Optical CO2 Sensor Research Articles

An emission based optical CO2 sensor fabricated on grating-like TiO2 substrates using HPTS

TiO2 is a widely used material in various applications, including photo-catalysis, sensing, and dye-sensitized solar cells. In this work, we presented a stable and sensitive CO2 sensor working on principle of emission signals of the HPTS dye immobilized on TiO2 substrates whose effectiverefractive indicesin the parallel and perpendicular grating orientations evidenced earlier. The HPTS exhibited 8.4-fold enhanced emission signal on the offered substrates with respect to the previously reported intensities recorded for the polymeric supports. The emission peaks of the HPTS exhibited CO2 induced intensity quenching when excited at 466 nm. Calibration sensitivity of the offered composites has been tested exposing the sensor materials to varying concentrations of the CO2 between 0.0 and 100.0 % pCO2 and correlating the measured fluorescence intensity with the corresponding CO2 levels. The dye revealed enhanced CO2 induced response exhibiting the I0/100 values of 11.9, 13.3, 11.2 and 6.5. We also recorded bi-exponential excited state lifetimes for the HPTS on four different test materials both in the absence and presence of the CO2. The emission based variations were followed as the analytical signal due to higher CO2-induced relative signal changes than that of the lifetime based variations. Herein we used the ion pair form of the HPTS in a protective chemical microenvironment and obtained considerable long term stability extending to16 mounts which can be attributed to the presence of the 1-butyl-3-methylimidazolium tetrafluoroborate as an internal buffering system in the sensing composition as well as the inert and robust structure of the substrate. The extremely high optical response, advantage of excitation with blue LEDs and long-term stability observed on grating-like TiO2 surfaces make the proposed system a promising design for the quantification of CO2 for further applications.

Liquid crystalline substances doped with carbon nanotubes as a sensitive medium of the CO2 sensor

The creation of highly sensitive optical CO2 sensors in air is an urgent problem, as it allows monitoring of the content of CO2 both indoors and in ambient air, where its level is usually 600…1000 ppm. As a sensitive element of the CO2 sensor, it is proposed to use a liquid crystal substance (cholesteric-nematic mixture based on 5CB with cholesteric impurities), supplemented with multi-layered carbon nanotubes. The spectral characteristics of the liquid crystal mixture in the range of 400…600 nm were studied. The content of carbon nanotubes ranged from 0.1 to 0.5 wt.%. It was established that with an increase in concentration in the range of 10…100 mg/m3, the transmission minimum shifts to the long-wave region of the spectrum. The maximum spectral sensitivity in this range is 6 nm ⁄ mg ⁄ m3. The researched material can be used as a sensitive element of an optical CO2 sensor. Further research should be conducted in the direction of investigating the interaction of such a composite with other gases, as well as finding opportunities to improve the properties of the composite. Perhaps the use of multi-walled carbon nanotubes.

An 8 mW Fully Integrated Regenerative Resonant MEMS CO2 Sensor Using Linear Polyethylenimine as a Capture Layer

A fully integrated regenerative CO2 MEMS sensor using a micro-resonator coated with Linear Polyethylenimine as an adsorbent layer is presented. The pyramidal cantilever micro-resonator used has a resonant frequency of 315.24 kHz with a Q factor of 1125 at atmospheric pressure. The micro-resonator was integrated with a sustaining amplifier that consumes 8 mW. The MEMS sensor sensitivity was characterized in a CO2 concentration range from 1200 to 10500 ppm, showing a frequency shift of −12 Hz at 1200 ppm with a slope of −3.50 mHz / ppm over the characterized range. The adsorption and recovery times are characterized to be as low as 170 seconds and 280 seconds, respectively. The impacts of pressure, temperature and humidity on the sensor were also characterized. The behavior of the MEMS sensor is compared to that of an optical CO2 sensor.

Highly efficient colorimetric CO2 sensors for monitoring CO2 leakage from carbon capture and storage sites

Carbon capture and storage (CCS) technology used for reducing anthropogenic CO2 emissions involves the capture of CO2 from industrial sources and its injection into geological sinks, such as oil reservoirs and abandoned gas fields. To ensure environmental and public safety in implementing CCS technology, efficient CO2-monitoring technology must be developed to detect potential CO2 leakage from CCS sites. Conventional CO2 sensors used for monitoring CCS sites are typically high in cost and require professional staff for maintenance. In this study, we developed a portable and low-cost colorimetric CO2 sensor with high soil CO2 detection efficiency for CCS sites. The sensor consists of a detection solution that contains the pH indicator cresol red encapsulated with a gas-permeable membrane. When CO2 enters the sensor through the membrane, the color of the pH indicator changes and this was quantified using an RGB (red, green, blue) application (app), an app that measures the RGB values of a given color. The change in G and B values of the detection solution showed a significant linear relationship with soil CO2 concentration determined via non-dispersive infra-red (NDIR) CO2 sensor (r2 = 0.98, p = 0.001), and thus these values were used for quantification of CO2 concentration. Tests using CO2-injection chamber showed that the optical CO2 sensors can detect soil CO2 concentration of 0.1 to 30% within a few minutes. Field studies conducted at a natural CO2 vent and an artificial CO2 leakage site showed that the optical CO2 sensors can be applied in analyzing surficial CO2 leakage patterns. The advantage of this optical CO2 sensor when applied to field monitoring is that it is inexpensive and has few installation restrictions. Therefore, this optical CO2 sensor has a strong potential for use in monitoring CO2 leakages from CCS sites.

A CO2optical sensor based on self-assembled metal–organic framework nanoparticles

An optical CO2sensor is fabricated by integration of a self-assembled, transparent film of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles onto bimodal optical waveguides. This sensor shows a limit of detection (LOD) of 774 ppm CO2, is robust, fast and reusable, and can be stored under humid conditions with no loss in performance.

Optical sensor for dual sensing of oxygen and carbon dioxide based on sensing films coated on filter paper.

An optical sensor for the dual sensing of oxygen (O2) and carbon dioxide (CO2) based on sensing films coated on filter paper is proposed. Ethyl cellulose (EC) doped with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and 7-amino-4-trifluoromethyl coumarin serve as the oxygen sensing material and reference blue emission dye for the pH indicator, respectively. The CO2 sensing layer includes the pH-sensitive fluorescent indicator 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt immobilized within the EC. The O2- and CO2-sensitive materials can both be excited with a 405 nm LED, and the two emission wavelengths can be detected separately. The experimental result reveals that the optical O2 and CO2 sensors have sensitivities of IN2 /I100%O2 =22.8 and IN2 /I100%CO2 =3.6, respectively. The response times of the optical O2 sensor were 15 s upon switching from nitrogen to O2 and 41 s when moving from O2 to nitrogen (N2). The response times of the optical CO2 sensor were 7 s upon switching from 100% N2 to 100% CO2 and 39 s when moving from 100% CO2 to 100% N2. The proposed optical dual sensor can be used for the simultaneous sensing of O2 and CO2 concentrations in environmental applications.

Optical CO2 Sensor with the Combination of Colorimetric Change of pH Indicator and Internal Reference Luminescent Dye

Abstract A new optical CO2 sensor based on luminescence intensity changes of europium(III) complex, tris(thenoyltrifluoroacetonato)europium(III) dihydrate complex ([Eu(tta)3]) due to the absorption change of pH-indicator dye (thymol blue) with CO2 was developed and its CO2 sensing properties were investigated. The observed luminescence intensity (I) from [Eu(tta)3] at 613 nm increased with increasing the CO2 concentration. The ratio I0/I100, where I0 and I100 represent the detected luminescence intensities from a layer exposed to 100% nitrogen and 100% CO2, respectively, that we takes the sensitivity of the sensor is estimated to be 16.0. The response times of the sensing film were 4.0 s for switching from nitrogen to CO2, and 36 s for switching from CO2 to nitrogen. The signal changes were fully reversible and no hysterisis was observed during the measurements.