Selective Gas Detection Research Articles

Selective room temperature ammonia gas detection using 2-amino pyridine functionalized graphene oxide

A stable and selective ammonia gas sensor has been prepared using 2-amino pyridine functionalized Graphene oxide (GO). The GO and functionalized GO was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, Scanning electron microscopy & Energy dispersive X-ray spectroscopy. The sensing film was prepared by drop casting the amide functionalized GO on SiO2/Si substrate. Aluminum contacts were made on the sensor device for electrical measurement. The prepared sensor response was investigated for different concentrations of ammonia gas varied from 50 ppm to 900 ppm. The value of sensor response observed at low concentration (i.e. at 50 ppm) and at high concentration (i.e. 900 ppm) was 8.5% & 55.6% respectively. The sensor device showed good response time (~20s) & recovery time (~120s). The sensor also exhibited good selectivity and stability towards ammonia gas.

Газочувствительные свойства слоев композитных оксидов на основе Cox Oy /MnO2–z

Газочувствительные свойства слоев композитных оксидов на основе Cox Oy /MnO2–z

Uniform hierarchical tetradecahedral SnO2/Zn2SnO4 composites for ultrafast response/recovery and selective gas detection at room temperature

In this work, hierarchical tetradecahedral SnO2/Zn2SnO4 composites were synthesized by a simple one-pot method without using surfactants and templates and have a uniform diameter of ~1 μm. Importantly, SnO2/Zn2SnO4 was used to manufacture gas sensor. After testing the sensor, it displays good selectivity to ethanol and excellent repeatability at room temperature (RT). It has ultra-fast response/recovery times with 9 s and 7 s at 200 ppm ethanol, respectively. Such enhanced gas-sensing performances are probably ascribed to the unique hierarchical tetradecahedral SnO2/Zn2SnO4 structure, the strong interfacial interaction and the existence of heterojunctions between Zn2SnO4 and SnO2.

Fabrication of ZnO@ZIF-8 gas sensors for selective gas detection

In this paper, zinc oxide nanorods encapsulated with a representative of the zeolithic imodazole based metal organic framework family (ZIF-8) is used as gas sensor material for the detection of hydrogen gas and benzene vapour. The material properties of this ZnO@ZIF-8 hybrid material was investigated by XRD, electron microscopy, Fourier transform infrared spectroscopy and gas sensing experiments. Selectivity and sensitivity of these thin films to various gases H2 and C6H6 were also studied. The ZnO@ZIF-8 sensor with the nanostructure showed a remarkable selective response to hydrogen gas as compared to the pristine ZnO nanorods sensor, while the ZnO sensor shows high sensitivity to H2 and C6H6. The ZnO@ZIF-8 sensor exhibits a significant selective response to hydrogen compared to the original ZnO nanorod sensor. This behavior can be attributed to the small pore aperture of ZIF-8, where H2 molecules it can easily spread through the ZIF-8 network and reach the ZnO surface. This result indicate that the selectivity of ZnO gas sensor can be regulated by surface ZIF-8 coating.

Facile conversion of zinc hydroxide carbonate to CaO-ZnO for selective CO2 gas detection

Tailored synthesis of heterostructures for low temperature (sub 200 °C) CO2 sensing continues to be a challenging task. The present study demonstrates CO2 sensing characteristics of CaO-ZnO heterostructures achieved by zinc hydroxide carbonate (Zn5(CO3)2(OH)6) conversion to ZnO using Ca(OH)2 at 50 °C. Control samples namely, Zn5(CO3)2(OH)6, Ca(OH)2, ZnO, and CaO integrated microsensors exhibited low sensitivity towards CO2 gas. However, CaO-ZnO heterostructures demonstrated significant sensitivity (26 to 91%) at 150 °C for gas concentration ranging from 100 to 10000 ppm, respectively. In this study, zinc hydroxide carbonate sensitized with 25 wt% Ca(OH)2 to form CaO-ZnO heterostructures (25CaZMS) displayed a promising sensitivity (77%) and selectivity (98%) towards 500 ppm CO2 gas. Moreover, the selectivity studies were conducted in the presence of 10 commonly found gases and their sensing performance was compared against CO2 gas in dry and humid conditions. The developed CaO-ZnO sensor exhibited faster kinetics in comparison to the control samples. Improved sensing performance observed here is attributed to the low-temperature synthesis route which resulted in a large number of active pores and high surface area morphology. Additionally, the high CO2 adsorption capacity of CaO combined with compatible n-type semiconductors in forming highly dynamic nano-interfaced heterostructure is a promising step towards developing a precise CO2 gas microsensor.

Selective Detection of Nitrogen-Containing Compound Gases.

N-containing gaseous compounds, such as trimethylamine (TMA), triethylamine (TEA), ammonia (NH3), nitrogen monoxide (NO), and nitrogen dioxide (NO2) exude irritating odors and are harmful to the human respiratory system at high concentrations. In this study, we investigated the sensing responses of five sensor materials—Al-doped ZnO (AZO) nanoparticles (NPs), Pt-loaded AZO NPs, a Pt-loaded WO3 (Pt-WO3) thin film, an Au-loaded WO3 (Au-WO3) thin film, and N-doped graphene—to the five aforementioned gases at a concentration of 10 parts per million (ppm). The ZnO- and WO3-based materials exhibited n-type semiconducting behavior, and their responses to tertiary amines were significantly higher than those of nitric oxides. The N-doped graphene exhibited p-type semiconducting behavior and responded only to nitric oxides. The Au- and Pt-WO3 thin films exhibited extremely high responses of approximately 100,000 for 10 ppm of triethylamine (TEA) and approximately −2700 for 10 ppm of NO2, respectively. These sensing responses are superior to those of previously reported sensors based on semiconducting metal oxides. On the basis of the sensing response results, we drew radar plots, which indicated that selective pattern recognition could be achieved by using the five sensing materials together. Thus, we demonstrated the possibility to distinguish each type of gas by applying the patterns to recognition techniques.

Hydrophobic Tungsten-Containing MFI-Type Zeolite Films for Exhaust Gas Detection.

The assembly of highly hydrophobic nanosized tungsten-containing MFI-type zeolite nanocrystals (W-MFI) in films and further use of the films for selective exhaust gas (CO, CO2, NO, and NO2) detection were investigated by operando IR spectroscopy. Because of the hydrophobic nature and presence of tungsten in the framework, the W-MFI films showed excellent sorption capacity toward all analytes, in comparison to the pure silica (Si-MFI) film. The high sensitivity of the W-MFI film toward low concentration of CO2 and NO2 (1-3 ppm) was demonstrated. In addition, the interactions between the analytes and zeolite films have been studied by quantum chemical calculation modeling of the W centers based on the density functional theory method.

Conductance quantization as a new selective sensing mechanism in dendritic point contacts

The diversity of techniques employed in modern sensing nanodevices is crucial for large-scale use of sensors in multifunctional technological cycles. We propose a new concept of selective detection of gases and liquids based on the formation of an original quantum system and registration of its energy states in dynamic mode using dendrite point contacts synthesized electrochemically in the probed medium. The in situ synthesis of nanosized dendrite point contacts is shaped by the cyclic switchover effect which takes place in an electrolyte in contact with the analyzed medium and results in consecutive cycles of the formation and destruction of an electrochemical gapless electrode system. Conductivity of such point contacts demonstrates quantum behavior driven by the shell effect which determines the geometry of their conducting channels. Temporal dependence of dendrite point contact electrical resistance measured in dynamic mode is characterized by a step-like structure which reflects the metastable quantum states of the system whose distribution can be presented in the form of a conductance histogram. The histogram is a unique fingerprint of the probed medium and can thus be used to unambiguously identify it. The dynamic mode scanning of the energy states of point contact quantum systems proposed here makes it possible to develop a universal method for selective detection of many gaseous and liquid media including such hard to detect substances as methane and rare gases. The new approach is expected to prove its efficiency in investigating quantum effects for various sensor applications and stimulate the development of the next generation of highly selective nanodevices. The new concept of selective detection of gases and liquids is based on the registration of quantum states of nanosized dendrite point contacts synthesized in the probed medium.

Mid-Infrared Tunable Laser-Based Broadband Fingerprint Absorption Spectroscopy for Trace Gas Sensing: A Review

The vast majority of gaseous chemical substances exhibit fundamental rovibrational absorption bands in the mid-infrared spectral region (2.5–25 μm), and the absorption of light by these fundamental bands provides a nearly universal means for their detection. A main feature of optical techniques is the non-intrusive in situ detection of trace gases. We reviewed primarily mid-infrared tunable laser-based broadband absorption spectroscopy for trace gas detection, focusing on 2008–2018. The scope of this paper is to discuss recent developments of system configuration, tunable lasers, detectors, broadband spectroscopic techniques, and their applications for sensitive, selective, and quantitative trace gas detection.

Expanded graphite/NiAl layered double hydroxide nanowires for ultra-sensitive, ultra-low detection limits and selective NO x gas detection at room temperature.

To develop an ultra-sensitive and selective NOx gas sensor with an ultra-low detection limit, expanded graphite/NiAl layered double hydroxide (EG/NA) nanowires were synthesized by using hydrothermal method with EG as a template and adjusting the amount of urea in the reaction. X-ray diffraction and transmission electron microscopy showed EG/NA3 nanowires with a diameter of 5–10 nm and a length greater than 100 nm uniformly dispersed on the expanded graphite nanosheet (>8 layers). The synergy between NiAl layered double hydroxide (NiAl-LDH) and expanded graphite (EG) improved the gas sensing properties of the composites. As expected, gas sensing tests showed that EG/NA composites have superior performance over pristine NiAl-LDH. In particular, the EG/NA3 nanowire material exhibited an ultra-high response (Ra/Rg = 17.65) with ultra-fast response time (about 2 s) to 100 ppm NOx, an ultra-low detection limit (10 ppb) and good selectivity at room temperature (RT, 24 ± 2 °C), which could meet a variety of application needs. Furthermore, the enhancement of the sensing response was attributed to the nanowire structure formed by NiAl-LDH in the EG interlayer and the conductive nanonetwork of interwoven nanowires.

Cavity-enhanced cantilever-enhanced photo-acoustic spectroscopy.

We have improved the sensitivity of a state-of-the-art cantilever-enhanced photo-acoustic trace gas sensor by combining it with an optical power build-up cavity. The build-up cavity enhances the photo-acoustic signal by a factor of ∼100, resulting in an exceptionally good normalised noise equivalent absorption (NNEA) value of 1.75 × 10-12 W cm-1 Hz-1/2. We demonstrate the sensor platform in the 1530 nm wavelength range with a simple distributed feedback diode laser, achieving 75 ppt sensitivity for C2H2 with a 10 s integration time.

Gas transport regulation in a MO/MOF interface for enhanced selective gas detection

The channel traffic of gas molecules with a similar sensing activity was modulated in MO@MOF chemiresistors by modification of the pores of the MOF sheath.

Substantial effect of Pd incorporation on the room temperature hydrogen sensing performance of ZnO/ITO nanowires prepared by spray pyrolysis method

The room temperature hydrogen sensing characteristics of Pd-decorated ZnO nanowires was fabricated on ITO substrate by spray pyrolysis technique. The crystal structure revealed that the Pd dopants were well integrated into ZnO wurtzite lattice. The average crystallite size decreased with increasing Pd dopant concentration. The band gap energies of the ZnO films were affected by the Pd concentration. The blue shift in the PL emission of Pd:ZnO film signify the modulation of band gap caused by Pd addition. The morphology of ZnO films changed from nanotubes to nanowires with Pd dopant concentration. The gas sensing measurement results demonstrated that the Pd:ZnO/ITO sensor revealed good response even for low concentration of H2, with characteristics reliant on the morphology, size of the grains and the increasing incorporation of Pd concentration. A doping level of 2 at.% palladium in ZnO was found to give optimum response. The lowest detection limit of hydrogen was found to be100 ppm. We strongly believe that the Pd:ZnO sensor with ITO underlayer can be widely used for selective hydrogen gas detection. It can be summarized that this high performance H2 sensor has potential for use as a portable room temperature gas sensor.

Fabrication of aggregated In2O3 nanospheres for highly sensitive acetaldehyde gas sensors

The selective detection of dangerous and explosive gases with high sensitivity is serious problem to safety of humans and industrial processes. Small sized nanoparticles aggregated into a nanospheres offer plenty of advantages such as large specific area, greater mass transportation, and diffusion of gas molecules deep inside the material towards efficient gas sensing applications. Herein, In2O3 nanoparticles aggregated into nanospheres were synthesized successfully through one step microwave hydrothermal method. The structure, morphology and chemical states of prepared In2O3 nanospheres were studied by XRD, TEM and XPS measurements. Furthermore, obtained In2O3 nanospheres were applied as a gas sensing layer for acetaldehyde (CH3CHO) detection. Acetaldehyde is an important volatile organic compound which is highly reactive, toxic and carcinogenic agent. Gas sensor based on In2O3 nanospheres shows high sensitivity for a wide range of CH3CHO concentration (1–100 ppm). Concentration dependent resistances during the exposure and oxidation reaction of CH3CHO gas were investigated. The obtained results in this work indicate that In2O3 nanospheres are prospective candidates for the fabrication of CH3CHO gas sensors.

(Invited) Suspended Graphene-Based Sensor for Real-Time and Highly Sensitive Monitoring of VOCs

Volatile organic compounds (VOCs) are emitted from solids or liquids with high vapor pressure and are often combustible and toxic, so on site real-time monitoring is vital. Currently photoionization detectors (PIDs) are used for VOC monitoring. PID devices are bulky and expensive to make and operated at high voltage to operate. As such there is a need for more portable and less expensive methods for detecting VOCs. We developed a novel gas sensor for (VOCs) detection. This technology utilizes suspended graphene membranes to provide real-time, ultrasensitive VOC detection. A freestanding graphene film suspended over an array of cavities or trench can offers increased surface area (twice over) and gives a direct method of sensing when VOCs adsorbed at the surface of graphene. Our sensor requires low voltages to operate, immediate response, high sensitivity and a larger theoretical range of detection than photoionization detectors sensors and it is a non-specific as PIDs. In this work, we shall present a 3 mm X 3 mm square chip, fabricated using conventional photolithography, containing an array of two terminal devices. Each individual device consists of a monolayer graphene sheet suspended over multiple cavities and clamped by two metal contacts. Suspended graphene, as opposed to substrate-based graphene, significantly reduces the surface charge hindrances and allows for ultrasensitive detection of gas molecules. The fabricated graphene chip has been successfully tested for toluene vapors. Currently, testing is underway to functionalize graphene for selective detection of different gases.

RES-Q-Trace: A Mobile CEAS-Based Demonstrator for Multi-Component Trace Gas Detection in the MIR.

Sensitive trace gas detection plays an important role in current challenges occurring in areas such as industrial process control and environmental monitoring. In particular, for medical breath analysis and for the detection of illegal substances, e.g., drugs and explosives, a selective and sensitive detection of trace gases in real-time is required. We report on a compact and transportable multi-component system (RES-Q-Trace) for molecular trace gas detection based on cavity-enhanced techniques in the mid-infrared (MIR). The RES-Q-Trace system can operate four independent continuous wave quantum or interband cascade lasers each combined with an optical cavity. Twice the method of off-axis cavity-enhanced absorption spectroscopy (OA-CEAS) was used, twice the method of optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS), respectively. Multi-functional software has been implemented (i) for the general system control; (ii) to drive the four different laser sources and (iii) to analyze the detector signals for concentration determination of several molecular species. For the validation of the versatility and the performance of the RES-Q-Trace instrument the species NO, N2O, CH4, C2H4 and C3H6O, with relevance in the fields of breath gas analysis and the detection of explosives have been monitored in the MIR with detection limits at atmospheric pressure in the ppb and ppt range.

Nanometer-Thick Newton Black Film for Selective Formaldehyde Gas Detection.

A fluorescence spectroscopic assay using Newton black film (NBF) for sensitive and selective detection of gaseous formaldehyde at room temperature is reported. The method relies on the Hantzsch reaction of formaldehyde with ammonium citrate and acetylacetone, plus a combination of the large surface area-to-volume ratio (5 × 108 m-1) and efficient uptake of gas by the nanometer-thick aqueous core of NBF. The assay has a limit of detection (LOD) of 4 ppb, a linear signal-to-concentration correlation up to 300 ppb of HCHO gas in the air, and a nonlinear monotonic increasing correlation in the range of 300 ppb to 1.2 ppm. It is unaffected by relevant analytes such as acetaldehyde, benzaldehyde, acetone, and propionaldehyde. We also demonstrate the sensing of formaldehyde outgassing from a plywood sample using this method and the results agree with the factory specifications.

Nanostructured Dielectric Fractals on Resonant Plasmonic Metasurfaces for Selective and Sensitive Optical Sensing of Volatile Compounds.

Advances in the understanding and fabrication of plasmonic nanostructures have led to a plethora of unprecedented optoelectronic and optochemical applications. Plasmon resonance has found widespread use in efficient optical transducers of refractive index changes in liquids. However, it has proven challenging to translate these achievements to the selective detection of gases, which typically adsorb non-specifically and induce refractive index changes below the detection limit. Here, it's shown that integration of tailored fractals of dielectric TiO2 nanoparticles on a plasmonic metasurface strongly enhances the interaction between the plasmonic field and volatile organic molecules and provides a means for their selective detection. Notably, this superior optical response is due to the enhancement of the interaction between the dielectric fractals and the plasmonic metasurface for thickness of up to 1.8 μm, much higher than the evanescent plasmonic near-field (≈30 nm) . Optimal dielectric-plasmonic structures allow measurements of changes in the refractive index of the gas mixture down to <8 × 10-6 at room temperature and selective identification of three exemplary volatile organic compounds. These findings provide a basis for the development of a novel family of dielectric-plasmonic materials with application extending from light harvesting and photocatalysts to contactless sensors for noninvasive medical diagnostics.

Sensitive and selective n-butanol gas detection based on ZnO nanocrystalline synthesized by a low-temperature solvothermal method

ZnO nanocrystalline with a few nanometers in size were synthesized by a low-temperature solvothermal method from zinc acetate dihydrate (Zn(CH3COO)2·2H2O), potassium hydroxide (KOH) and ethanol (C2H5OH). X ray diffraction (XRD), transmission electron microscopy (TEM) and X ray photoelectron spectroscopy (XPS) were used to characterize the structure, morphology, specific surface area and chemical state of the samples. The analyzed results indicate that the ZnO nanocrystalline with good dispersion are several nanometers in size about 10 nm. The ZnO nanocrystalline was used as sensing material to fabricate an indirect-heating structure sensor and its gas sensing properties are tested. At the optimal operating temperature (340 °C), its gas response toward 500 ppm n-butanol is 148.11 and the response and recovery time are 20 and 8 s, respectively. The test results show that the sensitivity of the as-prepared gas sensor has high selectivity to n-butanol and good response/recovery characteristics, linear response, short-term repeatability, as well as the long-term stability. The experimental results show that the gas sensor based on ZnO nanocrystalline can be used in the detection and real-time monitoring of toxic gases, especially n-butanol gas, which makes it to be highly promising candidate for practical detectors for n-butanol gas.

Dual sensitization of MWCNTs by co-decoration with p- and n-type metal oxide nanoparticles

We present a dual sensitization gas sensor for selective detection of either H2S or C2H5OH gases, based on ZnO/CuO nanoparticle (NP)-decorated MWCNTs. First, Cu-Zn layers of three different thickness (3, 6, 9 nm) were successfully deposited on the surfaces of CNTs by a sputtering process and subsequently converted to their corresponding oxides by thermal annealing. The gas sensing characteristics of metal oxide decorated-MWCNTs were studied in the presence of three gases, namely NO2, H2S, and C2H5OH. The best sensing properties were obtained when the Cu-Zn deposition layer was 6 nm thick. The optimized sensor showed extraordinary responses to both H2S and C2H5OH gases at working temperatures of 100 °C and 200 °C, respectively. Therefore, selectivity was tuned by selection of the working temperature. The sensing mechanisms of the metal oxide-decorated CNTs sensors are discussed in detail. The approach described, namely co-decoration of the surfaces of MWCNTs with different metal oxides, will be of great utility to researchers who wish to fabricate dual sensitive gas sensors.