Absence Of Oxide Research Articles

Advanced oxidation using sulfate radicals for the surface oxidation of Cu2O and the separation of copper via acid leaching

The effect of Na2S2O8 on Cu2O surface oxidation and leaching was investigated, and the presence of Na2S2O8 transforms the surface of Cu2O into more easily leachable CuO, resulting in a 35.50% increase in the extraction rate of Cu than that without Na2S2O8. In the acid leaching system, O atoms combined with H+ to form H2O, which was continuously separated from the surface to form vacancies. Cu(I) on the mineral surface formed Cu(0) and Cu(Ⅱ), of which Cu(Ⅱ) separated from the mineral surface and entered the solution, while Cu(0) was reconstructed on the surface, and a Cu-Cu metal bond with a bond length of 2.40 Å was appeared in the DFT calculation, which caused the content of Cu atom on the surface to be higher than that of O atom. After oxidation, high-spin Cu(Ⅱ) contributed by the 3d orbital appeared on the mineral surface. The Cu(Ⅱ) content of the oxidized Cu2O surface was 19.80% higher than that of the pure Cu2O surface, indicating that the copper on the oxidized Cu2O surface was more easily extracted. Moreover, the adsorption energy of chemical adsorption occurring in the presence of oxidant (−1.91 eV) was more negative than that in the absence of oxidant (−0.21 eV).

The Study of Mineral Composition and Free Iron Oxides in Sand Fraction for Tigris and Euphrates Rivers/Iraq

A study was carried out on the mineral composition and free Iron oxides of the sediments of the Tigris and Euphrates river. Two soils were selected representing the sediments of the Tigris (Al-Numaniyah) and Euphrates river (Al-Shamiya), and physical and chemical analyzes were conducted on them, the sand is separated by means of a sieve whose openings are (53 microns) in the presence and absence of oxides into sand separations (53-2000) micrometers, to prepare them for metallurgical examinations. The minerals of soil samples were examined by powder method using diffracted X-rays, and the results showed the following:The results of the diffracted X-ray examinations, the special results of the separated sand in the sediments of the Tigris river showed the presence of Quartz minerals (50.8 and 40.3%), Albite (13.3 and 10.3%) and Chlorite (3.3 and 8.3%) and Micas (5.4 and 6.4%) and Kaolinite (2.2 and 1.5%) for coarse and fine sand, respectively, and the percentage of free Iron oxides in coarse sand was (3.1%). and fine sand (2.9%), and the results of X-ray examinations of the sand separated in the sediments of the Euphrates river showed the presence of Quartz minerals (51.0 and 54.9%) and Albite (23.3 and 18.0%) and Chlorite (3.3 and 3.5%), and Mica (5.4 and 3.3%) and Kaolinite (2.2 and 1.1%) and the percentage of free Iron oxides separated by coarse and fine sand was (2.4 and 1.8) respectively.

Thiosulfate in the Upper Part of the Black Sea Anoxic Water Column

Thiosulfate is a sulfur compound in an intermediate oxidation state between sulfate and sulfide. It emerges during processes of sulfide oxidation in bacterial and chemical reactions. Thiosulfate plays a prominent role in oxidation of sulfide and its presence may clear the mechanism of redox reactions in the biogeochemical cycles of sulfur and carbon. This work presents the distribution of thiosulfate, determined by derivatization technique with reagent 2,2'-Dithiobis(5-nitropyridine), in the upper part of the Black Sea anoxic water column in 2018–2021. Observations were carried out annually at the station located seaward of Gelendzhik in the area of continental slope. Independently of observation time the concentration of thiosulfate rises depth wards simultaneously with increase of sulfide. The thiosulfate concentration above limit of detection 0.01 µM are found at water depth with density (σθ) of 16.3 kg/m3 and sulfide concentration of 8–11 µM. Thiosulfate reaches its maximum values of 0.30 µM at maximal studied depth of 600 m. We suggest that in the absence of oxidants in the anoxic waters the thiosulfate appearance is attributed to the process of sulfate reduction in reductive part of sulfur cycle. The thiosulfate disappears in the upper part of anoxic water column before the sulfide.

Nitriding model for zirconium based fuel cladding in severe accident codes

A model has been developed to describe the nitriding of partially oxidized zirconium based cladding during an air ingress sequence when the reaction has become starved of oxidant (oxygen and/or steam), and the subsequent re-oxidation of nitride following of restoration of coolant. Key aspects of the model are the estimation of oxygen-stabilised alpha zirconium, α-Zr(O), formed during pre-oxidation and its reaction with the nitrogen. Nitriding of metallic Zr is much slower than α-Zr(O), and plays a comparatively minor role. The model is based on data from separate-effects tests comprised pre-oxidation, nitriding in the absence of oxidant, and re-oxidation in the absence of nitrogen, which were used to derive the kinetic parameters for the main reaction processes. Developmental assessment was performed using the test results, demonstrating favourable agreement for the main reaction signatures. Independent assessment against Integral Test data is underway.

Chemical Composition and Physico-chemical Properties of Traditional Alkaline Salts (Lake Deposits and Plant-based Ash Salts) Sampled in Cameroon and Nigeria

Lake deposits and plant-based ash salts are food additives used in a variety of food preparations throughout the world. They exist in many colours and are found in market stalls in many countries. In the literature, they have been named traditional alkaline salts (TAS). Their colours (as identified by users) are their major quality determinant and are associated with their efficiency when used in food preparations. Up to now, no relationship has been established between their colours and their chemical composition and/or physico-chemical properties. Lake deposits (sampled in Cameroon and Nigeria), "white" plant-based ashes and evaporites of plant-based ash filtrates (sampled in Cameroon) found from the market have a buffer behaviour (pH of 10 and 11) while "green" and "black" plant-based ashes do not (pH = 12 to 14). The buffer behaviour is due to the simultaneous presence of carbonates and bicarbonates, combined with the absence of oxides, the pH of the resulting solutions was increased with increasing carbonates/bicarbonates ratio. The colours of evaporites of plant-based ash filtrates are similar (less than 6% of difference) in their chemical composition (sodium, potassium, carbonates and bicarbonates) and physico-chemical properties while the other TAS are not. "White" lake deposits have higher major ions (sodium, potassium, carbonates and bicarbonates) content than the "black" ones. There is always a toxicity risk (lead and cadmium) associated with the use of plant-based ash salts and sometimes "black" lake deposits while there is not a toxic risk associated with the use of the "white" colour of lake deposits. "Black" lake deposits sampled in Abuja, Nigeria have one and a half times more cadmium and lead than those sampled all over Cameroon when they contain these metals.

G-C3N4 supported Ag/AgCl@MIL-88A MOF based triple composites for highly efficient diuron photodegradation under visible LED light irradiation

In this work, a series of g-C3N4 supported Ag/AgCl doped MIL-88A composites were synthesized and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), and photoluminescence spectroscopy (PL). The photocatalytic performances of as-prepared composites were examined by the photodegradation of diuron (DRN), which is used as an herbicide in agriculture. The composites exhibit exceptional visible-light photocatalytic activities for photodegradation of DRN with complete degradation within 60 min in the absence of oxidants. However, in the presence of H2O2 or persulfate, complete degradation of DRN was achieved in 15 min and 30 min, respectively. The photocatalyst also gave very high conversions in water containing dissolved inorganic salts and natural organic matter (NOM). The Ag/AgCl@MIL-88A/g-C3N4 composite retained excellent photocatalytic properties after repeated use. Radical trapping experiments revealed that the most important reactive species in the photodegradation were O2−• and h+. Role of active radicals were discussed via proposed degradation mechanism for the degradation of DRN in the presence of MIL-88A/g-C3N4 and Ag/AgCl@MIL-88A/g-C3N4.

Electrochemical Analysis of Fe2+ Ions Behavior in the Metal Oxide Dispersions

Abstract This study aims at establishing how metal oxides (TiO2, Fe2O3, SiO2, and Al2O3) influence electrochemical activity of Fe2+ ions in solutions of different pH. Above pH 6.5 almost total uptake of Fe2+ ions from solution was reported for all oxides due to adsorption and oxidation of ferrous ions manifested by the reversal of the redox potential (Eh) trend. TiO2 and Fe2O3 revealed the strongest Fe2+ affinity and Al2O3 the weakest. X-ray photoelectron spectroscopy (XPS) indicated the transformation of precipitated Fe(OH)3 into FeOOH above pH 6.5. Square wave voltammetry (SWV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) have been used in experimental measurements applying the gold electrode. The changes in Ra (activation resistance of the Fe2+ electrooxidation) confirmed the beneficial effect of Fe2O3 and TiO2 on the rate of Fe2+ electrooxidation on the electrode. The linear relationship between the anodic peak current and the square root of the scanning rate proves that in the absence of oxides, the Fe2+ oxidation process is determined by the diffusion of the depolarizer to the electrode surface. In the presence of oxides, the relationships Ip = f ($\sqrt{\text{v}} $) are non-linear, and therefore the electrooxidation of Fe2+ ions is controlled by their adsorption on gold.

Biodegradation of petroleum hydrocarbons in a weathered, unsaturated soil is inhibited by peroxide oxidants

Field-weathered crude oil-containing soils have a residual concentration of hydrocarbons with complex chemical structure, low solubility, and high viscosity, often poorly amenable to microbial degradation. Hydrogen peroxide (H2O2)-based oxidation can generate oxygenated compounds that are smaller and/or more soluble and thus increase petroleum hydrocarbon biodegradability. In this study, we assessed the efficacy of H2O2-based oxidation under unsaturated soil conditions to promote biodegradation in a field-contaminated and weathered soil containing high concentrations of total petroleum hydrocarbons (25200 mg TPH kg−1) and total organic carbon (80900 mg TOC kg−1). Microcosms amended with three doses of 48 g H2O2 kg−1 soil (unactivated or Fe2+-activated) or 24 g sodium percarbonate kg−1 soil and nutrients did not show substantial TPH changes during the experiment. However, 7.6–41.8% of the TOC concentration was removed. Furthermore, production of DOC was enhanced and highest in the microcosms with oxidants, with approximately 20–40-fold DOC increase by the end of incubation. In the absence of oxidants, biostimulation led to > 50% TPH removal in 42 days. Oxidants limited TPH biodegradation by diminishing the viable concentration of microorganisms, altering the composition of the soil microbial communities, and/or creating inhibitory conditions in soil. Study’s findings underscore the importance of soil characteristics and petroleum hydrocarbon properties and inform on potential limitations of combined H2O2 oxidation and biodegradation in weathered soils.

ALOE VERA STABILIZED NANO SILVER-REDUCED GRAPHENE OXIDE NANO COMPOSITES FOR FACILE CATALYTIC DEGRADATION OF PONCEAU 4R AND EOSIN-Y DYES IN VISIBLE LIGHT

In this work nanocomposites comprising of reduced graphene oxide (rGO) and silver nanoparticles (AgNp) were prepared adopting eco friendlier components. Aloe vera plant extract was used as the stabilizing agent in the AgNp synthesis and graphite precursor being used in the rGO preparation. Size characterizations of AgNp-rGO nano composites were carried out from UV- Vis SPR, Powder XRD, HR-TEM and FE-SEM measurements. The catalytic ability of the fabricated green AgNp-rGO nano composites was confirmed by following the oxidative degradations of two popular dyes Ponceau 4R and Eosin-Y in aqueous medium under visible light irradiations at 25ºC. Reaction kinetic parameters such as overall pseudo first order rate coefficients ‘k’, % mineralization of dyes and effect of oxidant sodium peroxomono sulfate (Na2S2O5) were determined for the two dyes separately adopting visible light irradiation and nano composite catalyst inclusions. AgNp-rGO nano composites exhibited remarkable catalytic capacity under visible light irradiations of the dyes both in the presence and absence of oxidant. Among the dyes tested, Ponceau 4R degraded to a higher extent than Eosin-Y. The results point towards low cost advanced oxidation process and AgNp-rGO nano composites an efficient analytical tool for dye degradations.

Pilot-scale study on photodegradation of benzophenone-3 and benzophenone-8 ultraviolet filters enriched synthetic effluent

Ultraviolet (UV) filters are the significant ingredients of sunscreens, cosmetics, and other personal care products. They are used to guard human body against harmful UV radiations present in sunlight. In recent years, due to their excessive use, high UV filters concentrations have been detected in swimming pools. The present study was aimed to photodegrade the two most commonly used UV filters, namely benzophenone-3 (BP-3) and benzophenone-8 (BP-8) using pilot-scale advanced oxidation process (AOP) treatment. The photodegradation of selected UV filters was optimised under various oxidant systems viz. hydrogen peroxide (H2O2), potassium peroxomonosulphate (PMS), and potassium peroxodisulphate (PDS). In the absence of oxidant, the photodegradation rate of BP-3(58.25%) was higher than BP-8 (48.31%). The generation of SO4.- and.OH radicals enhanced the degradation of UV filters. Similar degradation trend (UVC < UVC/PMS < UVC/H2O2 < UVC/PDS) was observed for both BP-3 and BP-8 in presence of oxidants. However, on comparing the efficiency, the photodegradation of BP-3 was better in most of the UVC/oxidant systems. Generation of degradation by-products viz. bezonic acid, 2,4-dimethyl benzaldehyde, 2-methylphenyl benzoate, and benzyl alcohol was confirmed through mass spectroscopic (MS) analysis. Degradation mechanism of UV filters was proposed and overall process cost was estimated. The findings of the current study could be a baseline for treating swimming pools water.

Particularities of High Oxygen Content Biofuels Pyrolysis Process

Generating capacities supplied by solid biomass (renewable waste) gather at the moment less than 4.5% of the total renewable power installed worldwide. Given the two folded implications of such technology development and spreading (i.e. energy production and waste management), researches regarding efficient conversion processes and improved power facilities are of great interest currently. In this context, the paper addresses the particularities of high oxygen content biofuels pyrolysis, proposing innovative solutions to overcome the issues found in experimental investigations. Based on thorough experimental research conducted on agricultural wooden biomass and poultry manure, a number of problems arise. Among them, it is highlighted the heating in the absence of oxidants, an undesirable internal process caused by the high oxygen content, which contravenes the general principles regarding pyrolysis. Furthermore, the high oxygen content is associated with great moisture percentages. The present paper reveals the challenges determined by some negative aspects emerging during the pyrolysis of high oxygen content biofuels. Several solutions are proposed to improve the efficiency of the conversion process through adequate control. For instance, it is pointed out that the temperature level at which the pyrolysis process develops plays a crucial role in the general energy balance. On this matter, investigating poultry manure pyrolysis at low temperatures, a significant decrease of the final coke product is noticed. Poultry manure pyrolysis results as a suitable and simple solution to be employed for waste treatment purposes, as its combustible effects (combustible gases and semicoke / coke) are good candidates for energy production.

Radical Promoted Synthesis of Furoquinolines via Anomalous Dakin‐Type Reaction

AbstractA radical promoted approach for the selective synthesis of furo[3,2‐b]quinolines and benzylidene‐1,3‐dihydrofuro[3,4‐b]quinolines have been achieved from 2‐alkynyl quinoline‐3‐carbaldehydes by fine‐tuning of base and oxidant in good yields. In the presence of an oxidant, the reaction afforded the 5‐endo‐dig cyclized furoquinolines by decarbonylative intramolecular cyclization via a Dakin‐type reaction; however, in the absence of oxidant, 5‐exo‐dig cyclized products were obtained selectively through reductive intramolecular cyclization. The formation of furoquinolines was further supported by X‐ray crystallographic studies. The proposed mechanism was well supported by the control experiments.magnified image

Characterization and measurement of gamma radiation shielding of a new tungsten-lignin composite

This research has been carried on to analyze the capability of a new composite to be effectively used as shielding of gamma radiation. The preparation of a metal-organic composite formed by tungsten and Kraft lignin is presented. Samples have been characterized through X-rays and scanning electron microscopy measurements. The results led to the study of the different phase formations. The microscopic analyzes indicate that two different phases are present in the composite. The absence of oxidation in the process even after the temperature treatment imposed to form the sample has also been noticed. Measurements of the attenuation have been performed to study its ability to absorb gamma radiation. A sample of cobalt 60 (Co-60), for which the peak energies are at 1173 keV and 1332 keV, was used as a source of gamma radiation in the experiment of attenuation. The measured attenuation of gamma radiations when the composite is placed to act as a shield is only 16% smaller than the attenuation obtained for standard pure tungsten. This is a clear indication that the new metal-organic composite is suitable for the fabrication of devices dedicated to shielding radiation, with the advantage of being easier to manipulate.

A straightforward technique for removing titanium bases from screw-retained monolithic implant-supported prostheses

Monolithic screw-retained computer-aided design and computer-aided manufacturer (CAD-CAM) ceramics are widely used for implant-supported prostheses because of their efficiency in terms of manufacturing time, cost, and predictability.1,2 In this prosthetic design, a complete-contour prosthesis is typically milled in translucent zirconia or lithium disilicate and adhesively cemented under optimal conditions extraorally onto a titanium base, resulting in a screw-retained prosthesis.3,4 This method has the advantage of using prefabricated machined titanium bases that will not be processed in a furnace as in conventional techniques for metal-ceramic restorations, ensuring their structural integrity, absence of oxidation, and optimum fit.

Germanium-on-silicon waveguides for long-wave integrated photonics: ring resonance and thermo-optics.

Germanium-on-silicon (GOS) represents the leading platform for foundry-based long-wave infrared photonic integrated circuits (LWIR PICs), due to its CMOS compatibility and absence of oxides. We describe ring resonance (Q-factors between 2×103 and 1×104) and thermo-optic tunability in germanium-on-silicon waveguides throughout the long-wave-infrared. The ring resonances are characterized by Q-factors and couplings that agree with measurements of propagation loss (as low as 6 dB/cm) and simulations and are enabled by broadband edge coupling (12dB/facet over a 3 dB bandwidth of over 4 microns). We demonstrate the furthest into the infrared that ring resonators have been measured and show the potential of this platform for photonic integration and waveguide spectroscopy at wavelengths from 7 microns to beyond 11 microns.

Electrochemical Aziridination of Tetrasubstituted Alkenes with Ammonia

Ammonia (NH3) is an ideal nitrogen source in terms of availability, reactivity, safety, atom economy, environmental compatibility, and ease of isolation. However, its utility for amine synthesis is...

Uranium Extraction from Gattar Granite Sample After Leaching Using Nitrate Solution in Presence of Peroxide

The Gattar area is classified as one of the most important Egyptian uranium resources. In this work, the leaching of uranium from Gattar granitic ore containing 1138 ppm U using NaNO3 solution has been applied. The leaching factors of nitrate in the presence and absence of hydrogen peroxide as oxidant were studied and optimized. The obtained data show that uranium leaching in the absence of oxidants was only 46%. The main role of the peroxide is oxidizing the iron content to Fe3+ species, which is responsible for oxidizing the nonleachable U4+ to leachable U6+. Based on the obtained results with 0.005 M NaNO3 in the presence of 15 mmol l−1 H2O2 with a 4/1 liquid/solid ratio at 75°C for 6 h as optimum leaching conditions, the uranium leaching efficiency was 82.5%. The leach liquor was then subjected to an extraction step using 4% Alamine 336/kerosene. Alamine 336 extracted 92.3% from the leached uranium content. The resultant solvent was then treated with a carbonate solution to strip the loaded uranium. Finally, the carbonate solution was then treated with NaOH to precipitate the uranium species at pH 11.5.

Photocatalytic carbon dioxide reduction coupled with benzylamine oxidation over Zn-Bi2WO6 microflowers

Here, we demonstrate for the first time the formation of Zn-Bi2WO6 microflowers for the simultaneous photocatalytic CO2 reduction and benzylamine oxidation in absence of sacrificial agent or oxidant, and achieve high efficiency of energy utilization.

Wear Behavior of Metals in Dry Sliding against Molybdenum with Current Collection

The possibility of high electrical conductivity of dry sliding electrical contact against a molybdenum counterface was studied. It was found that metals W and Cu were not able to form a sliding electrical contact with high wear resistance at current density higher 100 A/cm2. The characteristics of the contacts of iron containing metals were slightly better than the contact characteristics of nonferrous metals owing to weaker adhesion. Using X-ray phase analysis, the absence of oxides in the sliding zone of nonferrous metals was shown. This led to their strong wear and low electrical conductivity of contact. In the contact zone of iron-containing samples, the formation of FeO was observed, which made it possible to reduce wear. This means that high electrical conductivity is unattainable in sliding with current collection against molybdenum.

A simple isolation of 211At using an anion-exchange spin column method

This study demonstrated the availability of an anion-exchange spin column method for the isolation of astatine-211 (211At) from bismuth (Bi). 211At was isolated in medium-to-excellent recovery efficiencies when loading 211At with 8M HCl (75.3–79.1%), and 8M HNO3 (35.9–54.3%). The processing time of the optimized protocol was about 40 minutes. A neutralized eluent afforded an 211At-labeled phenylalanine derivative even in the absence of oxidant (radiochemical yield: 75.4%). These results indicate the anion-exchange spin column is useful for the isolation of 211At and the following synthesis of astatinated compounds, which is the first to isolate 211At with an anion-exchange method.