Photochemistry of Nitrate Chemisorbed on Various Metal Oxide Surfaces

Atmospheric aerosols are known to provide an important surface for gas–solid interfaces that can lead to heterogeneous reactions impacting tropospheric chemistry. In this work, α-Fe2O3, TiO2, γ-Al2O3, SiO2 and ZnO, common components of atmospheric aerosols, served as models to investigate the gas–solid interface of nitric acid with aerosols in the presence of simulated solar radiation. Adsorbed nitrate and gaseous products can be continuously monitored with infrared spectroscopy (IR). Kinetic studies of adsorbed species were carried out using attenuated total reflectance infrared spectroscopy (ATR-FTIR). Ex situ simultaneous infrared spectroscopy of gas-phase products using a 2 m long path cell allowed the detection of gaseous products at early stages of the heterogeneous photochemical reaction. In addition, photoactive gaseous products, such as HONO, were detected as gas analysis was carried out outside the region of irradiation. All reactions were found to be first order with respect to adsorbed nitric acid and yielded gas-phase products such as NO, NO2, N2O4, N2O, and HONO. While the correlation between semiconductor properties of the metal oxide and the heterogeneous photochemical rate constant (j) is not direct, the semiconductor properties were found to play a role in the formation of relatively high proportions of greenhouse gas nitrous oxide (N2O)

Fate of Aqueous Iron Leached from Tropospheric Aerosols during Atmospheric Acidic Processing: A Study of the Effect of Humic-like Substances

Humic-like substances (HULIS) are complex organic molecules that can be found in the atmosphere as components of tropospheric aerosols or suspended in atmospheric water. HULIS are chelating agents and oxidation-reduction species, therefore these substances can affect the availability of aqueous iron, a heavy metal commonly leached from atmospheric particulate matter upon acidic processing. Specifically, chelating properties allow HULIS to remove aqueous iron from atmospheric water, while their redox properties can alter iron speciation. Ultimately, wet deposition of soluble iron can be influenced not only by HULIS but also by other ubiquitous atmospheric cations. In this work, we investigate the effect of HULIS on iron leached from atmospheric particles in the presence of aluminium ions, an environmentally abundant cation also chelated by HULIS. Colorimetric methods were used to examine the cation exchange (CE) of aluminium ions with both iron (II) and (III) ions in humic acids, a model system for HULIS. An effective chelation of aqueous phase iron with humic acids was observed during suspension experiments, with aqueous iron removed from aqueous phase into a HULIS complex. In addition, the redox properties of humic acids showed no oxidation of iron (II) after chelation by humic acid, but a fraction of iron (III) was reduced into the more bioavailable iron (II). Cation exchange with aluminium suggests that bioavailable iron (II) ions chelate with HULIS in a combination of exchangeable and inexchangeable iron, with a higher proportion of exchangeable iron incidence. Additionally, HULIS interaction with iron (III) ions shows chelating properties as well a reduction potential, producing aqueous and chelated iron (II) ions

Comparative Evaluation of Iron Leach from Different Sources of Fly Ash under Atmospherically Relevant Conditions

Fly ash, an iron-containing by-product of coal-fired power plants, has been observed in atmospheric aerosol plumes. Under the acidic atmospheric conditions resulting from the uptake of atmospheric gases, iron leached from fly ash can impact global biogeochemical cycles. However, the fly ash source region, as well as its generating power plant, plays an important role in the amount, speciation and lability of iron. Yet no comparative studies have been made on iron leached from fly ash from different sources. This study reports the iron mobilisation by proton-promoted dissolution from well-characterised fly ash samples from three distinctive locations: the USA Midwest, north-east India and Europe. In addition, pH dependency was also investigated. Proton-promoted dissolution showed a variability between source regions with a relative iron leach in the order USA Midwestern \u3e north-east Indian \u3e European ash. In addition, the initial rate of iron leach suggests that source region is indeed a determining factor in the iron leaching capacity of fly ash, because dissolution from Midwestern fly ash is also faster than both European and Indian ash. Finally, the combustion process of fly ash proved to be significant for the iron speciation, given that well-combusted fly ash samples leached mostly Fe3+ rather than bioavailable Fe2+. The role of fly ash should therefore be taken into account in order to better understand the effects of combustion particles in atmospheric iron deposition

Impact of zein and lignin‐PLGA biopolymer nanoparticles used as pesticide nanocarriers on soybean growth and yield under field conditions

Abstract Nanoparticles are being utilized in agriculture as fertilizers, pesticides, and agrochemical‐carriers. Designed to be biocompatible and degradable, biopolymer nanoparticles were developed as an alternative to metallic nanoparticles, and though safe‐by‐design, polymeric nanoparticles must be field‐tested prior to largescale use. Several field studies were conducted to observe detrimental effects of biopolymer nanoparticles on plant growth and yield using soybean, Glycine max (L.) Merr., as a model system. Biopolymer nanoparticles made from lignin or zein were applied as seed treatments to soybean seeds or as foliar sprays (zein only) to soybean plants. Studies using biopolymer nanoparticle seed treatments (nano‐STs) measured the germination rates and seedling growth were evaluated in the laboratory, while stand counts, plant height, growth stage, yield, and hundred‐seed weight were measured in the field. Foliar treatments assessed nanoparticle impact on flower abortion and pod production. To ensure nano‐STs would not compromise the plant's defensive capabilities, herbivore feeding was assessed using a leaf bioassay for defoliators and a seed damage index for pod feeders. Growth rate, percent germination, or root length were not impacted by nano‐STs. In the field, nano‐STs had no impact on stand counts, heights, growth stage, yield, and hundred‐seed weights. Leaf feeding assays and damage indices indicate plant susceptibility to herbivore attack was not increased due to nano‐STs. Foliar applications of zein nanoparticles did not increase flower abortion or decrease pod set. These results indicate that biopolymer nanoparticles have no negative effects on growth, yield, and herbivore susceptibility and should be suitable for use in agriculture

Cobalt Release from a Nanoscale Multiphase Lithiated Cobalt Phosphate Dominates Interaction with Shewanella oneidensis MR-1 and Bacillus subtilis SB491

Cobalt phosphate engineered nanomaterials (ENMs) are an important class of materials that are used as lithium ion battery cathodes, catalysts, and potentially as super capacitors. As production of these nanomaterials increases, so does the likelihood of their environmental release; however, to date, there are relatively few investigations of the impact of nanoscale metal phosphates on biological systems. Furthermore, nanomaterials used in commercial applications are often multiphase materials, and analysis of the toxic potential of mixtures of nanomaterials has been rare. In this work, we studied the interactions of two model environmental bacteria, Shewanella oneidensis MR-1 and Bacillus subtilis, with a multiphase lithiated cobalt phosphate (mLCP) nanomaterial. Using a growth-based viability assay, we found that mLCP was toxic to both bacteria used in this study. To understand the observed toxicity, we screened for production of reactive oxygen species (ROS) and release of Co2+ from mLCP using three abiotic fluorophores. We also used Newport Green DCF dye to show that cobalt was taken up by the bacteria after mLCP exposure. Using transmission electron microscopy, we noted that the mLCP was not associated with the bacterial cell surface. In order for us to further probe the mechanism of interaction of mLCP, the bacteria were exposed to an equivalent dose of cobalt ions that dissolved from mLCP, which recapitulated the changes in viability when the bacteria were exposed to mLCP, and it also recapitulated the observed bacterial uptake of cobalt. Taken together, this implicates the release of cobalt ions and their subsequent uptake by the bacteria as the major toxicity mechanism of mLCP. The properties of the ENM govern the release rate of cobalt, but the toxicity does not arise from nanospecific effects—and importantly, the chemical composition of the ENM may dictate the oxidation state of the metal centers and thus limit ROS production