochemical response at electrode level For the fi rst time, it is possible to observe one order of magnitude of reduction on breathing effect at the electrode level during cycling: the electrode thickness variation reduced down to 10%, comparing with 100% in the electrode with Si nanoparticles as active materials The Si–C yolk–shell nanocomposite electrode exhibits excellent capacity retention and high cycle effi ciency In situ transmission electron microscopy and fi nite element simulations consistently reveals that the dramatically enhanced performance is associated with the regulated breathing of the Si in the new composite, therefore the suppression of the overall electrode expansion
TL;DR: This study demonstrates a new type of high-performance metal-sulfur battery that is ideal for grid-scale energy-storage applications and can operate at as low as 150 °C with excellent performance.
Abstract: A potassium-sulfur battery using K(+) -conducting beta-alumina as the electrolyte to separate a molten potassium metal anode and a sulfur cathode is presented. The results indicate that the battery can operate at as low as 150 °C with excellent performance. This study demonstrates a new type of high-performance metal-sulfur battery that is ideal for grid-scale energy-storage applications.
TL;DR: Three-year field trials in China demonstrated that the cultivation of SUSIBA2 rice was associated with a significant reduction in methane emissions and a decrease in rhizospheric methanogen levels, indicating a sustainable means of providing increased starch content for food production while reducing greenhouse gas emissions from rice cultivation.
Abstract: Atmospheric methane is the second most important greenhouse gas after carbon dioxide, and is responsible for about 20% of the global warming effect since pre-industrial times. Rice paddies are the largest anthropogenic methane source and produce 7-17% of atmospheric methane. Warm waterlogged soil and exuded nutrients from rice roots provide ideal conditions for methanogenesis in paddies with annual methane emissions of 25-100-million tonnes. This scenario will be exacerbated by an expansion in rice cultivation needed to meet the escalating demand for food in the coming decades. There is an urgent need to establish sustainable technologies for increasing rice production while reducing methane fluxes from rice paddies. However, ongoing efforts for methane mitigation in rice paddies are mainly based on farming practices and measures that are difficult to implement. Despite proposed strategies to increase rice productivity and reduce methane emissions, no high-starch low-methane-emission rice has been developed. Here we show that the addition of a single transcription factor gene, barley SUSIBA2 (refs 7, 8), conferred a shift of carbon flux to SUSIBA2 rice, favouring the allocation of photosynthates to aboveground biomass over allocation to roots. The altered allocation resulted in an increased biomass and starch content in the seeds and stems, and suppressed methanogenesis, possibly through a reduction in root exudates. Three-year field trials in China demonstrated that the cultivation of SUSIBA2 rice was associated with a significant reduction in methane emissions and a decrease in rhizospheric methanogen levels. SUSIBA2 rice offers a sustainable means of providing increased starch content for food production while reducing greenhouse gas emissions from rice cultivation. Approaches to increase rice productivity and reduce methane emissions as seen in SUSIBA2 rice may be particularly beneficial in a future climate with rising temperatures resulting in increased methane emissions from paddies.
TL;DR: Results suggest that reduced-nitrogen organic compounds formed in reactions between atmospheric carbonyls and ammonia/amines are important BrC chromophores and it is demonstrated that improved separation by HPLC will significantly advance understanding of BrC chemistry.
Abstract: Atmospheric brown carbon (BrC) is an important contributor to light absorption and climate forcing by aerosols. Reactions between small water-soluble carbonyls and ammonia or amines have been identified as one of the potential pathways of BrC formation. However, detailed chemical characterization of BrC chromophores has been challenging and their formation mechanisms are still poorly understood. Understanding BrC formation is impeded by the lack of suitable methods which can unravel the variability and complexity of BrC mixtures. This study applies high performance liquid chromatography (HPLC) coupled to photodiode array (PDA) detector and high resolution mass spectrometry (HRMS) to investigate optical properties and chemical composition of individual BrC components produced through reactions of methylglyoxal (MG) and ammonium sulfate (AS), both of which are abundant in the atmospheric environment. A direct relationship between optical properties and chemical composition of 30 major BrC chromophores is es...
TL;DR: In this article, Humic-like substances (HULIS), the hydrophobic part of water-soluble organic carbon (WSOC), account for a significant fraction of PM2.5 mass, while residual oil combustion related to shipping was identified as a significant source of HULIS.
Abstract: . Humic-like substances (HULIS), the hydrophobic part of water-soluble organic carbon (WSOC), account for a significant fraction of PM2.5 mass. Their source studies are so far largely qualitative. In this study, HULIS and WSOC were determined in 100 PM2.5 samples collected in 2009 at an urban site (Guangzhou) and a suburban site (Nansha) in the Pearl River Delta in South China. The annual average concentration of HULIS was 4.83 and 4.71 μg m−3, constituting 8.5 and 10.2% of the PM2.5 mass, while HULIS-C (the carbon component of HULIS) contributed 48 and 57% of WSOC at the two sites, respectively. HULIS were found to correlate with biomass burning (BB) tracers (i.e., levoglucosan and K) and secondary species (e.g., SO42− and NH4+), suggesting its association with BB emissions and secondary formation processes. Sources of HULIS were investigated using positive matrix factorization analysis of PM2.5 chemical composition data, including major components and source markers. In addition to secondary formation process and BB emissions, residual oil combustion related to shipping was identified for the first time as a significant source of HULIS. Secondary formation process contributed the most, accounting for 49–82% of ambient HULIS at the two sites in different seasons. BB emissions contributed a seasonal average of 8–28%, with more contributions observed in the winter months (November–February) due to crop residue burning during harvest season. Residual oil combustion was revealed to be an important source at the suburban site in summer (44% of HULIS-C) due to its proximity to one of the ports and the shipping lane in the region. Vehicle emissions were found to contribute little to HULIS, but had contributions to the hydrophilic WSOC fraction. The contrast in contributions from different combustion sources to HULIS and hydrophilic WSOC suggests that primary sources of HULIS are linked to inefficient combustion. This source analysis suggests further study of HULIS be focused on secondary formation process and source characteristics of HULIS from BB and residual oil combustion.
TL;DR: Observations indicate that the difference between the Li surface diffusivity and bulk lithiation rate of the coatings dictates lithiation induced morphological evolution in the nanowires, and indicates that the reaction rate in the coating layer can be the limiting step for lithiation and therefore critically influences the rate performance of the battery.
Abstract: Silicon (Si)-based materials hold promise as the next-generation anodes for high-energy lithium (Li)-ion batteries. Enormous research efforts have been undertaken to mitigate the chemo-mechanical failure due to the large volume changes of Si during lithiation and delithiation cycles. It has been found that nanostructured Si coated with carbon or other functional materials can lead to significantly improved cyclability. However, the underlying mechanism and comparative performance of different coatings remain poorly understood. Herein, using in situ transmission electron microscopy (TEM) through a nanoscale half-cell battery, in combination with chemo-mechanical simulation, we explored the effect of thin (∼5 nm) alucone and Al2O3 coatings on the lithiation kinetics of Si nanowires (SiNWs). We observed that the alucone coating leads to a “V-shaped” lithiation front of the SiNWs, while the Al2O3 coating yields an “H-shaped” lithiation front. These observations indicate that the difference between the Li surf...
TL;DR: In situ transmission electron microscopy is used to investigate the lithiation/delithiation kinetics of SiNPs coated with a conductive polymer, polypyrrole (PPy), and it is rationalized that the self-discharging is driven by the internal compressive stress generated inside the lithiatedSiNPs due to the constraint effect of the coating layer.
Abstract: One of the key challenges of Si-based anodes for lithium ion batteries is the large volume change upon lithiation and delithiation, which commonly leads to electrochemi-mechanical degradation and subsequent fast capacity fading. Recent studies have shown that applying nanometer-thick coating layers on Si nanoparticle (SiNPs) enhances cyclability and capacity retention. However, it is far from clear how the coating layer function from the point of view of both surface chemistry and electrochemi-mechanical effect. Herein, we use in situ transmission electron microscopy to investigate the lithiation/delithiation kinetics of SiNPs coated with a conductive polymer, polypyrrole (PPy). We discovered that this coating layer can lead to “self-delithiation” or “self-discharging” at different stages of lithiation. We rationalized that the self-discharging is driven by the internal compressive stress generated inside the lithiated SiNPs due to the constraint effect of the coating layer. We also noticed that the criti...
TL;DR: The results suggest that biological redox cycling of structural Fe in phyllosilicates is a reversible process and has important implications for biogeochemical cycles of carbon, nitrogen, and other nutrients in natural environments.
Abstract: Biological redox cycling of structural Fe in phyllosilicates is an important but poorly understood process. The objective of this research was to study microbially mediated redox cycles of Fe in nontronite (NAu-2). During the reduction phase, structural Fe(III) in NAu-2 served as electron acceptor, lactate as electron donor, AQDS as electron shuttle, and dissimilatory Fe(III)-reducing bacterium Shewanella putrefaciens CN32 as mediator in bicarbonate- and PIPES-buffered media. During the oxidation phase, biogenic Fe(II) served as electron donor and nitrate as electron acceptor. Nitrate-dependent Fe(II)-oxidizing bacterium Pseudogulbenkiania sp. strain 2002 was added as mediator in the same media. For all three cycles, structural Fe in NAu-2 was able to reversibly undergo three redox cycles without significant dissolution. Fe(II) in bioreduced samples occurred in two distinct environments, at edges and in the interior of the NAu-2 structure. Nitrate reduction to nitrogen gas was coupled with oxidation of edge-Fe(II) and part of interior-Fe(II) under both buffer conditions, and its extent and rate did not change with Fe redox cycles. These results suggest that biological redox cycling of structural Fe in phyllosilicates is a reversible process and has important implications for biogeochemical cycles of carbon, nitrogen, and other nutrients in natural environments.
TL;DR: In this article, the authors summarize and highlight recent progress involving in situ TEM studies of energy storage materials, especially rechargeable batteries, and provide an overview of the in-person TEM imaging of batteries.
Abstract: Since the advent of the transmission electron microscope (TEM), continuing efforts have been made to image material under native and reaction environments that typically involve liquids, gases, and external stimuli. With the advances of aberration-corrected TEM for improving the imaging resolution, steady progress has been made on developing methodologies that allow imaging under dynamic operating conditions, or in situ TEM imaging. The success of in situ TEM imaging is closely associated with advances in microfabrication techniques that enable manipulation of nanoscale objects around the objective lens of the TEM. This study summarizes and highlights recent progress involving in situ TEM studies of energy storage materials, especially rechargeable batteries. The study is organized to cover both the in situ TEM techniques and the scientific discoveries made possible by in situ TEM imaging.
TL;DR: In this article, an Fe/SSZ-13 catalyst active in NH3-SCR was synthesized using a traditional aqueous solution ion exchange method under a protecting atmosphere of N2.
Abstract: Using a traditional aqueous solution ion-exchange method under a protecting atmosphere of N2, an Fe/SSZ-13 catalyst active in NH3-SCR was synthesized. Mossbauer and FTIR spectroscopies were used to probe the nature of the Fe sites. In the fresh sample, the majority of Fe species are extra-framework cations. The likely monomeric and dimeric ferric ions in hydrated form are [Fe(OH)2]+ and [HO Fe O Fe OH]2+, based on Mossbauer measurements. During the harsh hydrothermal aging (HTA) applied in this study, a majority of cationic Fe species convert to FeAlOx and clustered FeOx species, accompanied by dealumination of the SSZ-13 framework. The clustered FeOx species do not give a sextet Mossbauer spectrum, indicating that these are highly disordered. However, some Fe species in cationic positions remain after aging as determined from Mossbauer measurements and CO/NO FTIR titrations. NO/NH3 oxidation reaction tests reveal that dehydrated cationic Fe is substantially more active in catalyzing oxidation reactions than the hydrated ones. For NH3-SCR, enhancement of NO oxidation under ‘dry’ conditions promotes SCR rates below ∼300 °C. This is due mainly to contribution from the “fast” SCR channel. Above ∼300 °C, enhancement of NH3 oxidation under ‘dry’ conditions, however, becomes detrimental to NOx conversions. The HTA sample loses much of the SCR activity below ∼300 °C; however, above ∼400 °C much of the activity remains. This may suggest that the FeAlOx and FeOx species become active at such elevated temperatures. Alternatively, the high-temperature activity may be maintained by the remaining extra-framework cationic species. For potential practical applications, Fe/SSZ-13 may be used as a co-catalyst for Cu/CHA as integral aftertreatment SCR catalysts on the basis of the stable high temperature activity after hydrothermal aging.
TL;DR: The efficacy of the RT-TDDFT approach to calculate wide absorption spectra of two large chromophores relevant to photovoltaics and molecular switches and the calculations are compared with traditional linear-response TDDFT and experimental spectra.
Abstract: We assess the performance of real-time time-dependent density functional theory (RT-TDDFT) for the calculation of absorption spectra of 12 organic dye molecules relevant to photovoltaics and dye-sensitized solar cells with 8 exchange-correlation functionals (3 traditional, 3 global hybrids, and 2 range-separated hybrids). We compare the calculations with traditional linear-response (LR) TDDFT and experimental spectra. In addition, we demonstrate the efficacy of the RT-TDDFT approach to calculate wide absorption spectra of two large chromophores relevant to photovoltaics and molecular switches. RT-TDDFT generally requires longer simulation times, compared to LR-TDDFT, for absorption spectra of small systems. However, it becomes more effective for the calculation of wide absorption spectra of large molecular complexes and systems with very high densities of states.
TL;DR: In this article, two preparation methods, controlled adsorption and dry impregnation, are implemented to explore the effect of preparation method on the formation of active sites on alumina supported nickel catalysts.
Abstract: Nickel catalysts prepared by a variety of different methods are commonly used for reforming reactions such as methane dry reforming. Two preparation methods, controlled adsorption and dry impregnation, are implemented to explore the effect of preparation method on the formation of active sites on alumina supported nickel catalysts. By varying only the preparation method, comparison of catalysts that differ primarily in metal–support interactions, strong metal–support interaction (controlled adsorption) and weak metal–support interactions (dry impregnation), are obtained. For controlled adsorption, optimal synthesis conditions are identified using point of zero charge measurements, pH-precipitation experiments, and adsorption isotherms. Using these conditions, a catalyst with a higher dispersion and strong metal–support interactions is prepared. Physicochemical characterization by N2 physisorption, H2 chemisorption, temperature programmed reduction (TPR), transmission electron microscopy (TEM), and environmental TEM (ETEM) shows that the types of nickel sites formed strongly depend on the synthesis method. Methane dry reforming reactivity studies show stable catalytic performance for at least 9 h and provide additional insight into the types of active centers present. After reductive pretreatment, the nickel catalyst prepared by dry impregnation is found to primarily have nickel present as a surface NiAl2O4. In contrast, the active centers for the nickel catalyst prepared by controlled adsorption consist of nickel particles that are encapsulated by a nickel aluminate layer with 1–2 nm in thickness. Combustion analysis and XPS of spent catalysts reveal different amounts and nature of carbonaceous deposits as a function of the synthesis method.
TL;DR: Methods for probing single cell physiology and metabolism specific to metabolism and bioenergetics are reviewed, focusing on dynamic and high-content profiling strategies based on label-free and fluorescence microspectroscopy and microscopy.
TL;DR: It is demonstrated that positively charged nanoparticles are more likely to interact with Gram-negative bacteria than are negatively charged particles, and this interaction occurs primarily through lipopolysaccharides.
Abstract: Design of nanomedicines and nanoparticle-based antimicrobial and antifouling formulations and assessment of the potential implications of nanoparticle release into the environment requires understanding nanoparticle interaction with bacterial surfaces. Here we demonstrate the electrostatically driven association of functionalized nanoparticles with lipopolysaccharides of Gram-negative bacterial outer membranes and find that lipopolysaccharide structure influences the extent and location of binding relative to the outer leaflet-solution interface. By manipulating the lipopolysaccharide content in Shewanella oneidensis outer membranes, we observed the electrostatically driven interaction of cationic gold nanoparticles with the lipopolysaccharide-containing leaflet. We probed this interaction by quartz crystal microbalance with dissipation monitoring (QCM-D) and second harmonic generation (SHG) using solid-supported lipopolysaccharide-containing bilayers. The association of cationic nanoparticles increased with lipopolysaccharide content, while no association of anionic nanoparticles was observed. The harmonic-dependence of QCM-D measurements suggested that a population of the cationic nanoparticles was held at a distance from the outer leaflet-solution interface of bilayers containing smooth lipopolysaccharides (those bearing a long O-polysaccharide). Additionally, smooth lipopolysaccharides held the bulk of the associated cationic particles outside of the interfacial zone probed by SHG. Our results demonstrate that positively charged nanoparticles are more likely to interact with Gram-negative bacteria than are negatively charged particles, and this interaction occurs primarily through lipopolysaccharides.
TL;DR: In this paper, a series of cobalt nickel mixed oxide catalysts with varying ratios of Co to Ni, prepared by co-precipitation method, were applied to methane combustion.
Abstract: A series of cobalt nickel mixed oxide catalysts with the varying ratios of Co to Ni, prepared by co-precipitation method, were applied to methane combustion. Among the various ratios, cobalt nickel mixed oxides having the ratios of Co to Ni of (50:50) and (67:33) demonstrate the highest activity for methane combustion. Structural analysis obtained from X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) evidently demonstrates that CoNi (50:50) and (67:33) samples consist of NiCo2O4 and NiO phase and, more importantly, NiCo2O4 spinel structure is largely distorted, which is attributed to the insertion of Ni2+ ions into octahedral sites in Co3O4 spinel structure. Such structural disorder results in the enhanced portion of surface oxygen species, thus leading to the improved reducibility of the catalysts in the low temperature region as evidenced by temperature programmed reduction by hydrogen (H2 TPR) and X-ray photoelectron spectroscopy (XPS) O 1s results. They prove that structural disorder in cobalt nickel mixed oxides enhances the catalytic performance for methane combustion. Thus, it is concluded that a strong relationship between structural property and activity in cobalt nickel mixed oxide for methane combustion exists and, more importantly, distorted NiCo2O4 spinel structure is found to be an active site for methane combustion.
TL;DR: In this paper, the authors investigated the evolution of the electronic properties of epitaxial films deposited by molecular beam epitaxy (MBE) using x-ray diffraction, X-ray photo-emission spectroscopy, Rutherford backscattering spectrometry, xray absorption spectrograph, electrical transport, and ab initio modeling.
Abstract: We have investigated the evolution of the electronic properties of $\mathrm{L}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{S}{\mathrm{r}}_{x}\mathrm{Cr}{\mathrm{O}}_{3}\phantom{\rule{0.16em}{0ex}}(0\ensuremath{\le}x\ensuremath{\le}1)$ epitaxial films deposited by molecular beam epitaxy (MBE) using x-ray diffraction, x-ray photoemission spectroscopy, Rutherford backscattering spectrometry, x-ray absorption spectroscopy, electrical transport, and ab initio modeling. $\mathrm{LaCr}{\mathrm{O}}_{3}$ is an antiferromagnetic insulator, whereas $\mathrm{SrCr}{\mathrm{O}}_{3}$ is a metal. Substituting $\mathrm{S}{\mathrm{r}}^{2+}$ for $\mathrm{L}{\mathrm{a}}^{3+}$ in $\mathrm{LaCr}{\mathrm{O}}_{3}$ effectively dopes holes into the top of valence band, leading to $\mathrm{C}{\mathrm{r}}^{4+}$ (${3d}^{2}$) local electron configurations. Core-level and valence-band features monotonically shift to lower binding energy with increasing $x$, indicating downward movement of the Fermi level toward the valence band maximum. The material becomes a $p$-type semiconductor at lower doping levels and an insulator-to-metal transition is observed at $x\ensuremath{\ge}0.65$, but only when the films are deposited with in-plane compression via lattice-mismatched heteroepitaxy. Valence-band x-ray photoemission spectroscopy reveals diminution of electronic state density at the $\mathrm{Cr}\phantom{\rule{0.16em}{0ex}}d\phantom{\rule{0.16em}{0ex}}{t}_{2g}$-derived top of the valence band, while O K-edge x-ray absorption spectroscopy shows the development of a new unoccupied state above the Fermi level as holes are doped into $\mathrm{LaCr}{\mathrm{O}}_{3}$. The evolution of these bands with Sr concentration is accurately captured using density functional theory (DFT) with a Hubbard U correction of 3.0 eV $(\mathrm{DFT}+U)$. Resistivity data in the semiconducting regime $(x\ensuremath{\le}0.50)$ do not fit perfectly well to either a polaron hopping or band conduction model but are best interpreted in terms of a hybrid model. The activation energies extracted from these fits are well reproduced by $\mathrm{DFT}+U$.
TL;DR: In this paper, the authors present molecular-level investigations of how well-characterized silica-supported phospholipid bilayers formed from either pure DOPC or a 9:1 mixture of DOPc:DOTAP interact with positively and negatively charged 4 nm gold metal nanoparticles at pH 7.4 and NaCl concentrations ranging from 0.001 to 0.1 M.
Abstract: This work presents molecular-level investigations of how well-characterized silica-supported phospholipid bilayers formed from either pure DOPC or a 9:1 mixture of DOPC:DOTAP interact with positively and negatively charged 4 nm gold metal nanoparticles at pH 7.4 and NaCl concentrations ranging from 0.001 to 0.1 M. Second harmonic generation (SHG) charge screening measurements indicate the supported bilayers carry a negative interfacial potential. Resonantly enhanced SHG measurements probing electronic transitions within the gold core of the nanoparticles show the particles interact irreversibly with the supported bilayers at a range of concentrations. At 0.1 M NaCl, surface coverages for the particles functionalized with the negatively charged ligand mercaptopropionic acid (MPA) or wrapped in the cationic polyelectrolyte poly(allylamine) hydrochloride (PAH) are estimated from a joint analysis of QCM-D, XPS, AFM, and ToF-SIMS to be roughly 1 × 107 and 1 × 1011 particles cm–2, respectively. Results from com...