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Laser-induced synthesis and photocatalytic properties of hybrid organic–inorganic composite layers
摘要： A laser-based method was developed for the synthesis and simultaneous deposition of multicomponent hybrid thin layers consisting of nanoentities, graphene oxide (GO) platelets, transition metal oxide nanoparticles, urea, and graphitic carbon nitride (g-C3N4) for environmental applications. The photocatalytic properties of the layers were tested through the degradation of methyl orange organic dye probing molecule. It was further demonstrated that the synthesized hybrid compounds are suitable for the photodegradation of chloramphenicol, a widely used broad-spectrum antibiotic, active against Gram-positive and Gram-negative bacteria. However, released in aquatic media represents a serious environmental hazard, especially owing to the formation of antibiotic-resistant bacteria. The obtained results revealed that organic, urea molecules can become an alternative to noble metals co-catalysts, promoting the separation and transfer of photoinduced charge carriers in catalytic composite systems. Laser radiation induces the reduction of GO platelets and the formation of graphene-like material. During the same synthesis process, g-C3N4 was produced, by laser pyrolysis of urea molecules, without any additional heat treatment. The layers exhibit high photocatalytic activity, being a promising material for photodegradation of organic pollutants in wastewater.
关键词： transition metal oxide nanoparticles,urea,photocatalytic properties,hybrid organic–inorganic composite layers,graphene oxide,graphitic carbon nitride,methyl orange,laser-based synthesis,chloramphenicol
更新于2025-11-14 17:04:02
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Merging Photoredox PCET with Ni-Catalyzed Cross-Coupling: Cascade Amidoarylation of Unactivated Olefins
摘要： A rapid, highly diastereoselective amidoarylation of unactivated olefins was achieved to render medicinally privileged pyrrolidinone structures. Taking advantage of a photoredox proton-coupled electron transfer process, amidyl radicals were obtained from non-prefunctionalized N–H bonds under mild conditions, which were subsequently trapped by pendant olefins, delivering alkyl radicals for nickel-catalyzed cross-coupling. Mechanistic studies revealed the key balance between thermodynamically-driven radical generation and kinetically-driven cyclization, which led to expanding the scope toward urea and carbamate substrates.
关键词： urea,nickel catalysis,carbamate,unactivated olefins,proton-coupled electron transfer,amidoarylation,photoredox catalysis,pyrrolidinone
更新于2025-09-23 15:23:52
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Enzymatic method of urea determination in LTCC microfluidic system based on absorption photometry
摘要： In this paper a novel microanalytical system based on absorption photometry for urea determination in small-volume biological samples is described. The developed microsystem with built-in microreactor with urease immobilised on its surface was fabricated using low temperature co-fired ceramics (LTCC) technology. For detection of the ammonium ions – product of urea hydrolysis, the modified Berthelot’s reaction was applied and conditions of this reaction were optimised in a way to be suitable for analysis in microsystems and for particular application, with special regards to very small alternation of urea concentration in culture medium. The best results were obtained for reagent R1 composed of: 180 mM sodium salicylate, 15 mM sodium nitroprusside, 2 mM EDTA in phosphate buffer solution of pH 7 and reagent R2 containing 16.9 mM sodium hypochlorite in phosphate buffer solution of pH 12. Linear concentration range of urea detection with the use of the developed LTCC microfluidic system for the selected flow rate of 4 μl/min, was in the range up to 1 mM, and the calculated lower limit of detection – 0.002 mM. The developed microsystem enables urea determination in samples of post-culture medium and of cells lysates of minimised volume c.a. 1 μl. Preliminary studies related to determination of urea in real samples, performed using hepatic cells lysates and post-culture medium were successful. As reference methods, commercially available tests were applied. The determined urea concentration measured by means of the QuantiChrom? and BioMaxima test and by the developed method based on the LTCC microanalytical system differs by c.a. 9% and 2% respectively. To the best of our knowledge, this is the first urea analysis microsystem for use in cells culture studies characterised by: the smallest volume of sample – 1 μl, long lifetime with stable response - reduced by 14%, through experimental time span of 30 days as well as suitability for quasi-monitoring of cells in vitro with sampling rate - 6 samples per hour.
关键词： LTCC technology,enzymatic microreactor,microfluidic systems,lab-on-a-chip,enzymatic urea determination,absorption photometry
更新于2025-09-23 15:22:29
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Co2+a??coordinated NH2a??carbon quantum dots hybrid precursor for the rational synthesis of Coa??CoOX/Coa??Na??C ORR catalyst
摘要： For the goal of practical industrial development of fuel cells, design and synthesis of electrocatalysts for oxygen reduction reactions (ORR) with sustainable and high performance are of great significance. In this work, the coordination of NH2-carbon quantum dots (NCQDs) with Co2+ on carbon black was reasonably achieved via one-pot and low-cost hydrothermal treatment for the first time. Citric acid (CA) and urea (UA) were taken as carbon and nitrogen sources for NCQDs, respectively. The coordination of Co2+ and NCQDs were well-characterized using spectroscopic techniques such as FTIR, UV-visible absorption and fluorescence. Carbonization of carbon black-supported Co/NCQDs at 800 oC under N2 atmosphere endows the pyrolysis products with high catalytic activity. The Co-CoOX/Co-N-C possesses enhanced ORR performance in terms of positive onset-potential (～-0.079 V vs. SCE) and half wave potential (E1/2) (～-0.201 V vs. SCE), high stability, as well as the accelerated reaction kinetics.
关键词： urea (UA),Citric acid (CA),oxygen reduction reactions (ORR),NH2-carbon quantum dots (NCQDs)
更新于2025-09-23 15:19:57
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Determination of the isotopic composition of enriched materials using laser ablation molecular isotopic spectrometry: partial least squares and multivariate curve resolution for the determination of 15N content in enriched urea
摘要： A quantitative analytical method based on laser ablation molecular isotopic spectrometry (LAMIS) and multivariate analysis was developed and evaluated for the determination of the isotopic composition of enriched materials. The method consists preparing a concentrated solution of the enriched material, using small quantities of a sample (125 mg), and ensuring the economic efficiency of the analysis. Standard solutions of known isotopic contents are prepared by employing mixtures of urea highly enriched in 15N and urea of natural isotopic ratio and analyzed by mass spectrometry. A small volume (30 μL) of these solutions is delivered to a filter paper disc (3 cm diameter). After drying, the disc, offering a homogeneously distributed analyte, is presented to a LAMIS equipment to acquire the vibronic emission spectra containing information about the isotopologues of interest. To illustrate the proposed method, the content of 15N is determined in enriched samples of urea. In this case, each spectrum is normalized by the intensity of emission of the CN isotopologues for the electronic (Δν = 0) emission band at 387.1 nm, ensuring better accuracy. Selected regions and single wavelengths of the vibronic emission spectrum (Δν = + 1 or ? 1) related to CN species were employed to construct multivariate partial least squares (PLS) and univariate regression models to predict the isotopic content of new samples. Besides, the LAMIS data set was evaluated by multivariate curve resolution (MCR) algorithm. The best MCR and PLS models presented similar results regarding the accuracy to determine 15N content in enriched urea. MCR is capable of identifying spectral interferences and minimizing its effect. The results show that the proposed method based on LAMIS and PLS or MCR multivariate analysis can determine the 15N content in the range 5–50% with a root mean square error of prediction (RMSEP) respectively equal to 0.5 or 0.7% (m/m) in comparison with reference results obtained by mass spectrometry.
关键词： 15N determination in enriched urea,Laser ablation molecular isotopic spectrometry (LAMIS),Isotopic composition of enriched materials,Partial least squares,Multivariate regression,Multivariate curve resolution (MCR)
更新于2025-09-23 15:19:57
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Effects of different complexing agents on the physical properties of ZnO nanoparticles
摘要： ZnO nanoparticles have been synthesised via a co-precipitation method using different complexing agents. X-ray diffraction (XRD) analysis revealed that ZnO nanoparticles were composed of a single hexagonal wurtzite phase. Transmission electron microscopy (TEM) analysis indicates that the samples prepared without any complexing agent have slight agglomeration characteristics presenting a prismatic morphology and a wider size distribution from 22 to 72 nm, which provides good material packing density. However, samples synthesised using urea and glycine are similar and show spherical-like morphology. XRD and TEM analyses indicate that complexing agents also have an important role in the size of the ZnO nanoparticles, where the average particle size of 47 and 22 nm were obtained using urea and glycine, respectively.
关键词： size distribution,glycine,ZnO,complexing agents,co-precipitation,urea,morphology,nanoparticles
更新于2025-09-23 15:19:57
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Photocatalytic Dye and Cr(VI) Degradation Using a Metal-Free Polymeric g-C3N4 Synthesized from Solvent-Treated Urea
摘要： The development of visible-light-driven polymeric g-C3N4 is in response to an emerging demand for the photocatalytic dye degradation and reduction of hexavalent chromium ions. We report the synthesis of g-C3N4 from urea treated with various solvents such as methanol, ethanol, and ethylene glycol. The samples were characterized and the Williamson–Hall method was applied to investigate the lattice strain of the samples. The activity of the samples was evaluated by observing the degradation of methyl orange and K2Cr2O7 solution under light irradiation. Photocatalytic reaction kinetics were determined as pseudo-first-order and zero-order for the degradation of methyl orange and reduction of hexavalent chromium, respectively. Due to the inhibited charge separation resulting from the small lattice strain, reduced crystal imperfection, and sheet-like structure, g-C3N4 obtained from ethanol-treated urea exhibited the highest activity among the evaluated samples.
关键词： solvent-treated urea,Cr(VI) reduction,g-C3N4,photocatalytic degradation
更新于2025-09-19 17:15:36
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Raman Tracking the Activity of Urease in Saliva for Healthcare
摘要： The detection of urease activity in the oral cavity is considered to be an efficient way to prevent dental caries and also to screen for helicobacter pylori infection. Herein, a rapid surface enhanced Raman scattering (SERS) method is proposed to determine the activity of urease by using inositol hexaphosphate (IP6) stabilized silver nanoparticles (AgNPs@IP6) as an efficient SERS-active substrate. The determination was achieved by monitoring the SERS peak intensity of urea at 1003 cm-1. With urease increase, the response of urea at 1003 cm-1 decreases gradually, indicating the two has good correlation. A linear relationship between the absolute value of signal drop and urease concentration is observed in a range from 2.35 to 37.5 μg/mL. In addition, the rapid SERS method was used to evaluate the activity of urease in real sample of saliva without any pretreatment, exhibiting a promising potential for biomedical application.
关键词： Urease activity,Surface-enhanced Raman scattering,Urea,Healthcare
更新于2025-09-19 17:15:36
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Online Milk Quality Assessment during Milking Using Near-infrared Spectroscopic Sensing System
摘要： In recent times, there has been an urgent requirement for a technique that can be used by dairy farmers to assess the quality of milk of an individual cow during milking. A near-infrared (NIR) spectroscopic sensing system was designed on an experimental basis for the online assessment of the three major milk constituents (fat, protein, and lactose), solids not fat (SNF), milk urea nitrogen (MUN), and somatic cell count (SCC). This system was used to obtain the NIR spectra of non-homogenized milk during milking over a wavelength range of 700 to 1,050 nm. Calibration models for predicting three major milk constituents, SNF, MUN and SCC of non-homogenized milk were developed, and the precision and accuracy of the models were validated. The coefficients of determination, standard errors of prediction, and bias values showed high levels of precision and accuracy for the prediction of the considered parameters. The results indicated that the developed NIR spectroscopic sensing system can be used to assess milk quality in real-time during milking. This system can provide dairy farmers with information concerning milk quality and physiological condition of each cow, and can therefore optimize dairy farm management.
关键词： calibration models,milk constituents,somatic cell count,solids not fat,milk urea nitrogen
更新于2025-09-19 17:13:59
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Equidistant combination wavelength screening and step-by-step phase-out method for the near-infrared spectroscopic analysis of serum urea nitrogen
摘要： We applied near-infrared (NIR) spectroscopy with chemometrics for the rapid and reagent-free analysis of serum urea nitrogen (SUN). The modeling is based on the average effect of multiple sample partitions to achieve parameter selection with stability. A multiparameter optimization platform with Norris derivative filter–partial least squares (Norris-PLS) was developed to select the most suitable mode (d = 2, s = 33, g = 15). Using equidistant combination PLS (EC-PLS) with four parameters (initial wavelength I, number of wavelengths N, number of wavelength gaps G and latent variables LV), we performed wavelength screening after eliminating high-absorption wavebands. The optimal EC-PLS parameters were I = 1228 nm, N = 26, G = 16 and LV = 12. The root-mean-square error (SEP), correlation coefficient (RP) for prediction and ratio of performance-to-deviation (RPD) for validation were 1.03 mmol L?1, 0.992 and 7.6, respectively. We proposed the wavelength step-by-step phase-out PLS (WSP-PLS) to remove redundant wavelengths in the top 100 EC-PLS models with improved prediction performance. The combination of 19 wavelengths was identified as the optimal model for SUN. The SEP, RP and RPD in validation were 1.01 mmol L?1, 0.992 and 7.7, respectively. The prediction effect and wavelength complexity were better than those of EC-PLS. Our results showed that NIR spectroscopy combined with the EC-PLS and WSP-PLS methods enabled the high-precision analysis of SUN. WSP-PLS is a secondary optimization method that can further optimize any wavelength model obtained through other continuous or discrete strategies to establish a simple and better model.
关键词： wavelength step-by-step phase-out,near-infrared spectroscopic analysis,equidistant combination wavelength screening,Serum urea nitrogen,Norris derivative filter
更新于2025-09-19 17:13:59