Excess Of Urea Research Articles

Synthesis and structure of a manganese(II) coordination polymer assembled with 5-(tert-butyl)isophthalic acid and 1,3-dimethyl-2-imidazolidinone

Abstract A manganese(II) coordination polymer [Mn(tbip)(DMI)] n (1), (tbipH2 = 5-(tert-butyl)isophthalic acid, DMI = 1,3-dimethyl-2-imidazolidinone), has been synthesized under “urea-thermal conditions” (i.e. in an excess of urea). Its structure has been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis and IR spectra. Complex 1 crystallizes in the monoclinic space group P21/c with Z = 4. In 1, the [tbip]2− ligand bridges the Mn(II) cations to form infinite chains, and the neighbouring chains are connected through [tbip]2− ligands into layers.

Superfast adsorption of small and uncharged urea from water using post-sonicated iron-based metal-organic framework

Urea is widely used in fertilizer production for agricultural purposes which risks runoff into soil and water sources. An excess of urea can result in algal or toxic blooms which can poison wildlife or even humans by accumulation in food sources. The removal of urea from water is challenging due to the small size (0.254 nm) and uncharged surface of urea. Intensive research has been conducted on a variety of methods to remove environmental concentrations of urea using adsorbents, but most of them lack effective removal, require long (>2 h) process time, and lack re-generability. Metal-organic frameworks (MOFs) are the new generation of adsorbents with excellent structural and functional group tunability. In this study, we synthesized MIL-100 (Fe), an iron-based MOF, as an efficient adsorbent for the removal of uncharged urea from water. The urea adsorption capacity of MIL-100 (Fe) was tested under varying experimental conditions such as pH (2–10), temperature (25–65 °C), MOF concentration (25–400 ppm), and urea concentration (25–1000 ppm). The results showed the superfast adsorption (more than 85% removal within 2 min) of neutrally charged urea molecules on MIL-100 (Fe). The MOF was able to reach a maximum adsorption efficiency of around 85% with a maximum uptake capacity of 3321 mg/g. The MIL-100 (Fe) showed acceptable re-generability by retaining up to 90% removal efficiency after four regeneration cycles. The urea adsorption followed pseudo 2nd-order adsorption kinetics and dipole-dipole interactions and π-NH bonding were the primary adsorption mechanism.

Optical and Sensing Properties of Carbon Colloidal Particles Based on (Thio)urea and Citric Acid: Effect of the Components Ratio

Changing the composition of a precursors mixture is a powerful tool to tune the structure and properties of carbonaceous nanoparticles synthesized via the solvothermal route. We have addressed the influence of the ratio of urea or thiourea to citric acid during their solvothermal treatment in dimethylformamide on the optical and sensing properties of the obtained colloidal product. It has been found that the urea-derived products are more diverse in comparison with the thiourea-based ones. The excitation-dependent fluorescence of the products and their sensitivity to mercury(II) ions have been investigated; one to three types of fluorophores have been observed in the products depending on the composition. The nanoparticles prepared in excess of urea have been found more sensitive to the heavy metal, with the sensitivity of the long-wave emission band being superior.

Uticaj uree i glukoze na otpornost legure zlata 21K na koroziju u prisustvu veštačkog znoja

Corrosion resistance of Gold 21K alloy immersed in artificial sweat in the absence and presence of 100 ppm of urea and also 100 ppm of D-Glucose has been investigated by polarization study and AC impedance spectra. It is observed that Corrosion resistance of Gold 21K alloy immersed in artificial sweat in the presence of 100 ppm of urea / D-Glucose increases. Hence it is concluded that people wearing ornaments made of Gold 21K alloy need not worry about the excess of urea / D-Glucose in their sweat. When Gold 21K alloy is immersed in artificial sweat in the presence of 100 ppm of urea, Linear Polarisation Resistance value increases from 103389Ohmcm2 to 123437Ohmcm2 ; corrosion current decreases from 4.036 x10-7A/cm2 to 3.308 x10-7A/cm2 ; charge transfer resistance value increases from 10490 Ohmcm2 to 14070 Ohmcm2 ; impedance value increases from 4.253 to 4.324; double layer capacitance decreases from 4.862x10-10 F/cm2 to 3.625x10-10 F/cm2 , and phase angle increases from 38.91 to 70.14. When Gold 21K alloy is immersed in artificial sweat in the presence of 100 ppm of D-Glucose, Linear Polarisation Resistance value increases from 103389Ohmcm2 to 4817257Ohmcm2 ; corrosion current decreases from 4.036 x10-7A/cm2 to 0.161x10-7A/cm2 ; charge transfer resistance increases from 10490Ohmcm2 to 33300Ohmcm2 ; impedance value increases from 4.253 to 4.977; double layer capacitance decreases from 4.862x10-10 F/cm2 to 1.5315x10-10 F/cm2 , and phase angle increases from 38.91° to 79.74°.

Influence of the Fuel/Oxidant Ratio on the Elaboration of Binary Oxide Catalyst by a Microwave-Assisted Solution Combustion Method

Three series of binary metal oxide catalysts containing Ni, Cu, or Co oxides were prepared, fully characterized and tested in CO oxidation. The catalysts, with a constant transition metal loading of 10 wt%, were prepared from metal nitrates and urea mixtures by a microwave-assisted solution combustion method. The RV/OV ratio, corresponding to the stoichiometry of the reactants, calculated from their elemental oxidizing and reducing valences, was varied. In order to modify the redox character of the synthesis medium from the quantity of urea; an excess of urea was used for attaining reducing conditions, while a deficit of urea shifted the medium to oxidizing conditions. Three RV/OV ratios (0.9, 1.0, and 1.1) were selected to elaborate the different binary metal oxide catalysts, nine oxide catalysts were synthesized. Then, the influence of the stoichiometry (RV/OV ratio) on the bulk and surface properties of the binary metal oxide catalysts was investigated. Similarly, the influence of the RV/OV ratio on the CO oxidation activity was discussed and the optimal value of RV/OV ratio was identified. The results show that the increasing of the RV/OV ratio from 0.9 to 1.1, particularly in Ni- and Co-containing catalysts, induces stronger metal-aluminum interactions, in the form of aluminates phases, and that are correlated to the dramatic reduction of the CO oxidation activity. The best physicochemical properties and highest catalytic activities were achieved with the catalysts prepared in redox systems stoichiometrically balanced (RV/OV = 1). The Cu-containing catalysts presented the best catalytic activities in CO oxidation.

Synthesis of Wollastonite Powders by Combustion Method: Role of Amount of Fuel

The objective of this work has been the synthesis of wollastonite by solution combustion method. The novelty of this work has been obtaining the crystalline phase without the need of thermal treatments after the synthesis. For this purpose, urea was used as fuel. Calcium nitrate was selected as a source of calcium and colloidal silica served as a source of silicon. The effect of the amount of fuel on the combustion process was investigated. Temperature of the combustion reaction was followed by digital pyrometry. The obtained products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and specific surface area. The results showed that the combustion synthesis provides nanostructured powders characterized by a high surface area. When excess of urea was used, wollastonite-2M was obtained with a submicronic structure.

Intracellular urease activity in the lichen Cladonia verticillaris, and its implication for toxicity

Urea is currently used as a nitrogen fertilizer in many plant cultures, such as sugar cane. Several lichen species grow in the edges of the fields fertilized with urea. This implies that the hydrolysis of an excess of urea by soil bacteria or by the lichens themselves would increase the concentration of ammonia in the lichen thallus to a level that may be toxic to the photobiont. However, Cladonia verticillaris produces urease through positive feedback by urea supplied from the medium. This urease is partially secreted to the media or retained on the external surface of algal cells, as demonstrated herein by an adequate cytochemical reaction. This implies that ammonia produced by urea hydrolysis will be immediately dissolved in the water filling the intercellular spaces on the thallus. A possible protection mechanism against eventual ammonia toxicity, derived from the results described here, is also discussed.

Effect of propellant on the combustion synthesized Sr-doped LaMnO 3 powders

Lanthanum strontium manganite (LSM) powders of composition La 0.7Sr 0.3MnO 3 are good candidates for cathode application in solid oxide fuel cells. This paper reports the synthesis of LSM powders from nitrate precursors by the combustion method, using two different propellants (urea and glycine) and varying the propellant/nitrate ratio. Thermogravimetric analysis (TGA) revealed two or three decomposition stages of the as-synthesized samples, with complete burn out of organics at about 850–900 °C. X-ray diffraction (XRD) patterns showed formation of only LSM phase for the sample synthesized with excess of urea, whereas SrCO 3 and MnCO 3 phases were also found for the samples prepared from glycine. The powder is better crystallized when a homogeneous gel is formed before burning. The crystallite size calculated using the Scherrer equation is in the range of 15–20 nm. Scanning electron microscopy (SEM) revealed the presence of agglomerates, formed by fine particles of different shapes.

Influence of combustion aids on suspension combustion synthesis of mullite powders

Mullite powders were obtained by suspension combustion synthesis. The reaction was performed in a combustion reactor designed in the laboratory, which presents some advantages over other classical procedures (heating with a hot-plate, a furnace or a microwave oven). Aluminium nitrate, as a source of Al, and either TEOS or a colloidal silica suspension, as a source of Si, were used as reagents. Urea, at either 100 or 200% excess over the stoichiometric ratio, was used as fuel. NH 4NO 3, HNO 3, NH 4Cl and H 2O 2 were compared as combustion aids. Mullite phase with a high crystallinity and a high specific surface area was directly obtained by using aluminium nitrate, colloidal silica suspension, a 100% excess of urea and either NH 4NO 3 or H 2O 2. The selection of a combustion aid determines the characteristics of the as-synthesized powders. In addition to enthalpy predictions the reduction potential is a key parameter for the combustion to occur.

Steam reforming of methanol over copper–manganese spinel oxide catalysts

The steam reforming of methanol was studied over a series of copper–manganese spinel oxide catalysts prepared with the urea–nitrate combustion method. All catalysts showed high activity towards H 2 production with high selectivity. Synthesis parameters affected catalyst properties and, among the catalysts tested, the one prepared with 75% excess of urea and an atomic ratio Cu/(Cu + Mn) = 0.30 showed the highest activity. The results show that formation of the spinel Cu x Mn 3 − x O 4 phase in the oxidized catalysts is responsible for the high activity. Cu–Mn catalysts were found to be superior to CuO–CeO 2 catalysts prepared with the same technique.

Characteristic of hydrous iron (III) oxides prepared by homogeneous precipitation of iron (III) sulphate with urea

Hydrous iron (III) oxides agglomerated into uniform porous spherical clusters with submicrometre size and high specific surface area were obtained. Homogeneous precipitation of iron (III) sulphate was carried out in boiling aqueous solution that contained excess of urea. The prepared precursor precipitates were heated for 2 h at various temperature (from 200 to 800 °C) to yield fine iron oxides powders. The structure evolution during heating of powders was investigated by X-ray diffraction (XRD). The morphology and microstructure characteristics were also obtained by means of scanning electron microscopy (SEM), (BET) and (BJH). In order to see the phase transition temperature thermogravimetric analysis/differential thermal analysis studies were performed. It was found that formation of different hydrous iron (III) oxides was affected by experimental conditions: aging time, mixing procedure, pH and temperature.

Production of hydrogen via combined steam reforming of methanol over CuO–CeO 2 catalysts

Hydrogen production by (combined) steam reforming of methanol (CSRM) was investigated over CuO–CeO 2 catalysts prepared via the urea-combustion method. The characteristics of the resulting oxides were strongly influenced by the autoignition time during synthesis and the sample prepared with near stoichiometric quantity of urea had less favorable catalytic properties. Catalysts prepared from urea-rich or lean mixtures were more active and selective and an optimum behavior was obtained with 75% excess of urea and Cu/(Cu + Ce) ratio equal to 0.15. The higher methanol conversion in the CSRM process may be attributed to more efficient heat transfer in the bed due to combustion of part of methanol.

Influence of chemical synthesis on the crystallization and properties of zinc oxide

ZnO powders were synthesized using (a) the decomposing urea process and (b) crystallization from the suspensions obtained by abrupt mixing of Zn(NO 3) 2 and NH 4OH solutions. The samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), microelectrophoresis and BET. Basic zinc carbonate was always produced in decomposing urea solution at 95 °C in excess of urea and for times between 1 and 8 h. ZnO was produced by heating of basic zinc carbonate at 300–600 °C. The FT-IR spectrum of ZnO produced at 600 °C showed the superposition of three IR bands located at 565, 489 and 403 cm −1. The ZnO powder prepared at 300 °C showed the greatest specific surface area of 17.88 m 2 g −1. The precipitates obtained by abrupt adding of concentrated NH 4OH solution into Zn(NO 3) 2 solution corresponded to a complex compound with the general formula Zn 5(OH) 8(NO 3) 2(H 2O) 2− x (NH 3) x . Autoclaving of the aqueous suspension of this compound yielded ZnO. For these ZnO powders the relative intensity of the band at 498 cm −1 was substantially increased. On the other hand, the specific surface area of ZnO produced by autoclaving was found significantly decreased in relation to the urea process. Microelectrophoretic measurements with ZnO particles showed pH iep varying between 9.3 and 9.8. The zeta potentials measured for ZnO particles produced by the urea process were much higher than those measured for ZnO particles produced by autoclaving. TEM showed two different morphologies and different sizes of ZnO particles in dependence on the method of chemical synthesis. The difference in the FT-IR spectra of these two kinds of ZnO particles was ascribed to their microstructural properties. Microelectrophoretic and BET measurements were also related with the microstructure of ZnO particles.

Influence of urea on initiation and termination of reaction between nitric acid and formic acid

The influence of urea on initiation and termination of the reaction between nitric and formic acids was experimentally examined. The urea injection can terminate the denitration reaction in 2 to 10M salt-free nitric acid solutions and the simulated high level liquid wastes (HLLWs) with a nitric acid concentration of 2 to 6M. An excess of urea can interrupt the initiation of denitration in both simulated HLLW and salt-free nitric acid solutions. The initiation and termination of denitration are in relation with nitrous acid formation and decomposition. Urea reacts with nitrous acid easily in the denitrating solution and decomposes nitrous acid. As the urea concentration increases in the solution, the continuance of denitration become impossible because the decomposition rate of nitrous acid exceeds the generation rate. In addition, the nitrous acid concentration can not be high enough to initiate the denitration in the solution with an excess of urea because nitrous acid is decomposed by urea.

Diet selection in sheep: the ability of growing lambs to select a diet that meets their crude protein (nitrogen × 6.25) requirements

To test the proposition that sheep are able to select a diet that meets their crude protein (N x 6.25; CP) requirements, feeds L, A, B, C and H with the same energy content (11 MJ metabolizable energy/kg feed) but different CP contents (78, 109, 141, 172 and 235 g CP/kg fresh feed respectively) were formulated. In addition, feed U, which was feed L plus 21.4 g urea/kg (CP content 132 g/kg), was also made. The feeds were offered ad lib. either singly (n 4 per treatment) or as a choice between feed H and another feed (pairs LH, AH, BH, CH and UH; n 9 per feed pair) to individually penned Suffolk x Scottish mule wether lambs, over the live-weight range 25-45 kg. On the single feeds the rates of live-weight gain were 273, 326, 412, 418, 396 and 407 g/day (SE of difference (SED) 34; P < 0.01) and protein (excluding wool) gain were 27, 32, 44, 45, 41 and 39 g/d (SED 4; P < 0.001) for feeds L, A, B, C, H and U respectively. When sheep were given a choice between a feed below (L or A) and a feed above their CP requirements (H; as judged by the single-feeding treatments) the CP concentration selected was not different between the two pairs: 131 (SE 4) v. 133 (SE 4) g CP/kg feed for pairs LH and AH respectively. On the choices BH and CH (a choice between two feeds above requirements) the feed lower in CP was constantly preferred (874 (SE 33) and 910 (SE 33) g feed B and C respectively per kg total feed intake; CP selected was 157 and 178 g CP/kg respectively). However, this was not the case with the UH choice on which sheep consumed only 599 (SE 61) g feed U/kg total feed intake, resulting in a selection of a higher CP in their diet (173 g CP/kg). The live-weight gains of the animals given a choice between two feeds were 416, 387, 415, 410 and 383 g/d (SED 37) and protein gains were 45, 40, 46, 50 and 43 (SE 7) for pairs LH, AH, BH, CH and UH respectively, which were comparable with the best performance achieved on a single feed. The results suggest that sheep were able to select a diet that meets their CP requirements and avoid, at least to a certain extent, excess of protein intake.(ABSTRACT TRUNCATED AT 400 WORDS)

Lichen substrates and urease production and secretion: A physiological approach using four Antarctic species

Ramalina terebrata, C. regalis and S. alpinum produce urease in response to urea exogenously supplied. Enzyme activity is abolished by including 300 μM cycloheximide in the incubation media. Urease is affected by feed-back inhibition when ammonia is accumulated in the thalli. Lecania brialmontii has a constitutive urease which is strongly inhibited by an excess of urea. The enzyme is secreted to the media as a function of the soil in which lichens survive.

Synthesis and spectral properties of diethyl organylchalcogenoalkyl(alkyl)malonates, RX(CH 2) nCR′(COOC 2H 5) 2, and 5-alkyl-5-(organylchalcogenoalkyl)barbiturates, RX(CH 2) n[formula omitted]O (X = Se, Te)

Barbiturates substituted at the 5-position with organyltelluroalkyl or organylselenoalkyl groups were prepared by ring annulation of appropriately substituted diethyl malonates with urea or thiourea. The substituted diethyl malonates [phenyl-tellurobutyl(ethyl), i-propyltelluropropyl(ethyl), i-propyltelluropropyl(allyl), i-propylselenopropyl(ethyl), and phenylselenohexyl(methyl) were prepared in 55–91% yield by reaction of diethyl ω-bromoalkyl(alkyl)malonates with organyltellurolates or -selenolates (RXNa; X  Se, Te) in ethanol/benzene. The RXNa species were prepared by NaBH 4 reduction of the ditellurides (R 2Te 2) or diselenides (R 2Se 2) in ethanol/benzene. The ω-bromoalkyl(alkyl)malonates were obtained by reacting the sodio(alkyl)malonates, with α,ω-dibromoalkanes. Condensation of the diethyl organylchalcogenoalkyl(alkyl)malonates with an excess of urea or thiourea in dimethyl sulfoxide in the presence of potassium t-butoxide gave 5-organylchalcogenoalkyl-5-alkylbarbiturates or -thiobarbiturates. The following barbiturates were obtained in 28–84% yield: phenyltellurobutyl(ethyl), m.p. 100°C; i-propyltelluropropyl(ethyl), m.p. 119°C; i-propylselenopropyl(ethyl), m.p. 137°C; phenylselenohexyl(methyl), m.p. 124°C. The 5-substituted thiobarbiturates i-propyltelluropropyl(ethyl)- (m.p. 75°C) and i-propylselenopropyl(ethyl)thiobarbirurate (m.p. 83°C) were isolated in 32 and 20% yield, respectively. The barbiturates and thiobarbiturates were purified by chromatography and recrystallization and characterized by elemental analyses, mass spectrometry, 1H, 125Te and 77Se NMR spectroscopy and UV-VIS spectrometry. The chalcogenobarbiturates radiolabeled with 123mTe or 77Se may be useful as brain imaging agents.

The effect of additives on the practical electrolytic separation of hydrogen and deuterium. II. Separation factor at Hg in aqueous and non-aqueous media

Studies of the effects of additives on the electrolytic H/D separation factor,SH/D, previously reported in Part I [2] for Pt and Fe electrodes, are extended to the case of Hg for which the mechanism of cathodic H2 evolution is well established. The behaviour of urea and guanidine was investigated. In the case of urea, the separation factor at Hg is enhanced but decreases with increasing current density or cathodic potential. The dependence ofSH/D on current density can be correlated with the diminishing surface excess of urea with increasing negative potential. Experiments with proton sources other than H2O in liquid water were investigated by making measurements ofSH/D from solutions of H2O/HOD, CH3COOH/CH3COOD and CF3COOH/CF3COOD in CH3CN with NaClO4 as electrolyte. An interesting inverse H/D isotope effect arises with trifluoroacetic acid (TFA) as proton source; the effect is interpreted in terms of competitive reactions of H and D with TFA rather than unusual bonding and vibrational characteristics of the TFA activated complex. The results suggest that useful isotopic separations can be made by use of selective competitive reactions. A kinetic analysis of the inverse isotope effect is given.

Further studies of urea-catalyzed phosphorylation reactions.

We have analyzed the products formed when mixtures of a nucleoside and ammonium dihydrogen phosphate are heated with an excess of urea. If there is more phosphate than nucleoside in the mixture, compounds containing pyrophosphate bonds are obtained. If uridine, as nucleoside, is in excess over phosphate, di- and oligonucleotides are formed.

A Study on the Application of Urea Adduct Method on Mineral Oil Fraction (II)

Experiment on urea dewaxing to two varieties of kerosene fractions was carried out. When about 10% of paraffins were extracted from each kerosene, their freezing points were lowered to -70°C. Although dewaxing results differs according to the properties of mother kerosenes, the paraffins extracted were mainly normal paraffins. The melting points of the extracted paraffins were higher for those extracted with insufficient urea than those extracted with excess of urea. Depressing of freezing points by addition of gasoline were influenced by the properties of the blended gasoline and mother kerosene, and, at times deviated from Hepp's curve. Under the scope of this experiment, notable difference in the distillation curve (ASTM) was not observed between dewaxed and mother kerosenes.