Oxidation In Aqueous Media Research Articles

Vanadium (V) adsorption isotherms and kinetics using polypyrrole coated magnetized natural zeolite

Magnetized natural zeolite-polypyrrole (MZ-PPY) composite as a potential adsorbent for vanadium was prepared via polymerization of pyrrole monomer using FeCl3 oxidant in aqueous medium in which magnetized natural zeolite particles were suspended. The MZ-PPY composite was characterized by attenuated total reflectance Fourier transform infrared spectroscope (ATR-FTIR), field emission scanning electron microscope (FE-SEM) and high resolution transmission electron microscope (HR-TEM). Batch adsorption studies were performed to test the ability of the adsorbent to remove V(V) ions from aqueous solution. From sorption equilibrium modelling, the equilibrium data is well described by Langmuir, Sips and Redlich–Peterson isotherms while the adsorption kinetics is described by the pseudo-second order model. The Langmuir adsorption capacity is 65.0 mg/g at 298K. Thermodynamic parameters confirm the spontaneous and endothermic nature of the vanadium adsorption process. Meanwhile V(V) removal process is found not to be affected by co-existing ions. Furthermore, the material can be used in two adsorption cycles without compromising its capacity.

Aqueous zinc-organic polymer battery with a high rate performance and long lifetime

A novel redox-active polymer based on a 9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (exTTF) system in combination with a conjugated backbone was synthesized via rhodium (Rh)-catalyzed polymerization of 2-ethynyl(exTTF), leading to polymers with low polydispersities. Composite electrodes containing this polymer exhibited chemically reversible two-electron oxidation in aqueous media. The application of these electrodes as active cathode materials in hybrid zinc-organic batteries using an aqueous electrolyte enabled the production of air-stable charge storage systems with a theoretical capacity of 133 mAh g−1. These batteries featured high performance, charge/discharge rates of up to 120 C (30 s) and an ultra-long lifetime, of over 10 000 charge/discharge cycles (accompanied by a minor capacity loss of 14%). Finally, the polymer was compared with its nonconjugated derivative, revealing the positive influence of the conjugated backbone on the material activity owing to improved electron transfer within the polymer chain. Researchers in Germany have unlocked the secret to using water as an electrolyte in rechargeable batteries with a new conjugated polymer. Polymer batteries are flexible and lightweight, but a reliance on flammable organic solvents for electrolytes has raised concerns. Ulrich S. Schubert and colleagues synthesized a poly(acetylene)-based compound containing charge-active organosulphurs to improve battery safety while maintaining high performance. Water has a narrow range of stability under applied voltages, making it tricky to use as an electrolyte. The team's polymer, however, is capable of a reversible, two-electron oxidation reaction in this range. A prototype with the polymer cathode, a zinc anode and an aqueous electrolyte revealed the possibilities of this approach — the battery could be charged to its 1-volt potential within 30 seconds and had a lifetime exceeding 10,000 recharge cycles. The application of a conjugated polymer with 9,10-di(1,3-dithiol-2-ylidene)-9,10-dihydroanthracene (exTTF) units as cathode and zinc as anode enables an aqueous-based hybrid organic battery. This energy storage device features ultra-high rate performance of up to a full charge in 30 s and an extended lifetime up to 10 000 cycles.

ChemInform Abstract: TBAI/TBHP Mediated Oxidative Cross Coupling of Aryl Alkyl Ketones with H‐Phosphonates and H‐Phosphine Oxides in Water: Facile Access to Ketol Phosphates and Phosphinates.

Abstract A metal free cross coupling of aryl alkyl ketones with alkyl/aryl H-phosphonates and H-phosphine oxides using tetrabutylammonium iodide (TBAI) catalyst in the presence of tert -butyl hydroperoxide (TBHP) as terminal oxidant in aqueous media is developed. This new approach offers a direct and convenient route to access a wide range of ketol phosphates and phosphinates in moderate to good yields.

A Metal‐Free Oxidative Cross‐Dehydrogenative Coupling ofN‐Aryl Tetrahydroisoquinolines and 2‐Methylazaarenes Using a Recyclable Oxoammonium Salt as Oxidant in Aqueous Media

A metal‐free oxidative cross‐dehydrogenative coupling ofN‐aryl tetrahydroisoquinolines and 2‐methylazaarenes in water under mild conditions has been developed. 4‐Acetylamino‐2,2,6,6‐tetramethylpiperidine‐1‐oxoammonium tetrafluoroborate was employed as a mild oxidant that can be recovered and reused directly. The reaction proceeds through formation of an iminium ion in situ followed by condensation with various nucleophiles, providing the desired products in moderate to good yields.

Self-propagating solar light reduction of graphite oxide in water

Graphite Oxide (GtO) is commonly used as an intermediate material for preparation of graphene in the form of reduced graphene oxide (rGO). Being a semiconductor with tunable band gap rGO is often coupled with various photocatalysts to enhance their visible light activity. The behavior of such rGO-based composites could be affected after prolonged exposure to solar light. In the present work, the alteration of the GtO properties under solar light irradiation is investigated. Water dispersions of GtO manufactured by oxidation of natural graphite via Hummers method were irradiated into solar light simulator for different periods of time without addition of catalysts or reductive agent. The FT-IR analysis of the treated dispersions revealed gradual reduction of the GtO with the increase of the irradiation time. The XRD, FT-IR and XPS analyses of the obtained solid materials confirmed the transition of GtO to rGO under solar light irradiation. The reduction of the GtO was also manifested by the CV measurements that revealed stepwise increase of the specific capacitance connected with the restoration of the sp2 domains. Photothermal self-propagating reduction of graphene oxide in aqueous media under solar light irradiation is suggested as a possible mechanism. The self-photoreduction of GtO utilizing solar light provides a green, sustainable route towards preparation of reduced graphene oxide. However, the instability of the GtO and partially reduced GO under irradiation should be considered when choosing the field of its application.

TBAI/TBHP mediated oxidative cross coupling of aryl alkyl ketones with H-phosphonates and H-phosphine oxides in water: facile access to ketol phosphates and phosphinates

A metal free cross coupling of aryl alkyl ketones with alkyl/aryl H-phosphonates and H-phosphine oxides using tetrabutylammonium iodide (TBAI) catalyst in the presence of tert-butyl hydroperoxide (TBHP) as terminal oxidant in aqueous media is developed. This new approach offers a direct and convenient route to access a wide range of ketol phosphates and phosphinates in moderate to good yields.

The dispersion and aggregation of graphene oxide in aqueous media.

Graphene oxide (GO), as a typical two-dimensional material, possesses a range of oxygen-containing groups and shows surfactant and/or polyelectrolyte-like characteristics. Herein, GO sheets with narrow size distribution were prepared by an ultracentrifugation-based process and the aggregation behaviour of GO in pure water and an electrolyte aqueous solution were studied using laser light scattering (LLS). When adding common electrolytes, such as NaCl and MgCl2, into the GO dispersions, aggregation occurs and irreversible coagulation eventually occurs too. However, the GO dispersion can still remain stable when adding excess AlCl3. The zeta potential of the GO dispersion changes from negative to positive after the addition of access AlCl3, indicating that electrostatic repulsion is still responsible for the dispersion of GO, which is in good agreement with the LLS results. This finding on the dispersion of GO may be applied in the solution processing of GO. It also expands the scope of the design and preparation of new GO-based hybrid materials with different functions.

A Novel and Rapid Harvesting Method of Microalgae Using Saw Dust Coated Polypyrrole

In this study a simple and rapid harvesting method using electro conductive polymer coated saw dust has been presented as a new coagulant for separating Chlorella vulgaris from a diluted suspension. Polypyrrole (PPy) coated saw dust as a novel coagulant was prepared via in-situ polymerization of pyrrole (Py) monomer using FeCl3 oxidant in aqueous medium in which saw dust particles were suspended. The zeta potential of coagulant and C. vulgaris and X-ray photoelectron spectroscopic (XPS) analysis of coagulant were characterized. PPy maintain predominantly positive charge over a wide pH range (2-10) with an isoelectric point 10.4 while, C. vulgaris maintained negative surface charge from pH 5 and onward with isoelectric point 3.8. The microalgae showed the highest separation efficiency at pH 10. The maximal recovery efficiency reached more than 90% for microalgae at a stirring speed of 120 rpm within 7 min. The maximal adsorption capacity of C. vulgaris was 28.8 mg dry biomass/mg-saw dust coated PPy. The concentration factor obtained is higher than 32 which save energy and time associated with microalgal harvesting and allows a reduction in the equipment size necessary for biomass dewatering and improves the feasibility of using these microorganisms in biofuel or wastewater processes.

Comparative Stability Evaluation of Marketed Paracetamol IV Formulations in India

Paracetamol is a well-established drug widely used around the world for analgesic and antipyretic purposes in oral solid dosage forms. While paracetamol is stable in solid dosage form, intravenous formulations have significant stability related issues, as the drug is susceptible to hydrolysis and oxidation in aqueous media. Formation of hydrolytic product can be well controlled by adjusting the pH of formulation. However, control of oxidation of the drug during manufacturing and packaging is a challenge, as it requires sophisticated operational controls to remove dissolved oxygen and/or addition of compatible anti-oxidant. Seven commercially available paracetamol intravenous formulations from the Indian market were evaluated for their oxidative degradation potential. The study was performed in two tiers: i) to compare formation of oxidative products in selected stress degradation conditions; and ii) to determine presence of cysteine, an anti-oxidant excipient. Firstly, all formulations were subjected to thermal stress condition at 80oC for 7 days and oxidative stress condition with 2,2' -azobis (2-amidino-propane) dihydrochloride (AAPH) at 40oC for 48 hours. Of the seven formulations tested, one formulation (PerfalganTM, Manufactured by BMS) showed absence of oxidative products after both stress conditions. For tier II studies, a sensitive HILIC-MS/MS method was developed on API 4000 (AB Sciex) for the determination of cysteine presence. Only PerfalganTM showed presence of cysteine. Thus, PerfalganTM can be expected to have better stability compared to other marketed formulations. Overall, it is concluded that presence of an anti-oxidant in intravenous formulation could give additional advantage over stability of paracetamol. Key words: HILIC, LC-MS, Oxidative stress, Paracetamol, stability.

ChemInform Abstract: Broadening the Chemical Scope of Laccases: Selective Deprotection of N‐Benzyl Groups.

AbstractLaccase from Trametes versicolor along with TEMPO is found to be a very efficient catalytic system for the deprotection of N‐benzylated primary amines using oxygen as a mild oxidant in aqueous medium.

Catalytic oxidation of aqueous sulfide in the presence of ferrites (MFe2O4, M = Fe, Cu, Co)

In this work, the spinel structured iron oxides, MFe2O4 (M=Cu2+ and Co2+), magnetite (Fe3O4) and maghemite (γ-Fe2O3) were investigated as catalyst for the sulfide oxidation in aqueous medium. XRD, Mössbauer, BET, TPR, SEM/EDS and XPS analyses suggest the formation of the spinel phase with surface areas varying from 75 to 105m2g−1 and the metal ions Cu2+ and Co2+ located in the octahedral and tetrahedral sites. It was observed that the presence of Co and especially Cu strongly increased the catalytic activity for the oxidation of sulfide to polysulfides, i.e. Sx2− (x=1–4) and other SO species. The strong effect of Cu2+ is discussed in terms of thermodynamically favorable processes comprising a strong surface interaction of S2−–Cu2+, an electron transfer from sulfide to produce Cu1+ followed by an electron transfer from Cu1+ to Fe3+bulk.

Photoluminescent Porous Si/SiO2 Core/Shell Nanoparticles Prepared by Borate Oxidation

A systematic study on the activation of photoluminescence from luminescent porous silicon nanoparticles (LPSiNPs) by oxidation in aqueous media containing sodium tetraborate (borax) is presented. The treatment promotes surface oxidation of the porous silicon skeleton and consequently generates an electronically passivated material. Photoluminescence is ascribed to quantum confinement effects and to defects localized at the Si‐SiO2 interface, and the strong photoluminescence is attributed to passivation of nonradiative surface defects. The oxidation treatment (carried out at 20 °C) generates a gradual blue shift of the photoluminescence peak wavelength (from 800 nm to 630 nm), while the bandwidth remains relatively constant (≈210 nm). During the treatment period, the external quantum yield (λex = 365 nm) of photoluminescence increases to a maximum value of 23% after 200 min, and then it decreases at longer treatment times. The decrease in photoluminescence intensity at longer times is attributed to degradation and dissolution of the nanoparticles, which is inhibited at higher nanoparticle concentrations or by addition of free silicic acid.

Studies on the effect of bio-ionic liquid structures on the spontaneous reduction and dispersion stability of graphene oxide in aqueous media

Surface functionalization of graphene oxide (GO) by choline bicarbonate, choline hydroxide, choline formate and choline caproate resulted formation of partially reduced GO.

The Important Role of Hydroxyl on Oxidation Catalysis by Gold Nanoparticles

Although gold is generally considered to be a relatively inert metal, supported gold nanoparticles have demonstrated exceptionally high catalytic activity for the oxidation of carbon monoxide and alcohols at modest temperatures. In both cases, the presence of hydroxyl groups substantially promotes the reaction rate, presumably by participating in the reaction. Direct comparisons of CO oxidation to alcohol oxidation over gold catalysts have been difficult for scientists to explain. The former reaction is usually performed with gas phase reagents, whereas the latter reaction is often performed in the condensed phase. In this Account, we discuss the important role of hydroxyl for these two oxidation reactions catalyzed by gold, in terms of its influence on the turnover frequency. During CO oxidation over gold, a hydroxyl can directly react with CO to form COOH, which eventually decomposes to CO2. The gas phase CO oxidation reaction likely occurs at the gold-support interface, where adsorbed hydroxyl groups can be found after the addition of water to the feed. When we perform CO oxidation in liquid water, increasing the pH substantially promotes the reaction rate by providing an external source of hydroxyl. Likewise, we can also promote alcohol oxidations over gold catalysts in aqueous media by increasing the pH of the system. Since the hydroxyl groups are supplied through the reaction medium instead of on the support surface, the gold-support interface is much less important in the aqueous phase reactions. Even bulk gold powder becomes an active oxidation catalyst in alkaline water. The role of O2 in both CO and alcohol oxidation in aqueous media is to remove electrons from the gold surface that are deposited during oxidation, maintaining electroneutrality. Thus, the oxidation of CO and alcohols in water at high pH is analogous to the electrochemical oxidation reactions performed on gold electrodes. As the field of chemistry continues to encourage the development of sustainable chemical processes utilizing environmentally benign reaction conditions, the use of water as a "green" solvent becomes an attractive choice. In general, however, heterogeneous catalysts that scientists have developed over the last century for the petrochemical industry have not been optimized for use in aqueous media. Given the active role of water in oxidation reactions catalyzed by gold, additional research is needed to understand how water affects other catalytic transformations on traditional transition metal catalysts.

Low cytotoxic tissue adhesive based on oxidized dextran and epsilon‐poly‐l‐lysine

A novel adhesive hydrogel consisting of dextran and epsilon-poly(L-lysine) (dextran-PL) with multiple biomedical applications was developed. Periodate oxidation in aqueous media almost stoichiometrically introduces aldehyde groups in dextran molecules, and aldehyde dextran can react with the primary amino groups in epsilon-PL (ɛ-PL) at neutral pH to form a hydrogel. The gelation time of the hydrogel can be easily controlled by the extent of oxidation in dextran and of the acylation in ɛ-PL by anhydrides. The shear adhesion strength of dextran-PL was 10 times higher than that of fibrin glue, when wet collagen sheets were selected as test specimens. The cytotoxicity of aldehyde dextran and ɛ-PL were 1000 times lower than that of glutaraldehyde and poly(allylamine). The considerably low cytotoxicity of aldehyde dextran could be ascribed to its low reactivity with amine species when compared with glutaraldehyde. In contrast, a high reactivity of amino groups in ɛ-PL was observed when compared with glycine, L-lysine, and gelatin, which could be explained by their poor dissociation at neutral pH, thus leading to low cytotoxicity.

Photoassisted defluorination of fluorinated substrates and pharmaceuticals by a wide bandgap metal oxide in aqueous media

Persistent fluorinated substances, such as the fluorine-bearing pharmaceutical drugs Fluoxetine (FLX; Prozac) and Fluvoxamine maleate (FOM) together with several other substrates (fluorobenzoic acid and fluoroaliphatic model compounds), were photochemically defluorinated and degraded under UVC illumination in relatively good yields in the presence of a wide band gap metal oxide (β-Ga2O3) in heterogeneous aqueous media. The formation of fluoride ions increased with increasing illumination time under an inert nitrogen atmosphere, the transformation of the aromatic moiety was slower under these conditions, but nonetheless it did occur. The optimal amount of β-Ga2O3 loading for defluorination was 50 mg in aqueous media (0.10 mM, 100 mL); the optimal pH to defluorinate FLX was pH 6. Platinization (1 wt%) of the gallium oxide particles enhanced defluorination under an inert nitrogen atmosphere, but was decreased under an oxygen atmosphere; however, in the latter case the degradation of the substrates was facilitated as witnessed by loss of the aromatic moiety. The Ames test on the intermediate products from the photodegradation of FLX and 4-(trifluoromethyl)benzoic acid after long illumination times revealed that none were mutagenic.

One-step self-assembled synthesis of CuO with tunable hierarchical structures and their electrocatalytic properties for nitrite oxidation in aqueous media

Controlled synthesis of CuO with various hierarchical structures consisting of self-organized nanoparticles is realized by using n-octylamine (OLA) as a structure inducing agent via a facile hydrothermal synthetic method. The growth and assemblage of CuO can be finely tuned by selecting the preparative parameters. In particular, it is found that the degree of the hierarchical organization can be modulated by simply changing the amount of the n-octylamine and CuO nanoparticles exhibit self-assembled two-dimensional (2D) sheet-like, three-dimensional (3D) disk-like and bowknot-like architectures, respectively. In the present case, OLA serves as a capping surfactant that can modulate growth of CuO nanocrystals via hydrophobic forces between the OLA molecules. CuO nanoparticles can be self-assembled into different complex architectures depending on the strength of hydrophobic forces. Hierarchical sphere-like CuO assembled from nanorods can also be easily fabricated by adjusting the starting NaOH to CuCl2 volume ratio, in which OLA serves not only as the structure-directing agent, but also as a weak base agent to produce hydroxyl anions. The electrochemical performances of the as-synthesized different products for sensing nitrite oxidation are evaluated. The results reveal that the electrocatalytic activity is related to the secondary nanostructures. Compared to the others, the bowknot-shaped and sphere-shaped CuO products exhibit excellent electrocatalytic activity toward nitrite oxidation and fast current response in nitrite sensing because of their peculiar hierarchical structures with high BET surface areas and well-ordered pores.

Neuronal cells’ behavior on polypyrrole coated bacterial nanocellulose three-dimensional (3D) scaffolds

In this work, polypyrrole (PPy) was in situ polymerized onto the surface of bacterial nanocellulose (BNC) produced by Gluconacetobacter xylinus, by chemical oxidation in aqueous medium using ammonium persulfate. Composites (BNC/PPy) were produced with varying concentrations of pyrrole (Py). The produced BNC/PPy membranes were used as a template for the seeding of PC12 rat neuronal cells. Cell suspensions were directly seeded onto the surfaces of the BNC/PPy membranes. The Py concentration affected the behavior of neuronal cells that adhered and grew significantly more on BNC/PPy comparatively to BNC. Scanning electron microscopy (SEM) micrographs revealed that PC12 cells adhered on the surface of the BNC and BNC/PPy membranes. Conductive PPy coatings on nanofibers acting as an active interface for tissue engineering may be used to regulate cell activity through electrical stimulations.

Practical, ecofriendly, and highly efficient synthesis of 2-amino-4H-chromenes using nanocrystalline MgO as a reusable heterogeneous catalyst in aqueous media

A simple, efficient, and environmentally benign method has been developed for the synthesis of 2-amino-4H-chromenes under the heterogeneous catalysis of nanocrystalline magnesium oxide in aqueous media in excellent yields at room temperature. This method provides a green and improved pathway for the synthesis of chromenes in the terms of excellent yields, short reaction times and reusability catalyst.

On the key role of hydroxyl groups in platinum-catalysed alcohol oxidation in aqueous medium

In the aerobic selective oxidation of alcohols in aqueous medium in a batch reactor, it was observed that the addition of water to dioxane solvent (10–50 vol%) substantially increased the activity of a Pt/C catalyst. Periodic density functional theory (DFT) calculations were carried out to compare the reactivity of alcohols on the bare Pt(111) surface and in the presence of adsorbed water or hydroxyl groups, to explain the effect of water. The calculations indicate that the presence of adsorbed hydroxyl groups promotes the catalytic activity by participating directly in the catalytic pathways and reducing the activation barrier. Good agreement was found between the experiments in aqueous phase and these calculations. Further, decarbonylation of the aldehyde may be involved in the deactivation during oxidation of a primary alcohol.