O2 Absorption Research Articles

Mechanical force-induced oxygen vacancies facilitate enhanced piezo-photocatalytic activity in AgNbO3

Piezo-photocatalysis has emerged as a promising strategy for addressing environmental pollution and the rapidly escalating energy crisis. However, it is still challenging to improve its degradation rate constant. To address this issue, herein, we proposed an innovative strategy of combining both hydrothermal synthesis and high energy mechanical ball milling process in AgNbO3 (AN) photo-catalyst. It is interesting that the hydrothermally synthesized and ball-milled AN demonstrated a record degradation rate constant (k) of 0.213 min−1 for Rhodamine B (RhB), with an 11-fold improvement compared to the un-ball-milled samples. Furthermore, the degradation rate remained high level at 97.3 % after four cycles. The distinguished performance is attributed to the production of large amount of OVs (oxygen vacancies) in hydrothermally synthesized and ball-milled AN, which narrows the bandgap, reduces the recombination of photo-generated carriers, and enhances the absorption of O₂ and OH⁻, thereby efficiently generating superoxide radicals (•O₂⁻) and hydroxyl radicals (•OH). This work presents a novel approach for enhancing the piezo-photocatalytic activity of lead-free piezoelectric materials, which holds broad application prospects in the catalytic treatment of dye wastewater.

Improved Methods for Retrieval of Chlorophyll Fluorescence from Satellite Observation in the Far-Red Band Using Singular Value Decomposition Algorithm

Solar-induced chlorophyll fluorescence (SIF) is highly correlated with photosynthesis and can be used for estimating gross primary productivity (GPP) and monitoring vegetation stress. The far-red band of the solar Fraunhofer lines (FLs) is close to the strongest SIF emission peak and is unaffected by chlorophyll absorption, making it suitable for SIF intensity retrieval. In this study, we propose a retrieval window for far-red SIF, significantly enhancing the sensitivity of data-driven methods to SIF signals near 757 nm. This window introduces a weak O2 absorption band based on the FLs window, allowing for better separation of SIF signals from satellite spectra by altering the shape of specific singular vectors. Additionally, a frequency shift correction algorithm based on standard non-shifted reference spectra is proposed to discuss and eliminate the influence of the Doppler effect. SIF intensity retrieval was achieved using data from the GOSAT satellite, and the retrieved SIF was validated using GPP, enhanced vegetation index (EVI) from the MODIS platform, and published GOSAT SIF products. The validation results indicate that the SIF products provided in this study exhibit higher fitting goodness with GPP and EVI at high spatiotemporal resolutions, with improvements ranging from 55% to 129%. At low spatiotemporal resolutions, the SIF product provided in this study shows higher consistency with EVI and GPP spatially.

Investigation on Be, Mg, Ca, B, Ga, C, Si, and Ge atoms doped on Al (111) surface and their effect on oxygen adsorption: A first-principle calculation

Oxygen corrosion of the aluminum alloy has a substantial impact on the durability of engineering materials and equipment. To better understand how various alloy elements affect oxygen corrosion, we used first-principle DFT method to study the role of each given dopant atom (Be, Mg, Ca, B, Ga, C, Si, and Ge) in the formation of surface oxide film on the Al (111) surface, in the case replacing a surface Al atom. Our calculations show that the electron gain or loss abilities of these alloy elements differ from that of Al metal, with Be, B, C, and Si atoms tending to penetrate into the surface, Mg, Ca, and Ga atoms protruding, and Ge atom just embedded into the Al (111) surfaces. Additionally, the type of doping element at the Al (111) surface can greatly affect the O2 absorption, predicting that Ca-doped surface absorb the least amount of oxygen, followed by Si-doped surface, with Be-, Mg-, B-, Ga-, C-, and Ge-doped surfaces showing higher O2 absorption. Based on adsorption energy (Eads) and partial density of states (PDOS) analysis, we conclude that the doped Al (111) surfaces can make O2 adsorption different owing to the difference in electronic properties of the doping atoms. These insights draw a greater knowledge of the role of alloy elements in the oxygen corrosion of Al alloys, enabling guidance for designing more corrosion-resistant materials.

Effect of background wind and dissipation processes on the diurnal component of atmospheric solar tides

The radiation coming from the Sun heats the Earth’s atmosphere and generates atmospheric tides. In this paper, we model atmospheric tides in the presence of background wind and dissipation processes and investigate their effects. The equations for tidal oscillations of wind and temperature in the atmosphere encompass factors such as background wind, temperature profile, and background composition including ozone, carbon dioxide, hydro-magnetic interactions, Newtonian cooling, eddy, and molecular diffusion. These components interact to define the behavior of tidal phenomena comprehensively. Thermal forcing processes include the insolation absorption of H2O in the troposphere, O3 in the stratosphere, and a contribution from O2 absorption in the thermosphere. The method of solution for the equations is outlined for the solar diurnal tides during the March equinox by considering all these dissipation processes and the background wind. The obtained results are in good agreement with the Global Scale Wave Model (GSWM-00). It is found that the background wind plays significant role in affecting the horizontal wind oscillations below 100 km. At higher altitudes (100–200 km), the background wind, ion drag force, divergence of momentum, and heat fluxes due to molecular and eddy diffusion have a considerable role in affecting the zonal and meridional winds.

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.

Improving O₂ Absorption in PVDF Membrane with Cross-Linked Polymer Coatings

Surface modification of polyvinylidene fluoride (PVDF) membranes using various polymers, including chitosan, nylon, dopamine, and EDA, was examined through SEM and FTIR analyses. SEM imaging unveiled the preservation of membrane porosity post-modification, affirming successful polymer integration without pore obstruction. Nylon coatings induced alterations in surface morphology, with enlarged pore apertures and roughened surfaces attributed to formic acid exposure during dissolution. FTIR spectroscopy confirmed the presence of the respective polymers, exhibiting characteristic peaks for each. Notably, membranes coated with EDA exhibited enhanced CO2 absorption flux owing to their inherently hydrophilic nature and larger pore dimensions. Optimization of EDA coating parameters, including deposition time and concentration, revealed a direct correlation between increased EDA deposition and enhanced CO2 absorption flux, emphasizing the significant impact of these parameters on membrane performance in gas absorption. Consequently, tailored surface modifications offer a promising avenue for enhancing membrane functionality in gas separation applications

Surface Air‐Pressure Measurements From Space Using Differential Absorption Radar on the Right Wing of the 60 GHz Oxygen Band

AbstractSurface air pressure is one of the most important parameters used in Numerical Weather Prediction (NWP) models. Although it has been measured using weather stations on the ground for many decades, the numbers of measurements are sparse and concentrated on land. Few measurements from buoys and ships are available over ocean. Global measurements can only be achieved by using remote sensing from Space, which is challenging; however, a novel design using Differential Absorption Radar (DAR) can provide a potential solution. The technique relies on two facts: first the electromagnetic fields are absorbed mainly by oxygen and water vapor, and second that oxygen is well mixed. In this work we discuss a space‐borne concept, which aims at providing, over the ocean, consistent, and regular observations for determining surface air pressure from space by a design of a multi‐tone radar operating on the upper wing of the O2 absorption band with tones from 64 to 70 GHz. Simulations of radar vertical profiles based on the output of a state of‐the‐art microphysical retrievals applied to the A‐Train suite of sensors are exploited to establish the performance of such a system for surface pressure determination. In particular the identification and quantification of errors introduced by the presence of water vapor, cloud liquid water and rain water and the potential of a correction via the three‐tone method is discussed. Errors introduced by surface measurement noise and temperature profile uncertainties are discussed as well. Results show that accuracy between 2 and 5 hPa is at reach.

Optical properties of blue-light-emitting Y2 O3 :Ce nanophosphor for solid-state lighting application.

The structural, surface morphological, optical absorption and emission features of Y2 O3 :Ce (0%-5%) were studied. The samples had a body-centred cubic crystal structure. The undoped sample had a crystallite size of 29.03 nm, and it varied after doping with Ce. The grain size of the samples varied from 23.00 to 50.78 nm. All the samples exhibited a strong absorption band at 206 nm due to F-centre absorption and absorption involving the delocalised bands. In addition, the doped samples exhibited a secondary band at ~250 nm due to 4f → 5d transitions of Ce3+ ions. The optical bandgap of the undoped sample was found to be ~5.37 eV, and it decreased to 5.20 eV with an increase in Ce concentration to 5%. The undoped sample under 350-nm excitation exhibited a broad photoluminescence (PL) emission band with the maxima at 406 nm and a secondary band at 463 nm. In contrast, multiple PL peaks were centred at ~397, 436, 466, 488 and 563 nm in all the doped samples. The average lifetime of the emission band at 406 nm was 1.05 ns and that of the emission band at ~466 nm was 1.63 ns. The material has potential for solid-state lighting applications.

Highly sensitive detection of oxygen based on light-induced thermoelastic spectroscopy with a high power diode laser

Oxygen (O2) is a fundamental element in the atmosphere. It is important to detect it in various fields. In this paper, a sensitive O2 sensor based on light-induced thermoelastic spectroscopy (LITES) with a high power diode laser is reported. A distributed feedback (DFB) diode laser emitting at 760 nm with output power of 16.8 mW was employed as the light source. The O2 absorption line at 13144.54 cm-1 was selected for the investigation. Wavelength modulation spectroscopy (WMS) technique and second harmonic signal demodulation (2f) were adopted to improve the sensing performance. For the concentration dynamic range from 20% to 80%, a linear relationship between the amplitude of 2f signal and O2 concentration was demonstrated. Allan deviation analysis was conducted to evaluate the long-term stability of the sensor system and the minimum detection limit (MDL) was measured to be 583 ppm at the optimum integration time of 100 s. Further improvement of this O2-LITES sensor system was also discussed.

CO2-broadened lineshapes in the oxygen A-band

High-resolution spectra of O2 broadened by CO2 pressure with high signal/noise ratio (2500 at the absorbance equal 1) were recorded with a Bruker IFS 125 FTIR spectrometer in the 13,000–13,260 cm−1 spectral region. The multispectrum fitting procedure has been applied to recover the spectral line parameters from measurements using the Voigt and speed-dependent Voigt (SDV) profiles. The O2 absorption line parameters for 40 transitions were measured. The parameters for SDV profile were studied for the first time. The uncertainty of the broadening coefficients for the unblended O2 absorption lines was estimated to be <3 %. The determined parameters were compared to HITRAN2020 and literature data. The values of the self-broadening coefficients and intensities were in good agreement with literature data.

Ball-milled prepared Fe3O4-FeSAs-NPs@NC catalyst synergistically facilitate the generation of reactive oxygen species for oxidative trifluoromethylation of alkenes

Heterogeneous catalysts have recently regarded as a promising chose for the thermally-driven generation of the reactive oxygen species (ROS) through catalytic reactions with molecular oxygen, which can facilitate this process by specific geometric and electronic structure. However, the oxidative trifluoromethylation of alkenes to α-trifluoromethylated ketones by CF3SO2Na is rarely reported in this system. In this work, we report a one-pot polymerization ball milling strategy to construct precursor, and then pyrolyze it to obtain specific carbon nanotubes matrix with Fe/Fe3O4 nanoparticles and single atoms Fe. Remarkably, the optimized catalyst (Fe3O4-FeSAs-NPs@NC-1) displays excellent catalytic performance, broad substrates and recyclability for this fluorination reaction via radical pathway. Based on characterizations and mechanistic studies, we discover that the coexistence of Fe/Fe3O4 and Fe-Nx not only synergistically facilitates the catalytic efficiency in altering the electronic structure of Fe sites, but also benefits the absorption of O2 and the ability of the thermally-driven generating ROS which can activate CF3SO2Na to CF3 radical. This work offers a method of designing Fe-based catalysts and also opens up a new thermal-heterogeneous catalysis way for the oxidative trifluoromethylation of alkenes.

Impact of Storm‐Time Enhanced O2 Absorption on Disk Viewing N2 LBH Spectra: TIMED GUVI Observations

AbstractA comparison between storm‐time TIMED/GUVI FUV spectra in thermospheric composition disturbed (O/N2 &lt;∼140 km&gt; depleted and NO &lt;∼110 km&gt; enhanced) and undisturbed regions reveals the following features: (1) A clear decrease in N2 LBHS (140–150 nm) band intensities compared to that between 150 and 160 nm; (2) A significant spectral decrease around O 164.1 nm; (3) Two enhanced peaks between 170 and 185 nm. The feature (2) is clearly due to atomic oxygen density decrease in the low thermosphere. The feature (3) is caused by storm‐time production and transport of nitric oxide. An AURIC simulation reproduced feature (1) confirming that storm‐time enhancement in O2 density (∼120–170 km) and the wavelength dependent O2 absorption cross section are the source of observed feature (1). On the other hand, the feature (1) was not observed in the regions without O/N2 depletion. This further supports that O2 density enhancement is responsible for feature (1).

The Prospect of Detecting Volcanic Signatures on an ExoEarth Using Direct Imaging

The James Webb Space Telescope (JWST) has provided the first opportunity of studying the atmospheres of terrestrial exoplanets and estimating their surface conditions. Earth-sized planets around Sun-like stars are currently inaccessible with JWST, however, and will have to be observed using the next generation of telescopes with direct-imaging capabilities. Detecting active volcanism on an Earth-like planet would be particularly valuable as it would provide insight into its interior and provide context for the commonality of the interior states of Earth and Venus. In this work, we used a climate model to simulate four exoEarths over eight years with ongoing large igneous province eruptions with outputs ranging from 1.8 to 60 Gt of sulfur dioxide. The atmospheric data from the simulations were used to model direct-imaging observations between 0.2 and 2.0 μm, producing reflectance spectra for every month of each exoEarth simulation. We calculated the amount of observation time required to detect each of the major absorption features in the spectra, and we identified the most prominent effects that volcanism had on the reflectance spectra. These effects include changes in the size of the O3, O2, and H2O absorption features and changes in the slope of the spectrum. Of these changes, we conclude that the most detectable and least ambiguous evidence of volcanism are changes in both O3 absorption and the slope of the spectrum.

Edge engineering of carbon nitride for enhanced sacrificial agent-free photocatalytic H2O2 evolution

Photocatalytic oxygen reduction reaction (ORR) offers a green and sustainable route to produce H2O2. Electronic structure modulation and spin density distribution of the photocatalyst are crucial to the ORR activity. Heteroatom sulfur-doped and functionalized carbon nitride with abundant edge active sites is prepared for photocatalytic H2O2 generation. The as-obtained catalyst provides a faster H2O2 production rate of 416.7 μmol g−1h−1 under visible light (λ ≥ 420 nm) without using sacrificial agents. The enhanced photocatalytic performance is attributed to extended light absorption and improved carrier separation ability for the modulation of the electronic structure. The experimental and theoretic study demonstrates that sulfur doping and terminal group modulation show higher localized spin density, thus promoting the O2 absorption and the higher spin density and charge redistribution via edge active sites make the strong interaction between *OOH and the catalyst, which lowers the energy barrier of *OOH formation, thus facilitating the H2O2 generation.

Solar spectrum measured by waveguide spectral lens

We demonstrate solar spectrum measurement in the visible-near-infrared region by integrated waveguide spectral lens (WSL). Light through the chip is dispersed and focused on a camera placed at the designed distance without any free-space lens. Commercial polymer materials with low propagation loss near visible region are chosen for wafer-scale fabrication. The solar radiation is coupled to a fiber via a home-made setup and the captured light is transmitted over ∼ 50 m to the lab, where the spectrum is examined by two WSL chips for broadband and fine analysis, respectively. The observed O2 (687.7 nm, 761.9 nm) and H2O (718.4 nm) absorption lines are in good agreement with the results from a commercial optical spectral analyzer and the literature. This experiment proves the feasibility of using planar WSL chips as low-cost and versatile components for the development of compact and portable spectrometer equipment.

Diode laser absorption spectroscopy for real-time detection of breath oxygen

In this paper, a high-resolution laser absorption spectrometer is developed using a distributed feedback (DFB) diode laser in the spectral region near 760 nm, which is designed for the highly sensitive detection of oxygen (O2) in breathing gas. To investigate the spectrometer performance, O2 absorption line at 13146.580 cm−1 was selected, and detailed experiments on air-broadening coefficient, self-broadening coefficient and spectral line intensity were conducted. Compared to the corresponding data listed in the HITRAN2020 database, the results show that the errors for air-broadening coefficient, self-broadening coefficient and line intensity, were −6.832%, 4.082% and 4.667%, respectively. Finally, the developed laser absorption spectrometer was primarily evaluated for real-time analysis of O2 content in human breath analysis. The results indicate that the measured O2 concentrations in several volunteers range from 16% to 16.5%, which is in agreement with the levels reported in the literature for healthy humans.

Janus Dual Self-Strengthening Structure of Bi2 O3 /Gd2 O3 Nanofibrous Membranes for Superior X-Ray Shielding.

Bi2 O3 /rare earth oxide biphasic absorbers are attractive for high-efficiency X-ray shielding due to the complementary X-ray absorption effects. However, its application is severely hindered by poor interphasic contact. Here, a new Janus interface engineering strategy is reported for the construction of continuous and flexible Bi2 O3 /Gd2 O3 crystal nanofibrous membranes (FJNMs) with micro/nano dual self-strengthening interphasic adhesion. This strategy facilitates online micro-interlocking between Bi2 O3 /Gd2 O3 nanofibers and in situ nano-grain fusion between Bi2 O3 /Gd2 O3 crystals, significantly enhancing the adhesive strength at the Bi2 O3 /Gd2 O3 interface. Additionally, the synergistic shielding effect from Bi2 O3 /Gd2 O3 absorption and multiple reflections in Bi2 O3 and Gd2 O3 crystal lattices make the nanofibrous membranes a superior X-ray radiation barrier. The FJNMs demonstrate integrated features of exceptional X-ray shielding efficiency (91%-100%), robust interfacial adhesion (lap-shear strength >3.8MPa), prominent flexibility, lightweight, and outstanding breathability. The design concepts of fibrosing biphasic absorber assemblies pave the way for asymmetrically assembling biphasic materials, setting the stage for a fundamental shift in next-generation radiation shielding materials.

Cu-doped SnO2/rGO nanocomposites for ultrasensitive H2S detection at low temperature

Hydrogen sulfide (H2S) detection remains a significant concern and the sensitivity, selectivity, and detection limit must be balanced at low temperatures. Herein, we utilized a facile solvothermal method to prepare Cu-doped SnO2/rGO nanocomposites that have emerged as promising candidate materials for H2S sensors. Characterization of the Cu-SnO2/rGO was carried out to determine its surface morphology, chemical composition, and crystal defects. The optimal sensor response for 10 ppm H2S was ~1415.7 at 120 °C, which was over 320 times higher than that seen for pristine SnO2 CQDs (Ra/Rg = 4.4) at 280 °C. Moreover, the sensor material exhibited excellent selectivity, a superior linear working range (R2 = 0.991, 1–150 ppm), a fast response time (31 s to 2 ppm), and ppb-level H2S detection (Ra/Rg = 1.26 to 50 ppb) at 120 °C. In addition, the sensor maintained a high performance even at extremely high humidity (90%) and showed outstanding long-term stability. These superb H2S sensing properties were attributed to catalytic sensitization by the Cu dopant and a synergistic effect of the Cu-SnO2 and rGO, which offered abundant active sites for O2 and H2S absorption and accelerated the transfer of electrons/holes.

Microstructure evolution and reaction mechanism of reactive plasma sprayed Ti–C–N coatings

This investigation focuses on the feasibility of the reaction synthesis of Ti–C–N phase using plasma spraying powder mixture of Ti and graphite under nitrogen ion flame flow. To regularize the microstructure and properties of the sprayed Ti–C–N coating, the microstructure evolution of the Ti-graphite-N2 system was analyzed based on water quenching tests. The reaction pathway of the Ti-graphite-N2 system has been investigated by thermodynamic calculations and thermal analysis, revealing the mechanisms of the reaction during plasma spraying. The results show that the as-deposited coatings exhibit a typical layered structure consisting mainly of TiCxNy and TiO2. The quenched powders exhibit a melting process from irregular particles to smooth spherical particles, forming complete droplets with increasing spray distance. Based on phase evolution of the quenched powders and the thermal analysis of Ti powders or Ti/graphite powders under N2/Ar atmosphere, it found that the Ti powder can reacted with graphite or N2 by solid-solid or solid-gas reaction to form TiCx and TiNy, and TiNy can be formed preferentially as compared with TiCx phase. As the spraying distance increases, the Ti and graphite reactions are enhanced, and a pronounced TiCx phase can be detected once a large liquid Ti phase is formed. As the spray distance increases, formed TiNy and TiCx phases aggregate into droplets and rapidly transform into TiCxNy phase by solid-solution reactions. In addition, titanium oxide coexists in lamellae of Ti–C–N coatings due to the absorption and dissociation of O₂ from the atmosphere at the droplet surface.

Improved precision of radial velocity measurements after correction for telluric absorption

Context. The detection of planets around other stars by measurement of stellar radial velocity (RV) variations benefits from improvements to dedicated spectrographs that can lead to the achievement of a precision of 1 m s−1 or better. Spectral intervals within which stellar lines are contaminated by telluric lines are classically excluded from the RV processing. Aims. We aim to estimate the potential improvement of the precision of radial velocity measurements from telluric-absorption removal and subsequent extension of the useful spectral domain. Methods. We developed a correction method based on the online web service TAPAS that allows a synthetic atmospheric transmission spectrum to be determined for the time and location of observations. This method was applied to telluric H2O and O2 absorption removal from a series of 200 consecutive ESPRESSO exposures of the K2.5V star HD40307 available in ESO archives. We calculated the radial velocity using the standard cross-correlation function (CCF) method and Gaussian fit of the CCF, with uncorrected spectra and the ESPRESSO standard stellar binary mask on one hand, and telluric-corrected spectra and an augmented binary mask with 696 additional lines on the other. Results. We find that the precision of radial velocity measurements is improved in the second case, with a reduction of the average formal error from 1.04 m s−1 down to 0.78 m s−1 in the case of these ESPRESSO data and this stellar type for the red arm. Using an estimator of the minimal error based on the photon noise limit applied to the full CCF, the error is reduced from 0.89 m s−1 down to 0.78 m s−1. This corresponds to a significant decrease (by about 35%) in the observing time required to reach the same precision in the red part.