Hybrid mesoporous silicates: A distinct aspect to synthesis and application for decontamination of phenols.

Water pollution due to organic compounds is of great concern and efforts are being made to develop efficient adsorbents for remediation of toxic pollutants. The development of new functionalized materials with increased performance is growing to meet the regulatory standards in response to public concerns for environment. In this study, an attempt has been made to investigate the influence of synthesis parameters like the reaction temperature, the surfactant-to-silica ratio and reaction time on the structural and textural properties of novel ordered mesoporous silica hybrids. In order to understand the effect of different synthesis parameters, all the prepared materials were systematically characterized by various analytical, spectroscopic and imaging techniques such as XRD, BET, TG etc. It was deduced from these studies that the synthesis temperature influence greatly the structural order whereas both the P104/Na2SiO3 molar ratio and reaction time found to influence textural properties significantly. However, under optimized experimental condition, we could achieve the functionalized silica hybrids that offers successful incorporation of -Amino, -Glucidoxy, -Methacrylate, -Vinyl and -Phenyl moieties indicated by FTIR peaks at 793 cm-1, 2870 cm-1, 796 cm-1, 1630 cm-1 and 954 cm-1. XRD studies reveal orthorhombic and tetragonal symmetry for the hybrids and these materials were found to be thermally stable due to incorporation of organic moiety in silica matrix. Functionalized silica hybrids then applied as adsorbents demonstrated efficient and comparable removal of 4-aminophenol and p-nitrophenol in 20 min facilitated through organic moiety. Detailed modeling of the sorption using equilibrium and kinetic isotherms has been carried out to get an insight into the transport process. The adsorption isotherms of phenol derivatives are well-fitted with the Langmuir, Freundlich and Temkin Isotherms and the adsorption kinetics follows the pseudo second order model. The modeling confirms that the uptake is a chemisorption process.

Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community.

Little is known about the amount and infectiousness of influenza virus shed into exhaled breath. This contributes to uncertainty about the importance of airborne influenza transmission. We screened 355 symptomatic volunteers with acute respiratory illness and report 142 cases with confirmed influenza infection who provided 218 paired nasopharyngeal (NP) and 30-minute breath samples (coarse >5-µm and fine ≤5-µm fractions) on days 1-3 after symptom onset. We assessed viral RNA copy number for all samples and cultured NP swabs and fine aerosols. We recovered infectious virus from 52 (39%) of the fine aerosols and 150 (89%) of the NP swabs with valid cultures. The geometric mean RNA copy numbers were 3.8 × 104/30-minutes fine-, 1.2 × 104/30-minutes coarse-aerosol sample, and 8.2 × 108 per NP swab. Fine- and coarse-aerosol viral RNA were positively associated with body mass index and number of coughs and negatively associated with increasing days since symptom onset in adjusted models. Fine-aerosol viral RNA was also positively associated with having influenza vaccination for both the current and prior season. NP swab viral RNA was positively associated with upper respiratory symptoms and negatively associated with age but was not significantly associated with fine- or coarse-aerosol viral RNA or their predictors. Sneezing was rare, and sneezing and coughing were not necessary for infectious aerosol generation. Our observations suggest that influenza infection in the upper and lower airways are compartmentalized and independent.

Conductive One- and Two-Dimensional Structures Fabricated Using Oxidation-Resistant Cu-Sn Particles.

Cu-Sn powders are promising alternatives to Ag and Au in applications including printed electronics because of their low cost and high oxidation resistance. Further development requires knowledge of the conductivity of their corresponding one- and two-dimensional structures. Herein, CuSny (y = atom ratio of Sn/Cu) wires and films were produced by direct printing. In situ measurements of structural resistivities with variation of the temperature from 2 to 400 K in oxygen-free conditions revealed that CuSn0.1 wires have resistivities comparable to those of Cu wires. Furthermore, CuSn0.1 films exhibited significantly lower resistivity increases after being heated at 573 K in ambient air, compared with Cu films.

Methane emissions from the Marcellus Shale in southwestern Pennsylvania and northern West Virginia based on airborne measurements.

Natural gas production in the U.S. has increased rapidly over the past decade, along with concerns about methane (CH4) leakage (total fugitive emissions), and climate impacts. Quantification of CH4 emissions from oil and natural gas (O&NG) operations is important for establishing scientifically sound, cost-effective policies for mitigating greenhouse gases. We use aircraft measurements and a mass balance approach for three flight experiments in August and September 2015 to estimate CH4 emissions from O&NG operations in the southwestern Marcellus Shale region. We estimate the mean ± 1σ CH4 emission rate as 36.7 ± 1.9 kg CH4 s-1 (or 1.16 ± 0.06 Tg CH4 yr-1) with 59% coming from O&NG operations. We estimate the mean ± 1σ CH4 leak rate from O&NG operations as 3.9 ± 0.4% with a lower limit of 1.5% and an upper limit of 6.3%. This leak rate is broadly consistent with the results from several recent top-down studies but higher than the results from a few other observational studies as well as in the U.S. Environmental Protection Agency CH4 emission inventory. However, a substantial source of CH4 was found to contain little ethane (C2H6), possibly due to coalbed CH4 emitted either directly from coalmines or from wells drilled through coalbed layers. Although recent regulations requiring capture of gas from the completion venting step of the hydraulic fracturing appear to have reduced losses, our study suggests that for a 20 year time scale, energy derived from the combustion of natural gas extracted from this region will require further controls before it can exert a net climate benefit compared to coal.

Expected ozone benefits of reducing nitrogen oxide (NOx) emissions from coal-fired electricity generating units in the eastern United States.

On hot summer days in the eastern United States, electricity demand rises, mainly because of increased use of air conditioning. Power plants must provide this additional energy, emitting additional pollutants when meteorological conditions are primed for poor air quality. To evaluate the impact of summertime NOx emissions from coal-fired electricity generating units (EGUs) on surface ozone formation, we performed a series of sensitivity modeling forecast scenarios utilizing EPA 2018 version 6.0 emissions (2011 base year) and CMAQ v5.0.2. Coal-fired EGU NOx emissions were adjusted to match the lowest NOx rates observed during the ozone seasons (April 1-October 31) of 2005-2012 (Scenario A), where ozone decreased by 3-4 ppb in affected areas. When compared to the highest emissions rates during the same time period (Scenario B), ozone increased ∼4-7 ppb. NOx emission rates adjusted to match the observed rates from 2011 (Scenario C) increased ozone by ∼4-5 ppb. Finally in Scenario D, the impact of additional NOx reductions was determined by assuming installation of selective catalytic reduction (SCR) controls on all units lacking postcombustion controls; this decreased ozone by an additional 2-4 ppb relative to Scenario A. Following the announcement of a stricter 8-hour ozone standard, this analysis outlines a strategy that would help bring coastal areas in the mid-Atlantic region closer to attainment, and would also provide profound benefits for upwind states where most of the regional EGU NOx originates, even if additional capital investments are not made (Scenario A). IMPLICATIONS: With the 8-hr maximum ozone National Ambient Air Quality Standard (NAAQS) decreasing from 75 to 70 ppb, modeling results indicate that use of postcombustion controls on coal-fired power plants in 2018 could help keep regions in attainment. By operating already existing nitrogen oxide (NOx) removal devices to their full potential, ozone could be significantly curtailed, achieving ozone reductions by up to 5 ppb in areas around the source of emission and immediately downwind. Ozone improvements are also significant (1-2 ppb) for areas affected by cross-state transport, especially Mid-Atlantic coast regions that had struggled to meet the 75 ppb standard.

CAMx Ozone Source Attribution in the Eastern United States using Guidance from Observations during DISCOVER-AQ Maryland.

A Comprehensive Air-Quality Model with Extensions (CAMx) version 6.10 simulation was assessed through comparison with data acquired during NASA's 2011 DISCOVER-AQ Maryland field campaign. Comparisons for the baseline simulation (CB05 chemistry, EPA 2011 National Emissions Inventory) show a model overestimate of NOy by +86.2% and an underestimate of HCHO by -28.3%. We present a new model framework (CB6r2 chemistry, MEGAN v2.1 biogenic emissions, 50% reduction in mobile NOx, enhanced representation of isoprene nitrates) that better matches observations. The new model framework attributes 31.4% more surface ozone in Maryland to electric generating units (EGUs) and 34.6% less ozone to on-road mobile sources. Surface ozone becomes more NOx-limited throughout the eastern United States compared to the baseline simulation. The baseline model therefore likely underestimates the effectiveness of anthropogenic NOx reductions as well as the current contribution of EGUs to surface ozone.

Graphene-bonded and -encapsulated si nanoparticles for lithium ion battery anodes.

Silicon (Si) has been considered a very promising anode material for lithium ion batteries due to its high theoretical capacity. However, high-capacity Si nanoparticles usually suffer from low electronic conductivity, large volume change, and severe aggregation problems during lithiation and delithiation. In this paper, a unique nanostructured anode with Si nanoparticles bonded and wrapped by graphene is synthesized by a one-step aerosol spraying of surface-modified Si nanoparticles and graphene oxide suspension. The functional groups on the surface of Si nanoparticles (50-100 nm) not only react with graphene oxide and bind Si nanoparticles to the graphene oxide shell, but also prevent Si nanoparticles from aggregation, thus contributing to a uniform Si suspension. A homogeneous graphene-encapsulated Si nanoparticle morphology forms during the aerosol spraying process. The open-ended graphene shell with defects allows fast electrochemical lithiation/delithiation, and the void space inside the graphene shell accompanied by its strong mechanical strength can effectively accommodate the volume expansion of Si upon lithiation. The graphene shell provides good electronic conductivity for Si nanoparticles and prevents them from aggregating during charge/discharge cycles. The functionalized Si encapsulated by graphene sample exhibits a capacity of 2250 mAh g⁻¹ (based on the total mass of graphene and Si) at 0.1C and 1000 mAh g⁻¹ at 10C, and retains 85% of its initial capacity even after 120 charge/discharge cycles. The exceptional performance of graphene-encapsulated Si anodes combined with the scalable and one-step aerosol synthesis technique makes this material very promising for lithium ion batteries.

Biological templates for antireflective current collectors for photoelectrochemical cell applications.

Three-dimensional (3D) structures such as nanowires, nanotubes, and nanorods have the potential to increase surface area, reduce light reflection, and shorten charge carrier transport distances. The assembly of such structures thus holds great promise for enhancing photoelectrochemical solar cell efficiency. In this study, genetically modified Tobacco mosaic virus (TMV1cys) was used to form self-assembling 3D nanorod current collectors and low light-reflecting surfaces. Photoactive CuO was subsequently deposited by sputtering onto these patterned nanostructures, and these structures were examined for photocurrent activity. CuO thicknesses of 520 nm on TMV1cys patterned current collectors produced the highest photocurrent density of 3.15 mA/cm(2) yet reported for a similar sized CuO system. Reflectivity measurements are in agreement with full-wave electromagnetic simulations, which can be used as a design tool for optimizing the CuO system. Thus the combined effects of reducing charge carrier transport distance, increasing surface area, and the suppression of light reflection make these virus-templated surfaces ideal for photoelectrochemical applications.

Modification of a commercial cavity ring-down spectroscopy NO2 detector for enhanced sensitivity.

Nitrogen dioxide (NO(2)) plays a central role in atmospheric chemistry, air pollution, and biogeochemical cycles. Many analytical techniques have been developed to detect NO(2), but only chemiluminescence-based instruments are commonly, commercially available. There remains a need for a fast, light, and simple method to directly measure NO(2). In this work we describe the modification and characterization of a small, commercially available cavity ring-down spectroscopy (CRDS) NO(2) detector suitable for surface and aircraft monitoring. A metal oxide scrubber was added to remove NO(2), and provide a chemical zero, improving the detection limit (3sigma of the background noise) from several parts per billion by volume (ppbv) to 0.06 ppbv, integrated over 60 s. Known interferences by water and particles were removed using Nafion tubing and a 1 microm Teflon filter, respectively. A 95% response time of 18+/-1 s was observed for a step change in concentration. The CRDS detector was run in parallel to an ozone chemiluminescence device with photolytic conversion of NO(2) to NO. The two instruments measured ambient air in suburban Maryland. A least-squares fit to the comparison data resulted a slope of 0.960+/-0.002 and R of 0.995, showing agreement within experimental uncertainty.

Photocatalytic activity of a surface-modified anatase and rutile titania nanoparticle mixture.

Photocatalytic activity of mixtures of anatase and rutile titania nanoparticles, both bare and treated via capillary condensation of a silica precursor, was investigated by following photodegradation of methylene blue by ultraviolet light in an aqueous solution. The best observed activity for the physically mixed nanoparticles was seen at an anatase to rutile mass ratio of 4:1. This mixture was subject to capillary condensation of tetraethyl orthosilicate (TEOS) at various saturation ratios, followed by reaction of TEOS to form silica. Treatment at a saturation ratio of 1.2 improved photoactivity over that of the physical mixture, a result attributed to enhanced interphase connectivity and increased methylene blue adsorption onto silica.

Precipitation of nanocrystalline CeO2 using triethanolamine.

Synthesis of cerium oxide nanocrystallites via precipitation using triethanolamine is reported. The molecular water associated with the cerium nitrate precursor is exploited to generate hydroxyl ions with the help of triethanolamine, facilitating precipitation. The small crystallite diameter (3 nm) in the as prepared powder is believed to result from the limited amount of water present. Solvent type has no effect on the final crystallite size or structure; however, it plays an important role in the dispersion of the nanoparticles with dispersity of the particles increasing with increasing carbon chain length of the solvent alcohol used.

Flame synthesis of nanosized Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts for the water-gas shift (WGS) reaction.

A flame synthesis method has been used to prepare nanosized, high-surface-area Cu-Ce-O, Ni-Ce-O, and Fe-Ce-O catalysts from aqueous solutions of metal acetate precursors. The particles were formed by vaporization of the precursors followed by reaction and then gas to particle conversion. The specific surface areas of the synthesized powders ranged from 127 to 163 m(2)/g. High-resolution transmission electron microscope imaging showed that the particle diameters for the ceria materials are in the range of 3-10 nm, and a thin layer of amorphous material was observed on the surface of the particles. The presence and surface enrichment of the transition-metal oxides (CuO, NiO, and Fe(2)O(3)) on the ceria particles were detected using X-ray photoelectron spectroscopy. Electron energy-loss spectroscopic studies suggest the formation of a core-shell structure in the as-prepared particles. Extended X-ray absorption fine structure studies suggest that the dopants in all M-Ce-O systems are almost isostructural with their oxide counterparts, indicating the doping materials form separate oxide phases (CuO, Fe(2)O(3), NiO) within the host matrix (CeO(2)). Etching results confirm that most of the transition-metal oxides are present on the surface of CeO(2), easily dissolved by nitric acid. The performance of the flame-synthesized catalysts was examined toward water-gas shift (WGS) activity for fuel processing applications. The WGS activity of metal ceria catalysts decreases in the order Cu-Ce-O > Ni-Ce-O > Fe-Ce-O > CeO(2) with a feed mixture having a hydrogen to carbon monoxide (H(2)/CO) ratio of 1. There was no methane formation for these catalysts under the tested conditions.

Grand canonical Monte Carlo simulation study of capillary condensation between nanoparticles.

Capillary condensation at the nanoscale differs from condensation in the bulk phase, because it is a strong function of surface geometry and gas-surface interactions. Here, the effects of geometry on the thermodynamics of capillary condensation at the neck region between nanoparticles are investigated via a grand canonical Monte Carlo simulation using a two-dimensional lattice gas model. The microscopic details of the meniscus formation on various surface geometries are examined and compared with results of classical macromolecular theory, the Kelvin equation. We assume that the system is composed of a lattice gas and the surfaces of two particles are approximated by various shapes. The system is modeled on the basis of the molecular properties of the particle surface and lattice gas in our system corresponding to titania nanoparticles and tetraethoxy orthosilicate molecules, respectively. This system was chosen in order to reasonably emulate our previous experimental results for capillary condensation on nanoparticle surfaces. Qualitatively, our simulation results show that the specific geometry in the capillary zone, the surface-surface distance, and the saturation ratio are important for determining the onset and broadening of the liquid meniscus. The meniscus height increases continuously as the saturation ratio increases and the meniscus broadens faster above the saturation ratio of 0.90. The change of the radius of curvature of the particle surface affects the dimensions of the capillary zone, which drives more condensation in narrow zones and less condensation in wide zones. The increase of surface-surface distance results in the decrease of the meniscus height or even the disappearance of the meniscus entirely at lower saturation ratios. These effects are significant at the nanoscale and must be carefully considered in order to develop predictive relationships for meniscus height as a function of saturation conditions.

Synthesis of iron nanoparticles via chemical reduction with palladium ion seeds.

We report on the synthesis of highly monodisperse iron nanoparticles, using a chemical reduction method. Iron nanoparticles with an average diameter of 6 nm and a geometric standard deviation of 1.3 were synthesized at a pH of 9.50 from ferric chloride precursor with sodium borohydride as the reducing agent, polyacrylic acid as the dispersing agent, and palladium ions as seeds for iron nanoparticle nucleation. The resulting nanoparticles were ferromagnetic at 5 K and superparamagnetic at 350 K. The dispersing agent polyacrylic acid (PAA) was shown to prevent iron nanoparticles and possibly palladium clusters from aggregating; in the absence of PAA, only aggregated iron nanoparticles were obtained. The addition of palladium ions decreased the diameter of iron nanoparticles presumably by providing sites for heterogeneous nucleation onto palladium clusters. In the absence of palladium ions, the mean diameter of iron nanoparticles was approximately 110 nm and the standard deviation increased to 2.0. The pH of the solution also was found to have a significant effect on the particle diameter, likely by affecting PAA ionization and altering the conformation of the polymer chains. At lower pH (8.75), the PAA is less ionized and its ability to disperse palladium clusters is reduced, so the number of palladium seeds decreases. Therefore, the resulting iron nanoparticles were larger, 59 nm in diameter, versus 6 nm for nanoparticles formed at a pH of 9.50.

Capillary condensation onto titania (TiO2) nanoparticle agglomerates.

A capillary condensation process was developed for the purpose of forming interconnections between nanoparticles at low temperatures. The process was performed in a temperature-controlled flow chamber on nanoparticle agglomerates deposited at submonolayer coverage on a transmission electron microscope grid. The partial pressure of the condensing species, tetraethyl orthosilicate, and the temperature of the chamber were adjusted in order to obtain the various saturation conditions for capillary condensation. The modified samples were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, BET surface area method, and scanning transmission electron microscopy with electron energy-loss spectrometry. Experimental results show that bridge-shaped layers were dominantly formed in the neck region between particles and were composed of amorphous silica. The analysis of TEM micrographs verified that the coverage of the layers is strongly dependent on the saturation ratio. Image analysis of TEM micrographs shows that this dependency is qualitatively in agreement with theoretical predictions based on the classical Kelvin equation for the specific geometries in our system.

Evaluation of the microbial growth response to inorganic nanoparticles.

In order to enhance the utilization of inorganic nanoparticles in biological systems, it is important to develop a fundamental understanding of the influence they have on cellular health and function. Experiments were conducted to test silica, silica/iron oxide, and gold nanoparticles for their effects on the growth and activity of Escherichia coli (E. coli). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the morphology and quantify size distribution of the nanoparticles, respectively. TEM was also used to verify the interactions between composite iron oxide nanoparticles and E. coli. The results from DLS indicated that the inorganic nanoparticles formed small aggregates in the growth media. Growth studies measured the influence of the nanoparticles on cell proliferation at various concentrations, showing that the growth of E. coli in media containing the nanoparticles indicated no overt signs of toxicity.

A combined approach for the evaluation of a volatile organic compound emissions inventory.

Emissions inventories significantly affect photochemical air quality model performance and the development of effective control strategies. However, there have been very few studies to evaluate their accuracy. Here, to evaluate a volatile organic compound (VOC) emissions inventory, we implemented a combined approach: comparing the ratios of carbon bond (CB)-IV VOC groups to nitrogen oxides (NOx) or carbon monoxide (CO) using an emission preprocessing model, comparing the ratios of VOC source contributions from a source apportionment technique to NOx or CO, and comparing ratios of CB-IV VOC groups to NOx or CO and the absolute concentrations of CB-IV VOC groups using an air quality model, with the corresponding ratios and concentrations observed at three sites (Maryland, Washington, DC, and New Jersey). The comparisons of the ethene/NOx ratio, the xylene group (XYL)/NOx ratio, and ethene and XYL concentrations between estimates and measurements showed some differences, depending on the comparison approach, at the Maryland and Washington, DC sites. On the other hand, consistent results at the New Jersey site were observed, implying a possible overestimation of vehicle exhaust. However, in the case of the toluene group (TOL), which is emitted mainly from surface coating and printing sources in the solvent utilization category, the ratios of TOL/ NOx or CO, as well as the absolute concentrations revealed an overestimate of these solvent sources by a factor of 1.5 to 3 at all three sites. In addition, the overestimate of these solvent sources agreed with the comparisons of surface coating and printing source contributions relative to NOx from a source apportionment technique to the corresponding value of estimates at the Maryland site. Other studies have also suggested an overestimate of solvent sources, implying a possibility of inaccurate emission factors in estimating VOC emissions from surface coating and printing sources. We tested the impact of these overestimates with a chemical transport model and found little change in ozone but substantial changes in calculated secondary organic aerosol concentrations.

Magnetic iron oxide nanoparticles for biorecognition: evaluation of surface coverage and activity.

Modifying the surfaces of magnetic nanoparticles (MNPs) by the covalent attachment of biomolecules will enable their implementation as contrast agents for magnetic resonance imaging or as media for magnetically assisted bioseparations. In this paper we report both the surface coverage and the activity of IgG antibodies on MNPs. The antibodies were immobilized on gamma-Fe2O3 nanoparticles by conventional methods using aminopropyltriethoxy silane and subsequent activation by glutaraldehyde. Novel fluorescence methods were used to provide a quantitative evaluation of this well-known approach. Our results show that surface coverage can be stoichiometrically adjusted with saturated surface coverage occurring at approximately 36% of the theoretical limit. The saturated surface coverage corresponds to 34 antibody molecules bound to an average-sized MNP (32 nm diameter). We also show that the immobilized antibodies retain approximately 50% of their binding capacity at surface-saturated levels.

Polarized light scattering by dielectric and metallic spheres on oxidized silicon surfaces.

The polarization and intensity of light scattered by polystyrene latex and copper spheres with diameters of approximately 100 nm deposited onto silicon substrates containing various thicknesses of oxide films were measured with 532-nm light. The results are compared with a theory for scattering by a sphere on a surface, originally developed by others [Physica A 137, 209 (1986)] and extended to include coatings on the substrate. Nonlinear least-squares fits of the theory to the observations yield results that were consistent with differential mobility measurements of the particle diameter.

Polarized light scattering by dielectric and metallic spheres on silicon wafers.

The polarization and intensity of light scattered by monodisperse polystyrene latex and copper spheres, with diameters ranging from 92 to 218 nm, deposited on silicon substrates were measured with 442-, 532-, and 633-nm light. The results are compared with a theory for scattering by a sphere on a surface, originally developed by others [PhysicaA 137,209 (1986)], and extended to include coatings on the sphere and the substrate. The results show that accurate calculation of the scattering of light by a metal sphere requires that the near-field interaction between the sphere and its image be included in acomplete manner. The normal-incidence approximation does not suffice for this interaction, and the existence of any thin oxide layer on the substrate must be included in the calculation.