Spatial sensitivity to absorption changes for various near-infrared spectroscopy methods:A compendium review

This compendium review focuses on the spatial distribution of sensitivity to localized absorption changes in optically diffuse media,particularly for measurements relevant to near-infrared spectroscopy.The three temporal domains,continuous wave,frequency domain,and time domain,each obtain different optical data types whose changes may be related to effective homogeneous changes in the absorption coefficient.Sensitivity is the relationship between a localized perturbation and the recovered effective homogeneous absorption change.Therefore,spatial sensitivity maps representing the perturbation location can be generated for the numerous optical data types in the three temporal domains.The review first presents a history of the past 30 years of work investigating this sensitivity in optically diffuse media.These works are experimental and theoretical,presenting one-,two-,and three-dimensional sensitivity maps for different Near-Infrared Spectroscopy methods,domains,and data types.Following this history,we present a compendium of sensitivity maps organized by temporal domain and then data type.This compendium provides a valuable tool to compare the spatial sensitivity of various measurement methods and parameters in one document.Methods for one to generate these maps are provided in Appendix A,including the code.This historical review and comprehensive sensitivity map compendium provides a single source researchers may use to visualize,investigate,compare,and generate sensitivity to localized absorption change maps.

基于EEMs和UV-Vis法相结合的北方某城市原水三氯甲烷生成预测

以北方城市某水厂采集的原水作为研究对象,利用三维荧光光谱进行测定,通过计算荧光指数(FI)判断原水中溶解性有机物(DOM)的来源,并考察加氯后的三氯甲烷生成情况与水中DOM紫外-可见分光光谱特性之间的联系。结果表明,当水厂的原水中DOM主要为微生物的代谢产物时,加氯后三氯甲烷的生成量可通过测定溶解性有机物在280 nm处吸光度,进行负对数计算得到-lnA280来反映三氯甲烷生成量,由此提供了一种更加操作简单、成本较低的预测三氯甲烷质量浓度的方法。

Investigation of the sodium storage mechanism of iron fluoride hydrate cathodes using X-ray absorption spectroscopy and mossbauer spectroscopy

Elucidation of a reaction mechanism is the most critical aspect for designing electrodes for highperformance secondary batteries.Herein,we investigate the sodium insertion/extraction into an iron fluoride hydrate(FeF_(3)·0.5H_(2)O)electrode for sodium-ion batteries(SIBs).The electrode material is prepared by employing an ionic liquid 1-butyl-3-methylimidazolium-tetrafluoroborate,which serves as a reaction medium and precursor for F^(-)ions.The crystal structure of FeF_(3)·0.5H_(2)O is observed as pyrochlore type with large open 3-D tunnels and a unit cell volume of 1129A^(3).The morphology of FeF_(3)·0.5H_(2)O is spherical shape with a mesoporous structure.The microstructure analysis reveals primary particle size of around 10 nm.The FeF_(3)·0.5H_(2)O cathode exhibits stable discharge capacities of 158,210,and 284 mA h g^(-1) in three different potential ranges of 1.5-4.5,1.2-4.5,and 1.0-4.5 V,respectively at 0.05 C rate.The specific capacities remained stable in over 50 cycles in all three potential ranges,while the rate capability was best in the potential range of 1.5-4.5 V.The electrochemical sodium storage mechanism is studied using X-ray absorption spectroscopy,indicating higher conversion at a more discharged state.Ex-situ M?ssbauer spectroscopy strengthens the results for reversible reduction/oxidation of Fe.These results will be favorable to establish high-performance cathode materials with selective voltage window for SIBs.

Energy Transfer Dynamics between Carbon Quantum Dots and Molybdenum Disulfide Revealed by Transient Absorption Spectroscopy

Zero-dimensional environmentally friendly carbon quantum dots(CQDs)combined with two-di-mensional materials have a wide range of applications in optoelec-tronic devices.We combined steady-state and transient absorp-tion spectroscopies to study the energy transfer dynamics between CQDs and molybdenum disulfide(MoS_(2)).Transient absorption plots showed photoinduced absorption and stimulated emission features,which involved the intrinsic and defect states of CQDs.Adding MoS_(2)to CQDs solution,the lowest unoccupied molecular orbital of CQDs transferred energy to MoS_(2),which quenched the intrinsic emission at 390 nm.With addition of MoS_(2),CQD-MoS_(2)composites quenched defect emission at 490 nm and upward absorption,which originated from another energy transfer from the defect state.Two energy transfer paths between CQDs and MoS_(2)were efficiently manipulated by changing the concentration of MoS_(2),which laid a foundation for improving device performance.

Determination of Lead in Lime-preserved Egg by Microwave Digestion and Flame Atomic Absorption Spectroscopy

[Objectives] To establish a method for determining the lead content in lime-preserved eggs, to provide a theoretical basis for the quality control of production enterprises and the sampling and testing of supervision departments. [Methods] The lead content in lime-preserved eggs was measured by the microwave digestion and flame atomic absorption spectroscopy. [Results] The method had a correlation coefficient of r2=0.998 in the injection concentration range of 0-4 mg/L. The detection limit of the method was 0.008 2 mg/kg. In the range of 0.2 to 1.0 mg/kg addition concentration, the recovery rate of the method was 92.5%-108.0%, and the relative standard deviation(RSD) was <5%. [Conclusions] This method is accurate and reliable, simple and efficient, and is suitable for the detection of lead in lime-preserved eggs.

Synthesis of rare earth sulfides and their UV-vis absorption spectra

Rare earth sulfides were systematically synthesized via the sulfurization of their commercial oxide powders using CS2 gas to shorten sulfurization time, and their UV-vis absorption spectra were investigated. The appropriate sulfurization conditions were studied. For the rare earth sulfides with the same crystal structure, the sulfurization temperature showed increasing tendency with the decrease of rare earth element atomic radii. The UV-vis absorption spectra of rare earth sulfides did not depend on the crystal structure of rare earth sulfides, but on the 4f electronic structure of rare earth element. The data showed that the optical band gaps of rare earth sulfides were irregular, and the values ranged from 1.65 to 3.75 eV.

Near-ultraviolet Incoherent Broadband Cavity Enhanced Absorption Spectroscopy for OCIO and CH20 in Cl-initiated Photooxidation Experiment

Chlorine dioxide （OC10） is an important indicator for Cl-activation. The monitoring of OC10 appears to be crucial for understanding the chemistry of Cl-initialed oxidation and its impact on air quality in polluted coastal regions and industrialized areas. We report the development of a Xe arc lamp based near-ultraviolet （335-375 nm） incoherent broad- band cavity enhanced absorption spectroscopy （IBBCEAS） spectrometer for quantitative assessment of OC10 in an atmospheric simulation chamber. The important intermediate compound CH20, and other key atmospheric trace species （NO2） were also simultaneously measured. The instrumental performance shows a strong potential of this kind of IBBCEAS instrument for field and laboratory studies of atmospheric halogen chemistry.

In Situ X-ray Absorption Spectroscopy Studies of Nanoscale Electrocatalysts

Nanoscale electrocatalysts have exhibited promising activity and stability,improving the kinetics of numerous electrochemical reactions in renewable energy systems such as electrolyzers,fuel cells,and metal-air batteries.Due to the size effect,nano particles with extreme small size have high surface areas,complicated morphology,and various surface terminations,which make them different from their bulk phases and often undergo restructuring during the reactions.These restructured materials are hard to probe by conventional ex-situ characterizations,thus leaving the true reaction centers and/or active sites difficult to determine.Nowadays,in situ techniques,particularly X-ray absorption spectroscopy(XAS),have become an important tool to obtain oxidation states,electronic structure,and local bonding environments,which are critical to investigate the electrocatalysts under real reaction conditions.In this review,we go over the basic principles of XAS and highlight recent applications of in situ XAS in studies of nanoscale electrocatalysts.

Influence of laser intensity in second-harmonic detection with tunable diode laser multi-pass absorption spectroscopy

Tunable diode laser absorption spectroscopy （TDLAS） has been widely employed in atmospheric trace gases detection. The ratio of the second-harmonic signal to the intensity of laser beam incident to the multi-pass cell is proved to be proportional to the product of the path length and the gas concentration under any condition. A new calibration method based on this relation in TDLAS system for the measurement of trace gas concentration is proposed for the first time. The detection limit and the sensitivity of the system are below 110 and 31ppbv （parts-per-billion in volume）, respectively.

Measurements of Nighttime Nitrate Radical Concentrations in the Atmosphere by Long-Path Differential Optical Absorption Spectroscopy

The long-path differential optical absorption spectroscopy （LP-DOAS） technique was developed to mea- sure nighttime atmospheric nitrate radical （NO3） concentrations. An optimized retrieval method, resulting in a small residual structure and low detection limits, was developed to retrieve NO3. The time series of the NO3 concentration were collected from 17 to 24 March, 2006, where a nighttime average value of 15.8 ppt was observed. The interfering factors and errors are also discussed. These results indicate that the DOAS technique provides an essential tool for the quantification of NO3 concentration and in the study of its effects upon nighttime chemistry.

Hidden Relaxation Channels in Aqueous Methylene Blue after Functionalization of Graphene Oxide Probed by Transient Absorption Spectroscopy

The mixture of graphene oxide （GO） and dye molecules may provide some new applications due to unique electronic, optical, and structural properties. Methylene blue （MB）, a typ- ical anionic dye, can attach on GO via π-π stacking and electrostatic interaction, and the molecule removal process on GO has been observed. However, it remains unclear about the ultrafast carrier dynamics and the internal energy transfer pathways of the system which is composed of GO and MB. We have employed ultrafast optical pump-probe spectroscopy to investigate the excited dynamics of the GO-MB system dispersed in water by exciting the samples at 400 nm pump pulse. The pristine MB and GO dynamics are also analyzed in tandem for a direct comparison. Utilizing the global analysis to fit the measured signal via a sequential model, five lifetimes are acquired：（0.61±0.01） ps, （3.52±0.04） ps, （14.1±0.3） ps, （84±2） ps, and （3.66±0.08） ns. The ultrafast dynamics corresponding to these lifetimes was analyzed and the new relaxation processes were found in the GO-MB system, compared with the pristine MB. The results reveal that the functionalization of GO can alter the known decay pathways of MB via the energy transfer from GO to MB in system, the increased intermediate state, and the promoted energy transfer from triplet state MB to ground state oxygen molecules dissolved in aqueous sample.

In situ studies of energy-related electrochemical reactions using Raman and X-ray absorption spectroscopy

Electrochemical energy conversion technologies involving processes such as water splitting and O_(2)/CO_(2) reduction,provide promising solutions for addressing global energy scarcity and minimizing adverse environmental impact.However,due to a lack of an in-depth understanding of the reaction mechanisms and the nature of the active sites,further advancement of these techniques has been limited by the development of efficient and robust catalysts.Therefore,in situ characterization of these electrocatalytic processes under working conditions is essential.In this review,recent applications of in situ Raman spectroscopy and X-ray absorption spectroscopy for various nano-and single-atom catalysts in energy-related reactions are summarized.Notable cases are highlighted,including the capture of oxygen-containing intermediate species formed during the reduction of oxygen and oxidation of hydrogen,and the detection of catalyst structural transformations occurring with the change in potential during the evolution of oxygen and reduction of CO_(2).Finally,the challenges and outlook for advancing in situ spectroscopic technologies to gain a deeper fundamental understanding of these energy-related electrocatalytic processes are discussed.

Quantitative measurement of hydroxyl radical(OH) concentration in premixed flat flame by combining laser-induced fluorescence and direct absorption spectroscopy

An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence（LIF）methods is developed to quantitatively measure the concentrations of hydroxyl in CH;/air flat laminar flame. In our approach, particular attention is paid to the linear laser-induced fluorescence and absorption processes, and experimental details as well. Through measuring the temperature, LIF signal distribution and integrated absorption, spatially absolute OH concentrations profiles are successfully resolved. These experimental results are then compared with the numerical simulation. It is proved that the good quality of the results implies that this method is suitable for calibrating the OH-PLIF measurement in a practical combustor.

Determination of vanadium in food and traditional Chinese medicine by graphite furnace atomic absorption spectroscopy

Various experimental conditions were described for the vanadium determinationby graphite furnace atomic absorption spectroscopy (GFAAS). The experiments showed that whenatomization took place under the conditions where the combination of a pyrolytic coating graphitetube and fast raising temperature were used and the temperature was stable, the signal peak shapescould be improved, the sensitivity was enhanced, and the memory effect was removed. The vanadium infood and traditional Chinese medicinal herbs can be accurately determined using the standard curvemethod.

Application of Two-Dimensional Correlation UV-Vis Spectroscopy in Chinese Liquor Moutai Discrimination

Chinese liquor Moutai is the “National alcoholic drink” in China and plays a very important role of social activities in Chinese people’s life. In pursuit of high profits, some illegal counterfeit Moutai liquors have begun to appear in the market. Therefore, it is an urgent need for new techniques to discriminate the genuine and counterfeit Moutai liquor. In this work, the conventional Ultraviolet-Visible (UV-Vis) spectroscopy and two-dimensional correlation UV-Vis spectroscopy are applied to obtain the UV-Vis characteristic of Moutai liquor and counterfeit one, respectively. The experimental results reveal that the conventional UV-Vis spectra of the genuine and counterfeit Moutai liquor are similar. However, the two-dimensional correlation UV-Vis spectra of them are different and this method would be applied to differentiate the counterfeit Moutai liquor from the genuine Moutai liquor. Compared with conventional methods, this novel method has the advantages of easy operation, simple instrumentation and direct recognition, which make it a potential tool in the fields of food safety.

Local structural evolutions of CuO/ZnO/Al2O3 catalyst for methanol synthesis under operando conditions studied by in situ quick X-ray absorption spectroscopy

In situ quick X-ray absorption spectroscopy(QXAFS) at the Cu and Zn K-edge under operando conditions has been used to unravel the Cu/Zn interaction and identify possible active site of CuO/ZnO/Al_2O_3 catalyst for methanol synthesis. In this work, the catalyst, whose activity increases with the reaction temperature and pressure, was studied at calcined, reduced, and reacted conditions. TEM and EDX images for the calcined and reduced catalysts showed that copper was distributed uniformly at both conditions. TPR profile revealed two reduction peaks at 165 and 195 °C for copper species in the calcined catalyst. QXAFS results demonstrated that the calcined form consisted mainly of a mixed Cu O and Zn O, and it was progressively transformed into Cu metal particles and dispersed Zn O species as the reduction treatment. It was demonstrated that activation of the catalyst precursor occurred via a Cu^+intermediate, and the active catalyst predominantly consisted of metallic Cu and Zn O evenunder higher pressures. Structure of the active catalyst did not change with the temperature or pressure, indicating that the role of the Zn was mainly to improve Cu dispersion.This indicates the potential of QXAFS method in studying the structure evolutions of catalysts in methanol synthesis.

Sensitivity Enhancement in Uranium Determination by UV-Visible Spectroscopy Using Ion Imprinted Polymer

There is need to determination of uranium concentration at ppb level in environmental matrices.Due to low sensitivity of FAAS,UV-Visible Spectroscopy is generally used as measurement technique.In this study,ion-imprinted polymers(IIP)were prepared for uranyl ion(imprint ion)by formation of ternary(salicylaldoxime and 4-vinylpyridine)complex in 2-methoxy ethanol(porogen)following copolymerization with methacrylic acid(MAA)as a functional monomer and ethylene glycol dimethacrylate(EGDMA)as crosslinking monomer using 2,2-azobisisobutyronitrile as initiator.The synthesized polymers were characterized by FTIR and TGA analysis.ArsenazoⅢin 3M HClO_4 was used as complexing agent in the measurement step.The optimal pH for preconcentration was found to be between 3.5~6.5values.The developed method was applied to uranium(Ⅵ)determination in natural water samples.

In-situ high-energy-resolution X-ray absorption spectroscopy for UO2 oxidation at SSRF

Based on the high-energy-resolution fluorescence spectrometer on the BL14W1 beamline at Shanghai Synchrotron Radiation Facility,an in-situ high-energyresolution X-ray absorption spectroscopy technique,with an in-situ heating cell,was developed.The high-energyresolution fluorescence detection for X-ray absorption near-edge spectroscopy(HERFD-XANES) was tested in a UO_2 oxidation experiment to measure the UL_3-edge,with higher signal-to-noise ratio and higher-energy-resolution than conventional XANES.The technique has potential application for in-situ study of uranium-based materials.

UV-Vis Spectroscopy Study on Interaction between Microperoxidase-11 and Pr Ion Under Acid Rain Stress

Interaction between rare earth ion praseodymium (Pr(Ⅲ)) and MP11 with/without hydrogen ion (H +) in different media( aqueous, phosphate buffer, physiological condition) were studied by UV Vis spectroscopy. All the results indicate that Pr(Ⅲ) interacts with MP11, increasing the non planarity of porphyrin periphery, leading MP11 to form two conformations when titrated by Pr(Ⅲ). Excessive Pr(Ⅲ) acts as a contaminant in living organism. H + and Pr(Ⅲ) have antagonistic effect on MP11, suggesting that at suitable concentration under physiological conditions, Pr(Ⅲ) can be used as biomodulator in protecting plants from acid rain stress or in rehabilitating the harm.

Novel infrared differential optical absorption spectroscopy remote sensing system to measure carbon dioxide emission

A CO_2 infrared remote sensing system based on the algorithm of weighting function modified differential optical absorption spectroscopy(WFM-DOAS) is developed for measuring CO_2 emissions from pollution sources. The system is composed of a spectrometer with band from 900 nm to 1700 nm, a telescope with a field of view of 1.12?, a silica optical fiber, an automatic position adjuster, and the data acquisition and processing module. The performance is discussed,including the electronic noise of the charge-coupled device(CCD), the spectral shift, and detection limits. The resolution of the spectrometer is 0.4 nm, the detection limit is 8.5 × 10^(20)molecules·cm^(-2), and the relative retrieval error is < 1.5%.On May 26, 2018, a field experiment was performed to measure CO_2 emissions from the Feng-tai power plant, and a twodimensional distribution of CO_2 from the plume was obtained. The retrieved differential slant column densities(dSCDs)of CO_2 are around 2 × 10^(21) molecules·cm^(-2) in the unpolluted areas, 5.5 × 10^(21)molecules·cm^(-2) in the plume locations most strongly affected by local CO_2 emissions, and the fitting error is less than 2 × 10^(20)molecules·cm^(-2), which proves that the infrared remote sensing system has the characteristics of fast response and high precision, suitable for measuring CO_2 emission from the sources.