Showing papers on "Oxygen published in 2017"
TL;DR: Mechanistic insights into oxygen-induced photodegradation of perovskite films are reported, finding fast oxygen diffusion into CH3NH3PbI3 films is accompanied by photo-induced formation of highly reactive superoxide species from oxygen.
Abstract: Methylammonium lead halide perovskites are attracting intense interest as promising materials for next-generation solar cells, but serious issues related to long-term stability need to be addressed. Perovskite films based on CH3NH3PbI3 undergo rapid degradation when exposed to oxygen and light. Here, we report mechanistic insights into this oxygen-induced photodegradation from a range of experimental and computational techniques. We find fast oxygen diffusion into CH3NH3PbI3 films is accompanied by photo-induced formation of highly reactive superoxide species. Perovskite films composed of small crystallites show higher yields of superoxide and lower stability. Ab initio simulations indicate that iodide vacancies are the preferred sites in mediating the photo-induced formation of superoxide species from oxygen. Thin-film passivation with iodide salts is shown to enhance film and device stability. The understanding of degradation phenomena gained from this study is important for the future design and optimization of stable perovskite solar cells.
850 citations
TL;DR: The efficient generation of 1O2 using the PS/CNTs system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral conditions with the mineralization and toxicity evaluated.
703 citations
TL;DR: It is reported that a commercially available TiO2 with a large number of surface oxygen vacancies, when photoirradiated by UV light in pure water with N2, successfully produces NH3.
Abstract: Ammonia (NH3) is an essential chemical in modern society. It is currently manufactured by the Haber–Bosch process using H2 and N2 under extremely high-pressure (>200 bar) and high-temperature (>673 K) conditions. Photocatalytic NH3 production from water and N2 at atmospheric pressure and room temperature is ideal. Several semiconductor photocatalysts have been proposed, but all suffer from low efficiency. Here we report that a commercially available TiO2 with a large number of surface oxygen vacancies, when photoirradiated by UV light in pure water with N2, successfully produces NH3. The active sites for N2 reduction are the Ti3+ species on the oxygen vacancies. These species act as adsorption sites for N2 and trapping sites for the photoformed conduction band electrons. These properties therefore promote efficient reduction of N2 to NH3. The solar-to-chemical energy conversion efficiency is 0.02%, which is the highest efficiency among the early reported photocatalytic systems. This noble-metal-free TiO2 ...
628 citations
TL;DR: The first example of in situ exfoliated, edge-rich, oxygen-functionalized graphene on the surface of carbon fibers using Ar plasma treatment is successfully prepared and has a higher specific surface area and an increased number of active sites for OER and ORR.
Abstract: Metal-free electrocatalysts have been extensively developed to replace noble metal Pt and RuO2 catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in fuel cells or metal-air batteries. These electrocatalysts are usually deposited on a 3D conductive support (e.g., carbon paper or carbon cloth (CC)) to facilitate mass and electron transport. For practical applications, it is desirable to create in situ catalysts on the carbon fiber support to simplify the fabrication process for catalytic electrodes. In this study, the first example of in situ exfoliated, edge-rich, oxygen-functionalized graphene on the surface of carbon fibers using Ar plasma treatment is successfully prepared. Compared to pristine CC, the plasma-etched carbon cloth (P-CC) has a higher specific surface area and an increased number of active sites for OER and ORR. P-CC also displays good intrinsic electron conductivity and excellent mass transport. Theoretical studies show that P-CC has a low overpotential that is comparable to Pt-based catalysts, as a result of both defects and oxygen doping. This study provides a simple and effective approach for producing highly active in situ catalysts on a carbon support for OER and ORR.
563 citations
TL;DR: It is demonstrated that the resulting methanol incorporated a substantial fraction of gas-phase O2, suggesting that the controlled breakdown of H2O2 activates methane, which subsequently incorporates molecular oxygen through a radical process.
Abstract: The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. We used colloidal gold-palladium nanoparticles, rather than the same nanoparticles supported on titanium oxide, to oxidize methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Then, using isotopically labeled oxygen (O2) as an oxidant in the presence of hydrogen peroxide (H2O2), we demonstrated that the resulting methanol incorporated a substantial fraction (70%) of gas-phase O2. More oxygenated products were formed than the amount of H2O2 consumed, suggesting that the controlled breakdown of H2O2 activates methane, which subsequently incorporates molecular oxygen through a radical process. If a source of methyl radicals can be established, then the selective oxidation of methane to methanol using molecular oxygen is possible.
429 citations
TL;DR: In this paper, a correlation between surface activity and surface stability for OER catalysts was established, which is rooted in the formation of surface reactive oxygen atoms that act as electrophilic centres for water to react.
Abstract: The oxygen evolution reaction (OER) is of prime importance in multiple energy storage devices; however, deeper mechanistic understanding is required to design enhanced electrocatalysts for the reaction. Current understanding of the OER mechanism based on oxygen adsorption on a metallic surface site fails to fully explain the activity of iridium and ruthenium oxide surfaces, and the drastic surface reconstruction observed for the most active OER catalysts. Here we demonstrate, using La2LiIrO6 as a model catalyst, that the exceptionally high activity found for Ir-based catalysts arises from the formation of active surface oxygen atoms that act as electrophilic centres for water to react. Moreover, with the help of transmission electron microscopy, we observe drastic surface reconstruction and iridium migration from the bulk to the surface. Therefore, we establish a correlation between surface activity and surface stability for OER catalysts that is rooted in the formation of surface reactive oxygen.
387 citations
TL;DR: In this paper, a metal-free oxygen doped porous graphitic carbon nitride (OA-g-C3N4) was synthesized by condensation of oxalic acid and urea.
Abstract: A novel metal-free oxygen doped porous graphitic carbon nitride (OA-g-C3N4) was synthesized by condensation of oxalic acid and urea. The 40% OA-g-C3N4 catalyst can degrade bisphenol A (15 mg L−1) in 240 min with a mineralization rate as high as 56%. The markedly higher visible-light-driven oxidation activity of OA-g-C3N4 is attributed to the porous morphology and unique electrical structure. The porous structure of OA-g-C3N4 provides more active sites for adsorption and degradation of pollutants. Moreover, oxygen atoms in the tri-s-triazine units help to extend sufficient light absorption range up to 700 nm, improve the separation of charge-carriers and alter the position of valence band (VB) and conduction band (CB). The VB edge shifts from 1.95 eV to 2.46 eV due to the incorporation of O atoms, which leads to the change of active species in the photocatalytic reaction. Trapping experiment shows that superoxide radicals play the major role in the photocatalytic degradation of BPA on g-C3N4, while hydroxyl radical is the dominant active species in the photocatalytic degradation process over 40% OA-g-C3N4. This study presents a simple, economical and environment-friendly method to synthesized oxygen doped porous graphitic carbon nitride.
354 citations
TL;DR: A conceptual oxygen vacancy associated surface Fenton system without any metal ions leaching, exhibiting unprecedented surface chemistry based on the oxygen vacancy of electron-donor nature for heterolytic H2O2 dissociation.
Abstract: Understanding the chemistry of hydrogen peroxide (H2O2) decomposition and hydroxyl radical (•OH) transformation on the surface molecular level is a great challenge for the application of heterogeneous Fenton system in the fields of chemistry, environmental, and life science. We report in this study a conceptual oxygen vacancy associated surface Fenton system without any metal ions leaching, exhibiting unprecedented surface chemistry based on the oxygen vacancy of electron-donor nature for heterolytic H2O2 dissociation. By controlling the delicate surface structure of catalyst, this novel Fenton system allows the facile tuning of •OH existing form for targeted catalytic reactions with controlled reactivity and selectivity. On the model catalyst of BiOCl, the generated •OH tend to diffuse away from the (001) surface for the selective oxidation of dissolved pollutants in solution, but prefer to stay on the (010) surface, reacting with strongly adsorbed pollutants with high priority. These findings will exten...
345 citations
TL;DR: A clear atomic-level correlation between oxygen vacancies and carbon dioxide electroreduction is established, taking the synthetic oxygen-deficient cobalt oxide single-unit-cell layers as an example.
Abstract: The role of oxygen vacancies in carbon dioxide electroreduction remains somewhat unclear. Here we construct a model of oxygen vacancies confined in atomic layer, taking the synthetic oxygen-deficient cobalt oxide single-unit-cell layers as an example. Density functional theory calculations demonstrate the main defect is the oxygen(II) vacancy, while X-ray absorption fine structure spectroscopy reveals their distinct oxygen vacancy concentrations. Proton transfer is theoretically/experimentally demonstrated to be a rate-limiting step, while energy calculations unveil that the presence of oxygen(II) vacancies lower the rate-limiting activation barrier from 0.51 to 0.40 eV via stabilizing the formate anion radical intermediate, confirmed by the lowered onset potential from 0.81 to 0.78 V and decreased Tafel slope from 48 to 37 mV dec−1. Hence, vacancy-rich cobalt oxide single-unit-cell layers exhibit current densities of 2.7 mA cm−2 with ca. 85% formate selectivity during 40-h tests. This work establishes a clear atomic-level correlation between oxygen vacancies and carbon dioxide electroreduction. The role of oxygen vacancies in carbon dioxide reduction remains somewhat unclear. Here, the authors fabricate vacancy-rich and vacancy-poor Co3O4single-unit-cell layers, and demonstrate by X-ray absorption and DFT that the material is a promising platform for mechanistic studies of carbon dioxide reduction.
333 citations
TL;DR: In this article, three different TiO2 nanoparticles possessing surface oxygen vacancies (SO) and/or bulk single-electron-trapped oxygen vacancy (SETOV) were fabricated by dehydration or reduction of different titania precursors.
Abstract: Oxygen vacancies play an important role in many photocatalytic reaction, and have attracted enormous attention from the scientists and engineers. The surface or bulk oxygen vacancies have a different function in the photo-reaction process. Herein, three different TiO2 nanoparticles possessing surface oxygen vacancies (SO) and/or bulk single-electron-trapped oxygen vacancy (SETOV) were fabricated by dehydration or reduction of different titania precursors. The three kinds of TiO2 nanoparticles were characterized systematically by XRD, TEM, Raman, XPS, ESR, TG, UV–vis DRS, and PL techniques. The photocatalytic reduction results of CO2 indicated that both the bulk SETOVs and surface oxygen vacancies contributed to the enhancement of the light absorption, while the surface vacancies facilitated to the separation of the photo-generated charge carriers, and on the contrast, the bulk SETOVs acted as the recombination center. The co-existence of the surface and bulk oxygen vacancies exhibited a synergistic effect to improve the photoreduction efficiency of CO2 to CH4. Through adjusting the ratio of the surface and bulk oxygen vacancies and analyzing the positron lifetime and relative intensity by positron annihilation, the photoreduction efficiency of CO2 improved with the increase of the ratio of surface oxygen vacancies to bulk SETOVs.
322 citations
TL;DR: It is demonstrated that a single electron transfer process via a carbon radical, peroxide radical, or hydroxyl radical is involved in these aerobic oxidation and oxygenation reactions, which provide new approaches for the green synthesis of various α-keto amides, α- keto esters, ester, ketones, aldehydes, formamides, 2-oxoacetamidines, and tertiary α-hydroxy carbonyls.
Abstract: ConspectusThe selective oxidation of organic molecules is a fundamentally important component of modern synthetic chemistry. In the past decades, direct oxidative C–H and C–C bond functionalization has proved to be one of the most efficient and straightforward methods to synthesize complex products from simple and readily available starting materials. Among these oxidative processes, the use of molecular oxygen as a green and sustainable oxidant has attracted considerable attention because of its highly atom-economical, abundant, and environmentally friendly characteristics. The development of new protocols using molecular oxygen as an ideal oxidant is highly desirable in oxidation chemistry. More importantly, the oxygenation reaction of simple molecules using molecular oxygen as the oxygen source offers one of the most ideal processes for the construction of O-containing compounds. Aerobic oxidation and oxygenation by enzymes, such as monooxygenase, tyrosinase, and dopamine β-monooxygenase, have been obs...
TL;DR: It is shown that an injectable polymer-modified magnesium silicide (Mg2Si) nanoparticle can act as a DOA by scavenging oxygen in tumours and form by-products that block tumour capillaries from being reoxygenated.
Abstract: A material that rapidly absorbs molecular oxygen (known as an oxygen scavenger or deoxygenation agent (DOA)) has various industrial applications, such as in food preservation, anticorrosion of metal and coal deoxidation. Given that oxygen is vital to cancer growth, to starve tumours through the consumption of intratumoral oxygen is a potentially useful strategy in fighting cancer. Here we show that an injectable polymer-modified magnesium silicide (Mg2Si) nanoparticle can act as a DOA by scavenging oxygen in tumours and form by-products that block tumour capillaries from being reoxygenated. The nanoparticles are prepared by a self-propagating high-temperature synthesis strategy. In the acidic tumour microenvironment, the Mg2Si releases silane, which efficiently reacts with both tissue-dissolved and haemoglobin-bound oxygen to form silicon oxide (SiO2) aggregates. This in situ formation of SiO2 blocks the tumour blood capillaries and prevents tumours from receiving new supplies of oxygen and nutrients.
TL;DR: It is proposed that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy, which would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.
Abstract: Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO2RR). Using in situ ambient pressure X-ray photoelectron spectroscopy and quasi in situ electron energy-loss spectroscopy in a transmission electron microscope, we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts but no residual copper oxide. On the basis of these findings in combination with density functional theory simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO2RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.
TL;DR: In this paper, a 3D ordered macroporous (3DOM) LaFeO3 was used for chemical-looping reforming of methane (CLRM) for coproducing syngas and pure hydrogen.
Abstract: Chemical-looping reforming of methane (CLRM) offers an effective approach for coproducing syngas and pure hydrogen. In this work, CeO2 nano particles (2–3 nm) are well dispersed on the wall surface of three-dimensional ordered macroporous (3DOM) LaFeO3, obtaining a highly efficient oxygen carrier for the CLRM technology. The physical and chemical properties of the oxygen carriers were characterized by SEM, TEM, H2-TPR, XPS, XRD, CH4-TPR and CH4-TPD techniques. It is found that the presence of CeO2 on LaFeO3 results in the formation of Ce3+ and Fe2+ due to the CeO2-LaFeO3 interaction. The coexistence of Ce3+ and Fe2+ irons induces abundant oxygen vacancies on the mixed oxides, which strongly improves the reducibility, oxygen mobility and reactivity for methane oxidation. The presence of CeO2 also improves the resistance towards carbon deposition formation, and this allows the CeO2/LaFeO3 materials own high available oxygen storage capacity (available OSC, the maximum amount of oxygen consumed by methane reduction without the formation of carbon deposition). It is also noted that the agglomeration of CeO2 nano particles would reduce the reactivity of oxygen carriers. Among all the obtained samples, the 10% CeO2/LaFeO3 sample exhibits the highest yields of syngas (9.94 mmol g−1) and pure hydrogen (3.38 mmol g−1) without the formation of carbon deposition, which are much higher than that over the pure LaFeO3 sample (5.73 mmol g−1 for syngas yield and 2.00 mmol g−1 for hydrogen yield). In addition, the CeO2/LaFeO3 oxygen carrier also showed high stability during the successive CLRM testing either in the activity (yields of syngas and pure hydrogen) or structure (macroporous frameworks) aspect.
TL;DR: In this article, the authors show that singlet oxygen forms at the cathode of a lithium-oxygen cell during discharge and from the onset of charge, and accounts for the majority of parasitic reaction products.
Abstract: Non-aqueous metal-oxygen batteries depend critically on the reversible formation/decomposition of metal oxides on cycling. Irreversible parasitic reactions cause poor rechargeability, efficiency, and cycle life and have predominantly been ascribed to the reactivity of reduced oxygen species with cell components. These species, however, cannot fully explain the side reactions. Here we show that singlet oxygen forms at the cathode of a lithium-oxygen cell during discharge and from the onset of charge, and accounts for the majority of parasitic reaction products. The amount increases during discharge, early stages of charge, and charging at higher voltages, and is enhanced by the presence of trace water. Superoxide and peroxide appear to be involved in singlet oxygen generation. Singlet oxygen traps and quenchers can reduce parasitic reactions effectively. Awareness of the highly reactive singlet oxygen in non-aqueous metal-oxygen batteries gives a rationale for future research towards achieving highly reversible cell operation.
TL;DR: In this article, the authors present an overview of progress made in preparing oxygen defective metal oxide nanostructures and probing the role of oxygen vacancies on the performance of metal oxides.
TL;DR: In this article, the relationship between the oxygen species of cerium-based oxygen carriers and catalytic behavior was investigated by using CH3SH and Ce1-xYxO2-δ (x ǫ = 0, 0.25, 0., 50, 0, 75, and 1.0) solid solutions as examples.
Abstract: The relationship between the oxygen species of cerium-based oxygen carriers and catalytic behavior, namely the correlation between catalytic activity and surface lattice oxygen (OS-L) and that between catalytic stability and bulk lattice oxygen (OB-L), was investigated by using CH3SH and Ce1-xYxO2-δ (x = 0, 0.25, 0.50, 0.75, and 1.0) solid solutions as examples. Activity and stability experimental studies with corresponding XPS were performed to assess the role of definite surface oxygen in cerium-based oxygen carriers. The surface lattice oxygen (OS-L), rather than the surface adsorbed oxygen (OS-A), was observed to be responsible for the catalytic decomposition of CH3SH. Further, the difference in catalytic activity between CeO2 and Y-doped samples is closely associated with the insertion of Y3+ ion into the lattice of CeO2 leading to the loss of surface lattice oxygen (OS-L). H2-temperature programmed reduction (TPR), a specially designed H2-TPR, X-ray photoelectron spectroscopy, reaction product (CO and CO2) analysis, and oxygen storage capacity tests were performed to demonstrate the migration of bulk lattice oxygen, which was directly related to the catalytic stability of CeO2 and Y-doped catalysts. Direct evidences of the migration of bulk lattice oxygen over cerium-based oxygen carriers were obtained. Additionally, the migration rate of bulk lattice oxygen (OB-L) within Ce0.75Y0.25O2-δ was faster compared to the migration rate of bulk lattice oxygen (OB-L) of CeO2. Finally, improvements in catalytic stability are closely associated with the fact that bulk lattice oxygen (OB-L) participates in the decomposition of CH3SH through its faster migration to replenish surface lattice oxygen (OS-L). The factors that influenced the migration rate of bulk lattice oxygen (OB-L) were thus also subsequently investigated and discussed.
TL;DR: In this article, the authors investigated the photogeneration of reactive oxygen species (ROS) from biochar suspension by using FTIR, Raman, XPS and electron paramagnetic resonance (EPR) techniques.
Abstract: In this study, the photogeneration of reactive oxygen species (ROS) from biochar suspension was investigated. The characterizations of biochar particles before and after photochemical reactions were analyzed by using FTIR, Raman, XPS and electron paramagnetic resonance (EPR) techniques. It was found that the model pollutant diethyl phthalate (DEP) was efficiently degraded and partially mineralized under UV and simulated solar lights in biochar suspension, with hydroxyl radicals ( OH) and singlet oxygen (1O2) as the dominant ROS. EPR coupled with chemical probe methods and free radical quenching studies were used to quantify and elucidate the formation mechanism of OH and 1O2. The results indicated that biochar carbon matrix (BCM) accounted for 63.6%–74.6% of OH and 10%–44.7% of 1O2 formation, while dissolved organic matter (DOM) derived from biochar generated 46.7%–86.3% of 1O2 and 3.7%–12.5% of OH. BCM-bound persistent free radicals (BCM-PFRs) and quinone-like structure of BCM (BCM-Q) were the predominant factors affecting OH and 1O2 formation from BCM under light. Detailed ROS generation pathways are proposed as: (i) DOM from biochar particles contributes to OH and 1O2 formation via light-induced energy and electron transfer processes; (ii) BCM-Q forms excited triplet states (3[BCM-Q]*) under light irradiation and induces the formation 1O2; (iii) UV promotes the formation of BCM-PFRs, which transfer electrons to oxygen to form superoxide anion radical (O2 −), further yielding H2O2; and (iv) H2O2-dependent pathways including BCM-PFRs activation and photo-Fenton reaction are primarily responsible for OH production. Furthermore, BCM exhibits the excellent reusability towards DEP degradation during the three cycles under light.
TL;DR: In this paper, flexible BiOCl nanosheets with oxygen vacancies (BOC-OV) were successfully prepared and the enhanced exciton dissociation resulted in the superior CO2 conversion under UV-Vis light irradiation, where the light to carbon monoxide conversion efficiency reached up to 26.5 × 10−6.
Abstract: Layered bismuth oxychloride (BOC) exhibits highly efficient activity for photocatalytic environmental remediation due to the confinement effect induced excitonic photocatalytic process. However, the strong excitonic process suppresses catalytic reactions with photo-induced electrons, such as hydrogen generation, CO2 conversion and nitrogen fixation. Moreover, the wide band gap of BiOCl limits its application under visible light. In this study, flexible BiOCl nanosheets with oxygen vacancies (BOC-OV) were successfully prepared. Molecular oxygen activation, electronic spin resonance (ESR), transient photocurrent, transient absorption spectroscopy, and transient fluorescence spectroscopy indicated that oxygen vacancies induced exciton dissociation of flexible BiOCl nanosheets. Moreover, oxygen vacancies induced wide spectrum (UV-Vis) absorption. The enhanced exciton dissociation resulted in the superior CO2 conversion of BOC-OV under UV-Vis light irradiation, where the light to carbon monoxide (LTCO) conversion efficiency reached up to 26.5 × 10−6. Theoretical calculations and in situ Fourier transform infrared spectrometry (FT-IR) analysis revealed that the mechanism of oxygen vacancies improves the photocatalytic CO2 conversion with BOC-OV via the CO2 hydrogenation pathway. This study indicates that oxygen vacancies have a great influence on photocatalytic CO2 reduction due to their special surface and electron structure properties.
TL;DR: In this article, the authors show that singlet oxygen forms at the cathode of a lithium-oxygen cell during discharge and from the onset of charge, and accounts for the majority of parasitic reaction products.
Abstract: Non-aqueous metal–oxygen batteries depend critically on the reversible formation/decomposition of metal oxides on cycling. Irreversible parasitic reactions cause poor rechargeability, efficiency, and cycle life, and have predominantly been ascribed to the reactivity of reduced oxygen species with cell components. These species, however, cannot fully explain the side reactions. Here we show that singlet oxygen forms at the cathode of a lithium–oxygen cell during discharge and from the onset of charge, and accounts for the majority of parasitic reaction products. The amount increases during discharge, early stages of charge, and charging at higher voltages, and is enhanced by the presence of trace water. Superoxide and peroxide appear to be involved in singlet oxygen generation. Singlet oxygen traps and quenchers can reduce parasitic reactions effectively. Awareness of the highly reactive singlet oxygen in non-aqueous metal–oxygen batteries gives a rationale for future research towards achieving highly reversible cell operation. The application of Li–O2 batteries is hindered by severe parasitic reactions in battery cycling. Here the authors show that the highly reactive singlet oxygen is the main cause for the electrolyte and carbon electrode degradation on discharge and charge.
TL;DR: In this article, a Ni/CeO2 solid is exposed to CH4 and CO2 in a cyclic way to restore the oxygen capacity of the support and remove residual carbon formed at the surface.
Abstract: Chemical looping dry reforming of methane (CLDRM) is performed by exposing a Ni/CeO2 solid to CH4 and CO2 in a cyclic way. The solid acts as an oxygen vector producing syngas (CO + H2) during exposure to CH4, and is re-oxidized during exposure to CO2. Absence of CO2 during syngas production allows suppressing reverse water gas shift reaction and reaching high selectivity. Exposure to CO2 restores the oxygen capacity of the support and removes residual carbon formed at the surface, thus fully regenerating the catalyst. Solids were characterized by TPR, XRD, Raman scattering, and XPS. Results show that part of the Ni is reduced and remain in metallic state during the looping process. On the other hand, Ni2+ species in strong interaction with Ce cations are observed even after exposure to methane. Both Ni species play important roles on reactants activation and oxygen supply by the solid. Ni loading is a crucial parameter for controlling the reduction behavior of the support and therefore for CLDRM process optimization.
TL;DR: In this article, the authors evaluated the possibility of applying advanced photo-oxidation technique (Fenton oxidation process) for removal of the residuals organic pollutants present in cosmetic wastewater.
TL;DR: Mechanistic insights are provided into the mechanisms involved in cell death after treatment with PAM using methionine, tyrosine, tryptophan and arginine as an example.
Abstract: In order to identify aqueous species formed in Plasma activated media (PAM), quantitative investigations of reactive oxygen and nitrogen species (ROS, RNS) were performed and compared to Milli-Q water and culture media without and with Fetal Calf Serum. Electron paramagnetic resonance, fluorometric and colorimetric analysis were used to identify and quantify free radicals generated by helium plasma jet in these liquids. Results clearly show the formation of ROS such as hydroxyl radical, superoxide anion radical and singlet oxygen in order of the micromolar range of concentrations. Nitric oxide, hydrogen peroxide and nitrite-nitrate anions (in range of several hundred micromolars) are the major species observed in PAM. The composition of the medium has a major impact on the pH of the solution during plasma treatment, on the stability of the different RONS that are produced and on their reactivity with biomolecules. To emphasize the interactions of plasma with a complex medium, amino acid degradation by means of mass spectrometry was also investigated using methionine, tyrosine, tryptophan and arginine. All of these components such as long lifetime RONS and oxidized biological compounds may contribute to the cytotoxic effect of PAM. This study provides mechanistic insights into the mechanisms involved in cell death after treatment with PAM.
TL;DR: In this paper, the authors synthesize α-, β-, and γ-MnO2 catalysts with different tunnel structures for the catalytic oxidation of nitric oxide (NO).
TL;DR: In this article, a nanostructured films of cobalt oxide (Co3O4) on fluorine-doped tin oxide (FTO) substrates, made by first depositing Co onto FTO and heating in air at 400 °C, function as active electrocatalysts for the oxygen evolution reaction (OER) in 0.5 M H2SO4.
Abstract: Earth-abundant materials capable of catalyzing the electrochemical decomposition of water into molecular hydrogen and oxygen are necessary components of many affordable water-splitting technologies. However, water oxidation catalysts that facilitate sustained oxygen evolution at device-relevant current densities in strongly acidic electrolytes have been limited almost exclusively to precious metal oxides. Here, we show that nanostructured films of cobalt oxide (Co3O4) on fluorine-doped tin oxide (FTO) substrates, made by first depositing Co onto FTO and heating in air at 400 °C to produce films having a robust electrical and mechanical Co3O4/FTO interface, function as active electrocatalysts for the oxygen evolution reaction (OER) in 0.5 M H2SO4. The Co3O4/FTO electrodes evolve oxygen with near-quantitative Faradaic yields and maintain a current density of 10 mA/cm2 for over 12 h at a moderate overpotential of 570 mV. At lower current densities that require lower overpotentials, sustained oxygen productio...
TL;DR: The reaction rate constant, krxn,FFA, had a relatively small temperature dependence, no pH dependence and showed a small increase in the presence of high salt concentrations (+19% with 1 M NaCl) and is likely overestimated.
Abstract: The rate constant for the reaction between furfuryl alcohol (FFA) and singlet oxygen (1O2) in aqueous solution was measured as a function of temperature, pH and salt content employing both steady-state photolysis (β value determination) and time-resolved singlet oxygen phosphorescence methods. The latter provided more precise and reproducible data. The reaction rate constant, krxn,FFA, had a relatively small temperature dependence, no pH dependence and showed a small increase in the presence of high salt concentrations (+19% with 1 M NaCl). A critical review of the available literature suggested that the widely used value of 1.2 × 108 M−1 s−1 is likely overestimated. Therefore, we recommend the use of 1.00 × 108 M−1 s−1 for reactions performed in low ionic strength aqueous solutions (freshwater) at 22 °C. Furthermore, corrections are provided that should be applied when working at higher or lower temperatures, and/or at high salt concentrations (seawater).
TL;DR: In this paper, a dual-purpose strategy for enhanced molecular oxygen activation is established by in situ carbon homogeneous doping on ultrathin Bi2MoO6 nanosheets for the first time.
Abstract: Solar-driven activation of molecular oxygen, which harnesses light to produce reactive oxygen species for the removal of pollutants, is the most green and low-cost approach for environmental remediation. The energy coupling between photons, excitons, and oxygen is the crucial step in this reaction and still remains a challenge. In this study, a dual-purpose strategy for enhanced molecular oxygen activation is established by in situ carbon homogeneous doping on ultrathin Bi2MoO6 nanosheets for the first time. The C-doped ultrathin 2D material exhibits an enlarged bandgap straddling the electrochemical potential of O2 /•O2− and H2O /•OH, without any attenuation of light absorption. An internal electric field and shortened carrier-transportation distance are also found in the longitude orientation of the nanosheets ([001] axis), leading to a higher density of effective photogenerated carriers localized on the exposed {001} surface. As applied for the nitric oxide removal, the reactive rate over the ultrathin C-doped Bi2MoO6 nanosheets is 4.3 times higher than that over the bulk counterparts as a result of the increasing reactive oxygen species. This new proof-of-concept strategy not only realizes the band structure engineering and charge transportation regulation but also paves a new way to construct highly efficient photocatalytic materials.
TL;DR: A ROS-producing hybrid nanoparticle-based photosensitizer capable of maintaining high levels of ROS under both normoxic and hypoxic conditions is developed.
Abstract: Photodynamic therapy (PDT) is widely used to treat diverse diseases, but its dependence on oxygen to produce cytotoxic reactive oxygen species (ROS) diminishes the therapeutic effect in a hypoxic environment such as solid tumors. Here, we developed a ROS-producing hybrid nanoparticle-based photosensitizer capable of maintaining high levels of ROS under both normoxic and hypoxic conditions. Conjugation of an organometallic ruthenium complex (N3) to a TiO2 nanoparticle afforded TiO2-N3. Upon exposure of TiO2-N3 to light, the N3 injected electrons into TiO2 to produce three- and four-fold greater hydroxyl radicals and hydrogen peroxide, respectively, than TiO2 at 160 mmHg. TiO2-N3 maintained three-fold higher hydroxyl radicals than TiO2 under hypoxic conditions via N3-facilitated electron hole reduction of adsorbed water molecules. The incorporation of N3 transformed TiO2 from a dual type I and II PDT agent to a predominantly type I photosensitizer, irrespective of the oxygen content.
TL;DR: A novel room-temperature-phosphorescence (RTP)-based oxygen detection platform by constructing core-shell nanoparticles with water-soluble polymethyloxazoline shells and oxygen-permeable polystyrene cores crosslinked with metal-free purely organic phosphors, which shows a very high sensitivity for DO.
Abstract: Highly sensitive optical detection of oxygen including dissolved oxygen (DO) is of great interest in various applications. We devised a novel room temperature phosphorescence (RTP) based oxygen detection platform by constructing core-shell nanoparticles with water-soluble polymethyloxazoline shells and oxygen-permeable polystyrene core crosslinked with metal-free purely organic phosphors. The resulting nanoparticles show a very high sensitivity (limit of detection (LOD) of 60nM DO) and can be readily used for oxygen quantification in aqueous environments as well as gaseous phase.