Initial Rate Of Production Research Articles

Abrasion of sedimentary rocks as a source of hydrogen peroxide and nutrients to subglacial ecosystems

Abstract. Glaciers and ice sheets are renowned for their abrasive power, yet little is known of the mechanochemical reactions which are initiated by abrasion in these environments and their effect on subglacial biogeochemistry. Here, we use sedimentary rocks representative of different subglacial environments and from a previously glaciated terrain, along with subglacial sediments, to investigate the potential for subglacial erosion to generate H2O2 and to release bio-utilisable organic carbon and nutrients (N, Fe). Samples were crushed using a ball mill, water was added to rock powders within gastight vials, and samples were incubated in the dark at 4 ∘C. Headspace and water samples were taken immediately after the addition of water and then again after 5 and 25 h. Samples generated up to 1.5 µmol H2O2 g−1. The total sulfur content, a proxy for the sulfide content, did not correlate with H2O2 generation, suggesting that the pyrite content was not the sole determinant of net H2O2 production. Other factors including the presence of carbonates, Fe-driven Fenton reactions and the pH of the solution were also likely to be important in controlling both the initial rate of production and subsequent rates of destruction of H2O2. Further, we found that erosion can provide previously unaccounted sources of bio-utilisable energy substrates and nutrients, including up to 880 nmol CH4 g−1, 680 nmol H2 g−1, volatile fatty acids (up to 1.7 µmol acetate g−1) and 8.2 µmolNH4+g-1 to subglacial ecosystems. These results highlight the potentially important role that abrasion plays in providing nutrient and energy sources to subglacial microbial ecosystems underlain by sedimentary rocks.

Effect of Stoichiometry on Nanomagnetite Sulfidation.

Magnetite (Mt) has long been regarded as a stable phase with a low reactivity toward dissolved sulfide, but natural Mt with varying stoichiometries (the structural Fe(II)/Fe(III) ratio, xstru) might exhibit distinct reactivities in sulfidation. How Mt stoichiometry affects its sulfidation processes and products remains unknown. Here, we demonstrate that xstru is a master variable controlling the rates and extents of sulfide oxidation by magnetite nanoparticles (11 ± 2 nm). At pH = 7.0-8.0 and the initial Fe/S molar ratio of 10-50, the partially oxidized magnetite (xstru = 0.19-0.43) can oxidize dissolved sulfide to elemental sulfur (S0), but only surface adsorption of sulfide, without interfacial electron transfer (IET), occurs on the nearly stoichiometric magnetite (xstru = 0.47). The higher initial rate and extent of sulfide oxidation and S0 production are observed with the more oxidized magnetite that has the higher electron-accepting capability from surface-complexed sulfide (S(-II)(s)). The FeS clusters formed from magnetite sulfidation can be oxidized by the most oxidized magnetite with xstru = 0.19 but not by other magnetite particles. A linear relationship between the Gibbs free energy of reaction and the surface area-normalized initial rate of sulfide oxidation is observed in all experiments under the different conditions, suggesting the S(-II)(s)-magnetite IET dominates magnetite sulfidation at high Fe/S molar ratios and near-neutral pH.

Novel Corrugated Long Period Grating Surface Balloon-Shaped Heterocore-Structured Plastic Optical Fibre Sensor for Microalgal Bioethanol Production.

A novel long period grating (LPG) inscribed balloon-shaped heterocore-structured plastic optical fibre (POF) sensor is described and experimentally demonstrated for real-time measurement of the ultra-low concentrations of ethanol in microalgal bioethanol production applications. The heterocore structure is established by coupling a 250 μm core diameter POF between two 1000 μm diameter POFs, thus representing a large core-small core-large core configuration. Before coupling as a heterocore structure, the sensing region or small core fibre (SCF; i.e., 250 μm POF) is modified by polishing, LPG inscription, and macro bending into a balloon shape to enhance the sensitivity of the sensor. The sensor was characterized for ethanol-water solutions in the ethanol concentration ranges of 20 to 80 %v/v, 1 to 10 %v/v, 0.1 to 1 %v/v, and 0.00633 to 0.0633 %v/v demonstrating a maximum sensitivity of 3 × 106 %/RIU, a resolution of 7.9 × 10-6 RIU, and a limit of detection (LOD) of 9.7 × 10-6 RIU. The experimental results are included for the intended application of bioethanol production using microalgae. The characterization was performed in the ultra-low-level ethanol concentration range, i.e., 0.00633 to 0.03165 %v/v, that is present in real culturing and production conditions, e.g., ethanol-producing blue-green microalgae mixtures. The sensor demonstrated a maximum sensitivity of 210,632.8 %T/%v/v (or 5 × 106 %/RIU as referenced from the RI values of ethanol-water solutions), resolution of 2 × 10-4%v/v (or 9.4 × 10-6 RIU), and LOD of 4.9 × 10-4%v/v (or 2.3 × 10-5 RIU). Additionally, the response and recovery times of the sensor were investigated in the case of measurement in the air and the ethanol-microalgae mixtures. The experimentally verified, extremely high sensitivity and resolution and very low LOD corresponding to the initial rate of bioethanol production using microalgae of this sensor design, combined with ease of fabrication, low cost, and wide measurement range, makes it a promising candidate to be incorporated into the bioethanol production industry as a real-time sensing solution as well as in other ethanol sensing and/or RI sensing applications.

Photophysical Rate Constants and Oxygen Dependence for Si and Ge Rhodamine Zwitterions.

The family of group XIV rhodamine zwitterions are fluorescence probes with carbon, silicon, germanium, or tin substituted in the 10-position of the xanthene ring. Because of their inherent near-infrared fluorescence, photostability and high quantum yields in aqueous solutions, the Si and Ge containing fluorophores in this class have become increasingly important for fluorescent labeling of proteins and biological molecules. This study fully characterizes photophysical rates derived from a model consisting of a singlet ground state, the lowest singlet excited state, and the lowest triplet excited state for two exemplar group XIV rhodamine zwitterions, one containing Si and the other Ge. Within a simple Jablonski diagram, all radiative and non-radiative rates, including intersystem crossing and triplet depopulation rates, were measured as a function of oxygen concentration. It was shown that the triplet depopulation rates are intrinsically fast in comparison with traditional xanthene containing fluorophores, probably due to the increased spin-obit coupling from the Si and Ge substitution in the xanthene ring. Dissolved oxygen increases both the intersystem crossing and triplet depopulation rates. Stern-Volmer analysis was conducted to estimate rates of quenching by oxygen. The experimental data was used to estimate the initial rates for reactive oxygen production by Si and Ge containing fluorophores in aqueous solutions containing different concentrations of dissolved O2. These estimates showed a significantly slower initial rate of reactive oxygen production in comparison with rhodamine 6G. This goes a long way to explaining their inherent photostability. Spectroscopic experiments were also conducted in 77 K viscous aqueous glasses where it was observed that the fluorescence spectra remained unchanged, and the quantum yields increased from 0.53 to 0.84 and from 0.52 to 0.89 for the Si and Ge containing fluorophores respectively; no phosphorescence was observed. All intersystem crossing and triplet depopulation rates were measured using fluorescence correlation spectroscopy (FCS) and analyzed using a new method that extrapolated the power dependence of the FCS curves to optical saturation. This method was verified using published data.

Photoenhanced Water Electrolysis in Separate O2 and H2 Cells Using Pseudocapacitive Electrodes.

Water electrolysis has received much attention in recent years as a means of sustainable H2 production. However, many challenges remain in obtaining high-purity H2 and making large-scale production cost-effective. This study provides a strategy for integrating a two-cell water electrolysis system with solar energy storage. In our proposed system, CuO-Cu(OH)2/Cu2O was used as a redox mediator between oxygen and hydrogen evolution components. The system not only overcame the gas-mixing issue but also showed high gas generation performance. The redox reaction (charge/discharge) of CuO-Cu(OH)2/Cu2O led to a significant increase (51%) in the initial rate of H2 production from 111.7 μmol h–1 cm–2 in the dark to 168.9 μmol h–1 cm–2 under solar irradiation. The effects of light on the redox reaction of CuO-Cu(OH)2/Cu2O during water electrolysis were investigated by in situ X-ray absorption and photoemission spectroscopy. These results suggest that surface oxygen vacancies are created under irradiation and play an important role in increased capacitance and gas generation. These findings provide a new path to direct storage of abundant solar energy and low-cost sustainable hydrogen production.

Methane production from Sargassum muticum: effects of seasonality and of freshwater washes

Biogas production from Sargassum muticum, an invasive seaweed species to Europe, is hampered by low methane (CH4) yields during anaerobic digestion (AD), but causes are unclear. This research is the first to demonstrate the impact of extensive freshwater washing of spring- and summer-harvested S. muticum on the CH4 production rates and the biochemical methane potential (BMP). The findings reveal that the rate profile of CH4 production is affected by extensively washing the seaweed and is dependent on seasonality. Spring-harvested S. muticum had higher initial CH4 production rates compared to summer-harvested S. muticum. For spring-harvested S. muticum, the initial rate of CH4 production was lowered by extensive washing. In contrast, extensively washed summer-harvested S. muticum had a higher degradation rate and CH4 production rate relative to its non-extensively washed counterpart. The highest CH4 potentials accumulated by the treated and non-treated S. muticum are, however, statistically similar and not influenced by seasonality or extensive washing (p > 0.05). Potential causes for differences in the rate of CH4 production between summer- and spring-harvested S. muticum are discussed. The differences in CH4 production from treated summer- and spring-harvested S. muticum acts as a stepping stone to understanding the causes for low CH4 yields, which could allow for further enhancements in CH4 production from S. muticum.

Electromagnetic-field-assisted synthesis of Ni foam film-supported CoCu alloy microspheres composed of nanosheets: A high performance catalyst for the hydrolysis of ammonia borane

The development of low-cost catalysts with high activity and stability for the dehydrogenation of ammonia borane for hydrogen production becomes important in the field of heterogeneous catalysis. In this communication, an electromagnetic-field-assisted deposition process was adopted to prepare Ni foam supported CoCu alloy microspheres composed of nanosheets (CoCu/Ni). In the hydrolytic dehydrogenation of ammonia borane, the initial rate of hydrogen production for the as-prepared CoCu/Ni catalyst can reach 30.5 mol H2 min−1 molcat−1. Moreover, the CoCu/Ni catalyst maintained its activity after 10 consecutive catalytic cycles, demonstrating its high stability and good reusability.

UV–Vis-infrared light-driven thermocatalytic abatement of benzene on Fe doped OMS-2 nanorods enhanced by a novel photoactivation

The catalysts of Fe doped cryptomelanetype octahedral molecular sieve (OMS-2, KMn8O16) with different Fe/Mn molar ratio of 0.079, 0.097, and 0.122 were prepared by a hydrothermal redox method. The Fe doping considerably enhances the catalytic activity of OMS-2 for the catalytic abatement of benzene as one of typical VOCs. The Fe doped OMS-2 catalyst exhibits much higher catalytic activity than pure OMS-2 and Pt/Al2O3 (a commercial precious metal catalyst). The considerable promotion in the catalytic activity of OMS-2 is ascribed to the significant enhancement in the lattice oxygen activity of OMS-2 induced by the Fe doping. Remarkably, under the full solar spectrum (UV–Vis-IR) illumination from a Xe lamp, the Fe doped OMS-2 catalyst exhibits high catalytic activity and excellent durability for benzene abatement. Its very high initial rate of CO2 production (rCO2, 602.2µmolmin−1g−1) is 4 and 179 times higher than that of OMS-2 and TiO2(P25) (a benchmark photocatalyst), respectively. Even under the λ>690nm visible-infrared (Vis-IR) illumination, the Fe doped OMS-2 catalyst still demonstrates high catalytic activity with the rCO2 of 44.3µmolmin−1g−1. The high catalytic activity of the Fe doped OMS-2 catalyst under UV–Vis-IR illumination derives from the efficient solar-light-driven (SLD) thermocatalysis. The SLD thermocatalysis is ascribed to the high thermocatalytic activity of the Fe doped OMS-2 catalyst and its efficient photothermal conversion because of its strong UV–Vis-IR absorption. It is found that the SLD thermocatalytic activity of the Fe doped OMS-2 catalyst is further enhanced by a novel photoactivation effect, which is completely unlike the well-known photocatalysis on photocatalytic semiconductors (e.g. TiO2).

Laccase enzyme detoxifies hydrolysates and improves biogas production from hemp straw and miscanthus

The impact of various phenolic compounds, vanillic acid, ferulic acid, p-coumaric acid and 4-hydroxybenzoic acid on anaerobic digestion of lignocellulosic biomass (hemp straw and miscanthus) was studied. Such phenolic compounds have been known to inhibit biogas production during anaerobic digestion. The different phenolic compounds were added in various concentrations: 0, 100, 500, 1000 and 2000mg/L. A difference in inhibition of biomethane production between the phenolic compounds was noted. Hydrolysis rate, during anaerobic digestion of miscanthus was inhibited up to 50% by vanillic acid, while vanillic acid had no influence on the initial rate of biogas production during the anaerobic digestion of hemp straw. Miscanthus has a higher lignin concentration (12–30g/100gDM) making it less accessible for degradation, and in combination with phenolic compounds released after harsh pretreatments, it can cause severe inhibition levels during the anaerobic digestion, lowering biogas production. To counter the inhibition, lignin degrading enzymes can be used to remove or degrade the inhibitory phenolic compounds. The interaction of laccase and versatile peroxidase individually with the different phenolic compounds was studied to have insight in the polymerization of inhibitory compounds or breakdown of lignocellulose. Hemp straw and miscanthus were incubated with 0, 100 and 500mg/L of the different phenolic compounds for 0, 6 and 24h and pretreated with the lignin degrading enzymes. A laccase pretreatment successfully detoxified the substrate, while versatile peroxidase however was inhibited by 100mg/L of each of the individual phenolic compounds. Finally a combination of enzymatic detoxification and subsequent biogas production showed that a decrease in phenolic compounds by laccase treatment can considerably lower the inhibition levels of the biogas production.

Calcium extraction from steelmaking slag and production of precipitated calcium carbonate from calcium oxide for carbon dioxide fixation

Abstract We investigate the effect of ball milling and heat treatment on slag particle size, revealing that this parameter significantly influences the efficiency of calcium extraction. The efficiency and morphological properties of precipitated calcium carbonate (PCC) produced from calcium oxide were investigated for different extraction solvent, temperatures, CO2 injection rate and solvent concentration. As a result, ammonium chloride was determined to be the best extraction solvent for PCC production. Initial rate of PCC production is improved with increasing solvent concentrations and CO2 injection rate. The precipitated CaCO3 could be obtained in three different polymorphic forms, depending on the Gibbs free energy.

Promoter effect of Ga in Pt/Ga-TiO2 catalysts for the photo-production of H2 from aqueous solutions of ethanol

In this paper, the effect of Ga in Pt/Ga-TiO2 catalysts for photocatalytic H2 production from aqueous solutions of ethanol is studied. The fresh and post-reaction catalysts were characterized using different techniques including BET, XRD, TPR, SEM-EDX, XPS, CO chemisorption and in situ DRIFTS. The presence of Ga in Pt/TiO2-based catalysts increased the Pt dispersion and decreased the relative amount of surface oxidized Pt species. Pt/Ga-TiO2 catalysts showed more stable behaviour during the photocatalytic reaction than the reference Pt/TiO2. The Pt/0.2Ga-TiO2 catalyst showed a higher initial rate of production of H2 and produced a higher total amount of H2 than the monometallic Pt/TiO2. The promoter effect of Ga is analysed in the light of the surface characteristics of the catalysts.

Heteropolyacid catalysts for Diels-Alder cycloaddition of 2,5-dimethylfuran and ethylene to renewable p-xylene

The Diels-Alder cycloaddition of biomass-derived furans and subsequent dehydration are promising routes for the sustainable production of commodity chemicals such as p-xylene (PX). In this paper, we have investigated the catalytic performances of a range of phosphotungstic acid (HPW) and silicotungstic acid (HSiW) catalysts supported on various oxides, i.e., SiO2, Al2O3, TiO2 and ZrO2 and their structure-activity correlation in the conversion of 2,5-dimethylfuran (DMF) and ethylene to PX. The characterization studies of the catalysts using XRD, BET, Raman and 31P MAS-NMR spectroscopy reveal that all of the supported heteropolyacid (HPA) catalysts (except HPW/ZrO2) retain their Keggin structure on the surface of oxide supports. Results from ammonia- and n-propylamine-TPD studies show that all of the supported HPA catalysts possess well-defined Brønsted acid sites with the total acidity decreasing in the following order: HPA/SiO2>HPA/Al2O3>HPA/ZrO2>HPA/TiO2. The conversion of DMF and the initial rate of PX production generally increase with an increase in the total acidity, with HPA/SiO2 being the most active catalyst. The turnover frequency of PX production for HPA/SiO2 is also considerably greater than those for the HPAs supported on Al2O3, ZrO2, and TiO2, which suggests that the higher activity of HPA/SiO2 is at least partly due to the enhanced strength of Brønsted acid sites. Both the silica-supported HSiW and HPW catalysts demonstrate remarkably high PX selectivity (82–85%) at high DMF conversion (91–94%) at 250°C after 6h reaction. The effects of reaction conditions such as acid loading, reaction temperature, and reaction time have also been investigated with the most active silica-supported HSiW catalysts to optimize the PX yield.

Efficient approach for simultaneous CO and H2 production via photoreduction of CO2 with water over copper nanoparticles loaded TiO2

Photoreduction of CO2 with water to alternative fuels using low cost meterials is an efficient approach to mitigate CO2. The present work describes a series of copper nanoparticles (Cu-NPs) loaded on TiO2, here copper nanoparticles were separately prepared by chemical reduction method, and then loaded on freshly synthesized TiO2. Oxidized and reduced forms of Cu/TiO2 nanoparticles were obtained by calcination under air and H2 respectively. Prepared catalysts were characterized by XRD, SEM, EDX, HR-TEM, XPS, BET surface area analysis, TPR, UV–vis diffuse reflectance spectroscopy and spectrofluorometry. Catalytic potential of prepared catalysts was checked for photocatalytic reduction of CO2 with water vapor under UV-C irradiation. The effect of oxidation state and loading amount of Cu as well as irradiation wavelength was also investigated. CO and H2 were observed as photocatalytic products. Among all the photocatalysts, 1% Cu-Red/TiO2 exhibited the highest photoactivity, with an initial rate of CO and H2 production of 334 and 452μmolg−1h−1 respectively, under UV-C light. The photocatalytic role of the Cu-NPs surface giving contribution to overall reaction was confirmed by using Cu-NPs, 1% Cu-Oxi/SiO2 and 1% Cu-Red/SiO2. A plausible mechanism of CO2 reduction is suggested and computationally confirmed. Reaction mechanism includes stages of CO2 adsorption at the Cu-TiO2 interface, reduction into HCO2, and dissociation into adsorbed hydroxyls and CO. The most energy demanding step was found to be CO desorption that could be facilitated by 254nm quanta.

Abstract 610: Ineffective Suppression of Adipocyte Lipolysis in Metabolic Syndrome: An in vivo Test for Adipocyte Insulin Resistance

Background: Insulin resistance is a major contributor to metabolic syndrome, disrupting both glucose and non-esterified fatty acid (NEFA) dynamics through ineffective glucose clearance and decreased suppression of lipid droplet lipolysis. The minimal model of glucose dynamics is used for glycemic insulin sensitivity however it does not measure adipocyte insulin sensitivity, the primary determinant of plasma NEFA. An in-vivo approach to measuring adipocyte insulin sensitivity using NEFA is employed, comparing healthy and metabolic syndrome subjects. Both the models are employed to estimate insulin sensitivity and validate the NEFA approach. Objective: To test the use of NEFA kinetics to measure adipocyte insulin sensitivity compared to the glucose minimal model. Approach and results: Metabolic syndrome (n=56) and optimally healthy (n=14) subjects underwent a frequently sampled intravenous glucose tolerance test, and plasma analyzed for insulin, glucose, and NEFA. Insulin sensitivity ( S I ) and glucose effectiveness ( S G ) were calculated from the glucose minimal model. S I was 1.7 (mU/L) -1 min -1 and 0.40 (mU/L) -1 /min -1 and S G was 0.027 min -1 and 0.017 min -1 for the healthy and metabolic syndrome groups, respectively, indicating substantial glycemic insulin resistance in the latter. A model using glucose as the driver for NEFA kinetics was then applied. We found the initial rate of NEFA utilization by tissues (NU) was less, but the threshold glucose (tG) and glucose concentration required for a unit change in lipolysis inhibition ( G i ) were greater in metabolic syndrome verses healthy (NU: 0.050[0.045, 0.057] vs. 0.068[0.054, 0.086] p=0.03; tG: 6.7[6.2, 7.2] vs. 5.0[4.3, 5.9] p=0.001; G i : 0.30[0.25, 0.35] vs. 0.17[0.07, 0.27] p=0.02). No differences were found in initial rate of NEFA production or glucose utilization. Conclusion: Our results indicate that suppression of lipid-droplet lipolysis requires greater stimulus in metabolic syndrome compared to insulin sensitive adipocytes. Further, the rate of NEFA removal is less in metabolic syndrome. These results reveal components of insulin sensitivity not demonstrated by the glucose model. The NEFA model provides a measurement of adipocyte insulin sensitivity not captured by glycemic indices.

Unexpected Thiols Triggering Photoluminescent Enhancement of Cytidine Stabilized Au Nanoclusters for Sensitive Assays of Glutathione Reductase and Its Inhibitors Screening.

The photoluminescence (PL) of nonthiolate ligand capped Au nanoclusters (NCs) is usually quenched by thiols due to the tight adsorption of thiols to the Au surface and formation of larger non-PL species. However, we here report an unexpected PL enhancement of cytidine stabilized Au (AuCyt) NCs triggered by thiols, such as reduced glutathione (GSH) at sub-μM level, while such phenomena have not been observed for Au NCs capped with similar adenosine/cytidine nucleotides. The mass spectroscopic results indicate that this enhancement may be caused by the formation of smaller, but highly fluorescent, Au species etched by thiols. This enables the sensitive detection of GSH from 20 nM to 3 μM, with an ultralow detection limit of 2.0 nM. Moreover, the glutathione reductase (GR) activity can be determined by the initial rate of GSH production, i.e., the maximum PL increasing rate, with a linear range of 0.34-17.0 U/L (1 U means reduction of 1.0 μmol of oxidized glutathione per min at pH 7.6 at 25 °C) and a limit of detection of 0.34 U/L. This method allows the accurate assays of GR in clinical serum samples as well as the rapid screening of GR inhibitors, indicating its promising biomedical applications.

Optimizing light transport in scintillation crystals for time-of-flight PET: an experimental and optical Monte Carlo simulation study.

Achieving excellent timing resolution in gamma ray detectors is crucial in several applications such as medical imaging with time-of-flight positron emission tomography (TOF-PET). Although many factors impact the overall system timing resolution, the statistical nature of scintillation light, including photon production and transport in the crystal to the photodetector, is typically the limiting factor for modern scintillation detectors. In this study, we investigated the impact of surface treatment, in particular, roughening select areas of otherwise polished crystals, on light transport and timing resolution. A custom Monte Carlo photon tracking tool was used to gain insight into changes in light collection and timing resolution that were observed experimentally: select roughening configurations increased the light collection up to 25% and improved timing resolution by 15% compared to crystals with all polished surfaces. Simulations showed that partial surface roughening caused a greater number of photons to be reflected towards the photodetector and increased the initial rate of photoelectron production. This study provides a simple method to improve timing resolution and light collection in scintillator-based gamma ray detectors, a topic of high importance in the field of TOF-PET. Additionally, we demonstrated utility of our Monte Carlo simulation tool to accurately predict the effect of altering crystal surfaces on light collection and timing resolution.

Effect of POX genotype and Lip2p overexpression on lactone production and reconsumption by Yarrowia lipolytica using castor oil as substrate

γ-Decalactone production from ricinoleic acid biotransformation by Yarrowia lipolytica has drawn the attention of many authors and, in the last years, molecular and physiological developments were made through the use of engineered strains in novel culture conditions.The purpose of this work was to monitor the performance of modified Y. lipolytica strains in their lipid metabolism specifically at the β-oxidation pathway (MTLY40-2P strain, disrupted in the native genes POX2-5 and expressing an ectopic Aox2p-encoding gene) or at the triglyceride hydrolysis (JMY3010 strain, Lip2p overexpressed) using castor oil as substrate, in a lab-scale bioreactor. Using step-wise fed-batch cultures of MTLY40-2P strain, a γ-decalactone concentration of 7gL−1 was reached. γ-Decalactone reconsumption was prevented and hydroxylactone production was reduced by Y. lipolytica MTLY40-2P strain. Moreover, substantial increase in the initial rate of aroma production was obtained with strain overexpressing LIP2 gene due to the fast hydrolysis of castor oil.

Effect of Gold Nanoclusters on the Production of Ti3+ Defect Sites in Titanium Dioxide Nanoparticles under Ultraviolet and Soft X-ray Radiation

The production rate and saturation point of Ti3+ defect sites on titanium dioxide P-25 and anatase nanoparticles doped with Au101(PPh3)21Cl5 (Au101) metal nanoclusters were investigated under synchrotron X-ray irradiation alone, as well as combined X-ray and UV radiation. The saturation point in the growth of the normalized relative populations of Ti3+ centers on anatase and P-25 titania nanoparticles with and without Au101 nanoclusters present at the surface was found to vary with the type of support. It was influenced by the presence of gold nanoclusters: a higher concentration of Ti3+ centers was generated where gold nanoclusters were deposited onto anatase nanoparticles and irradiated by both X-ray and UV photons, compared with X-ray irradiation alone. Conversely, all samples based on the TiO2 P-25 support displayed reduced levels of Ti3+ center populations at the saturation points under combined X-ray and UV combined radiation, compared to the samples exposed exclusively to X-ray radiation. The initial rate of production of Ti3+ defect sites was found to decrease for combined UV and X-ray irradiation in the case when Au101 was deposited onto anatase. However, the opposite trend in the initial production rate of Ti3+ centers was observed in the case of Au101 deposited onto the TiO2 P-25 surface.

Iron(III)-induced activation of chloride from artificial sea-salt aerosol

Environmental context Inorganic, natural aerosols (sea-salt, mineral dust, glacial flour) and contributions of anthropogenic components (fly ash, dust from steel production and processing, etc.) contain iron that can be dissolved as FeIII in saline media. This study investigates photochemical processes in clouds and aerosols producing gas-phase Cl as a function of salt- and gas-phase composition employing a simulation chamber. Atomic Cl may contribute to the oxidative capacity of the troposphere, and our findings imply local sources. Abstract Artificial sea-salt aerosol, containing FeIII at various compositions, was investigated in a simulation chamber (made of Teflon) for the influence of pH and of the tropospheric trace gases NO2, O3 and SO2 on the photochemical activation of chloride. Atomic chlorine (Cl) was detected in the gas phase and quantified by the radical clock technique. Dilute brines with known FeIII content were nebulised until the relative humidity reached 70–90%. The resulting droplets (most abundant particle diameter: 0.35–0.46µm, initial surface area: up to 3×10–2cm2cm–3) were irradiated with simulated sunlight, and the consumption of a test mixture of hydrocarbons was evaluated for Cl, Br and OH. The initial rate of atomic Cl production per aerosol surface increased with FeIII and was ~1.9×1018 atoms cm–2s–1atCl–/FeIII=13. The presence of NO2 (~20 ppb) increased it to ~7×1018 atoms cm–2s–1, the presence of O3 (630 ppb) to ~9×1018 atoms cm–2s–1 and the presence of SO2 at 20 and 200 ppb inhibited the release slightly to ~1.7 and ~1.1×1018 atoms cm–2s–1. The observed production of atomic Cl is discussed with respect to pH and speciation of the photolabile aqueous FeIII complexes.

Copper–gallia interaction in Cu–Ga2O3–ZrO2 catalysts for methanol production from carbon oxide(s) hydrogenation

The impact of the interaction between copper and gallia was studied over a selected set of supported (2wt%) Cu on Ga2O3, ZrO2 and Ga2O3–ZrO2 catalysts, which were employed in the methanol synthesis from CO2 and CO mixtures. The higher initial rate of methanol production on the Cu/ZrO2 catalyst was accompanied by an activity loss of ∼35% after 5h on stream. However, all the gallated catalysts were notoriously more stable (and selective) than copper on pure zirconia was. Temperature-programmed reduction in H2, X-ray photoelectron spectroscopy and infrared spectroscopy of adsorbed CO results proved that temperatures higher than 553K are needed to completely reduced Cu2+ to metallic Cu particles in the gallia-containing catalysts, which was attributed to the formation of a CuGa2O4 nanospinel. The ternary Cu–Ga2O3–ZrO2 catalysts showed an intermediate behavior, quite dependent on the preparation protocol, which emphasizes the need for tuning the degree of Cu–oxides interactions. It is suggested that just a moderate copper–gallia interaction is beneficial in terms of both activity and selectivity but, also, that a detrimental loss of ‘active’ copper should be avoided.