Oxidation Of Aqueous Solutions Research Articles

Glucose Isomerization to Fructose Catalyzed by MgZr Mixed Oxides in Aqueous Solution

The catalytic isomerization of glucose to fructose plays a pivotal role in the application of biomass as a feedstock for chemicals. Herein, we propose a facile solid-state-grinding strategy to construct ZrO2/MgO mixed oxides, which offered an excellent fructose yield of over 34.55% and a high selectivity of 80.52% (80 °C, 2 h). The co-mingling of amphiphilic ZrO2 with MgO improved the unfavorable moderate/strongly basic site distribution on MgO, which can prohibit the side reactions during the reaction and enhance the fructose selectivity. Based on the catalyst characterizations, MgO was deposited on the ZrO2 surface by plugging the pores, and the addition of ZrO2 lessened the quantity of strongly basic sites of MgO. Additionally, the presence of ZrO2 largely enhanced the catalyst stability in comparison with pure MgO by recycling experiments.

Preparing high-performance microspheres based on the chitosan-assisted dispersion of reduced graphene oxide in aqueous solution for bilirubin removal

The removal of excess bilirubin from blood is of great clinical importance. Reduced graphene oxide (rGO) is often used to efficiently remove bilirubin. However, thin rGO pieces tend to aggregate in the aqueous phase because they are hydrophobic. In this context, we propose an effective strategy based on the chitosan-assisted (CS-assisted) dispersion of rGO to produce high-performance bilirubin-adsorbing microspheres. CS possesses a hydrophobic CH structure, which offers strong hydrophobic interactions with rGO that assist its dispersion, and the large number of hydrophilic sites of CS increases the hydrophilicity of rGO. CS serves as a dispersant in a surfactant-like manner to achieve a homogeneous and stable CS/rGO dispersion by simply and gently stirring CS and rGO in a LiOH/KOH/urea/H2O system. Subsequently, CS/rGO hybrid microspheres were prepared by emulsification. CS ensures blood compatibility as a base material, and the entrapped rGO contributes to mechanical strength and a high adsorption capacity. The CS/rGO microspheres exhibited a high bilirubin adsorption capacity (215.56 mg/g), which is significantly higher than those of the rGO and CS microspheres. The determined mass-transfer factors revealed that the rich pores of the CS/rGO microspheres promote mass transfer during bilirubin adsorption (equilibrium is almost achieved within 30 min). The CS/rGO microspheres are promising candidates for bilirubin removal owing to a combination of high strength, blood compatibility, and high adsorption capacity.

Principles determining the aggregation of graphene oxide in aqueous solutions: The effect of heterogeneous distribution of oxygen-containing groups

Molecular dynamics (MD) simulations were conducted to investigate the effects of heterogeneous distribution of oxygen-containing groups on the aggregation modes of graphene oxide (GO) flakes in aqueous solution. The results show that the aggregation of GO flakes can be divided into Brownian motion, adsorption, and adjustment steps, where the adsorption step further can be classified as point-falling-line-squeezing-plane (PFLSP) mode and bridge adsorption of confined water molecules mode. When the aggregation happens at the non-oxidized region, the successful aggregation is always accompanied by the PFLSP mode. In contrast, at the oxidized region, the bridge adsorption of CWMs mode is preferred.

Oxidation of Allura Red AC Using the NaHCO3-activated H2O2 System Catalyzed with Cobalt Supported on Al-PILC

The oxidation of aqueous solutions containing Allura Red AC (AR–AC) using bicarbonate-activated peroxide (BAP) and cobalt-impregnated pillared clay (Co/Al–PILC) as the catalyst was investigated. Using the CCD-RMS approach (central composite design–response surface methodology), the effects of dye, H2O2, and NaHCO3 concentrations on AR–AC degradation were studied. The decolorization, total nitrogen (TN), and total carbon (TC) removals were the analyzed responses, and the experimental data were fitted to empirical quadratic equations for these responses, obtaining coefficients of determination R2 and adjusted-R2 higher than 0.9528. The multi-objective optimization conditions were [dye] = 21.25 mg/L, [H2O2] = 2.59 mM, [NaHCO3] = 1.25 mM, and a catalyst loading of 2 g/L. Under these conditions, a decolorization greater than 99.43% was obtained, as well as TN and TC removals of 72.82 and 18.74%, respectively, with the added advantage of showing cobalt leaching below 0.01 mg/L. Chromatographic analyses (GC–MS and HPLC) were used to identify some reaction intermediates and by-products. This research showed that wastewater containing azo dyes may be treated using the cobalt-catalyzed BAP system in heterogeneous media.

Adsorption of polyacrylamides on mineral oxides: Effect of solution pH and polymer molecular weight

Acrylamide-based polymers such as polyacrylamide (PAM) and their derivatives are widely used as additives to enhance solid-liquid separation in the mineral processing industry. Thus, an investigation of polyacrylamide behaviour at oxide-aqueous solution interfaces is of vital importance. In this work, the adsorption of different molecular weight polyacrylamides onto iron oxides and silica was quantified at different pH values. Mineral oxides were characterised by zeta potential, particle size distribution, scanning electron microscopy images and X-ray diffraction. The Sauter mean D[3,2] diameter of the hematite, magnetite and silica were measured to be 0.8, 1.9, and 2.0 µm respectively. An anionic polyacrylamide (PAM A, MW 520 kg/mol) exhibited strong variation in adsorbed amount with pH, while the adsorption of two neutral polyacrylamides (PAM N, MW 40 & 5500 kg/mol) had a weak dependence on pH. All three polyacrylamides had similar adsorption capacity on the iron oxides particles, thus minimal influence of molecular weight was observed. The adsorption isotherms were fit to the Langmuir model to facilitate interpretation of the adsorption mechanism. The highest adsorption plateau density of 11.4 mg/m2 on magnetite and 7.4 mg/m2 on hematite for PAM A was found to be at lower pH. At the same pH, high molecular weight PAM N shows the highest adsorption plateau density of 7.8 mg/m2 and at unadjusted pH, low molecular weight PAM N adsorbs to 5.2 mg/m2 on magnetite. All PAM samples selectively adsorb on the iron oxide particles compared to silica particles. These quantified adsorbed amounts are concordant with the current use of high molecular weight PAM as an effective flocculant.

Study of the Effect of Nonselective Organic Solvent Nature on the Self-Organization of Amphiphilic Block Copolymers of D,L-Lactide and Ethylene Oxide in Aqueous Solution

The self-organization of biocompatible amphiphilic block copolymers of D,L-lactide and ethylene oxide with various hydrophobic poly(D,L-lactide) block length in aqueous media has been investigated. It has been shown that the nature of nonselective organic solvent has a considerable effect on the size, size polydispersity, and morphology of micelles of a block copolymer with a long poly(D,L-lactide) block. To elucidate the dependence of properties of block copolymer micelles on the common organic solvent type (acetone, tetrahydrofuran, N,N-dimethylformamide, and acetonitrile) various parameters of the used solvents have been estimated, and correlation between the Flory–Huggins coefficient and the surface tension between the hydrophobic block and the nonselective organic solvent and the parameters of micellar structures has been found.

Bidirectional host-guest interactions promote selective photocatalytic CO2 reduction coupled with alcohol oxidation in aqueous solution

Existing artificial photosynthesis systems often underperform due to challenges in water oxidation and extensive photogenerated carrier transfer. Herein, we demonstrate that β-cyclodextrin-decorated CdS nanocrystals (CdS-CD) can simultaneously anchor cobalt tetraphenyl porphyrin (CoTPP) catalysts and alcohol reductants onto CdS surfaces through bidirectional host-guest interactions between β-CD and CoTPP/alcohol. This configuration ensures swift electron transfer from CdS to β-CD bonded CoTPP, facilitating CO2 reduction to HCOOH. Results showcase a remarkable yield of 1610 μmol g−1 h−1 and a 96.5% selectivity. Meanwhile, photogenerated holes in CdS are efficiently neutralized by β-CD bonded furfuryl alcohol, achieving a furfural yield of 1567 μmol g−1 h−1 and > 99% selectivity. In contrast, the discrete CoTPP-CdS system achieved a HCOOH yield of only 306 μmol g−1 h−1 and a poor HCOOH selectivity of 46.4%. It was also observed that the CoTPP@CdS-CD system maintained high CO2-to-HCOOH conversion rates when using other alcohols as reductants.

Study of the Effect of Nonselective Organic Solvent Nature on the Self-Organization of Amphiphilic Block Copolymers of D,L-Lactide and Ethylene Oxide in Aqueous Solution

Study of the Effect of Nonselective Organic Solvent Nature on the Self-Organization of Amphiphilic Block Copolymers of D,L-Lactide and Ethylene Oxide in Aqueous Solution

Characterization of Benchtop-Fabricated Arrays of Nanowrinkled Surface Electrodes as a Nitric Oxide Electrochemical Sensor.

In this work, we present an accessible benchtop fabrication technique to obtain a planar array of gold nanowrinkled surface electrodes (ANSE) for the construction of electrochemical cells, specifically to monitor soluble biomarkers of interest in cell culture environments. We present a complete characterization of the array and its response as an electrochemical cell. To validate our sensor, we evaluated the device sensitivity to detect nitric oxide (NO), an important molecule produced by endothelial cells as a response to environmental signals such as mechanics and growth factors. While testing measurements of nitric oxide in aqueous solutions with isotonic salt concentrations, we evidenced the influence of the environmental conditions for such electrochemical measurements, showing that the aqueous medium, usually not accounted for, significantly impacts the outcome. Finally, we present the application of the electrochemical sensor for the detection of nitric oxide released from stimulated endothelial cells as a proof of concept.

Characterization of the Incorporation and Adsorption of Arsenate and Phosphate Ions into Iron Oxides in Aqueous Solutions

This article provides an overview of the incorporation and adsorption of arsenate and phosphate into iron oxides formed in aqueous solutions. Although arsenic (As) and phosphorus (P) and belong to the same group in the periodic table, As is usually toxic, whereas P is a biological element. Arsenate and phosphate ions can be incorporated into iron oxides through different routes, depending on the solution conditions. In aqueous solutions, the chemical state of Fe in iron oxides is FeII (ferrous) or FeIII (ferric), that of As is AsIII (arsenite) and AsV (arsenate), and that of phosphorus is PV (phosphate). The composition and structure of iron oxides, including ferric oxyhydroxides and hydroxides formed in aqueous solutions, are affected by solution conditions such as the electrochemical potential, pH, temperature, and the chemical state and composition of the relevant elements. Moreover, arsenate and phosphate ions are usually adsorbed on the surface of iron oxides in aqueous solutions, but the incorporation and adsorption of arsenate and phosphate ions in iron oxides cannot be easily explained using simple thermodynamic models. This is because these characteristics are accompanied by different stages of coprecipitation, incongruent dissolution of multicomponent iron oxides, and so on. Since hydrated iron-oxide particles are often very fine and poorly crystallized, they are difficult to filter. However, it has been shown that coarse polyhedral particles of hydrated iron oxide can be synthesized by oxidizing FeII ions. In addition, the coarse particles of hydrated iron oxide are transformed into agglomerates of fine FeIII oxides with a coarse outer shell by alkaline treatment, and these coarse porous iron-oxide particles exhibit good anion-adsorption capacity in aqueous solutions. The formation mechanisms of these different iron-oxide particles are discussed based on the results of the incorporation and adsorption of arsenate and phosphate ions in iron oxides in aqueous solutions.

Adsorption properties and mechanism of sepiolite to graphene oxide in aqueous solution

Graphene oxide (GO) is widely used in various fields such as improving the performance of cement-based materials and making composite materials due to its large specific surface area and abundant oxygen-containing functional groups. However, it has also caused water pollution. To remove GO in aqueous solution, sepiolite (SEP) was used to adsorb it. The effects of pH, adsorbent quality, GO concentration, temperature and adsorption time on the ability of SEP to adsorb GO were investigated. The materials were characterized by SAP and laser particle size analyzer, and the adsorption performance and mechanism of SEP for GO were further analyzed by XRD, FTIR, SEM, TEM, XPS, AFM, and Zeta potential microscopic tests. The results showed that: 1) Under the conditions of temperature 303 K, pH = 3, adsorbent mass 30 mg, and initial concentration of GO 100 mg/L, the adsorption effect was the best, and the adsorption rate reached 94.8 %. 2) The adsorption reached equilibrium at 2160 min, and the adsorption process was more in line with the pseudo-second-order adsorption kinetic equation, and the adsorption behavior was controlled by chemical effects. 3) The adsorption of SEP to GO is more consistent with the Langmuir and Temkin adsorption isotherm model, and the reaction is a spontaneous, endothermic, and entropy-increasing process. Experiments showed that SEP had a strong adsorption capacity for GO, which provides a reference for the treatment of toxic GO in aqueous solution and the realization of water ecological protection.

Quantitative Determination of Ascorbic Acid in Herbal Medicinal Products by HPLC

Ascorbic acid (vitamin C) is involved in many vital biochemical processes in the human body. Rose hips are a natural source of ascorbic acid. Rose hips are used in decoctions and many vitamin herbal teas. Russian compendial methods for the quantitative determination of ascorbic acid have certain limitations precluding its objective measurement in herbal drugs, herbal drug preparations, and herbal medicinal products.The aim of the study was to develop an analytical procedure for the quantitative determination of ascorbic acid in herbal drugs, herbal medicinal preparations, and herbal medicinal products using high performance liquid chromatography (HPLC).Materials and methods. The study involved two herbal medicinal products, Rose Hips (rose hips) and Vitamin Herbal Tea 2 (rose hips and rowan fruits), and reference standards for ascorbic acid, rutoside, quercetin, gallic acid, caffeic acid, chlorogenic acid, luteolin-7-glucoside, citric acid, DL-malic acid, thiamine, and pyridoxine hydrochloride. The authors used a 1260 Infinity II chromatograph with a diode array detector by Agilent and an Inertsil ODS-3 chromatographic column (250 mm × 4.6 mm, 5 µm) by GL Sciences. The HPLC system was operated in gradient elution mode, and the detector was set at 244 nm.Results. Ascorbic acid content in herbal drugs, herbal medicinal preparations, and herbal medicinal products can be determined by HPLC. Adequate sample preparation and chromatography conditions allow for inhibiting ascorbic acid oxidation in aqueous solutions for a period sufficient to complete testing (not less than 8 h).Conclusions. The authors developed a highly sensitive and selective HPLC procedure for the quantitative determination of ascorbic acid intended for the standardisation of herbal drugs, herbal medicinal preparations, and herbal medicinal products. The procedure is worthy of inclusion in the Rose Hips and Vitamin Herbal Tea 2 monographs of the State Pharmacopoeia of the Russian Federation. Switching to HPLC should not require lowering the limit for ascorbic acid (not less than 0.2%) established in the Rose Hips and Vitamin Herbal Tea 2 monographs for the titration method. The ascorbic acid content was below this limit in the vast majority of study samples. However, this discrepancy may be explained by the presence of dog rose (Rosa canina) species low in vitamin C, which should normally be used only as choleretics.

Reservoir computing with the electrochemical formation and reduction of gold oxide in aqueous solutions with a three-electrode electrochemical setup.

Supervised classification of handwritten digits via physical reservoir computing (PRC) using electrochemistry with a three-electrode electrochemical setup was demonstrated. Short-term memory required for the PRC was realized for 3 bit pulse patterns by adjusting the formation/reduction ratio of gold oxides, showing a wide potential of electrochemistry as resources of PR devices.

Is octavalent plutonium really formed during oxidation in alkaline aqueous solutions?

Abstract The solution, containing 2 M NaOH and 4.8 mM Pu(VI) mainly in ionic-dispersed phase, becomes dark blue during 2–3 min under ozonation. The absorption spectrum of the solution in the visible range coincides with the well-known absorption spectrum of Pu(VII). The addition in Pu(VII) solution of the aliquot of Pu(VI) solution reduces the absorbance of the solution at any wave length in proportion to dilution. Consequently there is no the influence of Pu(VI) on the absorption spectrum of Pu(VII). Thus, it is become obvious no Pu(VIII) formed in the course of ozonolysis of Pu(VII) alkaline solution. Additionally, crystalline Pu(VII) and Np(VII) compounds were synthesized, their electron absorption spectra were measured and compared with the ones of alkaline solutions. A similar structure of the spectra also indicates a heptavalent oxidation state of neptunium and plutonium in the synthesized crystalline compounds. Thus, the experimental results of this work, along with an analysis of the experimental results of other authors, presented in this work, make it possible to definitely conclude that at present time the highest of the known oxidation states of plutonium oxidation in aqueous solutions is the heptavalent state and all statements about the production of octavalent plutonium in aqueous solutions should be considered as unreasonable.

Electrochemical Oxidation in Aqueous Solutions of Organic Complexing Agents and Surfactants

Electrochemical Oxidation in Aqueous Solutions of Organic Complexing Agents and Surfactants

Dissolution of copper and copper oxide in aqueous solution containing amine or carboxylic acid

Dissolution of copper and copper oxide in aqueous solution containing amine or carboxylic acid

Co-solvent and temperature effect on conformation and hydration of polypropylene and polyethylene oxides in aqueous solutions

Understanding the origin of conformational changes of water-soluble polymers, as affected by external triggers such as temperature or co-solvent addition, is important from a fundamental perspective and for practical applications in responsive materials. Using atomistic molecular dynamics simulations we investigate conformational changes of polypropylene oxide (PPO) in connection to its hydration and capability to form hydrogen bonds upon either a temperature change or addition of another protic solvent (isobutyric acid, IBA) to aqueous solution. We demonstrate that upon addition of a very small amount of IBA, PPO starts to lose hydrogen bonds with water and form stable IBA-PEO hydrogen bonds, which act as a nucleation site for polymer collapse. With further addition of IBA, PPO resides at the IBA/water interface to retain some fraction of hydrogen bonds with water along with IBA-water hydrogen bonds. Unlike PEO where water mostly forms doubly-bonded hydrogen bonds (both hydrogens take part in h-bonding), PPO is hydrated by singly bonded water molecules in its hydration shell. As temperature increases breaking one of the hydrogen bonds in water doubly-bonded with PEO results in singly-bonded water. As a result, PEO retains water in its hydration shell even with a temperature increase and does not collapse upon temperature increase or IBA addition. Furthermore, PEO is capable of maintaining 80% of its hydrogen bonding with water even when it resides in an IBA-rich phase, while PPO retains less than 40% of hydrogen bonds with water while residing at the IBA/water interface. These results illustrate that hydrogen bonding and a polymer’s capability to maintain its hydration shell are the key factors in polymer responsiveness to external triggers, factors that should be taken into consideration upon responsive material design and applications.

Characterization of Formation of Ferrous and Ferric Oxides in Aqueous Solution from a Multidisciplinary Viewpoint

Characterization of Formation of Ferrous and Ferric Oxides in Aqueous Solution from a Multidisciplinary Viewpoint

Chemical and electrochemical water oxidation catalyzed by heteroleptic Ru(III) complexes of anionic 2,6 pyridine dicarboxylate ligand: Experimental and theoretical study

Herein we report two new mononuclear heteroleptic Ruthenium complexes, 1 and 2 with anionic N, O donor pyridine dicarboxylate (pdc2-) ligand along with neutral bipyridine moieties. The general formula of the complexes are [RuIII(pdc2-)(L1)Cl](1), [RuIII(pdc2-)(L2)Cl](2) (Where L1 = bipyridine, L2 = 4,4′-dimethylbipyridine). Synthesis, characterization and water oxidation catalytic properties of both complexes were investigated. A combined theoretical (DFT) and experimental study were carried out to investigate the catalytic (in presence of CAN) and electrocatalytic activity of 1 and 2 for water oxidation in aqueous solution at pH ∼ 1. During electrocatalysis, the catalytic activity wave has been detected in acetonitrile/water 1:9 (v/v) solution in the range 1.39–1.41 V vs SCE. pH based electrochemistry reveals that, water oxidation (at pH = 1) takes place via sequential proton-electron transfer process to form a RuV = O moiety, which oxidises water through I2M pathway. For water oxidation by CAN, both the molecules show appreciably high TOF values 3.47971 x10-4 s−1 and 1.183 × 10–3 s−1 for 1 and 2 respectively in comparison to similar molecules [1,2].

Microwave-Assisted Synthesis of Schiff Base Metal–Ligand Complexes with Copper and Nickel Centres for Electrochemical In Vitro Sensing of Nitric Oxide in an Aqueous Solution

Nitric oxide (NO), the smallest signalling molecule known in the human body, keeps blood vessels dilated, controls blood pressure, and has numerous other health regulatory effects. The use of Schiff base complexes incorporated onto electrodes to make electrochemical sensors has been explored as an effective method for the determination and quantification of nitric oxide in aqueous solutions. Schiff base ligands were complexed with Cu and Ni metal centres using the microwave synthesis method to produce metal–ligand complexes with enhanced capabilites for NO detection. The electrical current generated at the anode is directly proportional to NO concentrations in the solution through its oxidation to HNO3. Various characterisation techniques were implemented to verify the integrity of each step of metal–ligand synthesis as well as the final product produced, using FT-IR, UV-VIS, and TGA. The as-synthesised Schiff base complexes were electrodeposited on screen-printed carbon electrodes (SPCE) and electrochemically evaluated in a 0.1 M PBS. Furthermore, metal complexes were screened for their in vitro activity towards NO detection in an aqueous solution (PBS). The results show that the investigated sensors (SPCE/Ni-BPND and SPCE/Cu-BPND) respond positively toward NO detection. It was, therefore, identified that the two sensors also do not differ significantly in terms of precision, sensitivity, and lowest detection limit. The sensor strategies demonstrate the NO limits of detection of 0.22 µM and 0.09 µM, and they also demonstrate sensitivity values of 16.3 µA/µM and 13.1 µA/µM for SPCE/Cu-BPND and SPCE/Ni-BPND sensors, respectively.