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Sensitive, selective and rapid ammonia-sensing by gold nanoparticle-sensitized V2O5/CuWO4 heterojunctions for exhaled breath analysis
摘要： Marigold flower-like V2O5/CuWO4 heterojunctions were synthesized and its volatile organic compound (VOC)-sensing properties were tested and significantly enhanced after sensitizing by Au nanoparticles. Detailed characterizations were carried out by SEM, XRD and XPS to determine the morphology, crystal structure, elemental and chemical composition of the sensing materials, respectively. The fabricated gold-sensitized sensor was found to be rapidly responsive (a few seconds), highly sensitive to ammonia with good selectivity as compared to various types of VOCs. The limit of detection and linear range of sensor at 150°C were 212 ppb and 5-158 ppm, respectively, which is suitable for detection of exhaled breath ammonia of patients at their last stage of chronic kidney disease. Furthermore, it was found to be of high intra-day repeatability, which is properly explained by discussing the mechanism of NH3 sensing. Very long-term stability of the sensor was investigated over 56 days, once a week.
关键词： Ammonia-sensing,chronic kidney disease,exhaled breath analysis,Au-sensitized V2O5/CuWO4 heterojunctions
更新于2025-09-19 17:13:59
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Trace level toxic ammonia gas sensing of single-walled carbon nanotubes wrapped polyaniline nanofibers
摘要： This paper presents a two-step enhancement and a comprehensive analysis of single-walled carbon nanotubes (SWCNTs) wrapped polyaniline nanofiber (NPANI) ammonia (NH3) gas sensor at room temperature. SWCNT-PANI composites are successfully synthesized using an efficient and cost-effective rapid in situ chemical polymerization method. The structural morphology and modification of the samples are characterized using field-emission scanning electron microscopy and HRTEM. FTIR and Raman spectroscopic studies are also performed to gain a better insight into the chemical environmental interaction in the as-prepared nanocomposite. The analysis confirms the successful formation of the nanocomposite. The observed NH3 gas-sensing response at 10 ppm of SWCNT, f-SWCNT (functionalised SWCNT), and SWCNT-PANI composite sensors are 5%–6%, 18%–20%, and 24%–25%, respectively. The SWCNT-PANI composite sensors have shown higher repeatability, selectivity, long-term stability, and fast response-recovery characteristics as compared to f-SWCNTs and pristine SWCNT sensors. Concentration and temperature dependent gas-sensing studies are also analyzed. The sensor response also shows a linear relationship with NH3 gas concentration and an inverse relationship with increasing temperature.
关键词： Raman spectroscopy,rapid in situ chemical polymerization,ammonia gas sensor,polyaniline nanofiber,field-emission scanning electron microscopy,FTIR,HRTEM,room temperature,single-walled carbon nanotubes
更新于2025-09-19 17:13:59
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Instantaneous one-dimensional ammonia measurements with femtosecond two-photon laser-induced fluorescence (fs-TPLIF)
摘要： Ammonia (NH3) has been identified as a potential hydrogen-carrier fuel with no carbon emissions. Non-intrusive in-situ NH3 diagnostic technique is of great interest. In this work, femtosecond two-photon laser-induced fluorescence (fs-TPLIF) was demonstrated in NH3/N2 mixtures to achieve NH3 measurements. A femtosecond laser at 305 nm was used for two-photon excitation of NH3 to its excited state (XeC0), and the subsequent fluorescence at ~565 nm from transition C0-A was detected. In addition, a detection limit of 730 ppm was achieved in NH3/N2 mixtures. Furthermore, one-dimensional single-shot images of NH3 were obtained in both laminar and turbulent flow fields. This work is the first attempt of fs-TPLIF for polyatomic molecular gases measurements, and the obtained results indicate that fs-TPLIF could be a promising tool for NH3 measurements.
关键词： Laser-induced fluorescence,Femtosecond laser,Spectroscopy,Ammonia
更新于2025-09-16 10:30:52
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Direct Z-scheme photocatalytic removal of ammonia via the narrow band gap MoS2/N-doped graphene hybrid catalyst upon near-infrared irradiation
摘要： Near-infrared (NIR) irradiation accounts for approximately 54.3% of the solar spectrum. Therefore, MoS2 and N-doped graphene (NG) were utilised to fabricate a direct Z-scheme NIR-response photocatalytic system (MoS2/NG). The photocatalytic tests showed that MoS2/NG Z-scheme photocatalytic system can result in a 99.6% degradation ratio of ammonia under NIR irradiation, whereas the removal ratio of ammonia was only 64.0% using MoS2 as the photocatalyst under similar conditions. The catalytic e?ciency is still over 90.7% even if the MoS2/NG catalyst was used for ?ve runs, indicating that it is extremely stable. The kinetic research indicated the ?1. The average apparent rate constant kapp for ammonia degradation into N2 was at approximately 0.251 h enhanced photocatalytic activity of MoS2/NG was attributed to the more positive valence band level of the Z-scheme system.
关键词： MoS2/N-doped graphene,Near-infrared irradiation,Degradation ammonia,Narrow band gap,Z-scheme photocatalysis
更新于2025-09-12 10:27:22
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Synthesis of Perovskite CsPbBr <sub/>3</sub> Quantum Dots/Porous Boron Nitride Nanofiber Composites with Improved Stability and Their Reversible Optical Response to Ammonia
摘要： All-inorganic CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) have great potential for various applications due to their excellent photoluminescence properties. However, poor stability under long-term storage hinders their applications. Herein we report the utilization of porous boron nitride nanofibers (BNNFs) as a promising carrier for anchoring of CsPbBr3 QDs. Due to the good dispersion and immobilization of CsPbBr3 QDs, the resulting CsPbBr3/BNNF composites show excellent photostability and superior long-term storage stability in an air environment. Moreover, the CsPbBr3/BNNF composites exhibit an interesting ammonia-responsive behavior: i.e., a distinct decrease in photoluminescence intensity upon exposure to ammonia gas and the subsequent photoluminescence recovery after post-treatment in nitrogen gas. Even after treatment with ammonia gas for 3 h, the composites can still be recovered under nitrogen gas treatment. The fast response, reversibility, and stability of CsPbBr3/BNNF composites in the presence of ammonia gas could inspire a broader range of applications.
关键词： photostability,reversible optical response,perovskite quantum dots,boron nitride nanofibers,ammonia-responsive behavior
更新于2025-09-12 10:27:22
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Application of Near-Infrared Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) to the Detection of Ammonia in Exhaled Human Breath
摘要： The qualitative and quantitative analysis to trace gas in exhaled human breath has become a promising technique in biomedical applications such as disease diagnosis and health status monitoring. This paper describes an application of a high spectral resolution optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) for ammonia detection in exhaled human breath, and the main interference of gases such as CO2 and H2O are approximately eliminated at the same time. With appropriate optical feedback, a fibered distributed feedback (DFB) diode laser emitting at 1531.6 nm is locked to the resonance of a V-shaped cavity with a free spectral range (FSR) of 300 MHz and a finesse of 14,610. A minimum detectable absorption coefficient of αmin = 2.3 × 10?9 cm?1 is achieved in a single scan within 5 s, yielding a detection limit of 17 ppb for NH3 in breath gas at low pressure, and this stable system allows the detection limit down to 4.5 ppb when the spectra to be averaged over 16 laser scans. Different from typical CEAS with a static cavity, which is limited by the FSR in frequency space, the attainable spectral resolution of our experimental setup can be up to 0.002 cm?1 owing to the simultaneous laser frequency tuning and cavity dither. Hence, the absorption line profile is more accurate, which is most suitable for low-pressure trace gas detection. This work has great potential for accurate selectivity and high sensitivity applications in human breath analysis and atmosphere sciences.
关键词： trace gas detection,breath gas analysis,ammonia,optical feedback,cavity enhanced absorption spectroscopy
更新于2025-09-11 14:15:04
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3D, covalent and noncovalent hybrid materials based on 3-phenylcoumarin derivatives and single walled carbon nanotubes as gas sensing layers
摘要： In this work, the effect of different types of functionalization of single walled carbon nanotubes (SWCNT) with 3-phenylcoumarin derivatives on the chemiresistive sensor response to ammonia (10–50 ppm) was studied. Covalent functionalization of SWCNT was performed according to the Huisgen reaction of azide-alkyne 1,3-dipolar cycloaddition between mono alkyne-substituted 3-phenylcoumarin and single walled nanotubes modified by azide groups. Covalent functionalization was shown by IR- and X-ray photoelectron spectroscopy. To obtain the 3D hybrid material, the dialkyne functionalized 3-phenylcoumarin molecules were used as linkers between nanotubes. Third hybrid material was prepared by noncovalent functionalization of SWCNT, namely by adsorption of 7-propinyloxy-3-(p-propinyloxyphenyl)coumarin on SWCNT surface. It was shown that the 3D hybrid and the hybrid obtained by covalent functionalization exhibit 2 and 4 times higher sensor responses to ammonia compared to noncovalently functionalized SWCNT. The value of sensor response is in good correlation with the degree of functionalization of SWCNTs with coumarin molecules.
关键词： Non covalent functionalization,3D carbon nanostructures,Covalent functionalization,Carbon nanomaterials,Ammonia sensor,Coumarin
更新于2025-09-11 14:15:04
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Changes in enzyme activities and amino acids and their relations with phenolic compounds contents in okra treated by LED lights of different colors
摘要： Light-emitting diodes (LEDs) of different wavelengths or colors (i.e., white, red, blue, and green) were used to treat postharvest okra, which is a rich source of phenolic compounds. Relationships between changes in the activities of key enzymes involving in the formation of phenolics (i.e., 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase, chorismate mutase, anthranilate synthase, and phenylalanine ammonia lyase) and their contents upon different LED light treatments were for the first time investigated and are fully discussed. The contents of three intermediate amino acids (i.e., phenylalanine, tyrosine, and tryptophan) that formed during light treatments were also measured to confirm the enzyme activities data. White and blue light treatments increased the content of phenolics in the treated okra, while red and green lights increased the formation of other compounds. These results could be well explained by the changing levels of the measured enzyme activities and amino acids contents.
关键词： Non-thermal processing,Phenylalanine ammonia lyase,Fruits and vegetables,Phenylpropanoid pathway,Shikimate pathway,LED
更新于2025-09-11 14:15:04
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Chemically modified silica-based sensors: effect of the nature of organosilane
摘要： The use of organosilanes to produce hybrid materials, also known as ORMOSILs (organically modified silicas) can be a good strategy to tune a material’s properties, enabling, for example, the optimization of important features of chemical sensors such as specificity, sensitivity and response time. Thus, different hybrid silicas were prepared by the sol-gel method to be employed as a colorimetric sensor. The investigated organic groups for producing hybrid materials included methyl, octyl, octadecyl, vinyl, phenyl, aminopropyl, isocyanatopropyl, mercaptopropyl, chloropropyl, iodopropyl and glycidoxypropyl groups, and the pH indicator alizarin red was used as the encapsulated receptor element. The sensors were characterized using a set of complementary techniques such as UV-vis spectroscopy, cyclic and differential pulse voltammetry, nuclear magnetic resonance, nitrogen porosimetry, small-angle X-ray scattering and transmission electronic microscopy. The performance was evaluated according to the color change (ΔE* ab) by conducting a colorimetric analysis and measuring the response time after ammonia exposure, with results varying from 48 to 95 s. Additionally, other characteristics of the hybrid materials, such as their surface area, reticulation degree, texture and morphologic properties, were altered depending on the organic modification present in the silica network. The potentiality for material optimization, to achieve better sensor performance, depends on the employed organosilane.
关键词： colorimetric sensor,sol-gel,ammonia,ORMOSIL,organosilanes,hybrid silica
更新于2025-09-11 14:15:04
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Energy and exergy analysis of solar heat driven chiller under wide system boundary conditions
摘要： In the paper, a solar driven ammonia-water chiller is investigated, as one of the systems having potential for reduction of resources depletion. An energy and exergy analysis is proposed for correct diagnostics while designing and operating the cycle. The boundary conditions for the analyses are set in accordance with Professor Szargut’s primary instructions. They are however widened to solar collector component. Solar radiation is treated as the driving energy or exergy, respectively. The analyses are supplemented with a sensitivity diagnosis revealing the most significant parameters modifying the efficiency and irreversibilities distribution. According to the findings, design COP of the chiller equals 0.444 while its net exergy efficiency is 0.026. Solar collector component is the most burdened with exergy destruction and loss in the whole cycle.
关键词： Exergy analysis,irreversibility,solar radiation exergy,solar thermal collector,ammonia-water chiller
更新于2025-09-10 09:29:36