Optical Absorption Spectroscopy Research Articles

Nitric and nitrous acid formation in plasma-treated water: Decisive role of nitrogen oxides (NOx=1–3)

Nitrogen fixation using low-temperature plasma, particularly in relation to plasma-treated water (PTW) and its chemical and physical properties, has received a renewed research focus. Dissolving highly concentrated nitrogen oxides (NOx = 1–3) generated by air discharge into water results in the formation of two aqueous oxiacids (nitrous and nitric acids; HNOy = 2,3) and their conjugates (nitrate and nitrite ions; NOy-). Nonlinear formation of these species in PTW with respect to plasma conditions has been observed; however, the significance of the time-varying NOx on this nonlinearity has not yet been thoroughly investigated. Here, we demonstrate real-time observations of HNOy/NOy- as well as NOx production in a surface dielectric barrier discharge reactor containing distilled water. Synchronized two optical absorption spectroscopy systems were employed to simultaneously measure gas-phase NOx and liquid-phase HNOy/NOy- in the plasma reactor operated under different oxygen contents of 5, 20, and 50%. Our results showed that reducing the oxygen content in the reactor accelerated the chemical transition from O3 and NO3 to NO1,2, leading to a predominance of nitrite in PTW. Specifically, the NO3-rich period was extended with increasing O2 content, resulting in the production of nitrate-dominant PTW at low pH levels. Our findings highlight the potential for the selective generation of HNOy/NOy- in PTW through the active and passive control of NOx in a plasma reactor. The direct, real-time observation of NOx–HNOy/NOy- conversion presented here has potential for improving the control and optimization of PTW, thereby enhancing its applicability.

Photoexcited States Dynamics on Cu(II) Porphyrines-Nanographenes Dyads

Donor-acceptor systems have garnered significant attention in the fields of semiconducting materials and light harvesting.1 Particularly intriguing are porphyrin diads, wherein porphyrins are covalently bonded to nanographenes, forming a dyad with an expected electron transfer from the porphyrin to the nanographene. In our study, we leverage the excellent charge transport properties of Hexabenzocoronene (HBC) in combination with the superior light harvesting capabilities of Cu(II) porphyrins.The steady-state absorption spectra of the dyads exhibit a linear combination of HBC and porphyrin spectra, suggesting a low degree of electronic coupling in the ground state. Femtosecond optical transient absorption spectroscopy (TAS) has been employed to investigate the dynamics of photoexcited states. The TAS spectrum of the dyad displays a first derivative shape of the steady-state absorption, indicative of a photoinduced electron transfer within the system.2 These findings underscore the potential application of these systems as donor-acceptor systems, wherein the Cu(II) porphyrine serves as the source, transferring electrons to the HBC nanographene. This points towards promising applications of this system in photovoltaic devices. Figure 1. A) Cu(II) porphyrine B) Cu (II) porphyrine, HBC and Cu(II) porphyrine-HBC dyad absorption spectra C) Cu (II) porphyrine with C-H chains, HBC and Cu(II) porphyrinewith C-H chains-HBC dyad absorption spectra D)u (II) porphyrine with C-H chains.______________________________________________[1] H. Imahori, T. Umevama, Journal of Physical Chemistry C 2009, 113, 9029–9039.[2] Shengqiang Xiao; Mohamed E. El-Khouly; Yuliang Li; Zhenhai Gan; Huibiao Liu; Li Jiang; Yasuyuki Araki; Osamu Ito; Daoben Zhu J. Phys. Chem. B 2005, 109, 8, 3658–3667 Figure 1

Ground-based MAX-DOAS observations of tropospheric formaldehyde and nitrogen dioxide: Insights into ozone formation sensitivity

Tropospheric profiles of HCHO, NO2, and O3 are important for analyzing ozone formation mechanism. In this study, ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS), light detection and ranging (LIDAR), and in-situ measurements were simultaneously performed to diagnose ozone formation sensitivity at the Heshan Observatory in the Pearl River Delta (PRD) region from September to end October 2019. The profiles of tropospheric HCHO and NO2 were retrieved from MAX-DOAS measurements using an optimal estimation method. The retrieved surface HCHO and NO2 results were validated with 2,4-dinitrophenylhydrazine (DNPH) and Thermo 42i measurements, and the correlation coefficients (R) were 0.78 and 0.81, respectively. The retrieved tropospheric vertical column densities (VCDs) of HCHO and NO2 were compared with TROPOMI measurements, and the correlation coefficients (R) were 0.68 and 0.87, respectively. In addition, MAX-DOAS and LIDAR measurements were combined to diagnose a typical planetary boundary layer (PBL) ozone pollution episode from September 28 to October 10, 2019; this episode was analyzed using HCHO/NO2 ratio as an indicator and was found to be dominated by the VOC-sensitive regime. Moreover, the regime transition of ozone formation sensitivity was calculated using the surface HCHO/NO2 ratio and increased O3 from the MAX-DOAS and Thermo 49i measurements, with transition thresholds of 1.43 and 1.78, respectively. Based on this definition, the ozone formation sensitivity at Heshan Observatory varied from VOC-sensitive (< 0.2 km and > 0.8 km) to NOx-sensitive (0.3–0.7 km) to VOC-NOx-sensitive (0.2–0.3 km and 0.7–0.8 km). The results improve our understanding of ozone formation sensitivity in the PRD region.

Lithium isotope ratio analysis of geological samples using atomic absorption spectrometry with improved spectral resolution

This study introduces an improved spectrometric method with enhanced precision to determine isotope ratios in geological samples without chromatographic separation. Firstly, the improvement is achieved by increasing the spectral resolution of the spectrometer applied in well-known high-resolution continuum source atomic absorption spectrometry (HR-CS-AAS). The resulting resolving power and linear dispersion of the upgraded setup, which is denoted in the following as HR + CS-AAS, is well adapted to the line widths of the Li isotope components we investigated. Secondly, our proposed method combines optical absorption spectrometry with machine learning data analysis using an extreme gradient boosting algorithm (XGBoost). This method was applied to analyze certified geological reference materials with δLSVEC(7Li/6Li) (hereafter δ7Li) values ranging from −0.5 ‰ to 4.5 ‰. With a pixel related optical resolving power of λ/∆λ ≈ 780,000, we obtain precisions in δ7Li measurements from 1.0 ‰ to 2.5 ‰. The method is validated by comparing the results with multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), confirming its metrological compatibility. This work presents a fast, robust, and reliable method for δ7Li measurement in geological samples.

Ppb-Level Ammonia Sensor for Exhaled Breath Diagnosis Based on UV-DOAS Combined with Spectral Reconstruction Fitting Neural Network.

Ammonia (NH3) in exhaled breath (EB) has been a biomarker for kidney function, and accurate measurement of NH3 is essential for early screening of kidney disease. In this work, we report an optical sensor that combines ultraviolet differential optical absorption spectroscopy (UV-DOAS) and spectral reconstruction fitting neural network (SRFNN) for detecting NH3 in EB. UV-DOAS is introduced to eliminate interference from slow change absorption in the EB spectrum while spectral reconstruction fitting is proposed for the first time to map the original spectra onto the sine function spectra by the principle of least absolute deviations. The sine function spectra are then fitted by the least-squares method to eliminate noise signals and the interference of exhaled nitric oxide. Finally, the neural network is built to enable the detection of NH3 in EB at parts per billion (ppb) level. The laboratory results show that the detection range is 9.50-12425.82 ppb, the mean absolute percentage error (MAPE) is 0.83%, and the detection accuracy is 0.42%. Experimental results prove that the sensor can detect breath NH3 and identify EB in simulated patients and healthy people. Our sensor will serve as a new and effective system for detecting breath NH3 with high accuracy and stability in the medical field.

High-Spin State of a Ferrocene Electron Donor Revealed by Optical and X-ray Transient Absorption Spectroscopy.

Ferrocene is one of the most common electron donors, and mapping its ligand-field excited states is critical to designing donor-acceptor (D-A) molecules with long-lived charge transfer states. Although 3(d-d) states are commonly invoked in the photophysics of ferrocene complexes, mention of the high-spin 5(d-d) state is scarce. Here, we provide clear evidence of 5(d-d) formation in a bimetallic D-A molecule, ferrocenyl cobaltocenium hexafluorophosphate ([FcCc]PF6). Femtosecond optical transient absorption (OTA) spectroscopy reveals two distinct electronic excited states with 30 and 500 ps lifetimes. Using a combination of ultraviolet, visible, near-infrared, and short-wave infrared probe pulses, we capture the spectral features of these states over an ultrabroadband range spanning 320 to 2200 nm. Time-dependent density functional theory (DFT) calculations of the lowest triplet and quintet states, both primarily Fe(II) (d-d) in character, qualitatively agree with the experimental OTA spectra, allowing us to assign the 30 ps state as the 3(d-d) state and the 500 ps state as the high-spin 5(d-d) state. To confirm the ferrocene-centered high-spin character of the 500 ps state, we performed X-ray transient absorption (XTA) spectroscopy at the Fe and Co K edges. The Fe K-edge XTA spectrum at 150 ps shows a red shift of the absorption edge that is consistent with an Fe(II) high-spin state, as supported by ab initio calculations. The transient signal detected at the Co K-edge is 50× weaker, confirming the ferrocene-centered character of the excited state. Fitting of the transient extended X-ray absorption fine structure region yields an Fe-C bond length increase of 0.25 ± 0.1 Å in the excited state, as expected for the high-spin state based on DFT. Altogether, these results demonstrate that the high-spin state of ferrocene should be considered when designing donor-acceptor assemblies for photocatalysis and photovoltaics.

A convolutional neural networks method for tropospheric ozone vertical distribution retrieval from Multi-AXis Differential Optical Absorption Spectroscopy measurements

The vertical distribution of tropospheric ozone (O3) is crucial for understanding atmospheric physicochemical processes. A Convolutional Neural Networks (CNN) method for the retrieval of tropospheric O3 vertical distribution from ground-based Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements to tackle the issue of stratospheric O3 absorption interference faced by MAX-DOAS in obtaining tropospheric O3 profiles. Firstly, a hybrid model, named PCA-F_Regression-SVR, is developed to screen features sensitive to O3 inversion based on the MAX-DOAS spectra and EAC4 reanalysis O3 profiles, which incorporates Principal Component Analysis (PCA), F_Regression function, and Support Vector Regression (SVR) algorithm. Thus, these screened features for ancillary inversion include the profiles of temperature, specific humidity, fraction of cloud coverage, eastward and northward wind, the profiles of SO2, NO2, and HCHO, as well as season and time features to serve as sensitive factors. Secondly, the preprocessed MAX-DOAS spectra dataset and the sensitive factor dataset are utilized as input, while the O3 profiles of the EAC4 reanalysis dataset incorporating the surface O3 concentrations are employed as output for constructing the CNN model. The Mean Absolute Percentage Error (MAPE) decreases from 26 % to approximately 19 %. Finally, the CNN model is applied for inversion and comparison of tropospheric O3 profiles using independent input data. The CNN model effectively reproduces the O3 profiles of the EAC4 dataset, showing a Gaussian-like spatial distribution with peaks primarily around 950 hPa (550 m). Since the reanalysis data used for model training has been smoothed, the CNN model is insensitive to extreme values. This behavior can be attributed to the MAPE loss function, which evaluates Absolute Percentage Errors (APEs) of O₃ concentration at all altitudes, resulting in varying retrieval accuracy across different altitudes while maintaining overall MAPE control. Temporally, the CNN model tends to overestimate surface O3 in summer by around 20 μg/m3, primarily due to the influence of the temperature feature in the sensitivity factor dataset. In conclusion, leveraging MAX-DOAS spectra enables the retrieval of tropospheric O3 vertical distribution through the established CNN model.

High-resolution HO2 radical detection by optical feedback linear cavity-enhanced absorption spectroscopy

High-resolution HO2 radical detection by optical feedback linear cavity-enhanced absorption spectroscopy

Evaluating CHASER V4.0 global formaldehyde (HCHO) simulations using satellite, aircraft, and ground-based remote-sensing observations

Abstract. Formaldehyde (HCHO), a precursor to tropospheric ozone, is an important tracer of volatile organic compounds (VOCs) in the atmosphere. Two years (2019–2020) of HCHO simulations obtained from the global chemistry transport model CHASER at a horizontal resolution of 2.8° × 2.8° have been evaluated using the Tropospheric Monitoring Instrument (TROPOMI) and multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations. In situ measurements from the Atmospheric Tomography Mission (ATom) in 2018 were used to evaluate the HCHO simulations for 2018. CHASER reproduced the TROPOMI-observed global HCHO spatial distribution with a spatial correlation (r) of 0.93 and a negative bias of 7 %. The model showed a good capability to reproduce the observed magnitude of the HCHO seasonality in different regions, including the background conditions. The discrepancies between the model and satellite in the Asian regions were related mainly to the underestimated and missing anthropogenic emission inventories. The maximum difference between two HCHO simulations based on two different nitrogen oxide (NOx) emission inventories was 20 %. TROPOMI's finer spatial resolution than that of the Ozone Monitoring Instrument (OMI) sensor reduced the global model–satellite root-mean-square error (RMSE) by 20 %. The OMI- and TROPOMI-observed seasonal variations in HCHO abundances were consistent. The simulated seasonality showed better agreement with TROPOMI in most regions. The simulated HCHO and isoprene profiles correlated strongly (R=0.81) with the ATom observations. However, CHASER overestimated HCHO mixing ratios over dense vegetation areas in South America and the remote Pacific region (background condition), mainly within the planetary boundary layer (&lt; 2 km). The simulated seasonal variations in the HCHO columns showed good agreement (R&gt;0.70) with the MAX-DOAS observations and agreed within the 1σ standard deviation of the observed values. However, the temporal correlation (R∼0.40) was moderate on a daily scale. CHASER underestimated the HCHO levels at all sites, and the peak occurrences in the observed and simulated HCHO seasonality differed. The coarseness of the model's resolution could potentially lead to such discrepancies. Sensitivity studies showed that anthropogenic emissions were the highest contributor (up to ∼ 35 %) to the wintertime regional HCHO levels.

Enhancing Analytical Sensitivity and Selectivity for Methylene Blue Determination in Water Samples by Using Multiphase Electroextraction Coupled with Optical Absorption Spectroscopy and Surface-Enhanced Raman Scattering.

While optical analysis spectroscopy offers operational ease and low cost, it suffers from limitations regarding sensitivity when it comes to analyzing analytes at low concentrations. On the other hand, surface-enhanced Raman spectroscopy (SERS) offers high sensitivity but low selectivity in complex matrices. In this study, we have effectively addressed these challenges by integrating multiphase electroextraction (MPEE) as a sample preparation technique with these two spectroscopic methods for determining methylene blue (MB) dye in tap water samples. A Box-Behnken design was utilized for optimizing electroextraction parameters such as extraction time, pH, and acetonitrile percentage in the donor phase. After optimization, optical absorption spectroscopy results in a linear analytical curve within the range of 30 to 375 mg L-1 of MB, with method validation demonstrating high precision (relative standard deviation between 3.0 and 9.9%), recovery (99-105%), and detection and quantification limits of 1.3 and 4.0 μg L-1, respectively. On the other hand, using SERS, it was possible to detect MB in concentrations as low as 0.05 μg L-1. The extremely low concentrations of MB detected (in the range of a few ppb and ppt) and the acceptable validation performance parameters obtained highlight the potential of MPEE to enhance the applicability of spectroscopic techniques in routine analyses, especially when dealing with complex and challenging samples.

Spectroscopic properties of Pr3+-doped Titania-Silicate glass ceramic for photonic applications

Silicate-Titania (SiTi) glass-ceramics doped with Pr3+ (0.6, 1.6, 2.4 and 3.6 mol%) ions were prepared by sol-gel technique. The materials were characterized by powder XRD, FTIR, TEM, EDX, Optical absorption and Photoluminescence spectroscopy. The identification of non-bridging oxygen (NBO) formation and the removal of OH groups are validated through analysis of the FTIR spectra. Additionally, measurements using XRD and TEM showed that the samples contain nano-sized crystallites. The three phenomenological Judd–Ofelt (J–O) intensity parameters Ω2, Ω4, and Ω6 were obtained and used to analyze different radiative characteristics for the fluorescence levels of Pr3+ in the glass ceramic, including radiative lifetime, branching ratio, radiative transition probability and stimulated emission cross-section. Several emissions were observed in the visible region, among which the 1D2→3H4 in the orange-red region is the most intense. All of these reported branching ratios, stimulated emission cross-sections, and visible emission spectra point to the possibility of employing them as red region lasers. The CIE chromaticity coordinates from all of the emission spectra were also assessed to determine if these materials are suitable for orange-red phosphors. According to CIE chromaticity investigations, 1.6 mol% of Pr3+ ion concentration is ideal for SiTiPr glass-ceramic for use as red phosphors and possibly red lasers.

Online testing of extinction method of high-pressure natural gas oil mist based on light extinction

Abstract This paper proposes a theoretical model and scheme for accurately measuring droplet concentration in high-pressure natural gas environments, aiming for precise, online measurement of lubricating oil mist. The model integrates droplet behavior, light extinction properties of the medium, and pressure, using the light extinction method. It applies the Debye Series Expansion of Mie scattering to improve the light extinction coefficient for mediums such as lubricating oil particles. Differential Optical Absorption Spectroscopy is used to calculate the extinction index of natural gas at different pressures. The study innovates by replacing the traditional parallel light path with a non-parallel path that focuses the light beam, countering beam diameter expansion due to gas pressure. Empirical testing shows the method’s accuracy in online oil mist testing under 10 MPa pressure, with less than 5% error compared to offline methods. This work paves the way for future high-pressure gas particle monitoring, particularly in the oil and natural gas sector.

Color Centers in BaFBr Crystals: Experimental Study and Theoretical Modeling.

This study presents theoretical and experimental investigations into the electron and hole color centers in BaFBr crystals, characterizing their electronic and optical properties. Stoichiometric BaFBr crystals grown by the Steber method were used in the experiments. Radiation defects in BaFBr crystals were created by irradiation with 147 MeV 84Kr ions with up to fluences of 1010-1014 ions/cm2. The formation of electron color centers (F(F-), F2(F-), F2(Br-)) and hole aggregates was experimentally established by optical absorption spectroscopy. Performed measurements are compared with theoretical calculations. It allows us to determine the electron transition mechanisms and investigate the processes involved in photoluminescence emission in Eu-doped BaFBr materials to enhance the understanding of the fundamental electronic structure and properties of electron and hole color centers formed in BaFBr crystals.

Thermal annealing of radiation damages produced by swift 14N and 16O ions in LiF crystals

Annealing of color centers was studied in lithium fluoride crystals, irradiated with 23-MeV nitrogen and 28-MeV oxygen ions. Basing on the optical absorption spectroscopy and reaction-rate modelling, a new interpretation of the annealing kinetics at the practically important temperatures below 500 K is suggested. Proposed model explains simultaneous decrease of the F and F2/F3 + peaks as a result of migration of the F centers and formation of larger aggregates, and does not include additional assumptions about impurities and cation vacancies. It specifies the migration energy of the F centers in the ground state to be about 1.3 eV, that corresponds to earlier studies.

Modification of CdZnS nanoparticles on nanoporous FeVO4 photoanode to improve photoelectrochemical performance

Photoelectrochemical (PEC) performance of semiconductor photoanode can be significantly improved by regulating the energy band alignment to promote carrier separation. This study demonstrates the first application of CdZnS (CZS) nanoparticles to modify FeVO4 (FVO) nanostructure phoyoanode for PEC water splitting. The constructed FVO/CZS photoanode exhibits significantly enhanced PEC performance with a zero-bias solar-driven photocurrent density of 1.00 mA/cm2, which is 11 times and 4.5 times that of unmodified FVO and CZS, respectively. The Tests of the optical absorption and electrochemical spectroscopy demonstrate that the modification of CZS nanoparticles not only improves the light harvesting ability of the FVO/CZS heterojunction nanostructures in the wavelength of 300–500 nm but also establishes a type II band alignment between the interface of FVO and CZS that is conducive to the transport and separation of the charge carriers and prolongs charge lifetime. Consequently, synergistic actions of the improved light harvesting capacity, effective charge transport and separation and the prolonged carrier lifespan enable the designed and fabricated FVO/CZS heterojunction photoanode to get substantially augmented PEC water splitting performance. This work supplies an innovative guidance for designing FVO-based photoanodes to improve photoelectric conversion behavior from the perspective of interface engineering.

Measurement report: Combined use of MAX-DOAS and AERONET ground-based measurements in Montevideo, Uruguay, for the detection of distant biomass burning

Abstract. Biomass burning releases large amounts of aerosols and chemical species into the atmosphere, representing a major source of air pollutants. Emissions and by-products can be transported over long distances, presenting challenges in quantification. This is mainly done using satellites, which offer global coverage and data acquisition for places that are difficult to access. In this study, ground-based observations are used to assess the abundance of trace gases and aerosols. On 24 November 2020, a significant increase in formaldehyde was observed with a Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instrument located in Montevideo (Uruguay), and its vertical column densities reached values of 2.4×1016 molec. cm−2, more than twice the values observed during the previous days. This was accompanied by an increase in the aerosol levels measured by an AErosol RObotic NETwork (AERONET) photometer located at the same site. The aerosol optical depth (AOD) at 440 nm reached values close to 1, an order of magnitude larger than typical values in Montevideo. Our findings indicate that the increase was associated with the passage of a plume originating from distant biomass burning. This conclusion is supported by TROPOspheric Monitoring Instrument (TROPOMI) satellite observations as well as HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) simulations. The profiles of the gases and aerosols retrieved from the MAX-DOAS observations are consistent with the HYSPLIT analysis, showing the passage of a plume over Montevideo on 24 November located at a height of ∼ 1.5 km. This corroborates the finding that biomass burning events occurring about 800 km north of Montevideo can affect the local atmosphere through long-distance emissions transport. This study underscores the potential of ground-based atmospheric monitoring as a tool for detection of such events. Furthermore, it demonstrates greater sensitivity compared to satellite when it comes to detection of relatively small amounts of carbonyls like glyoxal and formaldehyde.

U(V) Stabilization via Aliovalent Incorporation of Ln(III) into Oxo-salt Framework.

Pentavalent uranium compounds are key components of uranium's redox chemistry and play important roles in environmental transport. Despite this, well-characterized U(V) compounds are scarce primarily because of their instability with respect to disproportionation to U(IV) and U(VI). In this work, we provide an alternate route to incorporation of U(V) into a crystalline lattice where different oxidation states of uranium can be stabilized through the incorporation of secondary cations with different sizes and charges. We show that iriginite-based crystalline layers allow for systematically replacing U(VI) with U(V) through aliovalent substitution of 2+ alkaline-earth or 3+ rare-earth cations as dopant ions under high-temperature conditions, specifically Ca(UVIO2)W4O14 and Ln(UVO2)W4O14 (Ln=Nd, Sm, Eu, Gd, Yb). Evidence for the existence of U(V) and U(VI) is supported by single-crystal X-ray diffraction, high energy resolution X-ray absorption near edge structure, X-ray photoelectron spectroscopy, and optical absorption spectroscopy. In contrast with other reported U(V) materials, the U(V) single crystals obtained using this route are relatively large (several centimeters) and easily reproducible, and thus provide a substantial improvement in the facile synthesis and stabilization of U(V).

Time-Resolved X-ray Emission Spectroscopy and Synthetic High-Spin Model Complexes Resolve Ambiguities in Excited-State Assignments of Transition-Metal Chromophores: A Case Study of Fe-Amido Complexes.

To fully harness the potential of abundant metal coordination complex photosensitizers, a detailed understanding of the molecular properties that dictate and control the electronic excited-state population dynamics initiated by light absorption is critical. In the absence of detectable luminescence, optical transient absorption (TA) spectroscopy is the most widely employed method for interpreting electron redistribution in such excited states, particularly for those with a charge-transfer character. The assignment of excited-state TA spectral features often relies on spectroelectrochemical measurements, where the transient absorption spectrum generated by a metal-to-ligand charge-transfer (MLCT) electronic excited state, for instance, can be approximated using steady-state spectra generated by electrochemical ligand reduction and metal oxidation and accounting for the loss of absorptions by the electronic ground state. However, the reliability of this approach can be clouded when multiple electronic configurations have similar optical signatures. Using a case study of Fe(II) complexes supported by benzannulated diarylamido ligands, we highlight an example of such an ambiguity and show how time-resolved X-ray emission spectroscopy (XES) measurements can reliably assign excited states from the perspective of the metal, particularly in conjunction with accurate synthetic models of ligand-field electronic excited states, leading to a reinterpretation of the long-lived excited state as a ligand-field metal-centered quintet state. A detailed analysis of the XES data on the long-lived excited state is presented, along with a discussion of the ultrafast dynamics following the photoexcitation of low-spin Fe(II)-Namido complexes using a high-spin ground-state analogue as a spectral model for the 5T2 excited state.

Enhancing photocatalytic activity of PrVO4: Optimization of synthesis method for efficient oxytetracycline degradation

In recent years, significant attention within the scientific community has been devoted to the advancement of highly efficient photocatalysts for the detection and remediation of environmentally hazardous pollutants. In this study, praseodymium vanadate (PrVO4) was synthesized using both hydrothermal (PrVO4:HM) and ultrasonic methods (PrVO4:UM), and subsequently employed for the degradation of oxytetracycline (OTC).The physicochemical characteristics of synthesized PrVO4 catalysts were thoroughly examined using a range of analytical and spectroscopic techniques. X-ray diffraction (XRD) analysis unveiled the tetragonal crystal structure of PrVO4:HM with a crystalline size of approximately 11 nm, while PrVO4:UM exhibited a slightly larger size of 14 nm. Field emission scanning electron microscopy (FESEM) showcased a nanoflake-like morphology for both PrVO4 catalysts. Optical absorption spectroscopy revealed a noteworthy red shift in band gap energy, decreasing from 3.21 to 3.14 eV for PrVO4:UM catalysts. Additionally, surface area analyses demonstrated a notable increase, from 61 to 78 m2g − 1, for PrVO4:UM catalysts. Comparative analysis revealed the superior efficacy of PrVO4:HM catalysts over PrVO4:UM catalyst in degrading OTC. PrVO4:HM catalysts achieved a remarkable OTC degradation efficiency of 99 % within 50 min and an impressive kinetic rate efficiency of 3.011 min−1. The efficacy of OTC removal using synthesized PrVO4 catalysts hinges upon several key factors, including the synthesis technique of the catalyst, pH adjustment during OTC treatment, dosage of PrVO4 catalyst applied, scavenger presence, catalyst stability, and the nature of the light source employed. These findings highlight the potential of hydrothermal synthesis methods for enhancing the performance of PrVO4 catalysts in environmental remediation applications.

Sensitive Detection of OCS Using Thermal Conversion Combined with Spectral Reconstruction Filtering Differential Optical Absorption Spectroscopy.

Carbonyl sulfide (OCS) is a toxic gas produced during industrial processes that poses risks to both human health and industrial equipment. Therefore, detecting OCS concentrations plays a crucial role in early hazard warning. This paper presents an online system for detecting OCS at the ppb level using thermal conversion and spectral reconstruction filtering differential optical absorption spectroscopy (SRF-DOAS). First, OCS, which is not suitable for DOAS due to its weak absorption characteristics, is completely transformed into SO2 with strong absorption characteristics under high-temperature conditions. Then, the spectral reconstruction filtering method (SRF) is proposed to eliminate the noise and interference. The core idea of the method is to arrange the spectrum according to the spectral intensity from small to large rather than wavelength, reconstructing the spectrum into a new spectrum with linear characteristics. The reconstructed spectrum can remove noise and interference by linear fitting and retain the characteristic of SO2 oscillation absorption. Next, we demonstrate the ability of the reconstructed spectral method to remove noise and interference by comparing the spectra of the inverse-reconstructed gas mixture and SO2. The relative deviation of 0.88% at 100 ppb and detection limit of 7.26 ppb*m for OCS were obtained using the SRF-DOAS method. Finally, the reliability of the system was confirmed by measurements of OCS concentrations in mixture gas of OCS and air, as well as in human exhaled breath.