The adsorption of nitrogen dioxide on gamma aluminium oxide (gamma-Al(2)O(3)) and alpha iron oxide (alpha-Fe(2)O(3)) particle surfaces under various conditions of relative humidity, presence of molecular oxygen and UV light has been investigated. X-Ray photoelectron spectroscopy (XPS) is used to monitor the different surface species that form under these environmental conditions. Adsorption of NO(2) on aluminum oxide particle surfaces results primarily in the formation of surface nitrate, NO(3)(-) with an oxidation state of +5, as indicated by a peak with binding energy of 407.3 eV in the N1s region. An additional minority species, sensitive to the presence of relative humidity and molecular oxygen, is also observed in the N1s region with lower binding energy of 405.9 eV. This peak is assigned to a surface species in the +4 oxidation state. When irradiated with UV light, other species form on the surface. These surface-bound photochemical products all have lower binding energy, between 400 and 402 eV, indicating reduced nitrogen species in the range of N oxidations states spanning +1 to -1. Co-adsorbed water decreases the amount of these reduced surface-bound products while the presence of molecular oxygen completely suppresses the formation of all reduced nitrogen species on aluminum oxide particle surfaces. For NO(2) on iron oxide particle surfaces, photoreduction is enhanced relative to gamma-Al(2)O(3) and surface bound photoreduced species are observed under all environmental conditions. Complementing the experimental data, N1s core electron binding energies (CEBEs) were calculated using DFT for a number of nitrogen-containing species in the gas phase and adsorbed on an Al(8)O(12) cluster. A range of CEBEs is calculated for various nitrogen species in different adsorption modes and oxidation states. These calculated values are discussed in light of the peaks observed in the XPS N1s region and the possible species that form following NO(2) adsorption and photoreaction on metal oxide particle surfaces under different conditions of relative humidity, presence of molecular oxygen and UV light.

The adsorption, thermal, and UV reactions of ethanol over a TiO 2 (110) single-crystal surface have been studied in the presence and the absence of molecular oxygen. Adsorption of ethanol is dissociative at room temperature and gives rise to two C1s peaks of equal intensities (at 285.2 and 286.5 eV) attributed to -CH 3 and -CH 2 O-groups, respectively. The surface coverage at saturation (of the dissociative adsorption mode at 300 K) is close to 0.5 with respect to Ti atoms. Thermal annealing resulted in the disappearance of the C1s signal attributed to both groups (-CH 3 and -CH 2 O-), with negligible oxidation of the ethoxide groups. The decrease of both peaks is not symmetric, it is attributed to water desorption consuming bridging surface oxygen followed by migration of ethoxide species into these defects in the process of healing surface oxygen atoms. Exposures to UV irradiation (3.2 eV) of the ethoxide covered surface in the presence of oxygen at 300 K resulted in considerable decrease of the ethoxide C1s peaks with irradiation time and the formation of a carboxylate peak at about 290 eV. This XPS C1s signal, attributed to both CH 3 COO(a) and HCOO(a) species, is most likely due to oxidation by the photoactive O 2or O 2 2species, formed by capture of the photoexited electrons at the conduction band (Ti 3d). The dependence of the rate of ethoxide decomposition on the O 2 pressure follows the expected Langmuir-Hinshelwood kinetics. The photoreaction cross section was estimated from the decay of the XPS C1s signal (starting from surface saturation) and was found equal to ca. 2 × 10 -18 cm -2 at 1 × 10 -6 Torr of O 2 . This figure compares well with that obtained for acetate decomposition under similar conditions on this same surface.

The adsorption of sulfur dioxide (SO 2 ) on titanium dioxide (TiO 2 ) nanoparticle surfaces at 296 K under a wide range of conditions has been investigated. X-ray photoelectron spectroscopy is used to investigate the surface speciation and surface coverage of sulfur-containing products on ca. 4 nm TiO 2 anatase particles that remain on the surface following adsorption of SO 2 . The effects of various environmental conditions of relative humidity, molecular oxygen, and broadband UV/vis irradiation as well as sample pretreatment were found to impact the speciation of adsorbed SO 2 as well as the saturation coverage. In particular, in the absence of light, the majority surface species upon SO 2 adsorption is found to be adsorbed sulfite. Broadband UV/vis irradiation during sulfur dioxide adsorption leads to an increase (nearly 2-fold) in the amount of adsorbed sulfur species, as compared to experiments with no light, and results in the formation of adsorbed sulfate. The formation of sulfate was quantitative in the presence of molecular oxygen. New surface species including chemisorbed molecular SO 2 were observed on samples that have been reduced in vacuum through argon ion sputtering. The total amount of adsorbed sulfur was impacted by surface hydroxyl group coverage and molecularly adsorbed water layer. Additionally, comparison of sulfur dioxide adsorption on 4 versus 32 nm sized anatase nanoparticles showed that surface saturation coverages of adsorbed sulfite on the 4 nm particles was almost twice that of 32 nm particles as measured by the S2p:Ti2p peak area ratios, thus showing an increase in the inherent adsorption capacity of the smaller particles. Proposed adsorption sites and mechanisms to account for the observed experimental data are discussed.

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The surface photochemistry of nitrate, formed from nitric acid adsorption, on hematite (α-Fe2O3) particle surfaces under different environmental conditions is investigated using X-ray photoelectron spectroscopy (XPS). Following exposure of α-Fe2O3 particle surfaces to gas-phase nitric acid, a peak in the N1s region is seen at 407.4 eV; this binding energy is indicative of adsorbed nitrate. Upon broadband irradiation with light (λ > 300 nm), the nitrate peak decreases in intensity as a result of a decrease in adsorbed nitrate on the surface. Concomitant with this decrease in the nitrate coverage, there is the appearance of two lower binding energy peaks in the N1s region at 401.7 and 400.3 eV, due to reduced nitrogen species. The formation as well as the stability of these reduced nitrogen species, identified as NO(-) and N(-), are further investigated as a function of water vapor pressure. Additionally, irradiation of adsorbed nitrate on α-Fe2O3 generates three nitrogen gas-phase products including NO2, NO, and N2O. As shown here, different environmental conditions of water vapor pressure and the presence of molecular oxygen greatly influence the relative photoproduct distribution from nitrate surface photochemistry. The atmospheric implications of these results are discussed.

Mineral dust aerosol is indisputably an important component of the Earth's atmosphere and provides a reactive surface for heterogeneous chemistry to occur. These reactions can alter concentrations of key trace atmospheric gases as well as change the physicochemical properties of the dust particles. The focus of this Perspective article is on several new mechanisms and reaction pathways identified in laboratory studies on components of mineral dust and on nanodust, a potentially new source of metal-containing dust from engineered nanomaterials. These reactions include surface photochemical mechanisms for renoxification and sulfur dioxide oxidation and size-dependent redox chemistry of metalcontaining dusts in low-pH environments including naturally occurring iron oxides and engineered metal nanoparticles. These newly identified reactions have the potential to play an important role in atmospheric chemistry.

The extent of metal−ligand orbital mixing and the degree of electronic coupling between [M(bpy)2]2+ fragments linked through a redox active 1,4-dihydroxy-2,5-bis(pyrazol-1‘-yl)benzene (p-L) bridge is described, where M is Os or Ru and bpy is 2,2‘-bipyridyl. This is the first reported example of osmium and ruthenium/osmium metals linked across a 1,4-dioxolene bridge. In fast scan cyclic voltammetry, the redox processes are reversible and four distinct one-electron processes are observed for the bridge and metal centers in the homo- and hetero-dinuclear complexes. The potential at which the first oxidation step occurs does not depend on the identity of the metal center. UV/vis spectroelectrochemistry, together with resonance Raman spectroscopy, suggests that the first two oxidation steps occur on the bridging ligand. For all complexes, an orbital mixing gradient occurs; metal−ligand orbital mixing increases in the order HQ ≪ SQ < Q (HQ is the reduced hydroquinone bridge, SQ the semiquinone, and Q the quinone), and M−L orbital mixing is enhanced in ruthenium compared with osmium. Analysis of the bipyridyl reductions shows that metal−metal coupling across the HQ bridge is essentially absent. For the first time, stable M(III) polypyridyl quinone complexes are reported. Electrochemical data suggest that communication across the quinone bridge is extensive, with substantial stabilization of the metalII/III mixed valence compounds. The results obtained are discussed with respect to the π acceptor properties of the bridge, the extent of metal−ligand orbital mixing and the relative back-donating properties of the metal centers. These results demonstrate the feasibility of controlling the extent of intercomponent communication by changing the identity of the metal centers and the oxidation state of the complex.

Green silver nanoparticle (AgNP) biosynthesis is facilitated by the enzyme mediated reduction of Ag ions by plants, fungi and bacteria. The antimicrobial activity of green AgNPs is useful to overcome the challenge of antimicrobial resistance. Antimicrobial properties of biosynthesized AgNPs depend on multiple factors including culture conditions and the microbial source. The antimicrobial activity of AgNPs biosynthesized by ATCC 27853, ATCC 25922, ATCC 25923 and (confirmed clinical isolate) were investigated in this study. Biosynthesis conditions (AgNO concentration, pH, incubation temperature and incubation time) were optimized to obtain the maximum AgNP yield. Presence of AgNPs was confirmed by observing a characteristic UV-Visible absorbance peak in 420-435 nm range. AgNP biosynthesis was optimal at 0.4 g/L AgNO concentration under alkaline conditions at 60-70 °C. The biosynthesized AgNPs showed higher stability compared to chemogenized AgNPs in the presence of electrolytes. AgNPs synthesized by were the most stable while NPs of were the least stable. AgNPs synthesized by and showed good antimicrobial potential against MRSA and. AgNPs synthesized by had greater antimicrobial activity. The antimicrobial activity of NPs may vary depending on the size and the morphology of NPs.