Saturated Urea Solution Research Articles

Preparation and characterization of starch carbamate modified natural sodium alginate composite hydrogel blend formulation and its application for slow-release fertilizer

The exploration of environmentally friendly slow-release fertilizer (SRF) based on natural bio-polymers is of great importance in the development of modern agriculture and horticulture. Herein, a novel starch carbamate (SC) modified sodium alginate (SA) hydrogel (SC/SAH) was prepared utilizing as-synthesized SC and natural SA through the cationic ions crosslinking method and ultimately the corresponding slow-release fertilizer (SC/SAH-SRF) was successfully developed by immersing the dried SC/SAH matrix into saturated urea solution. Due to the low gelation temperature and high viscosity of the synthesized SC, the formed SC/SAH exhibits significantly enhanced properties including excellent water absorbency up to 8.02 g/g with considerable repeatability, abundant pore structure and high hydrophilicity compared with the neat SAH and natural starch based hydrogel (NS/SAH). Accordingly, the SC/SAH leads to higher urea loading amount ∼ 1.28 g/g. Importantly, the resultant SC/SAH-SRF also shows superior slow-release performance, yielding a cumulative urea release of only 61.6 % within 10 h and almost completely release >16 h in water, what's more, only 58.5 % of the urea releases within 25 days and exceeding 50 days for complete release in soil column assays. The slow-release of urea from SC/SAH-SRF well complies for the first-order kinetics and accomplishes via a non-Fickian diffusion process. Moreover, the pot experiment demonstrates that the SC/SAH-SRF has higher growth promotion role for the maize seedlings than those of others. Consequently, this work provides a novel strategy for preparing environmentally friendly SRF by blending modified starch and hydrogel.

Preparation of Gypsum–Urea with Enhanced Sustainability from Flue Gas Desulfurization Gypsum in Saturated Urea Solution

Gypsum–urea is a kind of urea product with substantially reduced aqueous solubility and lower hygroscopicity that increases the soil retention time of urea and thus enhance its environmental sustainability. Here, gypsum–urea was prepared using bulk industrial solid waste flue gas desulfurization (FGD) gypsum as a raw material in a saturated urea solution via immobilizing urea molecules into the crystal lattice. The preparation process was achieved through a dissolution–recrystallization mechanism during which FGD gypsum dissolved into Ca2+ and SO42−, which then recrystallized with CO(NH2)2 to form gypsum–urea. The preparation process was almost completed within 10 min, and the formed gypsum–urea presented a uniform size distribution of 30–90 μm and a much lower hygroscopicity and nitrogen release efficiency than that of urea. With a high efficiency of synthesis, and sustainable features, and the recyclability of the saturated mother urea solution, the dissolution–recrystallization-based urea immobilization approach is highly promising regarding the preparation of gypsum–urea with the desired environmental sustainability and contributes to the realization of the sustainable reutilization of FGD gypsum.

Superior cycling stability of saturated graphitic carbon nitride in hydrogel reduced graphene oxide anode for Sodium-ion battery

A layered composite g-C3N4@RGO of graphitic carbon nitride (g-C3N4) and reduced graphene oxide (RGO) is reported as an anode material for rechargeable sodium ion batteries (SIBs). Initially, conducting interconnected hydrogel RGO was prepared by hydrothermal method and was further soaked in saturated urea solution, followed by calcination to synthesize g-C3N4@RGO composites. The coin type half cells were prepared by using composite g-C3N4@RGO and pristine RGO as anode and their electrochemical performances were compared. The prepared half-cell of the composite anode delivers maximum reversible specific discharge capacity of ∼ 170 mAh.g−1 and ∼ 160 mAh.g−1 at 0.1C and at 0.2C, respectively. Whereas, prepared half-cell using RGO anode shows maximum reversible discharge capacity of ∼ 146 mAh.g−1 and ∼ 133 mAh.g-1at 0.1C and 0.2C, respectively. This composite material g-C3N4@RGO shows excellent cyclability (2000 cycles) and columbic efficiency ∼ 100% with no capacity fading compared to the RGO. The binding of g-C3N4 with RGO prevents stacking of RGO sheets and provides macro and sub-micron porous structure for smooth intercalation and trapping of Na+-ions in composite g-C3N4@RGO anode during electrochemical cycling. The design of g-C3N4@RGO composite as a negative electrode improves the cell performance and offers effective strategy to develop low-cost and long cycle life SIBs.

Bulk properties and hydration numbers of components of water–salt, water–urea, and water–urea–salt systems

With an increase in the concentration of additives, the hydration numbers of compounds decrease. Thus, in a saturated 54.6% solution, urea loses approximately 3/4 of the initial amount of water, forming an aquacomplex of the composition (NH2)2CO∙H2O. In a supersaturated 44% solution, the sodium chloride aquacomplex is dehydrated by 2/3, and in a supersaturated 67% solution, sodium sulfate is dehydrated by 5/6. The density of these solutions is 1.354÷1.360 g/cm3 (44% NaCl) and 1.800÷1.849 g/cm3 (67% Na2SO4). In a saturated urea solution, NaNO3, NaCl, and Na2SO4 complexes lose 53÷55% of hydration water. It is shown that the interactions in the binary water–urea system somewhat increase the hydration number of the salts (structural hydration). The hydration water density, a structurally important characteristic, increases in the series of solutions of urea, NaNO3, NaCl, and Na2SO4. In the same series of additives, the excess volume of binary water–urea and water–salt systems becomes more negative.

Probing Composition and Molecular Mobility in Thin Spherical Films Using Nuclear Magnetic Resonance Measurements of Diffusion

The composition and molecular mobility within thin spherical liquid films have been investigated using nuclear magnetic resonance (NMR) diffusion measurements. These films were formed either on the surface of pores inside a sponge at low saturation or by adsorbed water on the outside of urea prills during caking. Using pulsed field gradient (PFG) NMR experiments, the molecular mobility within these liquid films was determined through analysis of the conditional probability density for displacement (propagator). Molecular diffusion coefficients were determined for films in the sponge and prill systems by fitting the experimental propagators using a model for diffusion on an array of isotropically distributed infinite planes. By comparing these diffusion coefficients with bulk diffusion coefficients for a range of concentrations of urea solutions (2.1 M, 6.2 M and saturated), it was possible to optimize the PFG experimental parameters to enable accurate determination of molecular diffusion in these spherical liquid films. Determination of the diffusion coefficients for a range of urea solutions in the sponge enabled identification of the composition of the film that formed on the surface of the urea prills. Analysis of these data showed that the liquid layers are composed of saturated urea solution covering the surface of the prills, with an estimated layer thickness on the order of 10–5 m. The shape of the propagators indicated the adsorbed water was uniformly distributed over the surface of the urea prills, rather than primarily in the meniscus between particles, which agrees with dye visualization experiments on a pair of urea prills during caking. This work provides the first quantitative measurements of diffusion in thin spherical films, which is a key parameter for determining what controls the presence and rate of bonding between adjacent particle surfaces.

Nitrate uptake improvement by modified activated carbons developed from two species of pine cones

Activated carbons from two species of pine cones (Pinus canariensis and Cupressus sempervirens) were prepared by phosphoric acid activation and tested for the removal of nitrate ions from aqueous solution. To investigate the feasibility of improving their nitrate adsorption capacity, two different post-treatments – a thermal treatment and a treatment with saturated urea solution – were also applied to the prepared activated carbons. Comparison of the treated and untreated activated carbons showed that both post-treatments improved the nitrate adsorption performance more than twice. The maximum adsorption capacity, as evaluated from determination of the adsorption isotherms for the P. canariensis based carbons, and their proper representation by the Langmuir model, demonstrated that the post-treatment with the urea solution led to activated carbons with increased nitrate removal effectiveness, even superior to other reported results. Enhancements in their adsorption capacity could be mainly ascribed to higher contents of nitrogen and basic functional groups, whereas porous structure of the activated carbons did not seem to play a key role in the nitrate uptake.

Concentrates of polyunsaturated fatty acids from Lappula squarosa seed oil

Polyunsaturated fatty acids (PUFA), gamma-linolenic (GLA), alpha-linolenic (ALA), and stearidonic (SA), exhibit high biological activity [1]. Various attempts have been made to prepare PUFA fractions enriched in one PUFA or another for use in drugs and dietary products. A method based on the different solubilities of sodium salts of FA in EtOH that was used for this enabled PUFA concentrates to be obtained from seed oil of Echium fastuosum, Borago officinalis, and Anchusa azurea (Boraginaceae) [2]. We obtained good results for the isolation of FA fractions enriched in ALA and GLA from linseed oil and seed oil of B. officinalis by using low-temperature crystallization at –80°C from CH3CN:Me2CO (7:3) [3]. The resulting fraction (mother liquor) from linseed oil, which contains 55% ALA, consisted of 88.5% ALA; from total FA of B. officinalis with 23.4% GLA, 88.3% of this FA. Crystallization of FA from hexane solution (10%) at –70°C enabled GLA and SA concentrates to be obtained from E. fastuosum seed oil. This method could be used on an industrial scale [4]. Fractions with high GLA and SA contents could be obtained by chromatographic methods such as HPLC, CC over silica gel and over silica gel impregnated with AgNO3, and centrifugal preparative chromatography (CPC). However, they are suitable only for laboratory studies [5]. Extraction by supercritical CO2 in order to isolate and enrich oils in GLA and SA did not give the desired result [6–8]. Fractionation of urea complexes of FA was used to isolate epoxytetraenoic acid from total FA of fish and microalgae [9]; a mixture of GLA with ALA, from FA of Ribes nigrum seed oil [10] and from FA of seed oil of A. azurea, E. fastuosum, and S. scophila [11]. As a rule, a urea:FA ratio of 4:1 (by mass) is used [9]. Production of FA fractions enriched with PUFA using urea complexes (clathrates) depends primarily on the initial set of PUFA and their content in the oil. The main difficulty in producing FA fractions with a high SA content is the presence in oils of SA and its precursor ALA. Until now, plants with oil that contains only SA have not been found [1]. Studies of seed lipids from several species of the family Boraginaceae indigenous to the Republic of Bashkortostan found that Lappula squarosa seed lipids contained >70% PUFA including >16% SA [12]. Separation of the FA from Lappula seed oil as the urea clathrates afforded fractions enriched with PUFA. For this, mild alkaline hydrolysis (10% KOH solution in MeOH, 70–80°C, 30 min) isolated from the oil the total FA. EtOH was used as the solvent to prepare the urea complexes because it was shown earlier that enrichment of PUFA in it occurred better by using FA from B. officinalis seed oil as an example [13]. FA were separated in two steps [13]. In the first step, a mixture of FA (0.8 g) was treated with a saturated solution of urea in EtOH (FA:urea ratio 1:3 by mass), stirred on a magnetic stirrer with heating (60°C) until totally dissolved, and left at room temperature for 3 h and then at 10°C for 24 h. The resulting clathrate crystals were separated on a Schott filter and washed with cold saturated urea solution in EtOH to produce mother liquor 1 and a precipitate of crystalline FA urea complexes, clathrates 1. The yield of FA fractions (mass% of starting FA) was 36.25 and 57.5, respectively (Table 1). Next, the FA compositions of the mother liquor and clathrates were analyzed. The mother liquor was evaporated to half the volume in a rotary evaporator, diluted with H2O, and extracted with Et2O in order to isolate the FA from it. The Et2O extracts were washed with H2O and dried over anhydrous Na2SO4. The solvent was evaporated. The resulting FA (0.29 g, mother liquor 1) were methylated by diazomethane and studied by GC (Table 1).

Conversion of biomass from an invasive species into activated carbons for removal of nitrate from wastewater

Development of activated carbons targeted at nitrate ion removal is investigated by chemical activation of sawdust from the invasive species Parkinsonia aculeata wood. Phosphoric acid and potassium hydroxide are comparatively used as activating agent. Its effect on main physico-chemical properties and on the effectiveness of the activated carbons in nitrate removal is compared with those determined for a commercial sample. Activated carbons developed with the base show the best effectiveness in nitrate removal, as determined from application of the Langmuir model to the experimental isotherms. The behavior is consistent with the development of surface basic groups and the more basic character of these carbons. Noticeable improvement in nitrate uptake for all the carbons is attained after treatment with a saturated urea solution, with removal levels of ∼80–90%, despite reductions in porous structures. Nitrate adsorption onto the urea-treated carbons is in direct correlation with their enhanced contents of elemental nitrogen. ► Chemically activated carbons from an unexplored biomass are developed with H 3 PO 4 acid and KOH. ► Effectiveness of the carbons in nitrate removal is examined. ► KOH-derived carbons show greater ability in nitrate uptake. ► Urea post-treatment of the carbons improves nitrate uptake in line with enhanced contents of elemental N.

Volume properties of a ternary system: Water-urea-amino acid. Dilute and concentrated solutions

Partial molar volumes \( \bar V_U^0 \) of amino acids in an aqueous urea solution are studied. For a saturated urea solution \( \bar V_U^0 \) equals the molar volume of the amino acid, therefore, in the saturated solution, the amino acid dissolves without changing the system volume. Hydrophobic effects are manifested in the volumetric characteristics only in dilute (<1 mol/kg) urea solutions. Within a three-layer hydration model, the numbers of amino acid hydration are found. By the example of alanine and leucine, it is shown that their decrease with increasing urea concentration is determined by a zwitterionic moiety and does not depend on the size of the hydrocarbon radical of the amino acid.

Kinetics of Nitrogen Doped TiO&lt;sub&gt;2&lt;/sub&gt; for Degradation of Rhodamine B

Nitrogen doped TiO2 Photocatalysts was prepared by ultrasonic dispersion method based on the predominated materials as tetrabutyl titanate with the dopant of saturated Urea solution. The dynamic behavior of nitrogen doped TiO2 for the degradation of rhodamine B was researched on the catalyst volume and the effects of pH value on photocatalysis ratio. Results showed that the catalytic reaction was accord with the first class reaction dynamic model. When the catalyst was 0.1g and the pH value close to 7, the degradation ratio was the maximum.

Interfaces between a Saturated Aqueous Urea Solution and Crystalline Urea: A Molecular Dynamics Study

Interfaces between a saturated urea solution and crystalline urea surfaces have been studied by means of molecular dynamics simulations. Mean densities of solute urea and water at both (001) and (110) interfaces show an enhanced adsorption probability for solute urea compared to water. Orientation distributions and positions in the horizontal plane have been calculated for urea molecules in the first adsorption layer. These indicate a preorganization for growth of a new crystal layer at the (001) interface. The adsorbed urea molecules at the (110) interface, on the other hand, are much more randomly distributed and oriented than at the (001) interface and even show a slight preference for wrong positions above the crystal surface. This indicates an increased interfacial entropy which may stabilize the (110) crystal surface.

The mechanism of the fixation of tissue components by osmium tetroxide via hydrogen bonding

Considerable electron density, observable in membranous elements in thin sections of buffered OsO4-fixed tissue with electron microscopy, was removed by the action of K4Fe(CN)6 in acetic acid. This reagent reacted only with Os(VIII) and not with lower oxidation states of osmium to give an insoluble crystalline precipitate, K2FeOs(CN)6. Supporting this finding was the fact that the osmate esters, Os(VI), originally synthesized by Criegee (8, 9), were unreactive with acetic ferrocyanide. Acetic acid alone decreased membrane density of fixed sections by simple protonation but did not remove osmium from osmate esters. Further, fresh tissue incubated in a saturated urea solution, then fixed in buffered OsO4 not only failed to blacken, as routinely observed after OsO4 fixation, but also tissue structure was poorly preserved and membranous structures showed less electron density. Tissue fixed in a 1:1 solution of urea and OsO4 also demonstrated competition between the two compounds for binding sites in membranes. Thus, osmium in the Os(VIII) state appears responsible for some, if not much, of the membrane density, and is probably hydrogen bound in its native state as OsO4, to protein and to aliphatic side chains of lipid in membranes. Theoretical calculations pertaining to molecular interactions of OsO4 urea, and model proteins and lipids indicate that the above mechanistic hypothesis of the interaction of OsO4 with tissue components is favored over the mechanism of osmate ester formation with the double bonds in lipids as has been believed to date.

Urease reaction rates at low water activity.

Hydrolysis of urea by urease takes place in ‘dry’ urea-urease mixture exposed to discrete water vapor pressures from 100% to 20% relative humidity and at 2°C to 70°C. A discontinuity in enzymatic activities is observed at the transition of urea from a solid to a deliquescent solution. Urease is inactivated more readily at higher relative humidities in saturated urea solution than at lower relative humidities where water for urea hydrolysis is adsorbed on enzyme-protein only. Hydrolysis of urea by urease proceeds at a measurable rate in concentrated solutions of urea and of urea hydrolysis products, ammonium carbonate and bicarbonate, in the absence of ionic strength or pH stabilizing agents.

Mushroom polyphenol oxidase I. Purification and general properties

1. 1. A method of purification of mushroom polyphenol oxidase (tyrosinase) ( o-diphenol:O 2 oxidoreductase, EC 1.10.3.1) is described. This method was found reproducible and has consistently given a homogenous preparation of high specific activity in a reasonable yield. 2. 2. The molecular weight of the enzyme is 128 000 ± 5% by sedimentation velocity diffusion, 118 000 by the Archibald method and 133 000 ± 10 000 by light-scattering measurements. 3. 3. The enzyme dissociates into subunits in saturated urea solution, and is completely inactivated. This dissociation is reversible, but the inactivation is not. 4. 4. The enzyme contains 0.20% or near to 0.20% of copper, exclusively or prevalently in the cuprous form. Ageing of the enzyme is accompanied by a lowering of the specific activity and a partial oxidation of the copper. 5. 5. The holoenzyme can be reconstructed by adding Cu 2+ to the apoenzyme. The molecular properties of the apo and of the holoenzyme appear to be identical. 6. 6. As a consequence of preparative procedures the enzyme may suffer different alterations which result in preparations apparently homogenous but of a significantly lowered specific activity.

Field experiments on uptake of nitrogen from leaf sprays by sugar beet

When the leaves of sugar-beet crops were sprayed on six occasions in late September and early October with 100 gal./acre of a 3% solution of ammonium nitrate or equivalent urea, in two experiments about 70% of the nitrogen was recovered in the plants in mid-October, compared with 40% recovered from applications of the same amounts of fertilizer to the soil at the same times. In a third experiment the recovery from similar sprayings with urea solution was less than 40%, but very little nitrogen was absorbed from soil dressings, so that the difference between the recoveries from spray and soil applications was nearly the same as in the other experiments.Nitrogen per cent of dry matter in all parts of the plant was increased by the sprays. More than half of the nitrogen absorbed from the sprays was in the leaf laminae, and the remainder was equally divided between petioles (including crowns) and roots. Between 20 and 30% of the nitrogen supplied in spray in the first two experiments was converted to protein in the leaf laminae, and half of this was present as soluble protein precipitable by trichloracetic acid, a fraction that is extracted in the largescale preparation of leaf protein.Spraying slightly increased the dry-matter yield of the tops, but not of the roots. It reduced the sugar content of the roots by about 1% of fresh weight. In one experiment it had no effect on sugar yield; in the others it caused losses of 2 and 5 cwt./acre.The recovery of nitrogen in the tops from a single low-volume spraying (12½ or 25 gal./acre) with nearly saturated urea solution was about the same as from repeated high-volume sprays supplying the same total amount of nitrogen, but in the roots it was higher from the single than from the repeated sprays.