Urea Hydrogen Research Articles

Ni\u2013Fe phosphide deposited carbon felt as free-standing bifunctional catalyst electrode for urea electrolysis

A free-standing catalyst electrode for the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) in a urea electrolysis cell was synthesized by electroplating a Ni–Fe alloy onto carbon felt, followed by phosphidation (P-NiFe@CF). The prepared P-NiFe@CF catalyst consisted of Ni5P4, NiP2, and FeP with 3D flower-like P-NiFe architecture on CF. P-NiFe@CF exhibited excellent electrocatalytic activity for the UOR (demanding only 1.39 V (vs. RHE) to achieve 200 mA cm−2), and for the HER with a low overpotential of 0.023 V (vs. RHE) at 10 mA cm−2, indicating its feasibility as a bifunctional catalyst electrode for urea electrolysis. A urea electrolysis cell with P-NiFe@CF as both the free-standing anode and cathode generated a current density of 10 mA cm−2 at a cell potential of 1.37 V (vs. RHE), which is considerably lower than that of water electrolysis, and also lower than previously reported values. The results indicate that the P-NiFe@CF catalyst electrodes can be used as free-standing bifunctional electrodes for urea electrolyzers.

One-pot hydrothermal synthesis of carbon dots-immobilized hydrozincite for ZnO-based nanocomposite lighting applications

ABSTRACT The immobilization of fluorescent nanomaterials in host–guest systems is one of the important factors for the further development of light-emitting properties in nanocomposite materials. In this study, one-pot hydrothermal synthesis was performed to generate advanced fluorescent nanocomposite by immobilizing carbon dots (C-dots) in a layered hydrozincite matrix while synthesizing them in a reaction solution. The one-pot reaction was performed by hydrothermal treatment starting from zinc acetate, urea, and diammonium hydrogen citrate in solution as precursor. The reaction condition that C-dots and hydrozincite could be synthesized together in a one-pot hydrothermal reaction at 200°C was investigated by adjusting the pH of the precursor, and the formation criteria depending on the pH were discussed. Based on the changes in crystal structure and in the surface state of the resulting composite powder compared with the single hydrozincite powder, the interaction that contributed to the immobilization of carbon dots was discussed. The fluorescence properties of the C-dots immobilized zinc compounds were characterized. Further sintering under an appropriate condition for the C-dots–hydrozincite composite allowed conversion into the C-dots–zinc oxide composite exhibiting quite different fluorescent characteristics.

Molecular Features of Reline and Homologous Deep Eutectic Solvents Contributing to Nonideal Mixing Behavior.

Deep eutectic solvents based on choline chloride and a series of urea derivatives are studied by molecular dynamics simulations with the aim to identify molecular features contributing to nonideal mixing behavior of these compounds. In case of reline, a mixture of choline chloride and urea in 1:2 ratio, urea molecules provide sufficient hydrogen bond donor sites to take up the chloride anions into their polar network. Replacing any of the hydrogen atoms of urea by a methyl group strongly pushes the anion to interact with these alkyl chains, resulting in a positive deviation of the activity coefficients of choline chloride compared to reline. Furthermore, the oxygen atom of urea can interact with the nitrogen atom of the cation. This enables the chloride anion to move off-center of the cation toward the hydrogen atom of its hydroxyl group, possessing stronger directional Coulomb interactions than the nitrogen atom of the cation. The substitution of urea's hydrogen atoms in cis position to the carbonyl group as in 1,3-dimethylurea, pushes the newly introduced nonpolar alkyl chains toward the nitrogen atom of the cation. This effect can be responsible for the experimentally observed increase of the activity coefficient of the urea derivative compared to urea. Additionally, indications for formation of nonpolar domains within the liquid and, thus, nanoscale segregation is visible as soon as one hydrogen atom of urea is replaced by an alkyl group.

ПРИДАНИЕ ОГНЕЗАЩИТНЫХ СВОЙСТВ ЦЕЛЛЮЛОЗНЫМ ТЕКСТИЛЬНЫМ МАТЕРИАЛАМ С ПРИМЕНЕНИЕМ ЗОЛЬ - ГЕЛЬ ТЕХНОЛОГИИ

The article presents studies on the use of a new composition based on sodium silicate, urea and sodium hydrogen phosphate to impart fire-retardant properties to cellulosic textile materials. The influence of the concentration of the starting components, temperature, and heat treatment time on the flame retardant properties was studied. The change in the fire retardant properties of cotton fabric is given for three heat treatment modes: at 80, 90 and 100 °C. Compared to the initial fabric, the samples treated with a flame retardant have indicators of flame retardant properties. Untreated fabric with a size of 220×170 mm when tested for flammability at an ignition time of 15 s completely burns out in 60 s. In samples treated with a flame retardant, at an ignition time of 15 s, the smoldering time is practically reduced to zero. With an increase in the concentration of the flame retardant, and the temperature of the heat treatment, the loss of material strength, breaking load, and the appearance of the fabric change slightly. Using electron scanning microscopy and energy dispersive microanalysis, it was shown that pure cotton fabric contains 68.77% carbon and 31.22% oxygen; after modification, particles of sodium – 0.02%, phosphorus – 0.04% and potassium – 0.05% are formed on the surface of the treated fabric. distributed fairly unevenly. It has been shown that in cellulosic materials modified with compositions based on sodium silicate and urea, sodium hydrogen phosphate, flame retardant properties increase. The proposed composition provides the achievement of higher fire resistance. Processing can be carried out on standard equipment of finishing enterprises without the stage of high-temperature fixation of the drug.

INFLUENCE OF DIFFERENT METHODS OF WHITENING ON THE STRUCTURE OF HARD TISSUES OF TEETH

Nowadays 74% of people believe that an imperfect smile has a negative impact on their careers, and 92% believe that it is one that contributes to success in their personal lives. The desire of patients to have an aesthetically perfect smile has always aroused great interest from dentists and has led to the active development of such a trend in aesthetic dentistry, such as teeth whitening. The color of the crowns of teeth and the inherent color characteristics play an important role in the perception of the appearance of the person, the formation of his image and self-esteem. Therefore, they affect the quality of life of a person due to his dental health. There are 5 main treatments for altered teeth: microabrasion, teeth whitening, direct restoration of composites, veneering, restoration of ceramic and metal-ceramic crowns. In recent years, conservative treatments, which include different types of whitening, have been favored to achieve maximum aesthetic results in the correction of altered teeth. For whitening, a considerable number of different remedies are offered that allow the tooth color to change relatively quickly. Nowadays, the world of dental practice is increasingly paying attention to the development of more cost-effective methods that meet the aesthetic needs of patients. The most common procedure for improving the color of the crowns of teeth today is whitening, which does not affect the reduction of the volume of hard tissues of the tooth. Teeth whitening is a restoration of the natural color of the teeth with the application of a chemical agent that oxidizes the organic pigments of the hard tissues of the tooth. Bleaching process is possible due to the ability of the active chemical components ( carbamide peroxide, hydrogen peroxide) to penetrate into enamel and dentin to all parts of the tooth. These substances break down into oxygen radicals, which destroy the colored pigments, the formation of which leads to discoloration of the teeth. The structure of the tooth does not change. Nowadays, home, professional and combined teeth whitening are widely used. The effect of bleaching is analyzed using a scanning electron microscope. Most studies did not report significant changes in the surface morphology of enamel after bleaching with low concentrations of urea peroxide and hydrogen peroxide. Similarly, studies evaluating the effects of higher concentrations of hydrogen peroxide (35%) and carbamidee peroxide (35%) have also reported no significant changes in the morphology of the enamel surface. In general, it is obvious that tooth sensitivity is a common clinical side effect after a teeth whitening procedure. However, the sensitivity is transient and disappears shortly after the bleaching procedure has been stopped.

A chemoselective ipso-hydroxylation of arylboronic acids using urea-hydrogen peroxide under catalyst free condition

An efficient and practical method for the chemoselective ipso-hydroxylation of arylboronic acids is demonstrated using urea-hydrogen peroxide under catalyst free condition at room temperature. Remarkably, oxidation sensitive functional groups such as olefin, aldehyde, alcohol, ketone, and sulfide as well as heterocycles such as pyridine and thiophene were tolerated under the standard reaction condition. In addition to the solution phase, a solid phase ipso-hydroxylation of arylboronic acids has been investigated with urea hydrogen peroxide. The scope and limitations of the solid phase protocol is discussed.

Predicting Cocrystallization Based on Heterodimer Energies: The Case of N,N′-Diphenylureas and Triphenylphosphine Oxide

Diarylureas frequently assemble into structures with one-dimensional H-bonded chain motifs. Herein, we examine the ability of triphenylphosphine oxide (TPPO) to disrupt the H-bonding motif in 14 different meta-substituted N,N′-diphenylureas (mXPU) and form cocrystals; 1:1 mXPU:TPPO cocrystals were obtained in 9 of 14 cases examined (64% success rate). Cocrystals adopt five different lattice types, all of which show unsymmetrical H-bonded [R21(6)] dimers between the urea hydrogens and the phosphine oxygen. Heterodimer (mXPU···TPPO) and homodimer (mXPU···mXPU) interaction energies, ΔEint, calculated using density functional theory at the B3LYP/6-31G(d,p) level were used to rationalize the experimental results. A clear trend was observed in which cocrystals were experimentally realized only in cases in which the differences in heterodimer versus homodimer energy, ΔΔEint, were greater than ∼5.3–6 kcal/mol. Although calculated interaction energies are a simplified measure of the system thermodynamics, these re...

Oxidation of Benzylic Alcohols with Urea Hydrogen Peroxide/Calcium Chloride in PEGDME250

However, most of the aforementionedreagent systems are generally exotic, toxic, and expensivewhich limit their practical applications. In addition, hydro-gen peroxide is considered to be an ideal green oxidant forthe oxidation reactions of alcohol s due to its low toxicity andready availability. However, utilization of hydrogen peroxidefor the alcohol oxidation reactions generally required use oftransition metal based peroxo-complexes as activators.

Isatinphenylsemicarbazones as efficient colorimetric sensors for fluoride and acetate anions – Anions induce tautomerism

The anion induced tautomerism of isatin-3-4-phenyl(semicarbazone) derivatives is studied herein. The interaction of F−, AcO−, H2PO4-, Br− or HSO4- anions with E and Z isomers of isatin-3-4-phenyl(semicarbazone) and N-methylisatin-3-4-phenyl(semicarbazone) as sensors influences the tautomeric equilibrium of these sensors in the liquid phase. This tautomeric equilibrium is affected by (1) the inter- and intra-molecular interactions’ modulation of isatinphenylsemicarbazone molecules due to the anion induced change in the solvation shell of receptor molecules and (2) the sensor–anion interaction with the urea hydrogens. The acid–base properties of anions and the difference in sensor structure influence the equilibrium ratio of the individual tautomeric forms. Here, the tautomeric equilibrium changes were indicated by “naked-eye” experiment, UV–VIS spectral and 1H NMR titration, resulting in confirmation that appropriate selection of experimental conditions leads to a high degree of sensor selectivity for some investigated anions. Sensors’ E and Z isomers differ in sensitivity, selectivity and sensing mechanism. Detection of F− or CH3COO− anions at high weakly basic anions’ excess is possible.

Effect of Chemical Additives on <I>Bacillus thuringiensis</I> (Bacillales: Bacillaceae) Against <I>Plutella xylostella</I> (Lepidoptera: Pyralidae)

To examine the effect of chemical additives on Bacillus thuringiensis (Berliner) against Plutella xylostella (L.), inorganic salts, nitrogenous compounds, protein solubilizing agents, and organic acids were selected and tested. The chosen materials are low in cost and environmentally safe. Results show that many inorganic salts can increase the activity of B. thuringiensis in a range of 1.31- to 3.08-fold. These include calcium acetate, calcium chloride, calcium hydroxide, calcium sulfate, calcium carbonate, sodium carbonate, sodium acetate, potassium hydroxide, potassium carbonate, potassium acetate, magnesium chloride, magnesium sulfate, and zinc sulfate. Nitrogenous compounds, including peptone, sodium nitrate, and ammonium nitrate, can enhance the activity of B. thuringiensis 1.62-, 1.32-, and 1.37-fold, respectively. Among the protein solubilizing agents, EDTA, urea, mercaptoethanol and dipotassium hydrogen phosphate increased the activity of B. thuringiensis 1.62- to 2.34-fold. Among the organic acids, maleic and citric acids boosted the activity 1.45- and 1.55-fold, respectively. Meanwhile, sodium benzoate and resorcinol led to 1.74- and 1.44-fold activity gains, respectively. Use of appropriate additives could provide great benefit not only in reducing the costs for field applications of biological insecticides but also by boosting the efficacy of B. thuringiensis.

Supramolecular trans-Coordinating Phosphine Ligands

We report a new urea-functionalized phosphorus ligand and palladium complexes thereof that self-associate by hydrogen bond formation. The solution studies of a urea-based phosphine ligand {m-[EtO(CO)CH2NH(CO)NH]C6H4PPh2}, 1, and the palladium complex (1)2PdMeCl, 2, show that intermolecular and intramolecular hydrogen-bonding, respectively, is present between the urea hydrogens and the carbonyl of a second urea moiety. Introduction of NBu4Cl to 2 results in the disruption of the self-association and the production of {[trans-(12Cl)PdMeCl]-[NBu4]+}, 3, with an anion-templated, bidentate phosphine ligand system. Although the ligands are hydrogen-bonding to the chloride anion, they remain in a trans configuration about the metal center. If another equivalent of 1 is added to 2, a zwitterionic palladium methyl complex ligated by three phosphine ligands is produced and the chloride anion is abstracted from the metal center into the resulting tris-urea hydrogen-bonding pocket, generating [(13Cl)PdMe], 4. If at −...

Epoxidation of chiral camphor N-enoylpyrazolidinones with methyl(trifluoromethyl)dioxirane and urea hydrogen peroxide/acid anhydride: reversal of stereoselectivity.

Both diastereomeric isomers of epoxides with high optical purity are obtained when camphor N-methacryloylpyrazolidinone (1a) and N-tigloylpyrazolidinone (1b) are treated with a urea hydrogen peroxide/TFAA and methyl(trifluoromethyl)dioxirane, respectively.

Observations on the transition-metal catalysed oxidation of alkanes in trifluoroacetic acid: urea–hydrogen peroxide/TFA as a convenient method for the oxidation of unactivated C–H bonds

Oxidation of cyclohexane in TFA using 30% aqueous H2O2 or urea–H2O2 (UHP) gives cyclohexyl trifluoroacetate in good yield, although the reaction is not accelerated by rhodium or ruthenium catalysts casting doubt on earlier claims on the role of transition-metals in oxidations in TFA.

Influence of diethanolamine on hard segment ordering in flexible polyurethane foams

In this study the microphase separation and structural organization of the hard segment domains were studied as a function of diethanolamine (DEOA) content for two series of model foams based on toluene diisocyanate (TDI) and glycerol initiated ethylene-oxide-capped propylene-oxide or glycerol initiated propylene-oxide. It was found that as the DEOA content was increased, the more disordered the hard segment domains became. Extractions in dimethyl formamide (DMF) showed that increasing the DEOA content increased the gel fraction, confirming that DEOA further crosslinked the system. More importantly, it was also found that the hard segment domains were also influenced by the DEOA content where the foams lacking DEOA had a much higher level of short range ordering. This was first confirmed by wide-angle x-ray scattering (WAXS) patterns where the amorphous character was much more pronounced as the DEOA content was increased. In addition, Fourier transform infrared (FTIR) data from the carbonyl region showed that the level of bidentate urea or strong hydrogen bonding also decreased as the DEOA content was increased, confirming that the short range ordering does decrease with increased DEOA content. This observation is believed to help explain the greater ease of “plasticization” by temperature and moisture observed of foams that included DEOA in their formulation. This was exemplified by comparing the load relaxation behavior at a low temperature (35°C) and a high temperature (100°C) between two foams varying in DEOA content. At ambient conditions (40°C, 35%RH), the foam with DEOA exhibited slightly higher loads at any given loading time, while at elevated conditions (100°C, 98%RH), there was very little difference between the two foams. Although the observed load relaxation behavior was mostly a result of the increased crosslinking, the increased closed cell content induced by the greater crosslinking also contributed to the load values. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:525–537, 1997

Multipoint recognition of carboxylates by neutral hosts in non-polar solvents

A neutral molecular receptor of carboxylates has been developed using the convergent ureas as the binding site. The data indicate that chelation of the carboxylates occurs by the urea hydrogens. Asymmetric centers in the host are shown to influence the nmr spectrum of a guest bound within.

Crosslinked and noncrosslinked diisocyanate‐linked elastomers containing substituted urea groups

AbstractA study was made of the preparation and properties of diisocyanate‐linked elastomers prepared from polyoxypropylene glycol (POPG), toluene‐2,4‐diisocyanate (TDI), and toluene‐2,4‐diamine (TDA). The chemical structure and gelation of a series of prepolymers were investigated first. Next, many series of elastomers were prepared at 60°C. in open molds and at 110°C. in closed molds from mixtures in which values of the ratio of isocyanate groups to the sum of the hydroxyl groups and amino groups (R1) and the ratio of the amino groups to hydroxyl groups (R2) were systematically varied. Cure at 60°C. gave tough, noncrosslinked elastomers, the properties apparently resulting from interchain attractive forces, while cure at 110°C. gave covalently crosslinked elastomers having rather similar properties. Glass‐transition temperatures increased linearly with the concentration of substituted urethane groups but were independent of the concentration of substituted urea groups. An explanation for the surprising behavior is presented. The noncrosslinked elastomers were soluble in N,N‐dimethylacetamide (DMA) and similar solvents. Intrinsic viscosities in DMA were found to increase with R1 at constant R2. Young's modulus, tensile strength, and ultimate elongation were determined between −23 and 82°C. At elevated temperatures, the crosslinked elastomers showed near‐equilibrium moduli, while the noncrosslinked ones did not. The number of chains per milliliter for the crosslinked elastomers was calculated from the quantities of excess isocyanate and urea hydrogens, along with an assumed topology for the network. The moduli for both types of elastomers were related to chemical composition. Various relationships between the ultimate properties and equilibrium moduli were evaluated. Extensions up to 5000% with elastic recoveries of better than 90% were noted.