Formation Of Molecular Oxygen Research Articles

Corrosion Investigation by Scanning Electrochemical Microscopy of AISI 446 and Ti-Coated AISI 446 Ferritic Stainless Steel as Potential Material for Bipolar Plate in PEMWE

AbstractThe components of proton exchange membrane water electrolysers frequently experience corrosion issues, especially at high anodic polarization, that restrict the use of more affordable alternatives to titanium. Here, we investigate localized corrosion processes of bare and Ti-coated AISI 446 ferritic stainless steel under anodic polarization by scanning electrochemical microscopy (SECM) in sodium sulphate and potassium chloride solutions. SECM approach curves and area scans measured at open-circuit potential (OCP) of the samples in the feedback mode using a redox mediator evidence a negative feedback effect caused by the surface passive film. For the anodic polarization of the sample, the substrate generation-tip collection mode enables to observe local generation of iron (II) ions, as well as formation of molecular oxygen. For the uncoated AISI 446 sample, localized corrosion is detected in sodium sulphate solution simultaneously with oxygen formation at anodic potentials of 1.0 V vs. Ag/AgCl, whereas significant pitting corrosion is observed even at 0.2 V vs. Ag/AgCl in potassium chloride solution. The Ti-coated AISI 446 sample reveals enhanced corrosion resistance in both test solutions, without any evidence of iron (II) ions generation at anodic potentials of 1.2 V vs. Ag/AgCl, where only oxygen formation is observed.

Photoinduced Toxicity Caused by Gold Nanozymes and Photodynamic Dye Encapsulated in Submicron Polymer Shell

AbstractThe development of nanozymes, artificial enzymes made from inorganic nanoparticles, is widely studied due to their affordability, durability, and strength. Gold nanoparticles (AuNPs) are employed to imitate peroxidase, glucose oxidase, lactate oxidase, superoxide dismutase, and catalase. The last one transforms intracellular hydrogen peroxide into molecular oxygen, whose deficiency is characteristic of the hypoxic tumor microenvironment. Thus, gold nanoparticles are thought to enhance the overall effectiveness of photodynamic therapy. However, the enzyme‐like activity of nanoparticles rapidly decreases in biological media, due to the aggregation and formation of the so‐called “protein corona”. In this study, polymeric submicrocapsules loaded with AuNPs and a photodynamic dye are fabricated via Layer‐by‐Layer (LbL) assembly. The enhancement of photodynamic treatment efficacy by in situ production of oxygen by the catalase‐like effect of AuNPs is investigated. Polymeric capsules are thoroughly characterized in terms of physicochemical and catalytic properties, and as a proof of concept, their therapeutic potential is evaluated in vitro. Furthermore, encapsulated AuNPs shows significantly lower aggregation both upon storage and during the reaction course. The results shows that the polymer capsules, containing AuNPs and photodynamic dye, show significantly higher light‐induced cytotoxicity in comparison to the individual photodynamic dye, suggesting a synergistic effect between the formation of molecular oxygen by catalase‐like gold nanozymes and photodynamic action.

The electron–proton bottleneck of photosynthetic oxygen evolution

Photosynthesis fuels life on Earth by storing solar energy in chemical form. Today’s oxygen-rich atmosphere has resulted from the splitting of water at the protein-bound manganese cluster of photosystem II during photosynthesis. Formation of molecular oxygen starts from a state with four accumulated electron holes, the S4 state—which was postulated half a century ago1 and remains largely uncharacterized. Here we resolve this key stage of photosynthetic O2 formation and its crucial mechanistic role. We tracked 230,000 excitation cycles of dark-adapted photosystems with microsecond infrared spectroscopy. Combining these results with computational chemistry reveals that a crucial proton vacancy is initally created through gated sidechain deprotonation. Subsequently, a reactive oxygen radical is formed in a single-electron, multi-proton transfer event. This is the slowest step in photosynthetic O2 formation, with a moderate energetic barrier and marked entropic slowdown. We identify the S4 state as the oxygen-radical state; its formation is followed by fast O–O bonding and O2 release. In conjunction with previous breakthroughs in experimental and computational investigations, a compelling atomistic picture of photosynthetic O2 formation emerges. Our results provide insights into a biological process that is likely to have occurred unchanged for the past three billion years, which we expect to support the knowledge-based design of artificial water-splitting systems.

CeO2−δ Nanoparticles Supported on SnNb2O6 Nanosheets for Selective Catalytic Reduction of NOx with NH3

Selective catalytic reduction with NH3 (NH3-SCR) is an effective technique for purifying flue gas by removing nitrogen oxides, and the catalyst plays a key role in this technology. For the purpose of developing novel, highly efficient, green, and vanadium-free catalysts, SnNb2O6 nanosheets were synthesized successfully by hydrothermal and solid reactions and confirmed by XRD and TEM. These nanosheets were first used as a support for CeO2−δ to prepare environmentally friendly Ce/SnNb2O6 catalysts for NH3-SCR. These Ce/SnNb2O6 catalysts had more than 90% NOx conversion and 98% N2 selectivity at 250–400 °C and a high space velocity of 120,000 mL/(g·h), which is higher than the per surface area performance of the previously reported Ce-based NH3-SCR catalysts. To explore the factors for this increased activity, NH3-TPD, H2-TPR, and XPS data were analyzed in detail. The results indicated that Ce/SnNb2O6 nanocatalysts have more acid and oxidative sites than Ce/SnO2 and Ce/Nb2O5. In addition, the surface of Ce/SnNb2O6 contained 39.4% Sn4+ ions, which synergize with Ce as additional redox sites. The effect of electron transfer between Sn and Ce at the interface promoted the formation of molecular oxygen and cycling of redox sites. Kinetic studies showed that Ce/SnNb2O6 had a low apparent activation energy of 38.0 kJ/mol, which reduced the difficulty of the reaction. DFT studies indicated that the adsorption energy of NH3 in SnNb2O6 was 429.7 kJ/mol, which is much higher than that of other common supports, meaning that NH3 is much easier to adsorb on SnNb2O6 nanosheets, therefore showing higher catalytic performance. Moreover, in situ DRIFTS analysis showed the changes in the dominant mechanisms: the L–H and E–R mechanism coexist at 300 °C, while most of the reactions follow the E–R mechanism at 400 °C. This study can provide new insights into the development of new Ce-based NH3-SCR catalysts to control NOx emissions from stationary sources.

A Model for Radiolysis in a Flowing-Water Target during High-Intensity Proton Irradiation.

At the Facility for Rare Isotope Beams (FRIB), interactions between heavy-ion beams and beam-dump water will create a wide variety of radionuclides which can be accessed by a technique known as “isotope harvesting”. However, irradiation of water is always accompanied by the creation of numerous radical, ionic, and molecular radiolysis products. Some of the radiolysis products have sufficiently long lifetimes to accumulate in the irradiated water and affect the harvesting chemistry. Here we investigate the formation of hydrogen peroxide, molecular hydrogen, and molecular oxygen during a high-intensity proton irradiation of a flowing-water isotope-harvesting target and compare the experimental results to simulations. The simulations kinetically model the chemical reactions occurring in the homogeneous phase of radiolysis in flowing water and establish an “effective yield”. In both the experiment and simulations, the bulk quantities of H2, H2O2, and O2 are considerably lower than predicted by primary radiolysis yields (escape yields), meaning that in the high beam intensity regime the homogeneous phase reactions have a considerable impact on the overall chemical composition of the water. Further, it could be shown that for radiation which is characterized by a limited linear energy transfer, such as the here applied protons, the bulk outcome of the microscopic kinetic modeling could be estimated by a simplified steady-state model.

First‐principles insights on anion redox activity in NaxFe1/8Ni1/8Mn3/4O2: Toward efficient high‐energy cathodes for Na‐ion batteries

AbstractIn the search for high‐energy cathode materials for Na‐ion batteries (NIBs), Fe‐doped layered transition metal oxides have been recently proposed as promising systems that can ensure improved reversible capacity at high working voltage. Exploiting the anionic redox chemistry in this class of materials represents a great advance for the energy storage community, but uncontrolled oxidation process can lead to the formation of unbound molecular oxygen, with detrimental effects on overall capacity and stability upon cycling. The higher TM–O covalency provided by Fe doping seems to prevent oxygen loss and ensure full capacity recovery. Understanding anionic processes and the underlying mechanism with atomistic details can reinforce the experimental efforts and help to outline rational design strategies for novel high‐performing NIB cathodes. To this end, we present a state‐of‐the‐art first‐principles study on the P2‐type NaxTMO2 (TM = Fe, Ni, and Mn—NFNMO) oxide. We compare structural and electronic features of stoichiometric (NaxFe0.125Ni0.125Mn0.75O2) and Mn‐deficient (NaxFe0.125Ni0.125Mn0.68O2) NFNMO to identify and discuss the contribution of each element sublattice on charge compensation processes. Although Mn deficiency is predicted to increase the cathode working voltage, we find the charge compensation being mostly exerted by the Ni and Fe sublattices. Oxygen redox is unfold via the formation of superoxide species at low Na loads with a preferential breaking of more labile Ni–O bonds and binding to Fe atoms. Our calculations predict no release of molecular O2 upon desodiation, thus highlighting the key role of Fe dopant that provides a good TM–O bond strength, preventing oxygen loss while still enabling anionic redox reactions at high voltages with extra reversible capacity.

Electron-Stimulated Formation and Release of Molecular Hydrogen and Oxygen from Boehmite Nanoplatelet Films

The production and release of H2 and O2 during and after electron (100–1000 eV) irradiation of boehmite nanoplatelet films was studied. H2 and O2 produced during irradiation likely correspond to electron-induced dissociation of the hydroxyls primarily in the terminal surface layers of the boehmite followed by the H· + H· → H2(g) and O + O → O2(g) combinative desorption reactions as well as the abstraction reactions H· + >OH– → H2(g) + >O·̅. Postirradiation temperature-programmed desorption shows a temperature-dependent release of H2 but no additional release of O2. This process likely involves diffusion and recombination of H· atoms initially trapped between the γ-AlOOH planes followed by recombination at edge and surface sites. H2 production upon thermal-annealing-irradiated material shows no dependence on incident electron flux, suggesting the precursor species (H·) trapped within the bulk are long-lived.

Generation of Hydrogen and Oxygen from Water by Solar Energy Conversion

Photosynthesis is considered to be one of the promising areas of cheap and environmentally friendly energy. Photosynthesis involves the process of water oxidation with the formation of molecular oxygen and hydrogen as byproducts. The aim of the present article is to review the energy (light) phase of photosynthesis based on the published X-ray studies of photosystems I and II (PS-I and PS-II). Using modern ideas about semiconductors and biological semiconductor structures, the mechanisms of H+, O2↑, e− generation from water are described. At the initial stage, PS II produces hydrogen peroxide from water as a result of the photoenzymatic reaction, which is oxidized in the active center of PS-II on the Mn4CaO5 cluster to form O2↑, H+, e−. Mn4+ is reduced to Mn2+ and then oxidized to Mn4+ with the transfer of reducing the equivalents of PS-I. The electrons formed are transported to PS-I (P 700), where the electrochemical reaction of water decomposition takes place in a two-electrode electrolysis system with the formation of gaseous oxygen and hydrogen. The proposed functioning mechanisms of PS-I and PS-II can be used in the development of environmentally friendly technologies for the production of molecular hydrogen.

RESEARCH OF COMBUSTION MODES DURING LAYER-BURNING OF SHUBARKUL COAL ON THE FIRE GRATE WITH THE HAND FURNACE OF THE KSVR-0.43 HOT WATER BOILER

Experience shows that the trend towards using solid fuels in the energy sector of Kazakhstan will be implemented for a rather long time. At the same time, the global trend is currently tightening environmental requirements. They set the task to continue improving coal combustion efficiency and minimize emissions of harmful substances and greenhouse gases into the atmosphere. This article aims to conduct complex thermal engineering tests of the KCVr-0.43 hot water boiler. For this, the following measurement and control tools were used: the standard boiler room secondary devices, an industrial gas analyzer Testo-350, a control (reading) module Testo-454 with temperature probes and a Pitot tube, a soot number meter Testo-308, a temperature meter 2TPM1, a portable liquid flow meter Vzlet-PRC and a stopwatch. All they had valid verification and calibration certificates. An analysis of the gas composition and technical parameters of the KCVr-0.43 hot water boiler in the investigated operation mode with Shubarkul coal during a long-term test showed that it seems possible to operate boilers of this series under low load conditions without boosting air and fuel. They can reduce emissions of toxic NOx and greenhouse gases CO2 into the atmosphere. In this case, burning Shubarkul coal without forcing through the air is characterized by significant carbon monoxide CO emissions. The formed nitrogen oxides NOx decompose in reactions with CO with the formation of molecular nitrogen and oxygen. Burning, coke residue in the layer, coal-burning stages, emissions of harmful substances.

Excited States of Thio-2′-deoxyuridine Bearing an Extended π-Conjugated System: 3′,5′-Di-O-acetyl-5-phenylethynyl-4-thio-2′-deoxyuridine

A new thio-2'-deoxyuridine with an extended π-conjugated group was successfully synthesized: 3',5'-di-O-acetyl-5-phenylethynyl-4-thio-2'-deoxyuridine. The thio-2'-deoxyuridine derivative has a large red-shifted absorption band in the UVA region and also shows fluorescence, a rare photo-property among thionucleobases/thionucleosides. The triplet-triplet absorption spectrum and the rate constants (the intrinsic decay rate constant of the triplet state, the self-quenching rate constant, and the quenching rate constant of the triplet state by an oxygen molecule) of the thio-2'-deoxyuridine were obtained by transient absorption spectroscopy. The quantum yield of intersystem crossing and the quantum yield of singlet molecular oxygen formation (ϕΔ) under an oxygen atmosphere were also determined. The ϕΔ value of the new thio-2'-deoxyuridine was found to be substantially higher than all reported values of other thio-2'-deoxyribonucleosides in low oxygen concentrations similar to cancer cell environments. The fluorescence quantum yield depended on the excitation wavelength, revealing certain photochemical reactions in the higher excited singlet states. However, when excited into the higher excited state with non-resonant two-photon absorption, the ϕΔ of the thio-2'-deoxyuridine derivative was found to remain sufficiently large. These findings should be very useful for the development of thio-2'-deoxyribonucleoside-based pharmaceuticals as DNA-specific photosensitizers for photochemotherapy.

Lowering the Operating Temperature of Perovskite Catalysts for N2O Decomposition through Control of Preparation Methods

Discovering catalysts that can decompose N2O at low temperatures represents a major challenge in modern catalysis. The effect of preparative route on N2O-decomposition activity has been examined for a PrBaCoO3 perovskite catalyst. Initially, a citric acid preparation was utilised where the A site ratio was altered in order to increase phase purity. Comparable compositions were then prepared by an oxalic acid precipitation method and by a supercritical anti-solvent technique to produce perovskites with a higher surface area (> 30 m2g-1). By altering the A site ratios it was possible to reduce the temperature required to produce a pure phase perovskite whilst maintaining a higher-surface area. The use of the different preparation methods resulted in perovskites with varying properties, as determined by N2 adsorption, XPS and O2-TPD. This work confirms the importance of lattice oxygen species that have high oxygen mobility for enhanced decomposition of N2O, as oxygen recombination is considered the rate-limiting step. Here, the formation of molecular oxygen is limited by surface adsorbed O species being within a distance at which oxygen recombination is possible. The most active PrBaCo-based catalyst did not have the highest percentage of lattice oxygen as shown by XPS, however, the catalytic activity could be correlated to the mobile oxygen species and high surface area. The PrBaCo-based catalyst prepared by supercritical anti-solvent converted 50 % of the N2O present in the feed (T50) at 410 °C, which represents a significant improvement over reported catalytic performance measured under similar conditions.

Surface sensitization of TiO2 nanorod mats by electrodeposition of ZIF-67 for water photo-oxidation

Results reported in this research paper are related to the photo-oxidation of water into molecular oxygen, using n-type photoelectrodes operated with the support of an external electric bias. These photoanodes are made of 1 cm2 rectangular glass substrates, surface-covered by thin films of conductive fluorine-doped tin oxide (FTO). Thin mats of titanium dioxide nanorods (TDNRs) have been deposited over the FTO surfaces. The TDNRs have then been sensitized by surface deposition of cobalt dodecahedral Zeolitic Imidazolate Framework (ZIF-67) metal organic framwork (MOF). ZIF-67 has been deposited using a two-step process: (i) deposition of cobalt hydroxide by chronoamperometry; (ii) in-situ transformation of cobalt hydroxide into ZIF-67 by chemical reaction with a solution of 2-methylimidazol. The amount of ZIF-67 has been adjusted by monitoring the duration of the electro-reduction step. The photoanodes have been characterized by scanning electron microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and UV–Vis absorption spectroscopy. The photoelectrochemical responses of the different photoanodes have been measured under chopped illumination conditions. Dark currents as high as 100–150 μA/cm2 and photocurrents of only 10–15 μA/cm2 have been measured on fresh samples with large MOF contents, at an operating potential of +1.0 V vs. saturated calomel electrode, 25 °C, under UV–Vis irradiation. No dark current and photocurrents close to 40 μA/cm2 have been measured on samples with low MOF contents. The dynamics of charge transfer leading to the formation of molecular oxygen has been analyzed by photoelectrochemical impedance spectroscopy to understand the interplay between the OER electroactivity and photoelectroactivity. It is shown that large MOF contents induce two contradictory effects: the first one (faster charge transfer kinetics) is desirable while the second one (faster charge recombination kinetics) is not desirable. Only limited MOF contents are beneficial to maximize the photocurrent density.

Selenocysteine as a Substrate, an Inhibitor and a Mechanistic Probe for Bacterial and Fungal Iron-Dependent Sulfoxide Synthases.

Sulfoxide synthases are non-heme iron enzymes that participate in the biosynthesis of thiohistidines, such as ergothioneine and ovothiol A. The sulfoxide synthase EgtB from Chloracidobacterium thermophilum (CthEgtB) catalyzes oxidative coupling between the side chains of N-α-trimethyl histidine (TMH) and cysteine (Cys) in a reaction that entails complete reduction of molecular oxygen, carbon-sulfur (C-S) and sulfur-oxygen (S-O) bond formation as well as carbon-hydrogen (C-H) bond cleavage. In this report, we show that CthEgtB and other bacterial sulfoxide synthases cannot efficiently accept selenocysteine (SeCys) as a substrate in place of cysteine. In contrast, the sulfoxide synthase from the filamentous fungus Chaetomium thermophilum (CthEgt1) catalyzes C-S and C-Se bond formation at almost equal efficiency. We discuss evidence suggesting that this functional difference between bacterial and fungal sulfoxide synthases emerges from different modes of oxygen activation.

The elusive photocatalytic water splitting reaction using sunlight on suspended nanoparticles: is there a way forward?

For many decades hydrogen production from water by photocatalytic methods has been pursued over a variety of semiconductor powder catalysts featuring many structures and compositions. The stoichiometric formation of molecular hydrogen and oxygen has stayed largely elusive.

Rotational and vibrational fingerprints of the oxywater cation (H2OO+), a possible precursor to abiotic O2

The oxywater cation (H2OO+) has been suggested as a possible intermediate in the abiotic formation of molecular oxygen in the gas phase potentially relating to the chemistry of comets or the upper atmosphere. Accurate spectroscopic data of the oxywater cation is required for astrochemical or atmospheric observations to have any ability to support or refute the role that this molecule could play in such processes. This work improves upon the existing literature by using a quartic force field approach at a high-level of theory and examines both the X∼2A′ and 14A″ states of H2OO+. The weaker bonding in the quartet state makes it behave more like water than the doublet state, but both are notably different from gas phase water. Both states have four bright vibrational peaks corresponding to the two OH stretches, the out-of-plane bend, and the symmetric bend. These bands will probably still be in the same range as those from H2O in some cases making H2OO+ non-trivial to differentiate from water in the infrared. Fortunately, both states of the molecule have large dipole moments (3.91 D & 1.96 D, respective of the X∼2A′ and 14A″ states) allowing them to be detected, distinguished, and characterized in the laboratory or potentially using ground-based radio telescopes with the spectroscopic data generated here.

The Effect of Gold Nanoparticle Concentration and Laser Fluence on the Laser-Induced Water Decomposition

This Article covers the influence of the concentration of gold nanoparticles on laser-induced water decomposition. It was established that addition of gold nanoparticles intensifies laser-induced water decomposition by almost 2 orders of magnitude. The water decomposition rate was shown to be maximal at a nanoparticle concentration around 1010 NP/mL, whereas a decrease or increase of nanoparticle concentration leads to a decrease of water decomposition rate. It was demonstrated that, if the concentration of nanoparticles in water-based colloid was less than 1010 NP/mL, laser irradiation of the colloid caused formation of molecular hydrogen, hydrogen peroxide, and molecular oxygen. If the concentration of nanoparticles exceeded 1011 NP/mL, only two products, molecular hydrogen and hydrogen peroxide, were formed. Correlations between the water decomposition rate and the main optical and acoustic parameters of optical breakdown-generated plasma were investigated. Variants of laser-induced decomposition of colloidal solutions of nanoparticles based on organic solvents (ethanol, propanol-2, butanol-2, diethyl ether) were also analyzed.

Determining the role of redox-active materials during laser-induced water decomposition.

Laser ablation in liquids (LAL) drives the decomposition of the liquid inducing the formation of a large number of different redox equivalents and gases. This not only leads to shielding effects and a decrease of the nanoparticle (NP) productivity but also can directly affect the NP properties such as the oxidation degree. In this study, we demonstrate that liquid decomposition during laser ablation in water is triggered by the redox activity of the 7 different bulk materials used; Au, Pt, Ag, Cu, Fe, Ti and Al, as well as by the reactivity of water with the plasma. Laser ablation of less-noble metals like aluminum leads to a massive gas evolution up to 390 cm3 per hour with molar hydrogen to oxygen ratios of 17.1. For more noble metals such as gold and platinum, water splitting induced by LAL is the dominant feature leading to gas volume formation rates of 10 up to 30 cm3 per hour and molar hydrogen to oxygen ratios of 1.2. We quantify the material-dependent ablation rate, shielding effects as well as the amount of hydrogen peroxide produced, directly affecting the yield and oxidation of the nanoparticles on the long-time scale.

Oxidised micrometeorites as evidence for low atmospheric pressure on the early Earth.

Reconstructing a record of the partial pressure of molecular oxygen in Earth’s atmosphere is key for understanding macroevolutionary and environmental change over geological history. Recently, the oxidation state of iron in micrometeorites has been taken to imply the presence of modern Earth concentrations of oxygen in the upper atmosphere at 2.7 Ga, and therefore a highly chemically stratified atmosphere (Tomkins et al., 2016). We here explore the possibility that the mixing ratio of oxygen in Earth’s upper atmosphere, that probed by micrometeorites, may instead be sensitive to the surface atmospheric pressure. We find that the concentrations of oxygen in the upper atmosphere required for micrometeorite oxidation are achieved for a 0.3 bar atmosphere. In this case, significant water vapour reaches high up in the atmosphere and is photodissociated, leading to the formation of molecular oxygen. The presence of oxidised iron in micrometeorites at 2.7 Ga may therefore be further evidence that the atmospheric pressure at the surface of the early Earth was substantially lower than it is today.

Impact of water on the BrO + HO2 gas-phase reaction: mechanism, kinetics and products.

The BrO + HO2 reaction, which participates in the cycle of ozone removal via BrOH formation, was explored both in the absence and in the presence of water using ab initio calculations. Two main sets of products, (i) HBr + O3 and (ii) BrOH + O2, are formed regardless of the presence of water, following a hydrogen abstraction mechanism. The HBr + O3 products are formed from the intermediate BrOOOH adduct, whereas BrOH + O2 are formed either from the intermediate OBrOOH adduct or via a barrierless hydrogen transfer from HO2 to BrO. Owing to the formation of molecular oxygen that can bear different spin configurations, the formation of BrOH + O2 products was examined both on the singlet and the triplet surfaces. Under relevant atmospheric temperatures and pressure, the formation of products (i) is energetically and kinetically less favorable than that of products (ii). The rate coefficient at 298 K for the HBr + O3 formation was determined to be 2.00 × 10-20 cm3 molecule-1 s-1, and found to decrease by 1-2 orders of magnitude when one or both reactants are clustered with water. For the formation of BrOH + O2, a rate coefficient of 2.21 × 10-11 cm3 molecule-1 s-1 is determined on both singlet and triplet surfaces in the absence of water. Though this rate coefficient slightly decreases for the hydrated reactions, the fractions of the reactants that are effectively complexed with water are not high enough to shift the overall BrOH + O2 formation rate. The current study further indicates that humidity plays a negligible role in ozone removal via the BrO + HO2 reaction.

Influence of Eu2O3 on phase crystallization and nanocrystals formation in tellurite glasses

Glasses of the 17ZnO·32CdO·51TeO2 system doped with Eu2O3 (0–0.75 mol per 100 mol of oxides) were obtained. Non-isothermal differential scanning calorimetry (DSC) tests showed that the glass transition temperature varied in the range of 354° to 371 °C with the addition of Eu2O3. The samples were exposed to a thermal treatment in a laboratory oven at 420 °C. X-ray diffraction analysis of the treated samples showed crystalline phases of a variety of metallic oxides, the intensities of which decreased as the Eu doping amount in the samples increased. In all samples, the strongest peak corresponded to ZnTeO3 with a crystallite size of about 36 nm. Fourier Transform Infrared Spectroscopy showed that CdO and ZnO change their role from modifier to a glass former. Raman spectra showed characteristic bands corresponding to γ–TeO2. The observations suggest that Eu2O3 induced structural changes which in turn led to the formation of molecular oxygen in the interstitial network. Deconvolution analysis of Raman spectra and High-Resolution Transmission Electron Microscopy images confirmed the formation of Te2O5, ZnTeO3 and Te nanocrystals. Photoluminescence analysis showed that Eu ions are incorporated as Eu3+ and no reduction occurred after heat treatment.