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Development of Synthetic Methods to Grow Long-Wavelength Infrared-Emitting HgTe Quantum Dots in Dimethylformamide
摘要： Most successful syntheses of long wavelength infrared (IR) absorbing/emitting Hg-chalcogenide quantum dots (QDs) use either aqueous or organic solvent-based methods. Accounts of IR QD growth in aprotic solvents such as dimethyl sulfoxide (DMSO) or dimethyl formamide (DMF) are much less common, and yet producing QDs in such solvents can be useful from the perspective of further reactions to conjugate or incorporate the QDs with other materials since such solvents can be a useful meeting ground for both organic and ionic solutes. Here we start by demonstrating long wavelength infrared emission (across the wide spectral range up to 4500 nm) in HgTe QDs grown in DMF under basic conditions. Whilst many existing synthetic approaches use soluble chalcogen precursors in adduct, salt or organo-chalcogenide forms, we have opted to take the approach of using slow addition of gaseous H2Te generated under programmed control, which allowed us to investigate the growth kinetics in order to manipulate the different competing processes, and to obtain larger HgTe QDs with the best size distributions on a repeatable and controlled basis. We demonstrate how the nucleation process of HgTe QDs can be carried out analogously to how it occurs in classic hot injection syntheses, but in our case at a far lower (sub-ambient) temperature owing to the use of a much more labile Te precursor. We also demonstrate the use of a two stage, seeded QD growth process which allows the synthesis conditions for the initial nucleation step and the subsequent enlargement stage to be decoupled, in other words the QD concentration during the enlargement phase need not be forced to be excessively large by the choice of nucleation conditions. This approach should eventually be extendable to making >5000 nm emitting HgTe QD based materials, and the use of aprotic solvents will offer compatibility with other nanomaterial chemistries, e.g. oxide glass formers etc., for the synthesis of composites. By comparing the emission spectra of HgTe QDs grown in DMF with those grown in DMSO, we show that polaron mediated coupling to ligand and solvents, previously seen when using DMSO, can be substantially suppressed using our new synthetic method.
关键词： nucleation,dimethylformamide,synthetic methods,growth kinetics,HgTe quantum dots,infrared emission
更新于2025-09-23 15:19:57
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Infrared Spectroscopic and Kinetic Characterization on the Photolysis of Nitrite in Alcohol-Containing Aqueous Solutions
摘要： Nitrite is regarded as a potential OH and NO precursor in aqueous solution upon ultraviolet photolysis. A step-scan Fourier-transform interferometer was employed to collect the transient infrared difference spectra upon excitation of the sodium nitrite aqueous solution in the presence of methanol and ethanol upon 355 nm pulsed excitation. The photolytic intermediates were proposed to be NO and NO2 via the direct dissociation from NO2? and the rapid reaction of OH and NO2?, respectively. Coupled with the theoretical calculations of the absolute energies and harmonic wavenumbers of relevant species using B3LYP density functional theory with the C-PCM model to account for the medium effect of H2O, a transient band at 1860?2030 cm?1 could be attributed to dissolved N2O3 isomers that could be quickly generated from NO + NO2. On the basis of the predicted thermodynamics, the reactions of alcohols with N2O3 were less thermodynamically favorable than that of water, resulting in a slightly decelerated depletion rate of N2O3 in alcohol-containing aqueous solution. Comparing the transient population of N2O3 in the absence and presence of CH3OH or C2H5OH, the upper-bound bimolecular rate coefficient of NO or NO2 with alcohols is reported as 7.3 × 103 M?1 s?1 for the first time. The spectroscopic and kinetic evidence of the reactivity of alcohols with NO, NO2, and N2O3 are provided to augment the roles of alcohols and NxOy in solution or in aqueous aerosol photochemistry.
关键词： Alcohols,Kinetics,Nitrite,Infrared spectroscopy,Aqueous solution,Photolysis
更新于2025-09-23 15:19:57
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Ultraviolet absorption cross-section measurements of shock-heated O2 from 2,000a??8,400 K using a tunable laser
摘要： Accurate spectroscopic modeling is critical when measuring time-resolved, state-specific chemical kinetics of diatomic molecules. Here, a spectroscopic model (Stanford model) was developed to accurately simulate oxygen absorption cross-sections in the Schumann-Runge system for non-equilibrium conditions. Cross-sections of shock-heated oxygen (O2) have been measured using a picosecond pulsed ultraviolet (UV) laser, and the viability of two spectroscopic models has been demonstrated. Measurements were taken behind reflected shocks in 2% and 5% O2 in argon (Ar) mixtures around 211.2 nm and 236.9 nm up to initial post-reflected shock temperatures of 10,700 K. Cross-sections were plotted against vibrational temperature and compared to calculated cross-sections from the Stanford model and the Adjusted Spectrum model. Vibrational temperatures for cross-section measurements were calculated for plateaus and peaks in experimental absorbances using a Bethe-Teller relaxation model up to 6,000 K and a steady-state approach above 6,000 K. Vibrational temperatures calculated using the steady-state approach were 3–5% higher than coupled vibration-dissociation (CVD) calculations. The experimental cross-sections agree to within 15% of the Stanford model for both wavelength regimes.
关键词： Spectroscopy,Oxygen,High-temperature,Chemical kinetics,Ultraviolet absorption,Shock tube,Cross-sections,Lasers
更新于2025-09-23 15:19:57
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Versatile, Aqueous Soluble C <sub/>2</sub> N Quantum Dots with Enriched Active Edges and Oxygenated Groups
摘要： C2N has emerged as a new family of promising two-dimensional (2D) layered frameworks in both fundamental studies and potential applications. Transforming bulk C2N into zero-dimensional quantum dots (QDs) could induce unique quantum confinement and edge effects that produce improved or new properties. Despite their appealing potential, C2NQDs remain unexplored, and their intriguing properties and a fundamental understanding of their prominent edge effects are still not well understood. Here, we report the first synthesis of water-soluble C2NQDs via a top-down approach without any foreign stabilizer and exploit their linear/nonlinear optical properties and unique edge-preferential electrocatalytic activity toward polysulfides for versatile applications. The resultant dispersant-free C2NQDs with an average size of sub-5 nm feature rich oxygen-carrying groups and active edges, not only enabling excellent dispersion in water but also creating interesting multifunctionality. They can emit not only blue one-photon luminescence (OPL) under UV excitation but also green two-photon luminescence (TPL), enabling their use as a new fluorescent ink. Interestingly, when C2NQDs are introduced to modify commercial separators, they can function as new metal-free catalysts to boost polysulfide redox kinetics and endow Li-S batteries with excellent cycling stability, high rate capability and large areal capacity (7.0 mA h cm-2) at a high sulfur loading of 8.0 mg cm-2. Detailed theoretical and experimental results indicate that the edge of C2N is more favorable for trapping and catalyzing the polysulfide conversion than the terrace and that the synergy between the active edges and oxygenated groups enriched in C2NQDs remarkably improves polysulfide immobilization and catalytic conversion.
关键词： fluorescent ink,multifunctionality,C2N quantum dots,Li-S batteries,polysulfide redox kinetics,water-soluble
更新于2025-09-23 15:19:57
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Different role of graphene for nonisothermal crystallization behavior of graphene filled poly(ether ether ketone) by different perparation methods
摘要： The nonisothermal crystallization investigation on different contents of graphene filled PEEK nanocomposites by ball milling and solution dispersed was performed on differential scanning calorimetry. Jeziorny and Mo's methods were selected to evaluate the result, so as to investigate the nonisothermal crystallization kinetics of pure PEEK and two kinds of PEEK/GE nanocomposites. Mo's method was demonstrated to be the most appropriate model to represent the crystallization behavior for neat PEEK and PEEK/GE nanocomposites under nonisothermal condition. The result showed that the absolute degree of crystallinity of both PEEK/GE nanocomposites decreased with increasing the content of graphene, but increased the nucleation activity for the nanocomposites. When the addition of graphene was 1 wt%, the dispersed method affected the crystallization mechanisms obviously, either promoting or hindering the polymer matrix crystallization. Overall, the method that filling graphene to PEEK matrix had influence on the nonisothermal crystallization process, hence affected the properties of nanocomposites.
关键词： dispersed methods,nonisothermal crystallization kinetics,nucleation activity,graphene,PEEK
更新于2025-09-23 15:19:57
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Carbon quantum dots modified anatase/rutile TiO2 photoanode with dramatically enhanced photoelectrochemical performance
摘要： Titanium dioxide (TiO2) is a promising photoanode material for photoelectrochemical (PEC) water splitting, but the severe bulk recombination of photongenerated carriers, the sluggish oxygen evolution reaction (OER) kinetics and the poor visible light response are the main bottleneck problems. Here, the carbon quantum dots (CQDs) modified anatase/rutile TiO2 photoanode (CQDs/A/R-TiO2) was designed by growth of anatase TiO2 nanothorns on the rutile TiO2 nanorods and further surface modification of CQDs. The results revealed that A/R-TiO2 heterojunction significantly suppressed the bulk recombination of photogenerated carriers. With further incorporation of CQDs into A/R-TiO2, dramatical improvement of OER kinetics and light harvesting were obtained. The bulk charge separation efficiency (ηbulk) and the surface charge injection efficiency (ηsurface) of CQDs/A/R-TiO2 are 1.69 and 5.74 times higher than that of the pristine TiO2 at 0.6 V vs. RHE, respectively. The photocurrent of CQDs/A/R-TiO2 is increased by 11.72 times and the onset potential of CQDs/A/R-TiO2 is negatively shifted by 240 mV.
关键词： Anatase/rutile TiO2 heterojunction,Carbon quantum dots,Bulk and surface charge transfer kinetics,PEC,Light harvesting
更新于2025-09-23 15:19:57
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Theoretical investigation on the kinetics and mechanism of the synthesis of fluorescent 3,8-disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles
摘要： 3,8-Disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles show very interesting optical properties. In some cases, they have higher quantum yields compared to well-known fluorescent dyes such as fluorescein. Hitherto, no detailed theoretical study has been reported on the mechanism of the synthesis of the titled compounds, hence an accurate and detailed theoretical investigation on the synthesis of these dyes is desirable. In this paper, density functional theory (DFT) methods have been employed to investigate the most reasonable mechanism in formation of these fluorophores. All species and related transition states were optimised and the relative energies of all species and the activation energies for all proposed mechanisms were obtained. Comparing the Ea values of all pathways reveals that intramolecular electrophilic aromatic substitution is the most plausible mechanism for the cyclisation reaction in the preparation of these dyes. Also, the effects of substituents in positions 3 and 8 were investigated and the results show that electron-donor substituents can reduce the activation energy for formation of the σ complex in the electrophilic aromatic substitution.
关键词： kinetics,intramolecular electrophilic aromatic substitution,thermodynamics,5-a]acridine,DFT calculations,imidazo[4,substituent effects
更新于2025-09-19 17:15:36
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Kinetics of crystallization in 13.2Li2O-67.6SiO2-14.49Al2O3-3.3TiO2-0.4BaO-0.97ZnO glass ceramic powder: Part I: A model-free vs. model-fitting approach
摘要： Crystallization kinetics of lithium aluminosilicate glass powder has been investigated by model-free and model–fitting methods. Non-isothermal experiments were carried out using differential scanning calorimetry (DSC) to monitor crystallization behavior. Model-free activation energy has been calculated based on Ozawa-Flynn-wall (OFW), Kissinger-Akahira-Sunose (KAS) and Friedman (FR) methods during crystallization progress. Although activation energy does not significantly differ between the models (400 to 470 kJ/mol), partial Avrami coefficient n(α) varies considerably with rate and crystallization progress. A better description of the crystallization behavior could be observed by the comparison of model-free and model fitting methods. The conformity of one model has been approved with comparison of theoretical DSC curve and experimental results. Finally, a model which can more accurately describe the crystallization behavior of this material was suggested.
关键词： aluminosilicate,Kinetics,model-free,model-fitting,lithium,crystallization.
更新于2025-09-19 17:15:36
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Microwave discharge electrodeless mercury lamp (Hg-MDEL): an energetic, mechanistic and kinetic approach to the degradation of Prozac?
摘要： A photochemical reactor composed of an Hg-MDEL was applied in photodegradation studies of fluoxetine (Prozac?). The reactor exhibited to be an efficient hydroxyl radical generation system, since constant of formation of OH? formation is optimized through the adjustment of this parameter. An increase in the initial hydroxycoumarin (4HC) and 7-hydroxycoumarin (7HC) solutions resulted in the kinetics constant value, the mean kinetic constant was k = 10.64 ± 1.25 min -1 and R 2 = 0.943 ± 0.131. The Prozac? photodegradation studies showed that the application of the pseudo-first-order applied for degradation of Prozac?, the study of variation of the microwave power allowed a concentration of Prozac from 33 to 134 μmol L-1 resulted in a 21% decrease in the kinetic significant increase in the rate of degradation of the Prozac?, indicating that the hydroxyl radical the OH? quantification studies conducted with coumarin (COU), 4- kOH = 3.14 ± 0.18 min-1. When the Hg-MDEL reactor was 100% for its highest concentration (134 μmol L-1) at the time of 0.75 min. As for the solution of Prozac? 101 μmol L-1, the energy consumption was 6 kWh g-1, achieving a removal of 99%. formation of hydroxyl radicals, a high degradation rate of organic compounds (Prozac?, COU influence exerted by the transformation products. In general, the total removal of Prozac? was kinetics should be limited to the time of up to 0.50 min for the respective system, due to the Finally, the photochemical system presented in this work demonstrates a high efficiency in the and 7HC) and low energy consumption.
关键词： hydroxyl radical,direct photolysis,fluoxetine,pharmaceuticals,and kinetics,degradation mechanism
更新于2025-09-19 17:15:36
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Braiding kinetics and spectroscopy in photo-catalysis: the spectro-kinetic approach
摘要： The combination of kinetic and spectroscopic tools has become a key scientific methodology for the understanding of catalytic behavior but its application in photocatalysis has inherent difficulties due to the nature of the energy source of the reaction. This review article provides an overview of its use by, first, presenting mechanistically derived kinetic formulations and spectroscopic data handling methods including intrinsic expressions for light and, second, highlighting representative examples of application. To do it we consider universal catalytic systems, particularly (although not exclusively) titania-based materials, and the most frequent hole and/or electron triggered reaction schemes. This review also provides a general framework to pave the way for the future progress of the spectro-kinetic approach in the photocatalysis area.
关键词： spectroscopy,titania-based materials,kinetics,hole and electron triggered reactions,photocatalysis,spectro-kinetic approach
更新于2025-09-19 17:15:36