Oxygen-saturated Solution Research Articles

Reassessing the Photochemical Upcycling of Polystyrene Using Acridinium Salts.

Approaches aimed at deconstructing PS by photocatalytic means struggle to generate high-energy species capable of cleaving the C-H and C-C bonds of PS. We show herein that 9-mesityl-10-methylacridinium perchlorate (MA) is capable of upcycling various grades of PS susbstrates into benzoic acid (BAc) up to 40%, with small proportions of acetophenone and formic acid, under visible light (456 nm) or through solar radiation. Time-resolved emission and absorption spectroscopy evidence that a reaction with oxygen is the primary photochemical step in oxygen-saturated solutions, accounting for 77% of the photons absorbed vs. 1% for the direct reaction with PS. These results suggest a mechanism in which MA-mediated photocycling of PS to BAc occurs through the abstraction of benzylic H atoms by reactive oxygen species generated by energy or electron transfer from the excited state of MA. Addition of triplet O2 to these radicals, followed by intra- or inter-molecular hydrogen atom transfer (HAT), generates C- or O-centered radicals then undergoing β-scission or hydroperoxide fragmentation. The formation of intermediate oligomers functionalized by terminal carbonyl groups is demonstrated by both infrared analysis and mass spectrometry. These oligomers undergo further photoinduced conversion in the absence of MA, as evidenced by size exclusion chromatography analysis.

Nitrogen-functionalized catalyst synthesized using spent coffee ground biochar-cobalt hybrid for oxygen reduction reaction via pyrolysis and ball-milling

In this work, oxygen reduction reaction (ORR) catalysts were developed from a precursor of spent coffee ground-based biochar. Nitrogen doping was achieved via urea addition preceding a pyrolysis synthesis process, yielding nitrogen-doped biochar (NDB). Cobalt was deposited onto the NDB surface using a non-conventional ball-milling procedure. The microstructure of the synthesized samples was studied through Scanning Electron Microscopy (SEM), where a rather distorted surface, highlighted by prominent wrinkles (which doubled the surface area at 50.58 m2/g), was shown for nitrogen-doped samples. Moreover, the high energy ball-milling technique shows an almost perfect coverage of cobalt nanoparticles on the biochar surface through SEM/EDS and Raman results. Additionally, electrochemical testing was conducted using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry measurements conducted under nitrogen (inert) and oxygen-saturated alkaline solution (0.1 M KOH) conditions showed that nitrogen doping enhances the oxygen reduction reaction current (-1 vs -0.59 mA.cm−1 at -0.3 V vs Hg/HgO) and slightly reduces the onset potential compared to pristine biochar. Depositing cobalt onto the NDB surface had a minor adverse effect on the onset potential, but significantly increased the oxygen reduction reaction current, reaching a value of -2.09 mA.cm−2 at -0.3 V vs Hg/HgO. All catalysts were compared to a commercial carbon supported platinum catalyst (Pt10%C) to showcase the potential room of improvement for the developed catalysts.

Near-unity NIR phosphorescent quantum yield from a room-temperature solvated metal nanocluster.

Metal nanoclusters have emerged as promising near-infrared (NIR)-emissive materials, but their room-temperature photoluminescence quantum yield (PLQY), especially in solution, is often low (<10%). We studied the photophysics of Au22(tBuPhC≡C)18 (Au22) and its alloy counterpart Au16Cu6(tBuPhC≡C)18 (Au16Cu6) (where tBu is tert-butyl and Ph is phenyl) and found that copper (Cu) doping suppressed the nonradiative decay (~60-fold less) and promoted intersystem crossing rate (~300-fold higher). The Au16Cu6 nanocluster exhibited >99% PLQY in deaerated solution at room temperature with an emission maximum at 720 nanometers tailing to 950 nanometers and 61% PLQY in the oxygen-saturated solution. The approach to achieve near-unity PLQY could enable the development of highly emissive metal cluster materials.

Comparative Studies of g-C3N4 and C3N3S3 Organic Semiconductors-Synthesis, Properties, and Application in the Catalytic Oxygen Reduction.

Exfoliated g-C3N4 is a well-known semiconductor utilized in heterogenous photocatalysis and water splitting. An improvement in light harvesting and separation of photogenerated charge carriers may be obtained by polymer doping with sulfur. In this work, we incorporate sulfur into the polymer chain by chemical polymerization of trithiocyanuric acid (C3N3S3H3) to obtain C3N3S3. The XRD measurements and TEM images indicated that C3N3S3, in contrast to g-C3N4, does not exist in the form of a graphitic structure and is not exfoliated into thin lamellas. However, both polymers have similar optical properties and positions of the conduction and valence bands. The comparative studies of electrochemical oxygen reduction and hydrogen evolution indicated that the overpotentials for the two processes were smaller for C3N3S3 than for g-C3N4. The RDE experiments in the oxygen-saturated solutions of 0.1 M NaOH have shown that O2 is electrochemically reduced via the serial pathway with two electrons involved in the first step. The spectroscopic experiments using NBT demonstrated that both polymers reveal high activity in the photocatalytic reduction of oxygen to superoxide anion radical by the photogenerated electrons.

MoSe2 and NiCo2O4/NiO Based HybridNanostructure as Novel Electrocatalyst for High Performance Rechargeable Zinc-Air Battery

Efficient air electrocatalysts are needed to develop eco-friendly rechargeable Zinc-air (Zn-air) batteries for renewable energy storage. Here, we investigate the electrocatalytic activity of hydrothermally synthesized MoSe2, NiCo2O4/NiO and NiCo2O4/NiO-MoSe2 hybrid nanostructure by performing oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) studies. The NiCo2O4/NiO-MoSe2 hybrid nanostructure (Tafel slope∼ 54 mV decade−1) shows best electrocatalytic activity and stability for OER study among synthesized electrocatalysts. Further, the oxygen reduction behaviors of prepared catalysts have been observed in oxygen saturated electrolyte solution. The excellent electrocatalytic activity of hybrid nanostructure can be associated with its high electrochemical active surface area, number of active sites and possibly due to the presence of selenium vacancies and edges in MoSe2. Furthermore, we demonstrate Zn-air batteries with these electrocatalysts as air cathode, showing open circuit potential of 1.42 V, the specific capacity of 1023 mA h gZn−1 and energy density of 1195 W h kgZn−1, with high durability for hybrid nanostructure-based Zn-air battery. To the best of our knowledge, this is the first study demonstrating pristine MoSe2 and NiCo2O4/NiO-MoSe2 hybrid nanostructure-based cathodes for Zn-air batteries with excellent specific capacity and energy density.

QUALITY MANAGEMENT OF ZARRINEH RUD RIVER FOR AGRICULTURAL IRRIGATION USING QUAL2K SIMULATION MODEL

Zarrineh Rud river is one of the most important rivers in northwest of Iran. In this study, QUAL2K simulation model was used. The simulation parameters in this study were collected from 5 sampling stations. The results showed that the amount of oxygen saturated solution of Zarrineh Rud river varied between 7–8 mg / l, which is higher than the maximum standard value required. The results showed that BOD could increase by 16%, respectively, and should decrease by 70%. The station S5 at the river downstream with 3.53 mg/L DO deficit was the most critical point, and the 26th kilometer of the river with a DO deficit of 2.05 mg/L was the most critical point for maintaining the aquatic life; therefore, some scenario must be developed for waste load reduction at this station. In order to improve the quality of Zarrineh Rud river, construction of a wastewater treatment plant is necessary for Miandoab sugar factory.

Structural and Functional Characterization of Electron Transfer Complex between Cytochrome C and Cytochrome C Oxidase

The electron transfer (ET) system in the respiratory chain is terminated by the four-electron reduction of molecular oxygen in cytochrome c oxidase, concomitant with the proton pumping from the matrix to the intermembrane space in mitochondria. The last ET reaction in the respiratory chain is mediated by a small ET protein, cytochrome c (Cyt c), and the interprotein ET reaction from Cyt c to CcO plays crucial roles in the four-electron reduction of molecular oxygen and proton pumping essential for the ATP generation in mitochondria. Although the well-defined structures of Cyt c and CcO have been already reported and the structure of the ET complex between Cyt c and CcO is indispensable to examine the regulation mechanism for the ET reaction from Cyt c to CcO, the huge molecular weight of CcO as a membrane-bound protein and large dissociation constant of CcO to Cyt c have been prevented us from the detailed analysis of the ET reaction based on molecular spectroscopies and X-ray crystallography. However, we successfully determined the structure of the ET complex between Cyt c and CcO under steady-state turnover conditions by utilizing protein-protein docking simulation combined with the experimentally determined interaction site for CcO in Cyt c and the Michaelis constants for the ET reaction from various kinds of the Cyt c mutants to CcO. The complex structure determined by the simulation revealed that the ET distance between the redox centers of two proteins, heme iron of Cyt c (Fe c ) and cupper of the CuA site of CcO (CuA), is nearly 23 Å, which is much longer than that previously suggested. To experimentally confirm the ET distance between two redox centers, the ET rate from Cyt c to CcO in the Cyt c – CcO complex was determined by temperature-dependent flow-flash measurements. In the flow-flash measurements, the solution containing carbon monoxide bound CcO was rapidly mixed with the oxygen-saturated solution, and, after the mixing, the four-electron reduction reaction of molecular oxygen in CcO was initiated by irradiating flash light to the reaction mixture to dissociate carbon monoxide from heme a 3 of CcO and to bind molecular oxygen to the heme a 3 site. Associated with the reduction of molecular oxygen, the successive ET reactions from Cyt c to CcO are induced. The ET rate from Fe c of Cyt c to CuA of CcO can be determined by the oxidation rate of Fe c of Cyt c. Based on the Marcus equation for the ET reaction, the ET distance estimated from the oxidation rate of Cyt c was less than 19 Å, which is substantially shorter than the Fe c –CuA distance in the simulated Cyt c–CcO complex. This finding allows us to speculate that the “ET-active complex” showing the ET rate as detected in the flow-flush experiments would have a different binding orientation of Cyt c on CcO from that in the complex, “energetically stable complex”, determined by the previous docking simulation. To structurally characterize the “ET-active complex”, a protein-protein docking simulation under the structural restraint of the short Fe c –CuA distance was applied, and we found a stable complex structure showing that the Fe c –CuA distance is ~ 18 Å, corresponding to the experimentally determined ET distance (< 18.6 Å). The orientation of Cyt c on CcO in the newly determined Cyt c – CcO complex was significantly different from that in the “energetically stable complex”, suggesting the “conformational gating” where the thermal motions of the protein induce the conformational changes of the protein from the most energetically stable structure to the less stable but more active structure of the proteins. In the ET reaction from Cyt c to CcO, the “ET-active complex showing fast ET rate and the short ET distance between two redox centers would not be the most energetically stable structure in the Cyt c – CcO complexes and the structural fluctuation induced by the thermal motion would be a trigger to the conformational changes from the “energetically stable complex” to the “ET-active complex”. The much slower oxidation rate of Cyt c by CcO observed for the steady-state kinetics measurements also supports the “conformational gating” mechanism in the ET reaction from Cyt c to CcO, where the rate for the conformational changes from the “energetically stable complex” to the “ET-active complex” would be the rate-determinant step for the ET reaction from Cyt c to CcO.

Vibegron inhibits enhanced spontaneous contractions induced by anoxia/reoxygenation in isolated whole bladder from rats

It has been recently proposed that repeated bladder ischemia/reperfusion induced by chronic pelvic ischemia may lead to detrusor overactivity, followed by lower urinary tract symptoms. Vibegron is a selective β3-adrenoceptor agonist approved for the treatment of overactive bladder. Several studies have tested β3-adrenoceptor agonists using animal models with detrusor overactivity related to bladder ischemia/reperfusion. However, whether β3-adrenoceptor agonists directly affect ischemia/reperfusion-evoked detrusor overactivity is unclear. Therefore, we examined whether bladder anoxia/reoxygenation could enhance spontaneous bladder contractions (SBCs) and investigated the effect of vibegron on enhanced SBCs. Isolated whole bladders from rats were incubated with Krebs solution aerated with 95% N2 + 5% CO2 for 5 h (anoxia). Subsequently, the bathing solution was replaced with an oxygen-saturated solution (reoxygenation). Anoxia/reoxygenation caused enhancement of the amplitude but not the frequency of SBC compared with that before reoxygenation. Vibegron (0.3–30 μM) inhibited this increase in SBC amplitude, but not the frequency, in a dose-dependent manner. The inhibitory effect of vibegron was not affected by pretreatment with the adenylyl cyclase inhibitor SQ22536 (100 μM) or protein kinase A inhibitor KT5720 (1 μM) and was not accompanied by considerable changes in cyclic adenosine monophosphate (cAMP) content in the bladder. In contrast, the large conductance potassium channel inhibitor iberiotoxin (100 nM) suppressed the inhibitory effect of vibegron. These results suggest that bladder ischemia/reperfusion induces SBC enhancement and vibegron directly inhibits detrusor overactivity via the large conductance potassium channel, which involves β3-adrenoceptor, rather than the cAMP signaling pathway.

In-situ characterization of discharge products of lithium-oxygen battery using Flow Electrochemical Atomic Force Microscopy

The increasing interest in lithium-oxygen batteries (LOB), having the highest theoretical energy densities among the advanced lithium batteries, has triggered the search for in-situ characterization techniques, including Electrochemical Atomic Force Microscopy (EC-AFM). In this work we addressed the characterization of the formation and decomposition of lithium peroxide (Li2O2) on a carbon cathode using a modified AFM technique, called Flow Electrochemical Atomic Force Microscopy (FE-AFM), where an oxygen-saturated solution of the non-aqueous lithium electrolyte is circulated through a liquid AFM cell. This novel technique does not require keeping the AFM equipment inside a glove-box, and it allows performing a number of experiments using the same substrate with different electrolytes without disassembling the cell. We study the morphology of Li2O2 on graphite carbon using lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in dimethyl sulphoxide (DMSO) as electrolyte under different operational conditions, in order to compare our results with those reported using other electrolytes and in-situ and ex-situ EC-AFM.

Galvanic effect of pyrite on arsenic release from arsenopyrite dissolution in oxygen-depleted and oxygen-saturated circumneutral solutions

Arsenopyrite (FeAsS), the most common arsenic-bearing mineral, is usually found associated with pyrite (FeS2) in gold mining tailings. This work examined the galvanic effect of FeS2 on As release from FeAsS oxidation in circumneutral media under oxygen-depleted and oxygen-saturated conditions. The oxidation experiments were conducted with a flow-through reactor in the absence of FeS2 particles and in the presence of different contents of this sulfide. The results indicated that the permanent, physical contact between FeAsS and FeS2 particles causes an increase in the accumulated As release, mainly under O2-saturated conditions. At 30% wt. FeS2, the increases relatively to FeS2-free conditions were 82% and 117% in O2-depleted and O2-saturated solutions, respectively. At steady-state, the As release rates increased from (4.9 ± 0.5)× 10−4 µmol m−2 s−1 (0% wt. FeS2) to (1.1–1.9)× 10−3 µmol m−2 s−1 (5–30% wt. FeS2) under O2-saturated conditions. Analysis of FeAsS samples after oxidation revealed oxidized particles partially or entirely covered by precipitates with different sizes, shapes and compositions (e.g., As−S−bearing ferrihydrite, elemental sulfur, and As−O phases). A fine (3–4 nm thick) amorphous layer of S−As−bearing ferric oxy-hydroxide was also identified on oxidized FeAsS, with Fe(III) and As(III) species.

Radiation-induced polymerization of 3-hexylthiophene in oxygen-free and oxygen-saturated dichloromethane solvent

As alternative radiolytic approach, the synthesis of P3HT was made possible thanks to the oxidation of 3HT monomers by chloromethyl and dichloromethyl radicals or by their corresponding peroxyl radicals in situ produced by dichloromethane solvent radiolysis. Under two different experimental conditions, in oxygen-free solution and in oxygen-saturated solution, two different polymers, “P3HTN2” and “P3HTO2” respectively, were successfully synthesized. Both produced materials were discerned by several analytical and spectroscopic techniques. UV–Vis absorption spectroscopy results showed that the radiolytic yield of 3HT oxidation in dichloromethane solvent is higher under O2 atmosphere. Indeed, a dose of 75 kGy was needed to polymerize 10 mM in 3HT under N2 atmosphere, meanwhile a dose of 35 kGy was sufficient to polymerize the same amount of 3HT under O2. The average molecular weight of P3HTO2was found higher than that of P3HTN2 as revealed by SEC chromatography analysis. Also, P3HTO2exhibits better thermal stability than P3HTN2. ATR-FTIR spectroscopy revealed the specific presence into P3HTO2 polymers of some functional groups such as carbonyl, hydroxyl and carboxyl moieties, which clearly explains the difference between the morphological structures of P3HTN2 and P3HTO2 as highlighted by cryo-TEM, SEM and AFM microscopies. Finally, both radio-synthesized P3HTN2 and P3HTO2 polymers were found characterized by remarkably significant conductive, electronic and optical properties.

Light-Driven C-H Oxygenation of Methane with Chlorine Dioxide

Extensive efforts have been devoted towards the development of methods for the direct conversion from methane (CH4), ethane (CH3CH3), or other abundant natural gasses into useful products, such as the corresponding alcohols, aldehydes, ketones, and carboxylic acids, as liquid fuels and precursors of chemical and pharmaceutical products. Selective aerobic oxygenation of CH4 into liquid products without the concomitant formation of CO2 and CO has served as an elusive target reaction. The one-step transformation of CH4 into methanol (CH3OH) is carried out in nature using methane monooxygenases. However, under chemical conditions, the selective oxygenation of CH4 to CH3OH with molecular oxygen (O2) has been unknown because the oxidation of oxygenated products, CH3OH and formic acid (HCOOH) is much easier than that of CH4, leading to over-oxidation products such as CO and CO2.Here we show that chlorine dioxide radical (ClO2 •) acts as an efficient oxidizing agent in the selective oxygenation of methane under photoirradiation. A fluorous solvent, perfluorohexane (PFH, n-CF3(CF2)4CF3) was chosen as an ideal solvent for CH4 oxygenation for the following reasons. First, PFH is more inert than CH4. It is only comprised of strong C–F bonds and does not contain any C–H bonds; therefore, PFH does not react with CH3 • and Cl• intermediates in the oxygenation of CH4. Notably, PFH can dissolve gaseous substrates such as CH4, CH3CH3, and O2 very well. Additionally, oxygenated products such as CH3OH and HCOOH, as well as water, are insoluble in PFH. Thus, if a two-phase PFH/water system was used for the oxygenation of CH4, the reaction would occur in the fluorous phase, and the products would be transferred into the aqueous phase without further oxygenation to CO and CO2. Towards that end, herein, we report the two-phase photooxygenation of CH4 by molecular oxygen (O2) with chlorine dioxide radical (ClO2 •) in PFH/H2O under ambient conditions to produce oxygenated products such as CH3OH and HCOOH.The oxygenation of CH4 (1.0 mM) with ClO2 • (1.0 mM) did not proceed in the dark. In contrast, the photochemical oxygenation of CH4 with O2 occurred to form CH3OH and HCOOH under photoirradiation with a xenon lamp (500 W) in an aqueous solution at 298 K and 1 atm for 2 h. The yields of CH3OH and HCOOH were 5% and 25%, respectively, as determined by 1H NMR and gas chromatography-mass (GC-MS) spectroscopies. The conversion of CH4 was determined to be 30% by 1H NMR. The selectivity of the formation of CH3OH and HCOOH was >99%, based on the consumption of CH4.2 Further improvement of the product yield by employing a two-phase system instead by one-phase aqueous system, a CH4-saturated solution of PFH (1.0 mL) was added to an oxygen-saturated aqueous solution containing ClO2 • (1.0 mM) to prepare a two-phase system; oxygenation of CH4 (1.0 mM) in an aqueous liquid-liquid two-phase solution (1:1 v/v) comprised of PFH and distilled water was carried out under the same conditions. CH4 dissolved in the aqueous and fluorous phases was completely consumed following photoirradiation for 15 min. The product yields of CH3OH and HCOOH were improved to 14% and 85%, respectively, as determined by the 1H NMR analyses of the aqueous phase. The selectivity of the CH3OH and HCOOH formation was >99%, based on the initial concentration of CH4. The formation of further oxygenated products such as CO and CO2, was not observed under the present reaction conditions. The quantum yield of the photo-driven CH4 oxygenation was130%, as determined by actinometric measurements using monochromatized light. When CH4 was replaced with ethane (CH3CH3), light-driven oxygenation also occurred to yield CH3CH2OH (19%) and CH3COOH (78%) under the otherwise same reaction conditions. The photochemical oxygenation of methane is initiated by generation of chlorine radical and singlet oxygen from photoexcited state of ClO2 •, leading to the final products by aerobic radical chain processes. Thus, the present study provides an environmentally benign approach towards the photooxidation of organic compounds. The photochemical oxygenation using ClO2 • reported herein could be generalized to provide novel chemical reactions, which may have significant implications in synthetic, pharmaceutical and polymer chemistry.3 Ohkubo, K.; Hirose, K.; Shibata, T.; Takamori, K.; Fukuzumi, S. Phys. Org. Chem. 2017, 30, e3619.Ohkubo, K.; Hirose, K. Chem. Int. Ed. 2018, 57, 2126-2129.Ohkubo, K.; Asahara, H.; Inoue, T. Chem. Commun. 2019, 55, 4723-4726.

Sonochemiluminescence of lucigenin using amines as coreactant: Reactivity and mechanism studies

Sonochemiluminescence (SCL) from aqueous solution of lucigenin (Luc2+) has been studied using aliphatic amines as coreactant. The SCL intensity are strongly dependent on the dissolved gases such as air, oxygen, nitrogen and argon. The most strong SCL signals are observed from oxygen saturated alkaline solution containing Luc2+ when small amount of trialkylamine, such as tripropylamine (TPrA) was added into the solution. In an ultrasonic field, TPrA can adsorb onto the cavitation bubble/solution interface where TPrA is oxidized by OH to form a radical cation TPrA+ and subsequently produce a highly reducing TPrA species through a deprotonation reaction of the TPrA+. TPrA is suggested to initiate the reduction reactions of Luc2+ and molecule oxygen to produce Luc+ and superoxide radical anion (O2−), respectively. The radical-radical coupling reaction between Luc+ and O2− is expected to initiate the light emission. The production of O2− is examined by spectrofluorometric method using 2-(2-pyridyl)benzothiazoline as a fluorescent probe. The results show that the production of O2− by ultrasound was more efficient in oxygen saturated solution in the presence of coreactants, consistent with the results with SCL measurements.

Promoting Active Electronic States in LaFeO3 Thin-Films Photocathodes via Alkaline-Earth Metal Substitution.

The effects of alkaline-earth metal cation (AMC; Mg2+, Ca2+, Sr2+, and Ba2+) substitution on the photoelectrochemical properties of phase-pure LaFeO3 (LFO) thin-films are elucidated by X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance, and electrochemical impedance spectroscopy (EIS). XRD confirms the formation of single-phase cubic LFO thin films with a rather complex dependence on the nature of the AMC and extent of substitution. Interestingly, subtle trends in lattice constant variations observed in XRD are closely correlated with shifts in the binding energies of Fe 2p3/2 and O 1s orbitals associated with the perovskite lattice. We establish a scaling factor between these two photoemission peaks, unveiling key correlation between Fe oxidation state and Fe-O covalency. Diffuse reflectance shows that optical transitions are little affected by AMC substitution below 10%, which are dominated by a direct bandgap transition close to 2.72 eV. Differential capacitance data obtained from EIS confirm the p-type characteristic of pristine LFO thin-films, revealing the presence of sub-bandgap electronic state (A-states) close to the valence band edge. The density of A-states is decreased upon AMC substitution, while the overall capacitance increases (increase in dopant level) and the apparent flat-band potential shifts toward more positive potentials. This behavior is consistent with the change in the valence band photoemission edge. In addition, capacitance data of cation-substituted films show the emergence of deeper states centered around 0.6 eV above the valence band edge (B-states). Photoelectrochemical responses toward the hydrogen evolution and oxygen reduction reactions in alkaline solutions show a complex dependence on alkaline-earth metal incorporation, reaching incident-photon-to-current conversion efficiency close to 20% in oxygen saturated solutions. We rationalize the photoresponses of the LFO films in terms of the effect sub-bandgap states on majority carrier mobility, charge transfer, and recombination kinetics.

Density, Surface Tension, and Properties of Nickel–Oxygen Melts

The structural and physicochemical properties (density and surface tension parameters) of the nickel melt containing a detrimental impurity (oxygen) in an amount of 0.01, 0.02, and 0.03 wt % of the pure nickel content are studied. The temperature dependences of the density of melts of the Ni–O system are characterized by higher values relative to the pure solvent and compression effect formation. Oxygen in the nickel melts possesses a high surface activity and also affects an increase in the surface tension under the heating conditions. The amount of oxygen adsorbed on the surface depends on the temperature and melting conditions. Under the heating and cooling conditions, the amount of the adsorbed substance at low temperatures is approximately twofold higher than that at high temperatures. In a content range of 0.018 wt % oxygen, the surface tension isotherms contain a minimum, the adsorption isotherms contain a maximum, and the density isotherms exhibit inflection points of the function. The appearance of specific points in the curves of the structure-sensitive properties makes it possible to predict the possibility of a structural transition caused by the decomposition of an oxygen-saturated γ-like liquid solution to a γ solution and microgroups of NiO oxide.

Relationship between polyphenolic content, antioxidant properties and oxygen consumption rate of different tannins in a model wine solution

The polyphenolic content and the antioxidant capacity of seven tannins with different botanical origin were measured with spectrophotometric methods (Folin-Ciocalteu, Total Polyphenols Index, DPPH, FRAP), HPLC (phloroglucinolysis), voltammetric analysis (Linear Sweep Voltammetry, LSV). The oxygen consumption rate (OCR) was measured in an oxygen saturated model wine solution, containing transition metals and metabisulphite, with a noninvasive luminescence-based technology. The results showed a high variability in polyphenolic concentration related to the botanical origin of tannins. The OCR determined over 21 days was described by quadratic equations, with coefficients varying with tannin botanical origin, dose and SO2 concentration. The tannins ranked differently for antioxidant capacity, depending on the kind of test. The oxygen consumption parameters were positively correlated only with the LSV data measured with anodic current between 100 and 1200 mV (LSV1200mV) and with the FRAP index.

Promoting Photodegradation Efficiency via a Heterojunction Photocatalyst Combining with Oxygen Direct and Fast Diffusion from the Gas Phase to Active Catalytic Sites.

The low solubility of oxygen in solution is the main obstacle for the biodegradation of organic pollutants in wastewater. To address this problem, inspired by the degradation mechanism of aerobic bacteria toward organic pollutants, a novel photodegradation system was presented and operated by a heterojunction photocatalyst combining with a hydrophobic triphase interface, allowing oxygen to directly diffuse from the gas phase to active catalytic sites submersed in polluted solutions. Especially, the heterojunction photocatalyst was fabricated by graphitic carbon nitride nanosheets (C3N4 NS) sensitized with 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin (TCPP). The resulting photocatalyst was coated on a certain part of the commercial superhydrophobic carbon paper (CP) and submersed in the polluted wastewater, while the other part of hydrophobic CP (without coating with C3N4-TCPP nanocomposite) was exposed to air to form a gas-liquid-solid tri-phase photodegradation system. With this system, the photodegradation rate was 10-fold higher than that of a conventional liquid/solid diphase system in oxygen-saturated solutions. This was, on one hand, due to the abundant oxygen on the surface of a photocatalyst coming from the fast and direct diffusion from the gas phase through the superhydrophobic nanoporous part of CP. On the other hand, the hybrid C3N4-TCPP nanocomposite enhanced the light absorption efficiency under simulated sunlight irradiation and restrained the recombination of photogenerated electron-hole. Moreover, the triphase photodegradation system was stable in aqueous solutions for a long time and can be reused almost without attenuation for five cycles, which provided a great potential to be utilized for practical wastewater treatment.

Assessing the feasibility of sequential aerobic respiration and heterotrophic denitrification of a high-strength mixture of phenol and its derivatives in the field single-well-drift test

Biological degradation of high strength phenol and its derivatives in groundwater is problematic because these compounds are toxic to human and microbes. To evaluate the feasibility of in situ bioremediation using sequential aerobic respiration and heterotrophic denitrification, a field single-well-drift test (SWDT) was conducted in groundwater contaminated with coal tar distillates. To stimulate indigenous phenol degrading microorganisms, a 1400 L of oxygen-saturated test solution containing bromide (3.96 ± 0.179 mmol-Br/L) and nitrate (5.34 ± 0.187 mmol NO3−-N/L) was injected into an aquifer. After injection of the test solution, significant consumption of dissolved oxygen (DO) was immediately observed; then, degradation of the methyl derivatives o-cresol and m,p-cresol was observed with average zero-order rate coefficients of 0.047 mmol/L/d and 0.23 mmol/L/d, respectively. After 73% of the injected DO was consumed, significant NO3− consumption was observed along with degradation of phenol and the dimethyl derivatives 2,4-xylenol and 3,5-xylenol, which had average zero-order rate coefficients of 0.17 mmol/L/d, 0.060 mmol/L/d, and 0.018 mmol/L/d, respectively. The production of CO2, NO2−, and N2O along with significant consumption of DO and NO3− suggest that phenolic compounds were biologically degraded by sequential aerobic respiration and heterotrophic denitrification. The results of 16s RNA analysis revealed that, after injection of the test solution, a bacterium that shared a 99% 16s rRNA sequence similarity with an uncultured bacterium revealed to be Pseudomonas stutzeri, a facultative heterotrophic denitrifier, was found in the aquifer. Thus, these results suggest that simultaneous injection of DO and NO3− is an appropriate in situ bioremediation strategy for degrading mixtures of high-strength phenolic compounds in an aquifer.

Enhancing the photo-corrosion resistance of ZnO nanowire photocatalysts.

Zinc oxide (ZnO) displays superior properties as a photocatalyst, compared to the more widely used TiO2. However, widespread application of ZnO is hampered by its high photo-corrosion in aqueous environments under UV irradiation. A systematic investigation of the effect of (i) post-production annealing, (ii) dissolved oxygen levels during photocatalysis and (iii) reactor configuration on the stability and photocatalytic activity (PCA) of ZnO nanowires, grown on either flat or circular supports, was conducted. Results show, for the first time, that it is possible to significantly enhance the photo-corrosion resistance of ZnO in water under UV irradiation while also increasing PCA. Oxygen plasma post-annealing of ZnO nanowire films led to a 46% higher photocatalytic degradation of phenol compared to as-produced films. In oxygen-saturated solutions, both thermally and oxygen plasma annealed ZnO revealed similar photo-corrosion resistance. Switching from a batch to a flow-through reactor, tripled phenol photodegradation under the same irradiation conditions from 19 to 57% due to enhanced mass transfer, while significantly increasing the stability and re-usability of the ZnO, with 5 repeat uses over 3 days showing no decrease in PCA. These results pave the way to more widespread use of photo-corrosion resistant ZnO in the degradation of organic pollutants in water.

Investigating retinal toxicity of a lutein-based dye in a model of isolated and perfused bovine retina

Retidyne™ is a new lutein-based dye for internal limiting membrane staining. It uses the intrinsic staining characteristics of lutein which is already known to act as an antioxidant and blue-light filter in the human retina. We investigated retinal tolerance to different staining times measured by the electroretinogram (ERG) of an isolated and perfused retina whole mount. For functionality, testing bovine retinas were prepared and perfused with an oxygen saturated standard solution and the ERG was recorded until stable b-wave amplitudes were reached. Then the perfusion was stopped and Retidyne™ was applied directly onto the retinal surface for exposure times of 60 or 120s. After restarting the perfusion with standard solution, the ERG amplitudes were monitored for 75min. To investigate the effects on photoreceptor function alone, 1mM asparate was added to block b-waves. For an exposure time of 60s amplitudes of a- and b-waves remained stable throughout the experiment. Exposure times of 120s caused an initial drop of amplitudes that reached statistical significance only for a-waves (a, - 21%, p = 0.047; b, - 14%, p = 0.052). This effect was only seen during the first minutes of the washout and the ERG recovered completely. In the model of isolated and perfused bovine retina, Retidyne™ showed a good safety profile for common intraoperatively used staining times. An initial toxic effect regarding the transient drop of amplitudes cannot be ruled out but the effect might also be explained by the partial blockage of the flashlight due to a more intense staining effect at the beginning of the washout.