Oxidation Of Aqueous Solutions Research Articles

Non-unity stoichiometric reversible electrode reactions. The effect of coupled kinetics and the oxidation of bromide

We explore via simulation, the cyclic voltammetry of the following mechanism involving a reversible electrode process coupled with a follow up reaction in which the product (B) of the electrode reaction reacts chemically with the reactant, A, to form a species C:2A−2e−⇄BB+A⇌kbkfC Such a mechanism is shown, under certain critical combinations of rate constant and reactant concentration to give rise to two voltammetric peaks despite the assumption of a single redox couple (A/B). This results from the formation of C during the first peak whilst the second peak, seen at more oxidizing potentials, reflects the dissociation of C releasing A. A mechanism of the type investigated may hold during the oxidation of bromide(Br−, A) in solution to form bromine(Br2, B) and tribromide (Br3−,C). Simulations are used to explore the conditions for which two peaks are expected in the bromide oxidation system in aqueous solution and for which the two following limiting cases operate3Br−−2e−⇄Br3− and2Br−−2e−⇄Br2 We report experimental data for the bromide oxidation in aqueous solution. These are interpreted via simulations using independent literature values for the rate and equilibrium constants for tribromide formation.

Modification of Surface Properties of Colloidal Suspensions of NixOy-SiO2 Mixed Oxides with Different Ni Contents by the Adsorption Layers of Poly(Vinyl Alcohol)

The adsorption and electrokinetic properties of hybrid silica materials composed of nickel and silicon oxides (NixOy-SiO2), characterized by different contents of nickel oxide (from 0.5 to 3 mmol/g SiO2), were examined. These solids were also modified by poly(vinyl alcohol) to change their surface characteristics. The polymer is non-toxic and very well soluble in water. Due to incomplete hydrolysis of the polymer acetate groups, its macromolecules become negatively charged. The limited range of studied pH (6–10) resulted from high solubility of nickel oxide at more acidic pH values. The spectrophotometric, surface charge and electrophoretic measurements indicated that PVA exhibits higher adsorption affinity for the surfaces of mixed oxide with a larger content of nickel in its structure. Moreover, the presence of polymeric layers on the solid surface influences considerably the structure of electrical double layer formed at the mixed oxide-aqueous solution interface.

Molecular Copper(I)-Copper(II) Photosensitizer-Catalyst Photoelectrode for Water Oxidation.

Copper(II)-based electrocatalysts for water oxidation in aqueous solution have been studied previously, but photodriving these systems still remains a challenge. In this work, a bis(diimine)copper(I)-based donor-chromophore-acceptor system is synthesized and applied as the light-harvesting component of a photoanode. This molecular assembly was integrated onto a zinc oxide nanowire surface, and upon photoexcitation, chronoamperometric studies reveal that the integrated triad can inject electrons directly into the conduction band of zinc oxide, generating oxidizing equivalents that are then transferred to a copper(II) water oxidation catalyst in aqueous solution, yielding O2 from water with a Faradaic efficiency of 76%.

Mechanistic Insight into pH-Dependent Luminol Chemiluminescence in Aqueous Solution.

Luminol is one of the best known chemiluminescent cyclic hydrazides used in basic solution. Owing to the complexity of luminol oxidation, the mechanism of luminol chemiluminescence (CL), especially in aqueous solution, has not yet been fully elucidated. Recent theoretical computations have confirmed that luminol CL originates from the chemiexcitation of a 1,2-dioxane-3,6-dione dianion (CP2-). This seems to be inconsistent with the luminol oxidation in aqueous solutions, where only the decomposition of a monoanionic peroxyketal (L-OOH) is confirmed to yield CL. In this work, we theoretically investigated the complete decomposition of L-OOH and the pKa of key intermediates in aqueous solutions using (time-dependent) density functional theory. L-OOH first cyclizes to an endoperoxide monoanion (EP-). When pH < pKa (EP-), EP- directly decomposes by a retro-Diels-Alder (rDA) reaction to an aminophthalate monoanion (AP-) without CL activity. Moreover, when pH > pKa (EP-), EP- deprotonates to dianionic EP2-, which rapidly eliminates N2 to CP2-, inducing chemiexcitation. This conclusion is supported by the pKa (EP-) ≈ 8 estimated in this work, which is consistent with the pH-dependent profile of luminol CL observed in previous experiments. Thus, the pH-dependent CL determined by the acidity of endoperoxides may provide a theoretical basis to design new cyclic hydrazides with CL activity at different pH.

Significantly high electromagnetic shielding effectiveness in polypyrrole synthesized by eco‐friendly and cost‐effective technique

AbstractA facile and eco‐friendly synthesis of polypyrrole from monomer pyrrole using nominal amount of ferric chloride hexahydrate (FeCl3.6H2O) oxidant in aqueous solution by chemically oxidative polymerization method has been reported. The use of aqueous solvent and ferric chloride hexahydrate salt in polypyrrole synthesis have an eco‐friendly route favorable for the production of polypyrrole in large quantities. The synthesized polypyrrole samples exhibit good electrical conductivity (2 S/cm) and yield of 80% for reaction time of 8 hr at 5°C. Quality and properties of polypyrrole samples have been thoroughly investigated with varying reaction time and temperature while other synthesis parameters like molar ratio of oxidant to monomer, oxidant concentration, and solvent were kept constant. X‐ray diffraction analysis of polypyrrole with a shorter reaction time shows the presence of iron oxide (Fe2O3) peaks. The complete reaction may not occur at shorter reaction times due to which residual ferric ions converted into Fe2O3. X‐ray photoelectron spectroscopy measurement of polypyrrole also confirms the formation of Fe2O3. Appropriate selection of reaction time and temperature produced pure phase polypyrrole with high yield and good conductivity. Synthesized polypyrrole by our eco‐friendly and cost‐effective technique exhibits prominent electromagnetic shielding effectiveness value of 30 dB in the X‐band (8–12 GHz).

Synthesis and stability against oxidation of random brush copolymers carrying PEO side chains and catechol moieties

Synthesis of well-defined random brush copolymers carrying PEO side chains and catechol moieties is reported. Kinetics of RAFT copolymerisation of PEO methacrylate and acetonide-protected dopamine methacrylamide was studied by SEC with quadruple detection including simultaneous recording of RI and UV responses, which enabled to calculate not only conversion of the monomers but also composition of the copolymers at a certain conversion. It was shown that the catechol brush copolymers were statistical without any gradient and characterised by rather low dispersity. The copolymers were characterised by 1H NMR, FT-IR and RAMAN spectroscopy, and stability of the copolymers against oxidation in aqueous solutions was studied by UV–vis spectroscopy. Neutral and alkaline aqueous solutions of the brush copolymers with unprotected catechol moieties were unstable and susceptible to colouring because of oxidation of catechol groups. Brush copolymers with acetonide-protected catechol moieties were stable during storage both in solid-state and in aqueous solutions of various pH. It was shown that protection of catechol groups by acetonide is very efficient and helps to preserve catechol brush polymers from oxidative environment and store them for a long time.

Conformation and Diffusivity of Ring and Linear Polyethylene Oxide in Aqueous Solution: Molecular Topology Dependent Concentration Effects and Comparison with Experimental Data

AbstractAtomistic molecular dynamics simulations are performed on aqueous solutions of ring and linear polyethylene oxide (PEO) under good solvent conditions for the investigation of their conformation and diffusion dynamics. The systems simulated span a wide range of molecular weights (from 2 to 10 k) and polymer concentrations. In the limit of infinite dilution, both conformational and dynamic properties appear to be practically molecular topology independent as far as their dependence on chain length and concentration is concerned, and a very favorable agreement is observed with respect to relevant well‐established theoretical predictions, experimental data, and earlier simulation studies. Crossing over to the semidilute regime, molecular topology starts to bear a distinct effect on the observed conformations of the two different molecular geometries. On the other hand, the diffusion dynamics of PEO in the semidilute regime appears to be practically molecular topology independent judging from the dependence of the chain center‐of‐mass diffusivity on chain length and concentration. Indeed, and despite the fact that ring molecules exhibit consistently a faster dynamics than their linear homologs over the entire concentration range simulated, the estimated concentration scalings for both types of architecture are strikingly similar. The findings of this work are compared with scaling arguments and available experimental data.

Riboflavin-photosensitized thiamine oxidation in aqueous solutions on exposure to ultraviolet and visible light

It was shown the irradiation of aqueous solutions of thiamine and riboflavin with ultraviolet UVA (315–400 nm) and visible light (λ &gt; 400 nm) leads to oxidation of thiamine to thiochrome and oxodihydrothiochrome. In absence of riboflavin in aerobic conditions thiamine oxidation to thiochrome was mainly due to reaction with singlet oxygen. Under anaerobic conditions, thiamine in the presence of riboflavin was photostable and UV and visible light irradiation of their aqueous solutions did not result in thiamine oxidation. Under aerobic conditions, thiochrome was oxidized to form oxodihydrothiohrome in reactions with singlet oxygen and riboflavin in triplet states. Under anaerobic conditions, oxidation of thiochrome to oxodihydrothiochrome occurred due to reaction with riboflavin in triplet state. Possible mechanisms of the damage of cellular eye structures due to inactivation of thiamine-dependent enzymes on exposure to intensive UVA and visible light in the presence of endogenous photosensitizer riboflavin are discussed.

The Role of Sodium-alkali Waste Gas Washing and Desulfurization Technology in the Exhaust Gas Treatment of Marine Diesel Engines

to reduce the concentration of sulfur oxide in the exhaust gas of marine diesel engines, the application of sodium-alkali waste gas washing and desulfurization technology in the exhaust gas treatment of marine diesel engines is explored. First, the reaction mechanism of sodium-alkali wet washing desulfurization technology is introduced, including the absorption process model of sulfur oxide, the absorption rate equation, the equation for absorbing sulfur oxide in aqueous solution, and the process of dissolving and absorbing sulfur oxide in sodium hydroxide solution. Then, a method to improve the absorption rate of sulfur oxides is proposed. Finally, the influence of load and pH of washing solution on desulfurization efficiency is discussed. The results show that the sodium-alkali waste gas washing and desulfurization technology has a good desulfurization efficiency. The desulfurization efficiency under different loads is more than 99%, and the maximum is 99.7%, which meets the desulfurization requirements of the national heavy oil exhaust gas treatment system. The higher the pH of washing solution, the more obvious the desulfurization efficiency. The results of this research provide a theoretical basis for the development of Chinese ships.

Hierarchical CuO microparticles constructed via underwater Leidenfrost process and their Fenton-like catalytic activity

In this report, a rapid and simple bottom-up approach to synthesize flower-like hierarchical CuO microparticles is demonstrated. Fabrication of microparticles with a mean size of 1.5 µm was successfully accomplished via hydrolysis of copper–ammonia complex at underwater dynamic Leidenfrost conditions and their structural, textural and chemical properties were examined. Besides, the Fenton-like catalytic activity of the as-prepared material is revealed by using caffeine micro-pollutant oxidation in aqueous solution. Complete degradation of caffeine with initial concentration of 10 ppm was observed after 170 min reaction time.

Palladium-polypyrrole composites as prospective catalysts for formaldehyde electrooxidation in alkaline solutions

Palladium-polypyrrole (Pd-PPy) composites synthesized via one-step and one-pot redox procedure have been tested as electrocatalysts for formaldehyde oxidation in aqueous solution under both inert and oxygen atmospheres. It has clearly been shown that inert electrode coated by the Pd-PPy composites demonstrates a high catalytic activity. Electrochemical response of Pd-PPy modified electrodes depends on the anodic potential range, pH and concentration of formaldehyde in solution as well as on the presence of oxygen in reaction atmosphere. It has been found that Pd-PPy composites are prospective materials for amperometric detection of formaldehyde in aqueous solution, even under oxygen atmosphere, as well as in the presence of methanol or/and formate-anions.

Extraction of peroxidase enzyme from different vegetables for biodetoxification of vat dyes

Vat dyes are main sources for polluting the wastewater of textile and other industrial effluents. For removal of these dyes specific strategies and techniques are important. An enzyme known as peroxides has the capacity to absorb these dyes from an aqueous solution and also to decolorize the textile effluents. The current study aimed, biodetoxification and decolorization of vat dyes, in which three vat dyes, vat dye green 9, vat dye yellow 2, vat dye black 27, were investigated using peroxides enzymes from different vegetables sources at different condition. Decolorization efficiency of dyes was studied with the addition of ammonium sulphate and hydrogen per oxide in aqueous solution. The decolorization effect of peroxides was observed at different stages at different conditions, like at the beginning, before the incubation and after the incubation in hot water bath and observed on different wavelength using UV-VIS6000 spectrophotometer. Best decolorization efficiency was observed by Vat dye Black 27, i.e., 0.750 nm at 600 nm wavelength then Vat dye Green 9 showed least efficiency which has been increased by 50% and the most decrease in decolorization observed in vat dye green 9 after incubation 0.031 nm at 480 wave length. Current study suggests that the peroxides from the vegetables sources have the ability of decolorization and biodetoxification of vat dyes from textile dye effluent and other industrial wastewater and therefore, this enzymatic approach can be used for the removal and biodetoxification of vat dyes from the wastewater as this method is environmental friendly and can be performed on low cost and in short time.

UV-assisted chemical oxidation of antihypertensive losartan in water

Population growth and deteriorating health issues have led to an increase in the consumption of angiotensin receptor blockers (ARBs), such as losartan (LOR), for treating high blood pressure and, as a result, to the frequent detection of these drugs in water and wastewater. The present study focuses on the oxidation of LOR by UV photolysis, UV(/Fe2+)-activated persulfate (PS) and hydrogen peroxide (H2O2) systems. The effects of operating parameters including pH value, reaction time, concentration of oxidant and activator on the efficacy of treatment were studied. The target compound degradation by direct UV photolysis, UV/PS and UV/H2O2 systems proved to be efficient and followed a pseudo-first-order kinetic model. The application of UV/oxidant systems even at lower PS or H2O2 concentrations resulted in more than 95% of LOR degradation in 10 min. In addition, the use of UV/Fe2+-activated oxidant systems led to a further increase in the kobs by improving the LOR oxidation in aqueous solution. The effectiveness of LOR mineralization based on total organic carbon (TOC) removal was also considered. The optimized results of the studied systems obtained in ultrapure water were used in groundwater to assess the effectiveness of LOR decomposition in more complex environmental matrix. Moreover, the acute toxicity of LOR solutions before and after the UV/Fe2+-activated PS and H2O2 oxidation to luminous bacteria (Vibrio fischeri) was investigated.

Multifunctional Chitosan–rGO Network Binder for Enhancing the Cycle Stability of Li–S Batteries

AbstractAlthough Li–S batteries are currently receiving great interest, due to their high energy density and the low cost of sulfur, practical applications are still inhibited by capacity fading that is caused by various undesirable processes. In this study, a new multifunctional network binder composed of chitosan and reduced graphene oxide (rGO) is introduced to enhance the capacitive performance of Li–S batteries. Chitosan is reacted with graphene oxide in aqueous solution to produce a homogenous network, which effectively enhances the redox system by entrapping lithium polysulfides, reinforces the mechanical properties, and allows electrical conductivity through the binder system. Collaborative relationship‐based chitosan–rGO network binder allows noteworthy improvement in the capacity decay of 0.016% per cycle at 1 C for 1000 cycles.

Revisiting the synthesis of poly(2-aminothiazole) for removal of Hg(II) in aqueous solution

The synthesis of poly(2-aminothiazole)(PAT) for selective removal of Hg(II) in aqueous solutions has been previously described [Ind. Eng. Chem. Res. 2016, 55, 4911–4918]. In the present work, the synthesis of PAT by chemical oxidation method using copper chloride as the oxidant in aqueous solution was revisited. The effects of the oxidant/monomer molar ratio and polymerization temperature on the polymerization yield and adsorption capacity were investigated. The PATs were characterized by FT-IR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Adsorption experiments for selected samples were carried out to investigate the adsorption properties for Hg(II). The effects of pH, contact time and initial Hg(II) concentration on the adsorption of Hg(II) were studied. The adsorption of PAT exhibited a Langmuir-type isotherm and the adsorption kinetics experiments revealed that the adsorption reached equilibrium within 7 h. Significantly improved Hg(II) adsorption capacity can be achieved with this new PAT preparative protocol.

Binding modes of Fe(III) with graphene oxide in aqueous solutions. Competition with Sr2+, Cs+, Na+ ions and Fe(III) chelators

The work is devoted to the analysis of the state of the Fe(III) ions in aqueous solutions of graphene oxide (GO) using NMR-relaxation method. The presence of graphene oxide in solution suppresses the hydrolysis of Fe(III) in a wide pH range, and provides high values of the spin-spin relaxivity of the Fe(III)-GO system. Experiments with varying concentrations of Fe (III) and GO demonstrate the presence of the two types of the sites on GO surface: the A-type sides that strongly bind cations (the source of high relaxivity), and the B-type sites, weakly binding cations (providing lower relaxivity). Addition of the single charged (Cs+, Na+) or double charged (Sr2+) cations to the Fe(III)-GO solutions leads to a decrease in relaxivity due to the displacement of the Fe(III) ions from A to B-type sites with the Na+ < Cs+ < Sr2+ increasing efficiency. The possibility of releasing bound Fe(III) from GO by using two different chelators (ethylenediaminetetraacetic acid (EDTA) and 3,4-dihydroxybenzoic acid (3.4-DHB)) was tested in a wide range of pH.

Effects of pH and electrolytes on the sheet-to-sheet aggregation mode of graphene oxide in aqueous solutions

Aggregation mode mediated by protonation and metal cations.

γ-Radiation and H2O2 induced oxidative dissolution of uranium(iv) oxide in aqueous solution containing phthalic acid.

This study aims to reveal possible involvements of organic acids in the oxidative dissolution of UO2. Using phthalic acid as a model compound, we have measured adsorption on UO2 and investigated effects on the reaction between H2O2 and UO2 and on oxidative dissolution induced by γ-irradiation. Significant adsorption of phthalic acid was observed even at neutral pH. However, the reaction between H2O2 and UO2 in phthalic acid solution induced oxidative dissolution of U(vi) similar to in aqueous bicarbonate solution. Moreover, degradation products of phthalic acid were not detected after the reaction of H2O2. These results indicate that even though phthalic acid adsorbs on the UO2 surface, it is not involved in the interfacial reaction of H2O2. In contrast, the dissolution of U by irradiation was inhibited in aqueous phthalic acid solution, whereas H2O2 generated by radiolysis was consumed by UO2. Based on these contrasting results, possible roles of radical species generated by water radiolysis were discussed.

Synthesizing copper phosphide in interacting of elemental phosphorus with copper (II) oxide in aqueous solutions

Synthesizing copper phosphide in interacting of elemental phosphorus with copper (II) oxide in aqueous solutions

Theoretical insight into the degradation of p-nitrophenol by OH radicals synergized with other active oxidants in aqueous solution

The degradation of p-nitrophenol (p-NP) based on OH radicals (HO∙), HO2 radicals (HO2∙) and O2 in aqueous solution was investigated using theoretical computational methods. The complete degradation mechanisms of reaction between p-NP and HO∙ were explored by density functional theory (DFT) methods. The 4-nitrophenoxy radicals and 1,2-dihydroxy-4-nitrocylohexadienyl radicals are confirmed to be major intermediates of the HO∙-initiated reactions in aqueous phase, which consistent with experimental results. The chemical structures of some products (2,4-dihydroxycyclohexa-2,4-dien-1-one and 4-nitrocyclohexa-3,5-diene-1,2-dione) which were not identified in the experiment are determined. New favorable formation channels for some intermediates were found. The primary reactions initiated by HO∙ or HO2∙ with p-NP reveals that HO∙-initiated degradation is the dominant reaction. HO2∙ and O2 can enhance the degradation extent of p-NP in further reactions. Rate constants of the elementary reactions and overall rate constants were calculated. In addition, the HO∙-initiated primary reactions in a water box of 500 water molecules were studied using Monte Carlo simulation. All the OH-addition reactions are barrierless and highly feasible. The observed dynamic reaction process is similar to the DFT calculation prediction. Furthermore, the eco-toxicity evaluation shows that important products are harmless or harmful to aquatic organisms, and are much less toxic than p-NP.