Aqueous Urea Solutions Research Articles

Corrosion behavior of mild steel in aqueous solutions of ammonium nitrate and urea

Corrosion behavior of mild steel in aqueous solutions of ammonium nitrate and urea

Gas hydrate inhibition by urea and its blends with vinyl lactam polymer: Paving the way to green hybrid inhibitors

Urea is an environmentally benign substance considered a promising gas hydrate inhibitor in flow assurance. Nevertheless, its effect on gas hydrate formation kinetics remains poorly understood. This study investigates the impact of urea and hybrid urea/polymer KHI samples on the nucleation and growth kinetics of sII natural gas hydrates. Hydrate formation was observed at a lower onset temperature with increasing urea and polymer concentration. The nucleation of sII hydrate in aqueous urea solutions occurred at a higher subcooling (7.50 ± 0.58 K at 30 mass%) than in pure water (5.17 ± 0.69 K). These findings indicate that urea acts as a nucleation inhibitor of sII hydrates, although its capacity is not as potent as that of polymer KHI.The analysis of the hydrate nucleation probability distributions revealed that the sII hydrate nucleation rate exhibited a significant decline, approximately one order of magnitude, at subcooling of 5.3–6 K for 20 mass% urea compared to water. A similar behavior was noticed in an aqueous solution of polymer KHI. Urea has succeeded in providing a total benefit of up to 10 K in hydrate onset temperature due to a shift in the hydrate stability zone and nucleation retardation.Consequently, urea is a green dual-acting anti-hydrate chemical that inhibits the formation of sII hydrates by thermodynamic and kinetic mechanisms. Besides, adding 10 mass% urea increases the cloud point temperature of vinyl lactam polymer Luvicap 55W by 14 K. Urea is an additive that considerably augments the stability of the polymer in aqueous solutions at elevated temperatures. These findings make urea an effective and environmentally friendly top-up inhibitor that significantly enhances the anti-hydrate properties of polymer KHI.

Amplifying the Differences in Aluminum‐Based Eutectic Electrolytes Through Electrodeposition on MXenes

AbstractTraditionally, rechargeable lithium metal battery systems relied on simple metal cationic species to enable metal nucleation and deposition. However, this mechanism is less applicable to room‐temperature rechargeable aluminum batteries (RABs), which utilize complex ionic species. This work takes advantage of two different MXenes, Mo2Ti2C3Tx and Ti3C2Tx, which have different metal‐termination group bond strengths, interlayer spacings, and surface termination compositions, to amplify and visualize the differences between two promising RAB electrolytes (i.e., urea/AlCl3 and EMImCl/AlCl3). This work allowed us to deduce the following: 1) despite lower coulombic efficiencies, smoother Al deposits are observed when the urea/AlCl3 electrolyte is used; 2) unknown side reactions occur in all the different scenarios, however, they are likely less reversible in the EMImCl/AlCl3 electrolyte; 3) metal‐halogen exchange reactions can occur in all scenarios, forming Al(OF)x and AlFx species; 4) the free urea in urea/AlCl3 electrolyte behaves differently from the urea in aqueous solutions. Overall, due to the characteristics of aluminum, RABs involve vastly different internal mechanisms, resulting in the need for audacious attempts toward system understanding.

Linker-induced hollow MOF embedded into arginine-modified montmorillonite for efficient urea removal: Adsorption behavior and mechanism analysis

The precise regulation of hollow metal–organic framework (HMOF) and the effective assembly with excellent guest materials present limitless potential for pollutant removal. In this work, the arginine-modified montmorillonite (AMMT) was preferentially prepared via room temperature impregnation approach, and then the AMMT-HMOF composite was effectively constructed through a one-pot method. During this process, linker-induced MOF to MOF route was proposed, i.e., solid ZIF-67 transformed into hollow MOF-74 (thicknesses: ∼25 nm). Of note, this route involves the transition from solid to hollow structures, as well as the change between different topologies. Next, the AMMT-HMOF composite was evaluated for adsorption experiments with urea in aqueous solution as the target molecule. Further speaking, the optimization experiments were conducted to analyze the impact of pH, contact time, adsorbent mass and original urea concentration towards the adsorption process. The as-fabricated absorbent presented a maximum adsorption capacity of 298.5 mg/g within 1 h, demonstrating adherence to pseudo-second-order kinetics and the Langmuir model. The excellent adsorption performance can be ascribed to the enlarged layer spacing of AMMT, as well as the fast mass transport and abundant diffusion channels in HMOF. Additionally, the mechanistic analyses revealed the existence of hydrogen bonding interactions between the adsorbent and urea. Meanwhile, the adsorbent displayed the outstanding morphological and structural stability after usage. According to our survey, this is the first time to use this linker-induced MOF-to-MOF strategy and predictably assemble with functionalized montmorillonite to construct the hollow MOF composite for urea adsorption.

Thermo‐responsive polymer to clean fouled forward osmosis membrane after wastewater treatment: Excellent flux recovery

AbstractThermally responsive polymers (TRPs) have gained significant attention in the past decade due to their unique phase transition behavior, those exhibiting changes in properties with temperature variations. In water, hydrophilic block copolymers form helical structures that can transform into hydrophobic globules above the lower critical solution temperature (LCST). Fouling is one of the limiting issues for the forward osmosis (FO) process in wastewater treatment. In this work, after the treatment of wastewater from the paper and pulp industries, foulants were removed from the surface of the commercial polyamide thin‐film composite membrane of the FO process using polyvinyl methyl ether (PVME), a TRP with an LCST of 35–37°C. PVME was mixed with different aqueous solutions to form cleaning solutions. Foulant cleaning experiments utilized a 1% PVME (w/v) solution in 300 mL of de‐ionized (DI) water, while 1 M NaCl solution served as the draw solution (DS) in the FO process. Comparing the water flux (J) and change in membrane hydraulic resistance (Rf) among pristine, fouled, and cleaned membranes revealed a 56.67% increase in water flux and a 51.68% decrease in membrane resistance after PVME mixed with DI water cleaning solution showcasing its effectiveness in improving membrane performance and reducing fouling. The cleaning efficiency of two solutions, that is, 1% PVME mixed in DI water and 1% PVME mixed in 1 M aqueous urea solution, is compared. Results showed that the former cleaning solution helped to obtain 32.62% higher water flux and 56.05% less membrane resistance. Various membrane characterizations are performed, such as field emission scanning electron microscopy (FE‐SEM), which characterizes the membrane's pore structure and surface morphology, while a contact angle analyzer assesses hydrophilicity. This research highlights the use of TRPs as effective cleaning agents, enhancing membrane performance by effectively removing foulants on the membrane surface. Investigating alternative cleaning solutions also provides insights for optimizing water treatment processes.Highlights Cleaning of fouled thin‐film composite membrane using thermal‐responsive polymers (TRPs). Polyvinyl methyl ether, a TRP with an lower critical solution temperature of 35–37°C used as a cleaning agent. 60% increase in water flux was observed after the single‐step cleaning process. Multiple uses of TRP for cleaning performed with no membrane damage.

Improving electrochemical performance of Ni-rich layered cathode material with combining Co-enriched compositional gradient and radial microstructure

Ni-rich complex layered oxides LiNixMnyCozO2 (x > 0.85) with a combined Ni/Co concentration gradient and radially oriented elongated plate-like primary particles were synthesized with hydrothermal microwave-assisted treatment of an as-prepared mixed hydroxide precursor with aqueous solution of Co source and urea followed by a high temperature annealing with a Li source. The radial distribution of plate-like primary crystallites in microwave-treated materials was achieved through Co-enrichment at the surface, which likely triggered the surface-to-bulk growth of plate-like particles rather than isotropic octahedral crystallites. The Co-modified cathode materials demonstrate greatly improved cycling stability (capacity fade per cycle of 0.04 ± 0.01%) compared to unmodified Ni-rich NMCs (capacity fade per cycle of 0.13 ± 0.02%) with similar Ni concentration, as well as good rate capability (215, 210, 199, 189, 178 and 160 mAh/g at C/10, C/5, C/2, 1C, 2C, and 5C rates at 2.7–4.3V vs Li/Li+). Enhanced electrochemical performance is linked to the improved mechanical integrity, which was achieved through radial microstructure organization of the agglomerates triggered by Co concentration gradient, suppressing the intragranular crack formation.

Infrared Thermography Investigation of Crystallization in Acoustically Levitated Supersaturated Aqueous Solution

In this study, crystallization in highly supersaturated aqueous urea solutions was investigated using in situ infrared thermography facilitated by an acoustic levitation apparatus. A notable contribution of this thermographic approach is the identification of a transient heat release signature, particularly pronounced beyond the solubility limit, indicating the enhanced formation of bonds between urea molecules in the supersaturated states. Surprisingly, the temporal evolution of the heat release measurements on an acoustically levitated droplet strongly suggests a two-stage process for urea crystallization. A comprehensive statistical analysis based on classical nucleation theory is used to further investigate the exceptionally high degree of supersaturation and the emergence of prominent heat signatures observed toward the onset of crystallization.

Study of Molecular Interactions of the H-1 Antihistamine Drug Chlorpheniramine (CP) in Water and in Aqueous Solutions of Urea, Glucose, and Sodium Chloride at Different Temperatures

Study of Molecular Interactions of the H-1 Antihistamine Drug Chlorpheniramine (CP) in Water and in Aqueous Solutions of Urea, Glucose, and Sodium Chloride at Different Temperatures

Counteracting Effects of Trimethylamine N-Oxide against Urea in Aqueous Solutions: Insights from Theoretical Two-Dimensional Infrared Spectroscopy.

The study of small osmolytes in their aqueous solutions has gained significant attention because of their relevance to structure and thermodynamics of proteins in aqueous media. Special attention has been given to the binary and ternary aqueous solutions of urea and trimethylamine N-oxide (TMAO). Urea is a well-known protein denaturant, while TMAO protects proteins in their native states. Interestingly, TMAO counteracts urea's ability to denature proteins when present in solutions with approximately half of the concentration of urea. Vibrational spectroscopy can improve our understanding of the molecular origin of this counteracting effect because of its sensitivity to local structure and dynamics. We present results of theoretical linear vibrational and two-dimensional infrared (2DIR) spectroscopy of water in the binary and ternary aqueous solutions of TMAO and urea. The 2DIR spectra are calculated using the electronic structure/molecular dynamics approach. The non-Condon effects in spectral transitions are incorporated in the theoretical calculations of 2DIR spectra. It is found that TMAO disrupts the local structure of water, while urea leaves it essentially unaffected. The 2DIR results show that both TMAO and urea slow down the dynamics of spectral diffusion of water. The extent of slowing down is found to be particularly significant for both hydration and bulk water in the presence of TMAO which can be attributed to strong hydrogen bonds between the water and TMAO molecules. The water molecules present in the hydration layer of the solutes in the ternary solutions are found to relax at even slower rates compared to that in their binary solutions in water. The hydrogen bonds between TMAO and urea are found to be not stable. Thus, the counteracting effect of TMAO against urea is seen to take place mainly through water-mediated interactions. Such TMAO-induced effects giving rise to more structured and slower hydrogen-bonded network are successfully captured through 2DIR spectroscopic calculations.

Solid–Polymer–Electrolyte Electrolysis of Urea Aqueous Solutions for Hydrogen Synthesis

Solid–Polymer–Electrolyte Electrolysis of Urea Aqueous Solutions for Hydrogen Synthesis

Tough and On-Demand Detachable Wet Tissue Adhesive Hydrogel Made from Catechol Derivatives with a Long Aliphatic Side Chain.

Wet adhesion is critical in cases of wound closure, but it is usually deterred by the hydration layer on tissues. Inspired by dopamine-mediated underwater adhesion in mussel foot proteins, wet tissue adhesives containing catechol with 2-3 carbons side chains are reported mostly. To make wet adhesion of this type of adhesives much tougher, catechol derivatives with a long aliphatic side chain (≈10 atoms length) are synthesized. Then, a series of strong wet tissue adhesive hydrogels are prepared through photoinduced copolymerization of acrylic acid with synthetic monomers. The adhesive hydrogel has a high cohesion strength, that is, tensile strength and strain, and toughness of ≈1800kPa, ≈540%, and ≈4100kJm-3 , respectively. Its interfacial toughness on wet and underwater porcine skin is respectively ≈1300 and ≈1100 Jm-2 , and its adhesion strength to wet porcine skin is ≈153kPa. These values are much higher than those of dopamine-based adhesives in the same conditions, demonstrating that the long aliphatic side chain on catechol can greatly improve the wet tissue-adhesion. Additionally, the tough interfacial adhesion can be broken on demand with 5wt.% aqueous urea solution. This adhesive hydrogel is highly promising in safe wound closure.

Structure and Properties of the Xerogels Based on Potassium Silicate Liquid Glass and Urea.

The xerogels based on the aqueous solutions of urea in potassium silicate liquid glass (PSLG) were produced by CO2 bubbling and investigated. The structure and chemical composition of the obtained materials were analyzed. Using the SEM, XRD, IR-FT, DSC, and low energy local EDS analysis, it was recognized that the dried gels (xerogels) contained three forms of urea: oval crystals of regular shape appeared onto the surface of xerogel particles; fibrous crystals were located in the silicate matrix; and molecules/ions were incorporated into the silicate matrix. It was shown that an increase in [(NH2)2CO] in the gel-forming system promoted increased contents in crystalline forms of urea as well as the diameter of the fiber-shaped urea crystals. A rate of the urea release in water from the granulated xerogels containing 5.8, 12.6, and 17.9 wt.% of urea was determined by the photometric method. It was determined that the obtained urea-containing xerogels were characterized with a slow release of urea, which continued up to 120 days, and could be used as controlled release fertilizers containing useful nutrients (N, K).

Effect of hemicellulose content on the solution properties of cellulose carbamates in NaOH/ZnO aqueous system

Hemicellulose removal from bleached bamboo pulp is key to produce qualified dissolving pulps. In this work, alkali/urea aqueous solution was firstly applied to remove hemicellulose in bleached bamboo pulp (BP). The effect of urea usage, time and temperature on the hemicellulose content of BP was studied. The reduction of hemicellulose content from 15.9 to 5.7 % was achieved in 6 wt% NaOH/1 wt% urea aqueous solution at 40 °C for 30 min. Cellulose carbamates (CCs) were obtained from the esterification of BP with urea. The dissolution behavior of CCs in NaOH/ZnO aqueous solutions with different degree of polymerization (DP), hemicellulose and nitrogen contents were studied by using optical microscope and rheology. The highest solubility was up to 97.7 % when the hemicellulose was 5.7 % and Mη was 6.5 × 104 (g/mol). With the decrease of hemicellulose content from 15.9 % to 8.60 % and 5.70 %, the gel temperature increased from 59.0, 69.0 to 73.4 °C. The apparent gelation time increased from 5640 to 12,120 s with the hemicellulose content increased from 8.60 % to 15.9 %. CC solution with 5.70 % hemicellulose always keeps a liquid-state (G" > G') until the test time reached 17,000 s. The results showed that the removal of hemicellulose, the decrease of DP and the increase of esterification endowed CC with higher solubility and solution stability.

Phase equilibrium data for clathrate hydrates formed in the systems of urea + (methane or carbon dioxide) + water

Subsea methane hydrates are expected as a potential natural gas resource. To develop gas production methods for the subsea methane hydrates, flow assurance technologies are necessary. Urea is one of the environmentally-friendly thermodynamic hydrate inhibitors (THIs) which is expected to be applicable for subsea methane hydrate systems. To evaluate its performance as a THI, a set of phase equilibrium data are necessary. In this study, we report phase equilibrium data for systems of urea + methane + water and urea + carbon dioxide + water in the range of aqueous compositions of urea up to its solubility limits. The present data for urea + methane + water ranged in pressures from 5 to 13 MPa and in urea mass fractions from 0.05 to 0.5. The comparison with the literature found that the inhibition effect of urea is a few kelvin weaker than that of methanol in the present measurement range. With the dense urea solutions, the system reached four phase equilibrium, i.e., solid urea–aqueous solution–gas–hydrate. At 13 MPa, approximately 13 K of inhibition temperature was obtained with 0.500 of feed mass fraction where solid urea was precipitated from the aqueous phase. In the urea + carbon dioxide + water systems, urea also worked as a THI. The maximum inhibition temperature was approximately 10 K with 0.400 of urea mass feed fraction at the four phase equilibrium. Based on the present equilibrium data and seafloor conditions of the subsea methane hydrates, it was found that urea can be used for the both systems of the methane gas production and the hydrate based carbon capture and storage.

Mechanistic Insights into Polyphenols' Aggregation Inhibition of α-Synuclein and Related Peptides.

While several polyphenols were found to either inhibit or modulate the aggregation of proteins implicated in neurodegenerative diseases, such as Parkinson's disease (PD), discrepant action mechanisms have been reported. This, in addition to some polyphenols' pan-assay interference compounds' reputation, casts some doubts concerning their therapeutic relevance. Here, we studied, through molecular dynamics and enhanced sampling methods, the aggregation of 11-mer peptides from the non-amyloid-β component, an aggregation-prone domain of α-synuclein (α-syn) implicated in PD and other synucleinopathies, in neat water and aqueous solutions of resveratrol (RSV) and gallic acid (GA). Further, simulations of the complete protein were carried out in aqueous urea, RSV, and GA solutions. Our results show that peptide aggregation is not disrupted by either phenolic compound. Thus, instead, intrusion of RSV and GA in the inter-peptide region induces a peptide-peptide re-orientation, favoring terminal interactions that manifest in the formation of barrierless solvent-separated configurations. Moreover, although the (poly)phenols induce a pronounced peptide dewetting at high concentrations, β-sheet-rich regions, a hallmark of α-syn aggregation, are not disrupted. Thus, our results indicate that, if anything, RSV and GA delay or modulate peptide aggregation at high concentrations via the stabilization of solvent-separated conformations as opposed to aggregation inhibition. Structural analysis of the full protein, however, shows that the (poly)phenols induce more extended conformations of α-syn, similar to urea, possibly also influencing its aggregation propensity. However, opposite to urea, the (poly)phenols reduce α-syn's conformational space, likely due to steric effects and a slowdown of the solvent dynamics. These effects are concentration-dependent and possibly unattainable at therapeutic-relevant concentrations. These results suggest that the aggregation inhibition activity of RSV and GA in vitro should involve, instead, either the non-covalent binding to oligomeric intermediates or the stabilization of the monomer and/or oligomers through the formation of covalent bonds of the respective quinones with α-syn. In addition, the enhanced aggregation tendency of the peptides observed here could be associated with the formation of non-toxic oligomers, reported for some polyphenols.

Oxygenated Triazine-Heptazine Heterostructure Creates an Enormous Ascension to the Visible Light Photocatalytic Hydrogen Evolution Performance of Porous C3 N4 Nanosheets.

A highly efficient g-C3 N4 photocatalyst is developed by a novel one-pot thermal polymerization method under a salt fog environment generated by heating the aqueous solution of urea and mixed metal salts of NaCl/KCl, namely SF-CN. Thanks to the synergistic effect of the oxygenation and chemical etching of the salt fog, the obtained SF-CN is an oxygenated ultrathin porous carbon nitride with an intermolecular triazine-heptazine heterostructure, meanwhile, shows enlarged specific surface area, greatly enhanced absorption of visible light, narrowed band gap with a lower conduction band, and an increased photocurrent response due to the effective separation of photogenerated holes and electrons, comparing to those of pristine g-C3 N4 . The theoretical simulations further reveal that the triazine-heptazine heterostructure possesses better photocatalytic hydrogen evolution (PHE) capability than pure triazine and heptazine carbon nitrides. In turn, SF-CN demonstrates an excellent visible light PHE rate of 18.13mmolh-1 g-1 , up to 259.00 times of that of pristine g-C3 N4 .

Corrosion of 1.4016 Ferritic Steel by Urea at High Temperature

The corrosion behavior of a ferritic unstabilized stainless steel 1.4016 during decomposition of aqueous urea solution at high temperature has been investigated. Corrosion was obtained from 100 h of cyclic heating (from room temperature up to 600 °C) and injection of aqueous urea solution on the steel plate in a laboratory-scale test bench. The evaluation procedure covered the metallographic analysis of corroded steel samples by high-resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (TEM). Uniform corrosion underneath deposits was found as one of the drivers for degradation of the steel. Damage happened by high-temperature depassivation of stainless steel due to the excess of the aggressive medium. Besides uniform corrosion, a nitridation layer underneath surface oxides together with chromium carbonitride particles precipitated through the whole depth of the sample was identified resulting in intergranular attack.

Effect of aqueous solutions of KCl, MgCl2, Dextrose and Urea on solvation behavior of aqueous myo-Inositol

Owing to the indispensable role of myo-Inositol (MI), a cyclic polyol, in biological, pharmaceutical and food industries, in this investigation, we herewith report the systematic data of densities (ρ) and speed of sound (u) of MI in water, aqueous electrolytic (0.06 mol∙kg−1 KCl/MgCl2) and non-electrolytic (0.06 mol∙kg−1 Dextrose/Urea) solutions at seven different temperatures T/K (=288.15–318.15) and ambient pressure over the dilute concentration range of (0.03–0.2) mol∙kg−1. The experimental data of density (ρ) and speed of sound (u) were further processed to obtain respective derived parameters, such as apparent molar volume of solute Vϕ, isentropic compressibility of solution κs and apparent molar isentropic compression of the solute Ks,ϕ. The limiting values of apparent molar volume Vϕ0, apparent molar isentropic compression Ksϕ0 and apparent molar expansibility Eϕ0 of solute have been computed. Further, the coefficient of thermal expansion α∗, second order derivative of limiting apparent molal volume ∂2Vϕ0/∂T2, hydration number (nH) and transfer properties (ΔtrVϕ0andΔtrKs,ϕ0) of MI have also been obtained. An attempt has been made to analyse the molecular interactions through the coulomb attenuated hybrid exchange–correlation density functional theory (DFT) by gaussian tool. The effect of temperature and the studied electrolytic and non-electrolytic moieties (i.e., KCl, MgCl2, Dextrose and Urea) have been discussed in the light of prevailing interactions between solute-co-solute and solvent molecules on the basis of co-sphere overlap model.

Effect of Dissolution Time on the Development of All-Cellulose Composites Using the NaOH/Urea Solvent System

Innovative and sustainable all-cellulose composites (ACCs) can be obtained by partial dissolution of cellulosic fibers and regeneration of the dissolved fraction. Among cellulose solvents, sodium hydroxide/urea solutions are recognized as promising low-environmental impact systems. In this work, filter paper (FP) was dissolved with a 7 wt% NaOH/12 wt% urea aqueous solution, kept at −18 °C for different time intervals, regenerated with distilled water and finally dried under different conditions. The developed films were characterized in terms of morphology, porosity, optical properties, crystalline structure, hydration and mechanical properties. The porosity of the composites decreased with dissolution time due to the progressive filling of voids as the cellulosic fibers’ surface skin layer was dissolved and regenerated. Samples treated for 4 h showed the minimum values of porosity and opacity, high hydration and a substantial change from cellulose I to cellulose II. Hot pressing during drying led to relevant improvements in ACCs stiffness and strength values.

Preparation and Properties of a Novel Biodegradable Composite Hydrogel Derived from Gelatin/Chitosan and Polylactic Acid as Slow-Release N Fertilizer

To improve the efficient use of nitrogen and decrease the environmental pollution of N losses, a novel and biodegradable composite hydrogel was prepared by chemical cross-linking synthesis using gelatin (Gel), chitosan (CS) and polylactic acid (PLA) as raw materials. Urea as the nitrogen source was loaded into this new biodegradable hydrogel using the solution immersion method. The chemical structures of the composite hydrogels were characterized and their properties were analyzed by XRD and XPS. The regulation of urea loading and the swelling behavior of the composite hydrogel under different temperature conditions were investigated; the release behavior and release model of the composite hydrogel in the aqueous phase was explored. The results show that the loading of urea is controllable in aqueous urea solution with different concentrations. In the water phase, it shows a three-stage sustained release behavior, that is, the initial release rate of urea is relatively fast, and the medium release rate of urea gradually slows down, and finally the nutrient release rate tends to be flat. The release behavior in the water phase fits to the Ritger-Peppas model. Within 10 min, 180 min and 900 min, the cumulative nutrient release rate of gelatin/chitosan/PLA-urea (GCPU) composite hydrogel is 20%, 70% and 86%, respectively. Compared with pure urea, The urea diffusion time of GCPU was extended by 1350-times. In addition, the GCPU also has good water absorption and water retention properties, in which average water content can reach as high as 4448%. All of the results in this work showed that GCPU hydrogel had good water absorption and retention and N slow-release properties, which are expected to be widely used in sustainable agriculture and forestry, especially in arid and degraded land.