Formaldehyde Gas Sensor Research Articles

Rice-grain Sm2O3/SmFeO3 nanoparticles as high selectivity formaldehyde gas sensor prepared by precipitation

In this study, rice-grain Sm2O3/SmFeO3 nanoparticles were fabricated by a convenient precipitation method. In addition, the structure and morphology of the Sm2O3/SmFeO3 nanoparticles were characterized by XRD, BET, SEM, and TEM. The XRD patterns reveal that diffraction peaks of Sm2O3/SmFeO3 nanoparticles are in excellent agreement with those of SmFeO3 and Sm2O3. By using the Debye–Scherrer equation, the average grain size of the rice-grain particles of the sample was calculated to be 23.4 nm. BET showed that the material has a larger specific surface area. SEM and TEM results indicate that the material comprises millet rice-grains. The resulting Sm2O3/SmFeO3-based sensor exhibited good sensitivity performance, with excellent selectivity for formaldehyde gas. At the optimum work temperature (190 °C), the response value, response time, and recovery time for 10 ppm formaldehyde were 44, 111 s, and 102 s, respectively. These results reveal that rice-grain Sm2O3/SmFeO3 material demonstrates promise as a formaldehyde-gas-sensitive material.

Construction, Application and Verification of a Novel Formaldehyde Gas Sensor System Based on Ni-Doped SnO2 Nanoparticles

An efficient formaldehyde (HCHO) gas sensor system based on nickel-doped tin oxide (Ni-doped SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) nanoparticle sensor and back-end circuit has been developed. Ni-doped SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles are prepared by a simple one-step hydrothermal method. To complete the function of detecting HCHO gas in real time, a back-end circuit suitable for resistance measurement of nanoparticle sensors and an organic light emitting diode screen which can display the output of gas concentration data are integrated as a portable device. Compared with the traditional HCHO detection device, this designed system exhibits better stability, excellent selectivity, and high response. Its detection limit is as low as 90 ppb. The gas response to 50 ppm HCHO is 67.63. Further for the quantitative evaluation, we refer to and modify the existing HCHO diffusion model, then carry out a practical test on the HCHO diffusion at the same time. The comparison between the theoretical fitting curve and the actual test curve matched well enough to reflect the potential of this system for the practical HCHO evaluation.

Suspended graphene arrays for gas sensing applications

Suspended graphene (SUS-G) has long been hailed as a potential ‘true graphene’ as its conductive properties are much closer to those of theoretical graphene. However, substantial issues with yield during any device fabrication process have severely limited its use to date. We report the successful fabrication of a fully operational prototype of a miniature 9 mm2 suspended graphene array sensor chip, incorporating 64 graphene sensor devices, each comprising of 180 SUS-G membranes with ever reported 56% fully intact graphene membranes for sensitive and selective gas sensing applications. While a bare sensor chip can operate as a sensitive gas sensor for a variety of gasses such as ammonia, nitrogen dioxide and carbon monoxide, down to ppm/ppb concentrations, a tetrafluorohydroquinone functionalized sensor acquires specificity to formaldehyde gas molecules with limited cross-sensitivity for ethanol, toluene and humidity. Unlike an equivalent device with fully supported functionalized graphene sensor, a functionalized SUS-G sensor can be furthermore reset to its baseline by using UV assisted desorption instead of substrate heating. The low power UV irradiation does not show severe damage to the SUS-G structures and loss of functional probes for the formaldehyde gas—a previously unreported feature. A resettable and selective formaldehyde gas sensor array with mass manufacturability, low power consumption and overall dimensions down to 1 mm2, would represent a significant technological step forward in the development of an electronic nose, for the simultaneous detection of multiple-target gases, with potential for integration in portable electronic devices and the internet of things.

Imidazole-based ionogel as room temperature benzene and formaldehyde sensor.

A room temperature benzene and formaldehyde gas sensor system with an ionogel as sensing material is presented. The sensing layer is fabricated employing poly(N-isopropylacrylamide) polymerized in the presence of 1-ethyl-3-methylimidazolium ethyl sulfate ionic liquid onto gold interdigitated electrodes. When the ionogel is exposed to increasing formaldehyde concentrations employing N2 as a carrier gas, a more stable response is observed in comparison to the bare ionic liquid, but no difference in sensitivity occurs. On the other hand, when air is used as carrier gas the sensitivity of the system towards formaldehyde is decreased byone order of magnitude. At room temperature, the proposed sensor exhibited in air higher sensitivities to benzene, at concentrations ranging between 4 and 20ppm resulting, in a limit of detection of 47ppb, which is below the standard permitted concentrations. The selectivity of the IL towards HCHO and C6H6 is demonstrated by the absence of response when another IL is employed. Humidity from the ambient air slightly affects the resistance of the system proving the protective role of the polymeric matrix. Furthermore, the gas sensor system showed fast response/recovery times considering the thickness of the material, suggesting that ionogel materials can be used as novel and highly efficient volatile organic compounds sensors operating at room temperature.Graphical abstract.

Nanostructured of SnO2/NiO composite as a highly selective formaldehyde gas sensor

Abstract

Enhanced gas sensing properties for formaldehyde based on ZnO/Zn2SnO4 composites from one-step hydrothermal synthesis

Formaldehyde gas sensor with high performance is indispensable for monitoring indoor air quality. Exploring novel nanostructured composites as gas sensing materials is considered to be a feasible way to enhance the sensing performance. In this work, one-step hydrothermal method was employed for facile synthesis of ZnO/Zn2SnO4 nanocomposites and the as-prepared sample took on a homogeneous hexagonal lamellar nanostructure with a diameter of 600 nm–900 nm and thickness of about 100 nm. Gas sensing properties of the sample were tested and the results demonstrated that the ZnO/Zn2SnO4 composites possessed excellent sensing performances to formaldehyde. At 160 °C, the ZnO/Zn2SnO4 composites based sensor exhibited a high response of 22.5 towards 100 ppm of formaldehyde and a detection limit as low as 500 ppb. Compared with pristine Zn2SnO4 and ZnO, ZnO/Zn2SnO4 composites showed higher sensitivity (increased by 80% and 120%), better selectivity and lower detection limit. The noteworthy improvement of formaldehyde sensing performances could be attributed to the synergetic effect as well as the formation of n-n type heterojunctions between Zn2SnO4 and ZnO. The mechanism involved in gas sensing performance of ZnO/Zn2SnO4 composites was also discussed.

Cu/SnO2 xerogels: a novel epoxide derived nanomaterial as formaldehyde gas sensor

Traditionally, sol–gel processing of metal oxides using organometallic precursors is expensive, nonaqueous, and complicated when it comes to two-or-more dissimilar metal oxides. Herein, we report a versatile epoxide-assisted non-organometallic, aqueous, and inexpensive synthesis route of developing Cu/SnO2 xerogels and their use as efficient formaldehyde (FA) gas sensors. The route utilizes easy to handle salts as precursors (tin and copper chlorides, in the present case) and organic epoxide (propylene oxide) as a gelation agent, which led to highly porous web matrix of Cu/SnO2. The obtained Cu/SnO2 xerogels, with 0–2 mol% Cu doping, were analyzed using XRD, Fourier transform infrared, UV–Vis, FE-SEM, TEM/HRTEM, and EDAX. As-developed xerogels showed their versatility in physico-chemical as well as FA gas sensing properties. By proper Cu-doping level in SnO2 matrix, the reduction in sensor operating temperature (325–275 °C) and enhancement in the gas response (S = 50–96%) are chronicled. The effects of gas sensing are represented by an epoxy-assisted Cu/SnO2 sol–gel process and the subsequent morphological and structural properties.

Design and evaluation of Cu-modified ZnO microspheres as a high performance formaldehyde sensor based on density functional theory

Based on Cu-modified ZnO (CZO), a highly sensitive gas sensor for formaldehyde (HCHO) detection at room temperature was prepared by the sol–gel method, and the sensing mechanism was studied by density functional theory. Calculations indicate that the binding energy of CZO to HCHO is higher than that of pure ZnO when Cu metal occupies the oxygen vacancy on the surface of ZnO, which is beneficial for CZO to capture more HCHO molecules. Moreover, Cu metal splits oxygen molecules in the air to form a large number of oxygen free radicals on the surface of CZO and react with HCHO molecules. The lowest band gap can be obtained when HCHO is adsorbed in CZO compared to other gases, which means CZO has better selectivity in the detection for HCHO. Experiments show that Cu metal can effectively improve the performance of ZnO for HCHO detection. CZO with 3 mol% Cu exhibits short response/recovery times (1.7 s/2.9 s) and the limit of detection (LOD) is 0.61 ppm at HCHO concentration of 1 ppm. Moreover, CZO displays the excellent endurance to humidity. Such a metal-modified ZnO offers great potential for the development of highly sensitive gas sensor for HCHO detection.

Determination of formaldehyde using a novel Pt-doped nano-sized sensitive material: Operating conditions optimization by response surface method

High working temperature is the main obstacle in the design of chemiluminescence gas sensor. In this paper, a novel formaldehyde gas sensor based on chemiluminescence on nano-Pt/Mo4V6Ti10O47 at lower temperature than 200 °C was reported. Formaldehyde can be oxidized on the catalyst and emit chemiluminescence of specific wavelength. The relative standard deviation (RSD) of the chemiluminescence intensities within 600 h by continually introducing 20 mg/m3 formaldehyde is less than 3%. There is a good linear relationship between the chemiluminescence intensity and the concentration of formaldehyde in the range of 0.007–77.0 mg/m3. The limit of detection (3σ) is 0.002 mg/m3. The experimental operating conditions optimized by response surface method are analytical wavelength of 488.07 nm, working temperature of 138.13 °C and carrier gas velocity of 164.15 mL/min, respectively. The sensitivity of the method can be increased by 4.7% under the optimized working conditions, which is especially important for determination of trace substances. The optimization method is universal for most of multi parameter processes. The sensing properties and chemiluminescence mechanism of formaldehyde on nano-Pt/Mo4V6Ti10O47 were investigated.

High-Performance Formaldehyde Gas Sensor Based on Cu-Doped Sn3O4 Hierarchical Nanoflowers

Gas sensors with high response, low operating temperature and superior selectivity are highly desired for monitoring toxic gases in the environment. Herein, a formaldehyde (HCHO) gas sensor with outstanding sensing properties is proposed based on Cu-doped Sn3O4 hierarchical nanoflowers that are synthesized via a facile hydrothermal method. The Cu-doped Sn3O4 gas sensors exhibit conspicuously improved sensing performance to HCHO compared with the pure Sn3O4 gas sensor at a relatively low operating temperature of 160°C. Specifically, the gas sensor based on the 4 wt% Cu-doped Sn3O4 composite exhibits a high response up to 53 toward 100 ppm HCHO, a fast response time of 5 s, and low detection limit of 1 ppm. In addition, the prepared Cu-doped Sn3O4 gas sensor possesses conspicuous advantages comprising a good selectivity, perfect reproducibility and excellent long-time stability. The sensing mechanism of the proposed gas sensor is explained by the electron depletion theory, and the possible reasons for the improvement of sensing properties by Cu doping are also discussed. It’s strongly believed that the Cu-doped Sn3O4 sensor has a practical application in HCHO detection.

Formaldehyde Gas Sensor Based on Melamine Foam and Tin Dioxide Composites

Formaldehyde (HCHO) is a volatile organic compound (VOC). It can caused great harm to human and environment. Since the increasing concerns of this problem, to develop effective methods to detect this toxic and hazardous gas has become more and more important , which play an important role in personal safety and environment protection. In this study, melamine foam and tin oxide composites were prepared by in-situ growth and subsequent treatment by using a simple hydrothermal reaction. The morphology, structure and sensing properties of the composites were systematically studied. The results show that tin oxide nanoparticles can grow well on the melamine foam skeleton through a simple hydrothermal reaction and has a good stable morphology. It is found that the three-dimensional spherical/skeletal composite material has better gas sensitivity and selectivity to formaldehyde gas than the pristine tin dioxide under a suitable concentration. The response of the composite to 5 ppm formaldehyde gas can reach 30.0 at 120°C. The reactant of formaldehyde on the surface of the material was studied by in situ IR. At the same time, melamine foam has a certain flexibility, which will have a good development for flexible, miniaturized and wearable formaldehyde sensor. Keywords：melamine foam plastics；tin oxide；formaldehyde；gas sensor Figure 1

Facile synthesis of stoichiometric InOCl mesoporous material for high performance formaldehyde gas sensors

In recent years, it is urgent and challenging to prepare highly sensitive and stable formaldehyde metal oxide gas sensing materials, as to in-situ detecting the indoor air pollutant. Here, stoichiometric InOCl mesoporous nanomaterial was synthesized by a facile sol-gel and successive calcination method. The dosage of HCl was found to be the key parameter for the stoichiometry of the InOCl, which was polycrystalline with mesopores of about 1.87 nm, as characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), N2 adsorption–desorption and X-ray photoelectron spectroscopy (XPS). Importantly, when used as formaldehyde gas sensor, it shows a high response of 45 to 50 ppm HCHO with response/recovery time of 18 s and 47 s at a low working temperature of 200 °C. In the meanwhile, it also exhibits high selectivity over other interfering gases such as 50 ppm ethanol, acetone, benzene and toluene, and good stability during 16 days gas sensing test. All these results show the promise of this mesoporous material for high performance formaldehyde gas sensing applications.

Development of Formaldehyde Gas Sensor that Exhibits Distinct Color Changes

Development of Formaldehyde Gas Sensor that Exhibits Distinct Color Changes

A facile approach of developing Al/SnO2 xerogels via epoxide assisted gelation: A highly versatile route for formaldehyde gas sensors

A robust synthesis approach to Al/SnO2 based formaldehyde gas sensing xerogels using epoxide assisted sol-gel chemistry is reported. The route utilizes simple tin and aluminum salt precursors in alcohol/water mixture, thus eliminating the need for organometallic precursors. Propylene oxide acts as a proton scavenger and drives metal hydroxide formation and subsequent polycondensation reactions. Al/SnO2 xerogels (with Al doping 1–4 mol%) were aged for 24 h to strengthen the gel network, followed by sintering and screen printed thick films formation. Prior to gas sensing investigations, the physico-chemical properties of the material were analysed using TG-DTA, XRD, FE-SEM, TEM, SAED, EDAX, UV–Visible and FTIR spectroscopic techniques. The developed material showcase tetragonal rutile structure of SnO2 with porous morphology required for effective gas diffusion. Al/SnO2 with 3 mol% doping level exhibited excellent gas sensing ability (Ra/Rg = 15 @ 300 °C operating temperature) towards barely 100 ppm formaldehyde concentration. Not only sensor response was got improved (from Ra/Rg value 5 to 15), but also the operating temperature got reduced from 325 °C to 300 °C). An effect of formaldehyde concentration, the sensor response got increased rapidly up to 100 ppm concentration, thereafter the increase in response was observed almost stagnant. By keeping the measurement parameters as is, the sensor performance was checked six times after the initial measurement with the interval of 10 days, which showed ~89% of its initial sensitivity. The developed material showcase the potentiality of being formaldehyde gas sensor.

Sn3O4/rGO heterostructure as a material for formaldehyde gas sensor with a wide detecting range and low operating temperature

High-performance formaldehyde (HCHO) sensors are highly desirable for environmental gas monitoring and industrial gas analysis. Herein, an HCHO sensor featuring an excellent sensing response is proposed to offer a broad detecting range and operate at a low temperature, by exploiting a flower-like composite based on a heterostructure consisting of Sn3O4 and reduced graphene oxide (rGO). The Sn3O4/rGO composites with different rGO contents and the pure Sn3O4 are successfully prepared by a facile one-step hydrothermal method, and their corresponding sensing properties toward HCHO are systematically investigated. The Sn3O4/rGO sensors exhibit a highly improved sensing response at a relatively low temperature compared with the pure Sn3O4 sensor. In particular, the Sn3O4/rGO sensor utilizing 0.75 mg of the rGO realizes a much higher sensing response across the wide range of 1−1000 ppm HCHO, and its response is up to 44 when it is exposed to 100 ppm of HCHO at 150 °C. Additionally, the proposed Sn3O4/rGO sensor shows a good sensing selectivity, excellent reproducibility, and long-term stability. By analyzing the sensing mechanisms of the pure Sn3O4 and Sn3O4/rGO composite, the enhanced sensing properties for the Sn3O4/rGO sensor can be ascribed to the heterostructure between Sn3O4 and rGO, which gives rise to a considerable resistance variation when the sensor is exposed to air and HCHO.

Porous LaFeO3 microspheres decorated with Au nanoparticles for superior formaldehyde gas-sensing performances

Formaldehyde is one of the most serious pollutants of volatile organic compounds in indoor environment. The monitoring of formaldehyde concentration of the indoor environment has become an urgent issue in modern society. In this paper, a facile wet-chemical method was used to prepare the catalytic Au nanoparticle-functionalized LaFeO3 porous microspheres with high formaldehyde (HCHO)-sensing performances. The Au/LaFeO3 nanocomposites were characterized by several common testing methods, such as XRD, SEM, EDS, TEM, and XPS. The results showed that Au nanoparticles were uniformly attached to the surface of porous LaFeO3 microspheres. And the gas-sensing experiments showed that Au nanoparticle-functionalized porous LaFeO3 microspheres showed high response even at low concentration (1 ppm), good selectivity, good reproducibility, and ultrafast response (2 s) and recovery (9 s) to formaldehyde. Therefore, the successful preparation of Au/LaFeO3 nanocomposites is expected to be used in the rapid detection of formaldehyde gas.

Pyrochlore Ca-doped Gd2Zr2O7 solid state electrolyte type sensor coupled with ZnO sensing electrode for sensitive detection of HCHO

Solid state electrolyte type formaldehyde (HCHO) gas sensors based on a novel pyrochlore structure Gd2Zr2O7 solid electrolyte coupled with rod-shaped ZnO sensing electrode (SE) were initially designed and fabricated in this paper. The incorporation of alkaline-earth metal Ca can significantly improve sensing performance of the Gd2Zr2O7 based sensors to HCHO. The response value (ΔV) of the sensors based on Gd2-xCaxZr2O7 (x = 0, 0.02, 0.05 and 0.1) varied approximately linear with the logarithm of HCHO concentration in the range of 1−100 ppm at 600 °C, with sensitivities of -25, -30, -15 and -5 mV/decade, respectively. The optimal sensor based on Gd1.98Ca0.02Zr2O7 (GCZ(0.02)) exhibited the excellent sensing characteristics with maximum response value (-61.3 mV) and extremely short response time (3 s) to 100 ppm HCHO. In addition, the GCZ(0.02) sensor also showed good selectivity and stability within 20-day period of continuous high-temperature aging under high-humidity condition. Conclusively, the sensing behavior and mechanism based on mixed potential were investigated and demonstrated by the mearsurement of the polarization curves.

A formaldehyde gas sensor with improved gas response and sub-ppm level detection limit based on NiO/NiFe2O4 composite nanotetrahedrons

Formaldehyde is a hazardous indoor volatile organic pollutant, thus selective and precise detection at a low concentration level is crucial. In this paper, NiO/NiFe2O4 nanocomposites were prepared through a simple two-step hydrothermal route and their gas sensing performances were investigated. SEM and TEM results showed that the composite products were NiO nanotetrahedrons decorated with numerous separated NiFe2O4 nanoparticles on the outer layer surface. XPS characterization confirmed that the as formed NiFe2O4 exhibited a p-type conductivity due to the hole transfer between Ni3+ and Ni2+ and therefore p-p isotype heterojunctions formed in the composite products. The element ratio of Fe to Ni was optimized to gain higher gas-sensing performance through adjusting the feeding amount of Fe3+ in the synthesis process. As a consequence, the gas sensor based on the sample NiFe-0.008 showed the highest response of 33.3–200 ppm formaldehyde vapor at 240 °C and a low detection limit of 200 ppb. The composite sensor also showed short response/recovery time and good long term stability. The enhanced gas sensing properties to formaldehyde can be attributed to the unique tetrahedral morphology and p-p heterojunction structure, which can provide more active sites and significantly enlarge resistance variation. This work will provide a new perspective of p-p heterojunction for the practical application in formaldehyde gas sensor.

A highly sensitive, selective and room temperature operatable formaldehyde gas sensor using chemiresistive g-C3N4/ZnO

g-C3N4/ZnO based gas sensor detects formaldehyde at room temperature in highly sensitive and selective manner.

Graphene Oxide@3D Hierarchical SnO2 Nanofiber/Nanosheets Nanocomposites for Highly Sensitive and Low-Temperature Formaldehyde Detection.

In this work, we reported a formaldehyde (HCHO) gas sensor with highly sensitive and selective gas-sensing performance at low operating temperature based on graphene oxide (GO)@SnO2 nanofiber/nanosheets (NF/NSs) nanocomposites. Hierarchical SnO2 NF/NSs coated with GO nanosheets showed enhanced sensing performance for HCHO gas, especially at low operating temperature. A series of characterization methods, including X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) were used to characterize their microstructures, morphologies, compositions, surface areas and so on. The sensing performance of GO@SnO2 NF/NSs nanocomposites was optimized by adjusting the loading amount of GO ranging from 0.25% to 1.25%. The results showed the optimum loading amount of 1% GO in GO@SnO2 NF/NSs nanocomposites not only exhibited the highest sensitivity value (Ra/Rg = 280 to 100 ppm HCHO gas) but also lowered the optimum operation temperature from 120 °C to 60 °C. The response value was about 4.5 times higher than that of pure hierarchical SnO2 NF/NSs (Ra/Rg = 64 to 100 ppm). GO@SnO2 NF/NSs nanocomposites showed lower detection limit down to 0.25 ppm HCHO and excellent selectivity against interfering gases (ethanol (C2H5OH), acetone (CH3COCH3), methanol (CH3OH), ammonia (NH3), methylbenzene (C7H8), benzene (C6H6) and water (H2O)). The enhanced sensing performance for HCHO was mainly ascribed to the high specific surface area, suitable electron transfer channels and the synergistic effect of the SnO2 NF/NSs and GO nanosheets network.