Condensation Of Urea Research Articles

Synthesis and application of Fe3O4@RHA nanocatalyst in the synthesis of polyhydroquinolines and dihydropyrimidinones (statistical approach to optimize parameters)

In this study, rice husk ash as silica source was obtained and then, by adding Fe3O4, Fe3O4@RHA core-shell nanocatalyst was prepared. The Fe3O4@RHA nanocatalyst was identified using VSM, XRD, FE-SEM, EDX, and FT-IR analysis, and the optimization of the effective parameters in the reaction was done using response surface methodology (RSM). This nanocatalyst had spherical particles with an average particle size of about 30 nm and good magnetic properties of about 42 emu/gr. The Fe3O4 particles encapsulated in RHA were easily recovered and showed good catalytic activity. Using Fe3O4@RHA biosynthesized nanocatalyst, polyhydroquinoline derivatives were obtained through multi-component condensation of ammonium acetate, aldehyde, ethyl acetoacetate, and dimedone, under solvent-free conditions at 80 °C, as well as dihydropyrimidinone derivatives through multi-component reactions by condensation of urea, aromatic aldehyde, and β-Keto ester under solvent-free conditions at 70 °C. Fe3O4@RHA nanocatalyst was introduced as a heterogeneous, stable, and environmentally compatible catalyst; in its production, dangerous materials, reagents, and solvents were avoided and it is environmentally friendly. In addition, it has the advantage of being recyclable, resulting in short reaction time, high product yield, and economically good performance.

Enhanced Photocatalytic Activity of Direct Z‐Scheme K4Nb6O17/Carbon‐Rich Melon Heterostructures

AbstractMelon (also known as graphitic carbon nitride, g‐C3N4) holds promise for photocatalysis, but challenges such as severe charge recombination, low oxidation potential, and sluggish exciton dissociation hinder its performance. Herein, a series of carbon‐rich, melon‐based photocatalysts are synthesized via one‐pot, temperature‐induced condensation of urea with the addition of a trace amount of citric acid. The addition of citric acid enhances crystallinity, extends melon chains, increases the C/N ratio, and improves π–π layer stacking of heptazine units, thereby enhancing charge transport properties and visible‐light harvesting capacity. These carbon nitride samples are then coupled with molten salt synthesized K4Nb6O17 crystals by a straightforward self‐assembly method to construct 2D/2D heterostructure photocatalysts. Z‐scheme electron transfer from K4Nb6O17 to the melon samples is established based on their work functions and band edge positions. This efficient charge transfer in the Z‐scheme heterostructure facilitates the spatial separation of charge carriers, resulting in a nearly fivefold enhancement in photocatalytic performance compared to the individual constituents.

One pot synthesis of multi-functional B doped g-C3N4-praseodymium oxide nanocomposites for colorimetric detection of Hg2+ ion and solar photocatalytic removal of toxic water pollutants

A novel praseodymium oxide-boron co-doped graphitic carbon nitride composite was synthesized via one-step solid-state thermal condensation of urea, orthoboric acid and praseodymium nitrate precursors. The prepared composites were characterized by various methods. All the prepared composites demonstrated multi-functional activities towards peroxidase-mimetic based colorimetric detection of Hg2+ ions and superior photocatalytic efficiency towards photodegradation of textile colorants, photoreduction of hexavalent chromium and nitro aromatics like para-nitro phenol (PNP) and para-nitro aniline (PNA). The superior photocatalytic activity can be attributed to the formation of type II heterojunction which facilitates charge separation and increases the lifetime of photogenerated charge pairs. As evident from the scavenger studies, these charge pairs are involved in the formation of superoxide and hydroxyl radicals. The superior activity of the optimum composite can be attributed to the porous flaky morphology, decreased optical band gap, heterojunction mediated charge separation, and praseodymium oxide's conductive nature. A linear range of about 0.25–800 nM of Hg2+ ions can be detected with a limit of detection (LOD) of 42.4 nM using the colorimetric strategy. The as-synthesized composite is thus a unique, efficient, economically viable, and excellent candidate for detecting and degrading various hazardous water pollutants.

Effect of surface modification of Fe/g-C3N4 catalyst on the product distribution in CO hydrogenation

Carbon nitride (g-C3N4) prepared using thermal condensation of urea was pretreated by H2O2/NH3·H2O and used as support to obtain Fe/g-C3N4 catalyst via impregnation method. The catalytic performance of the catalysts both before and after modification was investigated in CO hydrogenation. Combining detailed characterizations, such as XRD, SEM, TEM, FT-IR, TG, CO2-TPD, CO-TPD, H2-TPR, contact angle measurement, and N2 physical adsorption and desorption, we investigated the effects of surface pretreatment on the texture properties of Fe/g-C3N4 catalysts and the product distribution of CO hydrogenation. The results demonstrate that various pretreatment techniques have significant influences on the textural properties and catalytic performance of the catalysts. The prepared g-C3N4 with a typical honeycomb structure has strong interaction with highly dispersed Fe. Both before and after modification, the materials are hydrophilic, and the hydrophilicity is increased after treatment with H2O2 and NH3·H2O. Treatment with H2O2 enhances surface hydroxyl groups. NH3·H2O treatment improves surface amino groups, promotes CO adsorption, and facilitates the formation of Fe(NCN) phase. The surface basicity of all pretreated catalysts is enhanced. The water gas shift (WGS) reaction activity of the two-step modified catalyst Fe/AM-g-C3N4 was lower, and the CO2 selectivity in CO hydrogenation was reduced to 11.61%. Due to the enhanced basicity of Fe/AM-g-C3N4, the secondary hydrogenation ability of olefins was inhibited to obtain higher olefin selectivity with C= 2–C= 4 of 32.37% and an O/P value of 3.23.

Synthesis of CeO2 Nanoparticles Derived by Urea Condensation for Chemical Mechanical Polishing

Synthesis of CeO2 Nanoparticles Derived by Urea Condensation for Chemical Mechanical Polishing

Triazine-free polyimide for photocatalytic hydrogen production

Polyimide (PI) has received considerable attention as a promising donor-acceptor polymer for photocatalytic hydrogen production, yet the previous studies entirely focused on the exploration of triazine-based PI. Herein, we report for the first time triazine-free PI for photocatalytic hydrogen evolution. The triazine-free PI was synthesized by thermal condensation of urea and pyromellitic dianhydride. The resultant PI photocatalyst yielded a stable hydrogen evolution activity and an appreciable photocurrent response. This work manifests that triazine is not an indispensable unit for the photocatalytic hydrogen evolution activity of PI, which expands the chemical library of PI photocatalysts and opens up new opportunities for designing efficient polymeric photocatalysts.

Novel urea‐based compounds as solid‐solid phase change materials: 1,3‐bisstearoylurea and 1,1,3,3‐tetrastearoylurea for thermal energy storage applications

1,3-Bisstearoylurea and 1,1,3,3-tetrastearoylurea were produced as solid-solid phase change materials (SS-PCMs) for potential solar thermal energy storage (TES) applications via condensation of urea with the respective amount of carboxyl chloride (stearoyl chloride). Both 1,3-bisstearoylurea and 1,1,3,3-tetrastearoylurea were characterized by Fourier-transform infrared (FT-IR), 1H nuclear magnetic resonance, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis techniques. 1,3-Bisstearoylurea and 1,1,3,3-tetrastearoylurea had considerable melting/crystallization enthalpy. The reason for crystallization was structural symmetry and flexibility of long alkyl groups there. Di and tetra alkyl groups made it possible to discuss the structure-property relationship for organic PCMs. Besides, the compounds were characterized through DSC and FT-IR spectroscopy before and after thermal cycling to determine their thermal reliability. Solid-solid phase change enthalpies of them for melting and crystallization were found 95.86 and −87.6 Jg−1 for 1,3-bisstearoylurea, respectively and 27.7 and −25.8 Jg−1 for 1,1,3.3-tetrastearoylurea, respectively. Thermal conductivity was studied to increase by simply expanded graphite addition. The thermal endurance limits of 1,3-bisstearoylurea and 1,1,3,3-tetrastearoylurea compounds were studied using TG analysis.

Ultra-thin graphene/g-C3N4 nanosheets with in-plane heterojunction for enhanced visible-light photocatalytic hydrogen evolution performance

ABSTRACT Ultra-thin graphene/g-C3N4 nanosheets (CN/G) with in-plane heterojunction were prepared by facial two-step thermal condensation of urea and glucose under mild conditions to improve photocatalytic hydrogen evolution under visible-light irradiation. The characterisation indicated that graphene was connected to the end of g-C3N4. The thermal exfoliation process can transform the bulk structure of g-C3N4 into ultra-thin nanosheets. Consequently, photocatalytic activity for hydrogen evolution rate of CN/G-0.1 was 704 µmol g–1 h–1, about 14 times higher than that of pure g-C3N4 under visible light irradiation (λ > 420 nm). CN/G-0.1 also exhibited high stability from the cycling tests for 18 h and superior photocatalytic properties at 500 nm. In-plane graphene modification can significantly enhance visible-light absorption and promote photogenerated electron-hole pair separation. On the other hand, ultra-thin nanosheets can increase specific surface area (153.8 m2 g–1) and provide abundant active sites. This study provides a suitable method to prepare g-C3N4 based on highly efficient photocatalysts for metal-free photocatalytic hydrogen evolution.

Three-Component Condensation of Urea with Formaldehyde and Propane-1,3-diamine or Butane-1,4-diamine

Three-Component Condensation of Urea with Formaldehyde and Propane-1,3-diamine or Butane-1,4-diamine

Application of a calcined animal bone to synthesis of graphitic carbon nitride composite

ABSTRACT Graphitic carbon nitride (g-C3N4) is a polymeric organic semiconductor that has been extensively developed for various applications. In this study, composites of g-C3N4 and calcined animal bone (CAB) were facilely synthesized by calcining a mixture of urea and CAB at different temperatures. The results revealed that the calcination temperature influenced yield, crystallinity, and band gap of g-C3N4. In addition, ultraviolet–visible diffuse reflectance spectroscopy indicated a shift in absorption edge to the high wavelength side in the presence of CAB, implying that CAB promoted thermal condensation of urea. However, thermogravimetric measurements revealed that g-C3N4 yield decreased as the calcination temperature increased in the presence of CAB. This is because the amount of g-C3N4 was scarce when the mixture was calcined at 823 K. Furthermore, the results of differential thermal analysis indicated that g-C3N4 and its intermediates were oxidatively decomposed by CAB at 823 K.

Prebiotic Origin of Pre‐RNA Building Blocks in a Urea “Warm Little Pond” Scenario

Urea appears to be a key intermediate of important prebiotic synthetic pathways. Concentrated pools of urea likely existed on the surface of the early Earth, as urea is synthesized in significant quantities from hydrogen cyanide or cyanamide (widely accepted prebiotic molecules), it has extremely high water solubility, and it can concentrate to form eutectics from aqueous solutions. We propose a model for the origin of a variety of canonical and non-canonical nucleobases, including some known to form supramolecular assemblies that contain Watson-Crick-like base pairs.The dual nucleophilic-electrophilic character of urea makes it an ideal precursor for the formation of nitrogenous heterocycles. We propose a model for the origin of a variety of canonical and noncanonical nucleobases, including some known to form supramolecular assemblies that contain Watson-Crick-like base pairs. These reactions involve urea condensation with other prebiotic molecules (e. g., malonic acid) that could be driven by environmental cycles (e. g., freezing/thawing, drying/wetting). The resulting heterocycle assemblies are compatible with the formation of nucleosides and, possibly, the chemical evolution of molecular precursors to RNA. We show that urea eutectics at moderate temperature represent a robust prebiotic source of nitrogenous heterocycles. The simplicity of these pathways, and their independence from specific or rare geological events, support the idea of urea being of fundamental importance to the prebiotic chemistry that gave rise to life on Earth.

Production of Metal‐Free C, N Alternating Nanoplatelets and Their In Vivo Fluorescence Imaging Performance without Labeling

AbstractThe use of luminescent probes with proper optical and morphological properties, high serum stability, low cytotoxicity, and good biocompatibility is a cost‐effective method for bioimaging. In this work, a route is developed to produce a novel bioimaging probe framework. A C3N4 material (UCN‐H) is produced by thermal condensation of urea under humidified air treatment. Chemical characterizations reveal that the UCN‐H contains C3N4 networks with smaller grain sizes and more amine‐based functionalities at the edges than UCN, which is separately produced without the humidified air treatment. Highly stable aqueous dispersions including fluorescent C3N4 nanoplatelets are generated by sonication of the UCN‐H powder. The photoluminescence (PL), time resolved‐PL, and 2D excitation‐emission spectra of the dispersions show that the UCN‐H has less‐intra bandgap traps and longer PL lifetime than UCN. In confocal microscopic study using the nanoplatelets, clear fluorescent cell images are obtained without any cytosolic aggregation. In in vivo imaging studies with MDA‐MB‐231 tumor‐bearing mice models, persistently strong fluorescence signals are successfully observed on tumor lesions without any interference of autofluorescence from live tissues after their accumulation by passive tumor targeting. Ex vivo biodistribution and histology results are well‐matched with in vivo fluorescence imaging results.

Sunlight-driven photocatalytic degradation of rhodamine B dye by Ag/FeWO4/g-C3N4 composites

A wide range of processes have been adopted for environmental remediation; among them, photocatalysis appeared as an appealing strategy for degradation of organic pollutants. Heterogeneous photocatalysis efficiently dissociates the charge carriers and helps in reducing the rapid recombination rate of charge carriers resulting in enhanced photocatalytic degradation. A semiconductor photocatalyst graphitic carbon nitride (g-C3N4), when doped with metals or non-metals, showed increased degradation abilities. Hence, a ternary photocatalyst was synthesized by thermal condensation of urea coupled with ferric tungstate (FeWO4) and doped with a noble metal (Ag) resulting in visible light susceptive semiconductor photocatalyst Ag/FeWO4/g-C3N4. The characterization of the fabricated composite was done by Fourier transform infrared, scanning electron microscopy energy-dispersive X-ray, and X-ray diffraction. The Ag/FWO/GCN was used to degrade the rhodamine B (RhB) dye. Under sunlight, Ag/FeWO4/g-C3N4 showed enhanced photocatalytic degradation of rhodamine B dye, which was ascribed to the change in bandgap and reduced charge recombination. The parameters used for the optimization of the photocatalyst were pH, catalyst dose, oxidant dose, and irradiation time. The composite (Ag/FeWO4/g-C3N4) showed ~ 98% degradation of RhB dye under optimized conditions (i.e., pH = 8, catalyst dose = 50 mg/100 ml, oxidant dose = 9 mM, irradiation time = 120 min and RhB conc. 50 ppm).

On the influence of water on urea condensation reactions: a theoretical study

Abstract The influence of water molecules on the kinetics of urea condensation reactions was studied with high-level quantum chemical methods and statistical rate theory. The study focuses on the production of biuret, triuret, and cyanuric acid from urea because of their relevance as unwanted byproducts in the urea-based selective catalytic reduction (urea-SCR) exhaust after treatment of Diesel engines. In order to characterize the potential energy surfaces and molecular reaction pathways, calculations with explicitly-correlated coupled-cluster methods were performed. It turned out that the reactions proceed via pre-reactive complexes and the inclusion of one or two water molecules into the condensation mechanisms leads to a decrease of the energy barriers. This effect is particularly pronounced in the production of biuret. Due to the pre-reactive equilibria, the rates of the overall reactions can increase or decrease by incorporating water into the mechanism, depending on the temperature and water concentration. Under the conditions of urea-SCR, the studied reactions are too slow to contribute to the observed byproduct formation.

Innovative Developments for the Disposal of Spent Ethanolamines from a Carbon Dioxide Purification Unit on Ammonia Aggregates

Various options are considered for the processing of large-capacity waste of ethanolamines generated during long-term operation as absorbents in technological processes of carbon dioxide extraction from converted gas (from a mixture of CO2and hydrogen) in the production of ammonia type AM-76 and accumulation flue gas. Various innovative methods have been proposed for the disposal of spent mono- and methyldiethanolamines, which are in demand in various industries: in the process of urea condensation with a formaldehyde-containing product in the synthesis of adhesive and impregnating resins for woodworking, in the production of high-quality synthetic drying oils and substitutes for titanium white, in the manufacture of flame retardants and molding mixtures for metal structures and foundry molds in the metallurgical industry, when refining oil from hydrogen sulfide and mercaptans. This allowed us to solve the important environmental problem of the disposal of toxic waste, optimize the operation of a number of industries and reduce their environmental impact.

Simple approach using g-C3N4 to enable SnO2 anode high rate performance for Li ion battery

Synthesis of SnO2 powders with different shapes can be achieved by different approaches including wet and dry methods. One constrain of wet production is the complexity of process control that is not always possible when scale-up of active materials for electrodes is considered. On the other hand, simple solid state methods carried out at low temperatures with active carbon to prevent coarsening of particles are more feasible for industrial production. In this work, graphitic carbon nitride (g-C3N4) is prepared by thermal condensation of urea and directly used to synthesize SnO2@C3N4 for LIB anodes through a scalable solid state reaction. Such fast approach allows to obtain the active material with regular and homogeneous distribution of SnO2 over g-C3N4 phase. SnO2@C3N4 enables the cell to achieve very good rate capability and excellent stability upon prolonged cycling at high rates, suggesting the prospects for next-generation high-power and low cost lithium-based batteries.

Dual-defect-modified graphitic carbon nitride with boosted photocatalytic activity under visible light

The development of photocatalysts that efficiently degrade organic pollutants is an important environmental-remediation objective. To that end, we report a strategy for the ready fabrication of oxygen-doped graphitic carbon nitride (CN) with engendered nitrogen deficiencies. The addition of KOH and oxalic acid during the thermal condensation of urea led to a material that exhibits a significantly higher pseudo-first-order rate constant for the degradation of bisphenol A (BPA) (0.0225 min−1) compared to that of CN (0.00222 min−1). The enhanced photocatalytic activity for the degradation of BPA exhibited by the dual-defect-modified CN (Bt-OA-CN) is ascribable to a considerable red-shift in its light absorption compared to that of CN, as well as its modulated energy band structure and more-efficient charge separation. Furthermore, we confirmed that the in-situ-formed cyano groups in the Bt-OA-CN photocatalyst act as strong electron-withdrawing groups that efficiently separate and transfer photo-generated charge carriers to the surface of the photocatalyst. This study provides novel insight into the in-situ dual-defect strategy for g-C3N4, which is extendable to the modification of other photocatalysts; it also introduces Bt-OA-CN as a potential highly efficient visible-light-responsive photocatalyst for use in environmental-remediation applications.

Urease immobilization on magnetic micro/nano-cellulose dialdehydes: Urease inhibitory of Biginelli product in Hantzsch reaction by urea.

Micro/nano celluloses (MC)/NC) were magnetized by nanoγ-Fe2O3 into the nanoγ-Fe2O3@MC (NMMC) and nanoγ-Fe2O3@NC (NMMC) which oxidized to NMMCD and NMNCD dialdehydes for Schiff-base immobilization of urease as NMMCD/urease and NMMCD/urease. The relative enzyme-activity of the immobilized ureases were comparable with the free-urease, although 75%-80% of the enzyme activity preserved for NMMCD/urease and NMNCD/urease after six cycles. The compared catalytic activities of the NMMCD/urease and NMMCD/urease in Biginelli/Hantzsch reactions in water at 60 °C surprised us by 100% selectivity for the Biginelli product 3,4-dihydropyrimidin-2(1H)-one (DHPM1). With the superiority of NMNCD/urease, this high selectivity using immobilized ureases is owing to the admirable urease inhibitory of the formed Biginelli product DHPM1 by urea condensation instead of urea hydrolysis. The robust enzyme inhibitory of the DHPM1 for free urease was also confirmed by phenol red test to show the deactivation of enzyme for enzymatic hydrolysis of urea and ammonia production in water.

Amine-rich carbon nitride nanoparticles: Synthesis, covalent functionalization with proteins and application in a fluorescence quenching assay

Carbon nitride nanoparticles (CNNPs) have been employed as fluorescent sensing tools owing to their unique features, e.g. low cost production, high stability in water and high photoluminescence quantum yield. Here, an easy and versatile synthetic approach was exploited to design fluorescent nanoparticles with surface functionalities suitable for covalent binding to bioligands. High hydrophilic, brightly fluorescent CNNPs, rich of superficial amines, were obtained from the thermal condensation of urea and lysine (CNNPLys) and by tuning the precursor ratio and the heating time. Structure and size of the functionalized nanoparticles were characterized through infrared (IR) spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). Their optical properties were studied by ultraviolet-visible (UV-Vis) and fluorescence spectroscopy. The superficial primary amino groups, furnished by the lysine co-precursor, enabled for covalently linking CNNPLys to model proteins. The CNNPLys-protein conjugates excited under UV irradiation emit in the 400–450 nm visible range (quantum yield 24%). The applicability of CNNPLys as novel fluorescent probes was demonstrated by a fluorescence quenching assay, in which gold nanoparticles (GNPs) were attached to Staphylococcal protein A and employed to quench the CNNPLys fluorescence by resonant energy transfer (FRET). The quenching occurred upon formation of the specific binding between the GNP-linked protein A and CNNPLys-tagged immunoglobulins, while the inhibition of the binding resulted in the recovery of CNNPLys luminescence. The synthetic strategy, based on combining a “conjugated polymer”-forming unit (urea) and a co-precursor able to provide the desired functional group (lysine), allows designing innovative materials for the development of new generation fluorescence biosensors in which easily functionalized fluorophores are needed.

Synthesis and optimization of the trimesic acid modified polymeric carbon nitride for enhanced photocatalytic reduction of CO2

The conjugated co-monomer, trimesic acid (TMA) was integrated into the triazine framework of polymeric carbon nitride (PCN), synthesized through chemical condensation of urea. The TMA-modified carbon nitride samples obtained were named as CNU-TMA and it was utilized for the photocatalytic reduction of carbon dioxide (CO2) under visible light illumination. The induction of such electron donor-acceptor co-monomer (TMA) dominates the intramolecular structure of PCN by acting as a nucleophilic substitution substrate to facilitate the electron density in the π-electron conjugated system of PCN and thus elevate its photocatalytic activity. Also, this process of copolymerization with TMA, not only cause a significant diversion in the specific area, band gap, chemical composition, and structure of PCN but also promote efficient charge transport from ground state (HOMO) to the excited state (LUMO) of the PCN. For comparison, CNU samples modified with other co-monomers were prepared by the same method and were named as CNU-FDA (2,5-Furandicarboxylic acid), CNU-PDA (2,6-pyridinedicarboxylic acid), CNU-PTA (Phthalic acid). Similarly, co-monomer TMA was incorporated in other PCN precursors such as dyandicyanamide (DCDA), thiourea (SCN) and ammonium thiocyanate (NH2SCN) and was named as CND-TMA13.0, CNT-TMA13.0, and CNA-TMA13.0, respectively. Besides, the average weight ratio between urea and TMA was well tuned and also CNU-TMA13.0 gain a fabulous 16 fold-enhanced photocatalytic performance than blank CNU.