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Visible Light Driven Hydrogen Evolution by Molecular Nickel Catalysts with Time-Resolved Spectroscopic and DFT Insights
摘要： Hydrogen (H2) is a clean fuel that can potentially be a future solution for the storage of intermittent renewable energy. However, current H2 production is mainly dominated by the energy intensive steam reforming reaction, which consumes a fossil fuel, methane, and emits copious amounts of carbon dioxide as one of the byproducts. To address this challenge, we report a molecular catalyst that produces H2 from aqueous solutions, is composed of affordable, earth-abundant elements such as nickel, and has been incorporated into a system driven by visible light. Under optimized conditions, we observe a turnover number of 3880, among the best for photocatalytic H2 evolution with nickel complexes from water?methanol solutions. Through nanosecond transient absorption, electron paramagnetic resonance, and UV?vis spectroscopic measurements, and supported by density functional theory calculations, we report a detailed study of this photocatalytic H2 evolution cycle. We demonstrate that a one-electron reduced, predominantly ligand-centered, reactive Ni intermediate can be accessed under visible light irradiation using triethylamine as the sacrificial electron donor and reductive quencher of the initial photosensitizer excited state. In addition, the computational calculations suggest that the second coordination sphere ether arms can enhance the catalytic activity by promoting proton relay, similar to the mechanism among [FeFe] hydrogenases in nature. Our study can form the basis for future development of H2 evolution molecular catalysts that incorporate both ligand redox noninnocence and alternative second coordination sphere effects in artificial photosynthetic systems driven by visible light.
关键词： Proton relay,Second coordination sphere,DFT calculations,Time-resolved spectroscopy,Visible light photocatalysis,Hydrogen evolution,Molecular nickel catalysts
更新于2025-09-23 15:23:52
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Color-center formation and thermal recovery in X-ray and electron-irradiated magnesium aluminate spinel
摘要： We have studied the formation of color centers in magnesium aluminate spinel (MgAl2O4) by X-ray and electron irradiations near room temperature (RT). For this purpose, Cu Kα radiation and three electron energies (1.0, 1.4, and 2.5 MeV) were used for variable fluences (up to 4.2 × 10^18 cm^?2). Off-line UV-visible absorption spectra were recorded at RT as well as at low temperature down to 27 K after electron irradiation. The dependence of the production rate of F centers (oxygen vacancies) on the electron energy yields a threshold displacement energy of 190 ± 10 eV for oxygen atoms at RT, which is much higher than the determinations by molecular-dynamics simulations. Such a discrepancy is discussed on the basis of available migration data of point defects in spinel. Equipartition of F0 and F+ centers, i.e., the neutral (VO^x) and singly ionized (VO^.) oxygen vacancies, is reached for high electron fluences. Moreover, the evolution of the width of color-center absorption bands versus temperature is interpreted with the classical theory for F centers (neutral halogen vacancies) in alkali halides. The Stokes shifts are deduced from the temperature dependence of the absorption bandwidths of color centers like for alkali halides and alkaline-earth oxides. Finally, isothermal annealing data for long annealing time show a non-zero asymptotic behavior for both F0 and F+ centers. This uncommon behavior is interpreted by charge exchange processes leading to an equilibrium state between those two color centers.
关键词： thermal recovery,X-ray irradiation,color centers,threshold displacement energy,F centers,electron irradiation,absorption spectroscopy,magnesium aluminate spinel
更新于2025-09-23 15:23:52
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A cryogenic cylindrical ion trap velocity map imaging spectrometer
摘要： A cryogenic cylindrical ion trap velocity map imaging spectrometer has been developed to study photodissociation spectroscopy and dynamics of gaseous molecular ions and ionic complexes. A cylindrical ion trap made of oxygen-free copper is cryogenically cooled down to ～7 K by using a closed cycle helium refrigerator and is coupled to a velocity map imaging (VMI) spectrometer. The cold trap is used to cool down the internal temperature of mass selected ions and to reduce the velocity spread of ions after extraction from the trap. For CO2+ ions, a rotational temperature of ～12 K is estimated from the recorded [1 + 1] two-photon dissociation spectrum, and populations in spin-orbit excited X2Πg,1/2 and vibrationally excited states of CO2+ are found to be non-detectable, indicating an efficient internal cooling of the trapped ions. Based on the time-of-flight peak profile and the image of N3+ ions, the velocity spread of the ions extracted from the trap, both radially and axially, is interpreted as approximately ±25 m/s. An experimental image of fragmented Ar+ from 307 nm photodissociation of Ar2+ shows that, benefiting from the well-confined velocity spread of the cold Ar2+ ions, a VMI resolution of Δv/v ～ 2.2% has been obtained. The current instrument resolution is mainly limited by the residual radial speed spread of the parent ions after extraction from the trap.
关键词： cryogenic ion trap,velocity map imaging,ion cooling,photodissociation,spectroscopy
更新于2025-09-23 15:23:52
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Electronic properties of hybrid organic/inorganic semiconductor pn-junctions
摘要： Hybrid inorganic/organic semiconductor heterojunctions are candidates to expand the scope of purely organic or inorganic junctions in electronic and optoelectronic devices. Comprehensive understanding of bulk and interface doping on the junction’s electronic properties is therefore desirable. In this work, we elucidate the energy level alignment and its mechanisms at a prototypical hybrid pn-junction comprising ZnO (n-type) and p-doped N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) as semiconductors, using photoelectron spectroscopy. The level alignment can be quantitatively described by the interplay of contact-induced band and energy level bending in the inorganic and organic component away from the interface, and an interface dipole due to the push-back effect. By adjusting the dopant concentration in α-NPD, the position of the frontier energy levels of ZnO can be varied by over 0.5 eV and that of α-NPD by over 1 eV. The tunability of this pn-junction’s energy levels evidences the substantial potential of the hybrid approach for enhancing device functionality.
关键词： semiconductors,electronic properties,photoelectron spectroscopy,interfaces
更新于2025-09-23 15:23:52
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Ultrafast electron-lattice thermalization in copper and other noble metal nanoparticles
摘要： Using time-resolved ultrafast pump-probe spectroscopy we investigated the electron-lattice energy transfer in small copper nanospheres with diameters ranging from 3.2 to 23 nm, either embedded in a glass or dispersed in a solvent. Electron-lattice scattering rate is shown to increase with size reduction, in agreement with our previous results obtained on gold and silver nanoparticles in the low excitation regime. We attribute this effect to the reduction of the screening efficiency of electron–phonon interactions close to the nanoparticle surface. To understand the discrepancy between the results on the electron-lattice scattering in different metals reported in the literature (reduction, no dependence or increase with nanoparticle size), we discuss the experimental conditions required for the accurate determination of electron-lattice energy transfer time from time-resolved investigations in the weak and strong excitation regimes and present power-dependent experiments on gold nanospheres in solution. Our findings are derived from a theoretical analysis based on the two-temperature model predictions and on a complete modeling of the nanoparticle transient extinction cross-section through the resolution of Boltzmann equation in the presence of hot electrons.
关键词： pump-probe spectroscopy,copper nanoparticles,electron-lattice interactions,two-temperature model,ultrafast electron dynamics
更新于2025-09-23 15:23:52
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Maturity prediction of papaya using NIR spectroscopy
摘要： The use of NIR spectroscopy was evaluated to predict the maturity of papaya ‘IPB 1’ non-destructively during harvest time. The maturity was observed from the changes in water content, protein and soluble solid content. Samples of papaya were harvested at 14 days before commercial harvest date and continued for 7, 4 and 0 days later. NIRFlex N-500 (Büchi Labortechnik AG, Flawil, Switzerland) with spectral range of 1000-2400 nm was used as spectral acquisition of papaya in reflection mode. After dividing 124 spectra into calibration set and 62 spectra as independent prediction set, spectra in the calibration set were subjected to a partial least square method with pre-treatment processing to establish calibration model. Validation of calibration models on the independent prediction set indicated that the prediction accuracy with coefficient of determination (R2), SEC and SEP were 0.85, 0.59 and 0.58 for water content; 0.81, 0.1 and 0,1 for protein content and 0.90, 0.56, 0.76 for soluble solid content. It is concluded that NIR spectroscopy coupled with PLS models can be adopted for predicting maturity of papaya based on the water content, protein and soluble solid content.
关键词： non‐destructive,maturity,green mature papaya,NIR spectroscopy
更新于2025-09-23 15:23:52
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Spatial and Temporal Stability of Airglow Measured in the Meinel Band Window at 1191.3 nm
摘要： We report on the temporal and spatial fluctuations in the atmospheric brightness in the narrow band between Meinel emission lines at 1191.3 nm using a λ/Δλ = 320 near-infrared instrument. We present the instrument design and implementation, followed by a detailed analysis of data taken over the course of a night from Table Mountain Observatory. At low airmasses, the absolute sky brightness at this wavelength is found to be 5330 ± 30 nW m?2 sr?1, consistent with previous measurements of the inter-band airglow at these wavelengths. This amplitude is larger than simple models of the continuum component of the airglow emission at these wavelengths, confirming that an extra emissive or scattering component is required to explain the observations. We perform a detailed investigation of the noise properties of the data and find no evidence for a noise component associated with temporal instability in the inter-line continuum. This result demonstrates that in several hours of ～100 s integrations the noise performance of the instrument does not appear to significantly degrade from expectations, giving a proof of concept that near-infrared line intensity mapping may be feasible from ground-based sites.
关键词： techniques: imaging spectroscopy,site testing,atmospheric effects
更新于2025-09-23 15:23:52
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Signal enhancement in laser diode thermal desorption-triple quadrupole mass spectrometry analysis using microwell surface coatings
摘要： Laser diode thermal desorption (LDTD) is an ionization source usually coupled to triple quadrupole mass spectrometry (QqQMS) and specifically designed for laboratories requiring high-throughput analysis. It has been observed that surface coatings on LDTD microwell plates can improve the sensitivity of the analysis of small polar molecules. The objective of the present study is to understand and quantify the effect of microwell surface coatings on signal intensity of small organic molecules of clinical, environmental and forensic interest. Experiments showed that the peak areas of diclofenac, chloramphenicol, salicylic acid and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol obtained by LDTD-QqQMS increased by up to 3 orders of magnitude when using microwells coated with ethylenediaminetetraacetic acid (EDTA). Tests with different chelating agents and polytetrafluoroethylene as microwell surface coatings showed that nitrilotriacetic acid gave significantly higher peak areas for five out of the nine compounds that showed signal enhancement using chelating agents as coatings. Scanning electron microscopy studies of EDTA-coated and uncoated microwells showed that analytes deposited in the former formed more uniform and thinner films than in the latter. The enhancement effect of surface coatings in LDTD-QqQMS was explained mainly by the formation of homogenous and thinner layers of nanocrystals of analytes that are easier to desorb thermally than the layers formed when the analytes dry in direct contact with the bare stainless steel surface. Chemisorption of some analytes to the stainless steel surface of the microwell plate appeared to be a minor factor. Surface coatings widen the number of compounds analyzable by LDTD-QqQMS and can also improve sensitivity and limits of detection.
关键词： pharmaceuticals,high-throughput,hormones,pesticides,x-ray photoelectron spectroscopy,scanning electron microscopy,stainless steel,small organic molecules,chelating agents
更新于2025-09-23 15:23:52
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Symmetries of modes in Ni <sub/>3</sub> V <sub/>2</sub> O <sub/>8</sub> : Polarized Raman spectroscopy and ab initio phonon calculations
摘要： Knowledge of symmetries of vibrational modes is essential for understanding structural transitions and spin‐phonon coupling in multiferroics where phonons play a vital role. Using polarized Raman spectroscopy, we have identified and assigned symmetries of 30 out of the 36 expected zone‐centred phonon mode Raman active modes in Ni3V2O8. The wavenumbers are calculated using ab initio calculations. The gerade mode wavenumbers are compared with our polarized Raman data whereas ungerade mode wavenumbers are compared with the reported infrared measurements and a good agreement was observed between the experimentally measured wavenumbers and the calculated wavenumbers. The displacements of different types of vibrations calculated and visualized using ab initio phonon calculation are presented. These assignments will be useful for visualization of Raman modes that may be sensitive to different magnetic states and to explore spin–lattice coupling across magnetic transitions.
关键词： displacements of phonon modes,gerade and ungerade modes,polarized Raman spectroscopy,symmetries of Raman active modes,ab initio calculations
更新于2025-09-23 15:23:52
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New Assay Method Based on Raman Spectroscopy for Enzymes Reacting with Gaseous Substrates
摘要： Enzyme activity is typically assayed by quantitatively measuring the initial and final concentrations of the substrates and/or products over a defined time period. For enzymatic reactions involving gaseous substrates, the substrate concentrations can be estimated either directly by gas chromatography or mass spectrometry, or indirectly by absorption spectroscopy, if the catalytic reactions involve electron transfer with electron mediators that exhibit redox-dependent spectral changes. We have developed a new assay system for measuring the time course of enzymatic reactions involving gaseous substrates based on Raman spectroscopy. This system permits continuous monitoring of the gas composition in the reaction cuvette in a non-invasive manner over a prolonged time period. We have applied this system to the kinetic study of the [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F. This enzyme physiologically catalyzes the reversible oxidation of H2 and also possesses the non-physiological functions of H/D exchange and nuclear spin isomer conversion reactions. The proposed system has the additional advantage of enabling us to measure all of the hydrogenase-mediated reactions simultaneously. Using the proposed system, we confirmed that H2 (the fully exchanged product) is concomitantly produced alongside HD by the H/D exchange reaction in the D2/H2O system. Based on a kinetic model, the ratio of the rate constants of the H/D exchange reaction (k) at the active site and product release rate (kout) was estimated to be 1.9±0.2. The proposed assay method based on Raman spectroscopy can be applied to the investigation of other enzymes involving gaseous substrates.
关键词： kinetic experiment,H/D exchange reaction,quantitative analysis of gaseous substrates,Raman spectroscopy,non-invasive measurement,[NiFe] hydrogenase
更新于2025-09-23 15:23:52