Optical Gas Research Articles

Room temperature optical gas sensing properties of Na- doped zinc oxide nanoparticles: improving response and recovery time

Room temperature optical gas sensing properties of Na- doped zinc oxide nanoparticles: improving response and recovery time

Exploring the influence of Zn impurities on the structural, optical, and H2 sensor properties of ultrasonic spray pyrolysis-grown MgO thin films

Magnesium oxide (MgO) thin films, both pure and zinc (Zn) doped, were fabricated on soda lime glass substrates using ultrasonic spray pyrolysis. Zn was introduced at concentrations of 0.5 %, 1 %, 2 %, 4 %, and 8 %. The effects of these doping levels on the films' structural, morphological, optical, and H2 gas sensing properties were studied using XRD, SEM, EDAX, UV–vis spectroscopy, PL spectroscopy, gas sensing measurements, and XPS. The films showed a cubic crystal structure without secondary phases, and grain sizes generally decreased with doping. Morphological changes in nanocrystal shapes were noted due to impurities. Optimal doping enhanced MgO's absorbance, with a slight increase in bandgap. The PL spectra showed increased luminescent emissions with higher doping, due to defects from Zn ions. Pure films were responsive to H2 gas, while Zn-doped samples showed weaker responses. The XPS confirmed the expected chemical compositions.

Thermal mixing and structure of the jet in swirling crossflow

The dilution zone in modern aero-engine combustors is characterized by a strong swirling mainstream with weak transverse jets. This characteristic brings new challenges in homogenizing the temperature distribution at the combustor exit. Therefore, it is imperative to understand the temperature penetration and mixing process of the jet in swirling crossflow (JISCF). This investigation provides new insight in the temperature mixing process for a JISCF in nozzle exit diameter (D) at 7.4, 10.7, and 14 mm and jet to mainstream velocity ratio (VR) from 2.0 to 6.6. The temperature mixing process was measured in a specially designed optical assessable three-dome model gas turbine combustor by planar 1-methylnaphthalene (1-MN) tracer laser-induced fluorescence thermometry. A detailed quantitative measurement of temperature distribution is achieved through the spectral red shift in the fluorescence of 1-MN as the temperature increase. This diagnostic was employed to provide the first two-dimensional temperature distribution for the JISCF. The results showed that the swirling crossflows induce strong spanwise thermal advection, forming secondary low-temperature regions downstream. Generally, the flow structure and mixing process are governed by the interaction of jet and swirling flow. The jet flow parameters, including velocity ratio and diameter, changed the flow structures by changing the interaction between jet and swirling flow. Statistical results and proper orthogonal decomposition (POD) analyses showed a strong anisotropic mixing process in the downstream of the jet.

CoCorrole-Functionalized PCN-222 for Carbon Monoxide Selective Adsorption.

The high risk of CO poisoning justifies the need for indoor air quality control and warning systems based on the detection of low concentrations (ppm-ppb) of CO. Cobalt corrole complexes selectively bind CO vs. O2, CO2, N2, opening new fields of applications. By combining the CO chemisorption properties of cobalt corroles with the known sorption capacity of MOFs, we hope to obtain high performance sensing materials for CO detection. In addition, the exposed metal sites of MOFs lead to CO2 physisorption, allowing the co-detection of CO and CO2. In this work, PCN-222, a stable Zr-based MOF made from Ni(TCPP) with natural vacancies, has been used as a porous matrix for the grafting of electron-poor metallocorroles. The materials were characterized by powder XRD, SEM and optical microscopy, BET analyses and gas adsorption measurements at 298 K. No degradation of the crystalline structure of PCN-222 was observed. At 1 atm, the adsorbed CO(g) volumes measured for the best materials were 12.15 cm3 g-1 and 14.01 cm3 g-1 for CoCorr2@PCN-222 and CoCorr3@PCN-222 respectively, and both materials exhibited high CO chemisorption and selectivity against O2, N2, and CO2 at low pressure due to the highest energy of the chemisorption process vs physisorption.

Nanosized Porphyrinic Metal–Organic Frameworks for the Construction of Transparent Membranes as a Multiresponsive Optical Gas Sensor

The well‐known and excellent colorimetric sensing capacity of porphyrins, along with the exceptional structural properties of metal–organic frameworks (MOFs), make porphyrin‐based MOFs, such as PCN‐222, ideal candidates for the construction of a chemical sensor based on absorbance. However, to the best of authors’ knowledge, no high‐quality porphyrin‐based MOF gas sensors have been developed to date, most likely due to the difficulties in: 1) preparing nanosized porphyrin‐MOFs to minimize scattering in absorbance measurements; and 2) incorporating MOFs into transparent membranes for practical use. Herein, a simple and fast microwave‐assisted method for preparing high‐quality nanosized PCN‐222 crystals and their metalated derivatives PCN‐222(M) is reported to finely tune the sensing response. Next, the successful dispersion of these PCN‐222(M) nanoparticles into poly(dimethylsiloxane) to create flexible and transparent membranes is demonstrated. This integration yields a multiresponsive optical gas sensor exhibiting excellent sensitivity and the ability to discriminate between various volatile organic compounds via pattern recognition identification.

Suspended whispering gallery mode resonators made of different polymers and fabricated using drop-on-demand inkjet printing for gas sensing applications

Investigation of drop-on-demand inkjet printing as a fabrication method for an optical gas sensor reveals its potential to incorporate multiple sensing materials on a single microchip. Through this additive method, three distinct polymers—SU-8, polystyrene (PS), and polyhexamethylene biguanide (PHMB)—were deposited onto a silicon substrate and suspended, allowing the polymer microdroplets to expand freely. The coupling to these whispering gallery mode resonators with a tapered optical fiber allows measuring high quality factors exceeding 106. The gas sensing capabilities of all three polymers were studied for three different gases: isopropanol, water, and carbon dioxide. Sensitivities of up to 0.25pm/ppmv and limits of detection as low as 14ppmv were achieved.

DFT simulations of Al-doped MoTe2 monolayer as an HCHO and C2H3Cl gas sensor for status evaluation of a dry-type reactor in the HVDC converter station

This paper using the density functional theory (DFT) investigates the adsorption property of Al-doped MoTe2 (Al-MoTe2) monolayer upon two fault gas species of a dry-type reactor in the high-voltage direct-current (HVDC) convert station, namely HCHO and C2H3Cl molecules, to explore its potential as a typical gas sensor. Results reveal that the Al dopant can be stably anchored on the MoTe2 surface by replacing the Te atom, and the Al-MoTe2 monolayer performs chemisorption for two gas species. The analysis of charge density difference confirms the charge-transfer behaviour using the Hirshfeld population analysis, and the analysis of electronic property and desorption property uncovers the resistive gas sensing potential of Al-MoTe2 monolayer with higher sensing response in the HCHO system and shorter recovery time in the C2H3Cl system. Also, the work function-based and optical sensing potential of the Al-MoTe2 monolayer is elucidated from the analyses of the work function and dielectric function. All the findings in this work shed light on the favourable potential of the Al-MoTe2 monolayer as a resistance-type, work function-based or optical gas sensor upon two faults gases, which are beneficial for further exploration of such sensing material to evaluate the operation status of the dry-type reactors in the HVDC convert station.

Polyphenylene oxide based lossy mode resonance fiber sensor for the detection of volatile organic and inorganic compounds

This study presents the fabrication and characterization of a fiber optic gas sensor based on Lossy Mode Resonances (LMR). For the first time to our knowledge, a nanosized coating of polyphenylene oxide (PPO) is deposited on a cladding removed multimode silica fiber, serving both as the LMR supporting coating and sensitive overlay. The device exhibits a notable sensitivity of 2500 nm/RIU when immersed in glycerol-water based solutions. For gas detection, the PPO-based LMR device is exposed to varying concentrations of different volatile organic and inorganic compounds, including two alcohols (methanol and ethanol) and ammonia. The sensor demonstrates similar responses to methanol and ethanol gases with a sensitivity of about 0.56 nm/ppm and sensitivity of 0.25 nm/ppm to ammonia in the concentration range of 2.5–37.5 ppm, achieving limits of detection of a few ppm. To comprehensively evaluate the sensor performance, the investigation is also focused on the repeatability, reversibility, response times, as well as cross sensitivity to temperature and relative humidity.

Measuring Dissolved Methane in Aquatic Ecosystems Using An Optical Spectroscopy Gas Analyzer.

Measuring greenhouse gas (GHG) fluxes and pools in ecosystems are becoming increasingly common in ecological studies due to their relevance to climate change. With it, the need for analytical platforms adaptable to measuring different pools and fluxes within research groups also grows. This study aims to develop a procedure to use portable optical spectroscopy-based gas analyzers, originally designed and marketed for gas flux measurements, to measure GHG concentrations in aqueous samples. The protocol involves the traditional headspace equilibration technique followed by the injection of a headspace gas subsample into a chamber connected through a closed loop to the inlet and outlet ports of the gas analyzer. The chamber is fabricated from a generic mason jar and simple laboratory supplies, and it is an ideal solution for samples that may require pre-injection dilution. Methane concentrations measured with the chamber are tightly correlated (r2 > 0.98) with concentrations determined separately through gas chromatography-flame ionization detection (GC-FID) on subsamples from the same vials. The procedure is particularly relevant for field studies in remote areas where chromatography equipment and supplies are not readily available, offering a practical, cheaper, and more efficient solution for measuring methane and other dissolved greenhouse gas concentrations in aquatic systems.

Metrology for sensor networks: metrological traceability and measurement uncertainties for air quality monitoring

Abstract In situ calibration of sensors delivering SI traceable measurement results still provides an open question to the design and operation of sensor networks. Particularly when addressing low-cost sensors, currently, the use of sensor networks for air quality monitoring is limited by the low or unknown accuracy of measurements that they can achieve, while the data quality of individual sensor networks is mainly derived by algorithms. Standardization bodies like DIN and CEN therefore announced the need for investigations of validation methods on gas phase species and particulate matter on the one hand side, and for the development of fully digitized quality assurance/quality control and calibration techniques for sensor networks on the other (CEN/CENELEC, Opportunity for Standardisation to Contribute to the European Partnership on Metrology EPM under Horizon Europe). This contribution concentrates on the metrological traceability of sensor networks for air quality monitoring to the international system of units (SI) based on FAIRified intra-network communications (M. Wilkinson, et al., “The FAIR guiding principles for scientific data management and stewardship,” Sci. Data, vol. 3, 2016, Art. no. 160018) and including delocalized Optical Gas Standards operated according to the digital TILSAM method (O. Werhahn, et al., The TILSAM Method Adapted into Optical Gas Standards – Complementing Gaseous Reference Materials, PTB Open Access Repository, 2021). Informed by related activities in EURAMET (Partnership project FunSNM, EMNs COO & POLMO, TC-IM 1551) (European Metrology Network Climate and Ocean Observation (COO), European Metrology Network Pollution Monitoring (POLMO), EURAMET Project TC-IM 1551, Project Database) this contribution discusses the importance of measurement uncertainties in the context of sensor networks, comprising different sensor principles and promoting an efficient uptake of state-of-the-art methods. We discuss how the sensor network case can be addressed with sensors individually using the GUM principles (Joint Committee for Guides in Metrology, Guide to the Expression of Uncertainty in Measurement (GUM), JCGM 100: 2008 (E)). For sensor network measurements becoming metrologically traceable to the SI, documented and unbroken chains of calibrations need to be implemented each contributing to the measurement uncertainty. This applies to each individual sensor of the network including the potential gold standard among them, but also to the network’s output viewed as a single entity. The contribution provides first approaches to be tested and validated that are underpinned by fundamental design strategies for sensor networks. It follows on practical applications in real world scenarios aside from model uncertainties discussed in artificial intelligence prospects.

Large-scale growth of MoS2 hybrid layer by chemical vapor deposition with nanosheet promoter

Molybdenum disulfide (MoS2) serves as the representative transition metal dichalcogenide material, showing promise for diverse applications owing to its outstanding properties. Extensive research has been conducted on the growth of large-scale MoS2 films using chemical vapor deposition (CVD) with seeding accelerators for various device applications. In this study, we investigated the growth of large-scale MoS2 films for potential applications, in which our approach utilized CVD with a homogeneous nanosheet promoter (MoS2 flakes) and effectively minimized residue creation. Optical and structural analyses confirmed the successful synthesis of a large-scale MoS2 layer. Moreover, the decoration of metallic nanoparticles on the MoS2 surface was employed to enhance the functionalities of application devices such as optical sensors and gas sensors. The capability of MoS2 to act as a nucleation site for nanoparticles during synthesis offered an intriguing pathway for augmenting the attachment and performance of nanoparticles on the MoS2 surface. The photodetector, integrating a hybrid MoS2 layer and Cu nanoparticles, exhibited superior photodetection properties, attributed to the increased excitons at the interface between the metal electrodes and MoS2 films. Furthermore, in order to enhance the characteristics of the gas sensor, Pd nanoparticles were incorporated during the synthesis of MoS2 layers. This dynamic interface between Pd particles and MoS2 films presents an opportunity to explore novel materials with enhanced catalytic properties.

UV photosensitized N-CQDs@In2O3 ordered porous film elaborated optical fiber acetone gas sensor with ppb-level at room temperature

An optical fiber acetone gas sensor based on N-CQDs@In2O3 porous ordered thin film is proposed. The probe adopts the hollow malposition structure (HMS) to excite the evanescent field on the surface of hollow-core fiber (HCF). N-CQDs@In2O3 porous and ordered thin film was formed on the surface of optical fiber after calcining polystyrene (PS) microspheres at high temperature. The experimental results reveal the ultraviolet (UV) sensitization function for the proposed sensor at room temperature. The enhanced sensitivity is 7.1 pm/ppm, which is ∼5.9 times of the spiritual density of unsensitized sensor. In addition, the sensor has a limit of detection (LOD) of 500 ppb and excellent time response characteristics (response time 6.2 s and recovery time 7.1 s). The sensitization mechanism of N-CQDs to In2O3 is explained by the results of the universal density function (DFT). The frontier electron orbital studies show that N-CQDs@In2O3 has more abundant electron clouds. The good moisture resistance enables its stable performance in humid environment. UV sensitization is an effective way to improve the sensitivity of optical fiber gas sensor, which is of great significance for detecting the acetone gas with ultra-low concentration.

Long-Term Continuous Gas Diagnostics For Fuel Cell Systems: Development Of An Automatized Raman Metrology

Knowledge of the composition of gas flows in fuel cell systems is crucial for their understanding. In current research, this data is rarely recorded inline and in real-time due to the lack of suitable metrology. Here, we present an optical gas sensor. Green light (532 nm) from a 450 mW laser excites Raman scattering. A spectrometer analyzes the scattered light and a Python software extracts gas composition data automatized and in real-time. We designed a measurement cell that allows optical inline access to gas flow systems and is easy to implement. Therefore, common signal enhancement methods with more complex setups can not be applied. Literature data on scattering cross sections does not offer a reliable basis for calibration what constitutes the need for a gas conditioning system that allows fast preparation of well defined mixtures. We used it to present two principles of calibration. First, calibration based on relative scattering cross sections is the more stable possibility, because it is still valid in cases where laser power and integration time are changed. However, in consequence the results for one species are not independent from the other species. A poor signal, e.g. following from a low mole fraction in a single component, will introduce uncertainty in all components. We avoid that problem through direct linear correlation of signal strength of one species to its partial pressure, which is the second calibration variant. In this case, there is an influence of laser power and integration time. The additional information on overall pressure can be used in model systems, where the presence of undetected components can be ruled out. We can compare that information to pressure measurements to do plausibility checks on the Raman results in real-time. We apply the sensor in fuel cell system research, where measurement intervals of one second yield results of sufficient precision. Increasing integration time can further decrease the uncertainties where favorable. The measurement and data evaluation routines work stable and constant enough to monitor gas compositions in longterm operation. To date, the sensor can measure mixtures of nitrogen, oxygen, hydrogen and water vapor.

Methane Quantification Performance of the Quantitative Optical Gas Imaging (QOGI) System Using Single-Blind Controlled Release Assessment.

Quantitative optical gas imaging (QOGI) system can rapidly quantify leaks detected by optical gas imaging (OGI) cameras across the oil and gas supply chain. A comprehensive evaluation of the QOGI system's quantification capability is needed for the successful adoption of the technology. This study conducted single-blind experiments to examine the quantification performance of the FLIR QL320 QOGI system under near-field conditions at a pseudo-realistic, outdoor, controlled testing facility that mimics upstream and midstream natural gas operations. The study completed 357 individual measurements across 26 controlled releases and 71 camera positions for release rates between 0.1 kg Ch4/h and 2.9 kg Ch4/h of compressed natural gas (which accounts for more than 90% of typical component-level leaks in several production facilities). The majority (75%) of measurements were within a quantification factor of 3 (quantification error of -67% to 200%) with individual errors between -90% and 831%, which reduced to -79% to +297% when the mean of estimates of the same controlled release from multiple camera positions was considered. Performance improved with increasing release rate, using clear sky as plume background, and at wind speeds ≤1 mph relative to other measurement conditions.

Sub-ppt level detection of carbon monoxide and nitrous oxide enabled by mid-infrared doubly resonant photoacoustic spectroscopy.

We report highly sensitive detection of carbon monoxide (CO) and nitrous oxide (N2O) using doubly resonant photoacoustic spectroscopy paired with a quantum cascade laser (QCL) at 4.57 μm. The butterfly-packaged QCL is used to exploit the CO absorption line at 2190.02 cm-1 and the N2O absorption line at 2191.42 cm-1 by scanning the injection current. Leveraging the simultaneous acoustic and optical resonances and adopting a lower photoacoustic detection frequency, we achieve a minimum detection limit of 0.85 part-per-trillion (ppt) for CO over the 500 s averaging time, and 0.7 ppt for N2O over the 200 s averaging time. Our approach demonstrates record sensitivity for CO and N2O detection compared to state-of-the-art optical gas sensors.

Highly Uncertain Methane Leakage from Oil and Gas Wells in Canada Despite Measurement and Reporting.

Leakage of fluids from oil and gas wells is a source of the key greenhouse gas methane, and presents environmental risks, including groundwater contamination. A loss of well integrity can result in fluid leakage into the annular space between subsequent well casings (which is often vented to the atmosphere) or into the surrounding subsurface. In Canada, industry reporting on well integrity is often incomplete, leading government inventories to disagree on emission magnitudes. In this study, we model wellbore methane emissions using industry data in British Columbia and Alberta, Canada, finding that differing model assumptions to handle unclear/missing data have a strong influence on estimated emissions. Considering estimates derived from industry reporting and from independent measurement, wellbore emissions in the two provinces range anywhere from 23 to 176 kt of methane, representing 1.7-11.4% of their upstream sector methane emissions. Further, finding over 130 examples of measured leaks seemingly missing from industry reporting, we conclude that wellbore emissions, groundwater contamination, and broader environmental risks are underestimated. We provide recommendations to improve well integrity tracking through data quality assurance measures and increased testing. Finally, we find that ongoing optical gas imaging camera surveys could be an effective tool to augment wellbore testing requirements to minimize industry burden.

Engineering luminescent quantum dots through laser ablation of samarium oxide (Sm2O3): A novel approach for enhanced fiber optic gas sensing

Underexplored Sm2O3, with tunable redox and high-surface nanostructures, emerges as a promising volatile organic compounds (VOCs) sensor material for next-gen applications. This study presents the successful synthesis of novel Sm2O3 luminescent quantum dots using a unique pulsed laser ablation technique. Material characterization by FESEM, XRD, EDAX, and HRTEM confirmed the formation of cubic polycrystalline quantum dots. The optical properties were studied by UV-Vis absorption and PL spectroscopy. These quantum dots were then employed in clad-modified fiber optic gas sensors operating at room temperature. Sensor response towards various VOCs, including acetone, ethanol, methanol, and ammonia, were evaluated. Ethanol displayed remarkable sensitivity and selectivity among the other, with a response of 104 ×103 Counts/kPa at 25 °C for 500 ppm. Rapid response and recovery times of 48 and 55 seconds, respectively, further highlights the sensor’s performance. These results establish Sm2O3 quantum dots as a promising and highly effective material for ethanol sensing.

NH3 line broadening coefficients and intensities measurement and impurities determination in emerging applications: CCUS, Biomethane and H2

A mid-infrared quantum cascade laser (Mid-IR QCL) coupled with a Single Pass Cell and a Multi Pass Cell, was utilized to measure ammonia (NH3) absorption spectroscopic parameters and determine NH3 impurities toward three emerging applications. We for the first time measured the pressure broadening coefficients perturbed by Air, O2, N2, He, CO2, CH4, and H2 and the line intensities of six NH3 transition lines near 1084.6 cm−1. The measured NH3-He, NH3-Air, and NH3-CO2 broadening coefficients align with HITRAN database, while NH3-H2 coefficients exhibit a maximum discrepancy of 46 %. Deviations between the measured line intensities and HITRAN database are minimal. Nevertheless, the uncertainties of line intensities have been significantly reduced from 20 % in HITRAN to below 3 %. The newly measured line parameters are utilized to address NH3 impurity requirements outlined in CCUS (ISO 27913:2016), Biomethane (EN 16723:2016), and H2 (ISO 14687:2019) standards. Based on the concept of optical gas standard (OGS), the NH3 impurity detection requirements in all three standards have been fulfilled with an uncertainty of 1.35 %. The precision of the NH3-OGS is 800 part per trillion (ppt) with an integration time of 100 s. The repeatability of the NH3-OGS is 130 ppt for a continuous measurement time of 48 min. Notably, the NH3-OGS effectively addresses the highly nonlinear adsorption–desorption dynamics, underscoring the potential of OGS as a calibration-free and SI-traceable metrological gas analysis instrument.

Optimization design and evaluation of composited fiber optic sensors for monitoring ammonia gas with relative error calibration unit

In this paper, a relative error calibration unit has been designed to analyze and calibrate the common relative errors in optical fiber gas detection system based on directly absorption spectrum (DAS) technology. The ammonia gas was successfully encapsulated in one cut of hollow core fiber as the closed micro-cavity reference cell by dipping saturated solution and cascade-fusing fibers. Through the difference algorithm, the maximum relative error caused by the power fluctuation of the light source is reduced by 85.3 %; to reduce the temperature drift effect caused by optical fiber structure and ammonia absorbance, the calibration equation is obtained by fitting and inversion calculation. The temperature relative error decreases by 95 %. The proposed self-referencing hollow fiber gas sensing probe has a compact structure and can be used for precise monitoring of harmful gases in harsh environments such as narrow space, strong electromagnetic interference, high temperature and humidity.

Three-dimensional photonic crystal optical gas sensor for trace detection and ultrafast response of chemical warfare agent in atmospheric humidity

Chemical warfare agents (CWAs) are toxic that pose a threat to the environment and human health, even trace amounts of CWAs can be fatal. In view of this, there is an urgent need to develop gas sensors for trace detection and ultrafast response of CWAs. Herein, an optical gas sensor has been proposed based on metal−organic frameworks (MOFs) three−dimensional (3D) photonic crystal to detect trace CWAs’ simulant (dimethyl methylphosphonate, DMMP) in different atmospheric humidity (RH 20 %, RH 40 %, RH 60 %, RH 80 %). At relative humidity (RH) of 20 %, the sensor shows excellent selectivity of DMMP due to the specific interactions of van der Waals force between UiO−67 and phosphoryl oxygen (OP) group of DMMP (C3H9O3P), the ultrahigh sensitivity (42.7 ppb), ultrafast response (0.5 s) are profit from the ordered superstructure of 3D photonic crystal and its complete photonic bandgap. At higher humidity (RH 40%–80 %), the sensor shows excellent stability, long–term repeatability, and it still keeps ultrahigh sensitivity (12.1 ppb), ultrafast response (0.49 s) for DMMP at RH 80 %. Moreover, an optical gas sensor array has been prepared to solve the problem of cross−sensitive between DMMP and other CWAs at highest humidity (RH ≥ 80 %), the average classification accuracy can reach 98.6 %.