H2S Gas Sensor Research Articles

The Influence of Solvents on Polyaniline Nanofibers Synthesized by a Hydrothermal Method and their Application in Gas Sensors

Polyaniline nanofibers (PAni NFs) were successfully prepared using a hydrothermal technique. The spin-coating method was employed for depositing polyaniline nanofibers in different solvents such as water, 2-methoxyethanol and ethanol. During this process, surface morphological, optical, structural, and hydrogen sulfide (H2S) gas-sensing properties have been investigated for the polyaniline nanofibers. The results of the x-ray diffraction pattern showed a peak around 2θ ∼25°, which is referred to the (200) desirable direction for all samples. A field-emission scanning electron microscopy analysis of PAni showed NFs as a structure for all the films. Fourier-transform Infrared patterns confirmed the creation of the PAni. The preparation process of PAni NFs using water showed that a smaller energy gap value was realized during the optical properties examination. What is more, the solvent absorption studies indicated that the highest energy gap value was realized for 2-methoxyethanol. The H2S gas-sensing properties of PAni NFs films showed high sensitivity (23.67%) being achieved at the operating temperature of 150°C with a very fast recovery time and response time for PAni NFs that were prepared using water.

Structural modifications in Co–Zn nanoferrites by Gd substitution triggering to dielectric and gas sensing applications

The structural modifications in Co–Zn ferrites due to the substitution of Gd3+ ions and their credible use as low loss dielectrics and H2S gas sensors are reported in the present study. The structural modifications lead to the enhancement in physical properties of the ferrites making it suitable for the applications. The nanocrystals of Co0·7Zn0·3Fe2-xGdxO4 (0 ≤ x ≤ 0.1, Δx = 0.025) were obtained using self-ignited citrate sol-gel route of synthesis. The X-ray diffractograms of the ferrites were refined by Rietveld method using the full-proof pdf software. The refinement asserts the creation of mono phase spinel ferrite crystals. The morphology of ferrite crystals analyzed from scanning electron microscopy (SEM) profiles depict that the ferrites exhibit the porous nature. The transmission electron microscopy (TEM) images confirms the nanocrystalline nature of the ferrites with an average dimension of 25 nm and high resolution TEM (HRTEM) confirms the spinel phase created within the ferrites. The frequency variation of dielectric parameters was analyzed to study the relaxation phenomenon in ferrites. The values of dielectric constant, dielectric loss and loss tangent were reported to decline with frequency and the Gd3+composition (x). The a.c. electrical conductivity increases with frequency and decreases with composition ‘x’. The room temperature gas sensing response of the ferrite for the hazardous H2S gas was much higher than that for LPG, SO2, NO2 and H2 gases. The ferrite sample with x = 0.025 exhibits a better sensor performance for H2S gas with small recovery and response time. The nanocrystalline nature, porosity and morphology of the ferrites bear control over response and other parameters.

Sedum lineare flower-like ordered mesoporous In2O3/ZnO gas sensing materials with high sensitive response to H2S at room temperature prepared by self-assembled of 2D nanosheets

In this work, a kind of novel monodispersed sedum lineare flower-like ordered mesoporous In2O3/ZnO material was prepared by template method. The diameters of the sedum lineare flower-like structure In2O3/ZnO composite particles were much uniform which were self-assembled by 2D nanosheets with 118 nm thickness, and the ordered pores were distributed on the surface of the petals. The layered porous structure was conducive to the absorption of poisonous gas which improved gas sensitive property. The influences of the stirring temperature and In content to gas sensitive property and morphology were studied. The response (Ra/Rg) of the prepared In2O3/ZnO material reached to 10.2 towards 100 ppm H2S at room temperature (25 ± 3 °C) which was about 8.5 times of pure ZnO matrix, the detection limit was 1 ppm, and it also had much faster response and recovery time. Moreover, the In2O3/ZnO composite had excellent selectivity, cycling and long-term stability towards H2S which provided the advanced materials and synthetic method for developing H2S gas sensor. It had much outstanding advantages compared with the other reported H2S gas sensors at room temperature.

Synthesis and characterization of Cu-doped ZnO/RGO nanocomposites for room-temperature H2S gas sensor

Abstract The development of low or room temperature gas sensors having a response towards a particular target gas becomes a fascinating research topic for low power consumption applications. In this paper, a sensitive room-temperature hydrogen sulfide (H2S) gas sensors based on hydrothermally synthesized undoped zinc oxide (ZnO) and Cu-doped ZnO (CZO) nanostructures decorated with reduced graphene oxide (RGO) are successfully demonstrated. A simple air-spray deposition is employed as an effective method for uniform GO decoration on CZO nanostructured film which is further chemically reduced to form RGO. The influence of Cu-doping on crystallinity, surface-morphological, and chemical compositional properties of the material have been systematically investigated. The gas sensing properties of the synthesized nanocomposite sensors have been studied towards H2S at room temperatures (∼24 °C). Compared with undoped ZnO/RGO, 3CZO/RGO nanocomposite sensor exhibited a better response towards H2S. The sensor response increases almost linearly with the increase in H2S gas concentration and exhibits the evident response of 0.87%–100 ppm H2S at 24 °C with the response and recovery time of 14 and 32 s, and a theoretical limit of detection of about 136 ppb. The enhancement was accredited to the collegial effect of both Cu dopant and RGO. The sensor also shows good selective behavior towards H2S against H2. The H2S sensing mechanism associated with the p-type behavior of the 3CZO/RGO sensor is also discussed at length.

Hydrogen sulfide gas sensing properties of SnO2 thin films prepared by thermal evaporation technique

It is well known that the doped SnO2 thin films are widely used as H2S gas sensors. But the application of pure SnO2 thin films as sensors for different gases is not much explored area. In this paper an attempt has been made to prepare thin films of pure SnO2 with simple and cost-effective technique such as reactive thermal evaporation and use them for application as sensors for H2S gas. These thin films show marginal sensor signal for 5-150 ppm of H2S gas in the temperature range of 160 – 220 °C.

Hydrothermal Synthesis of Cu2ZnSnS4 Nanostructure and Their Application as H2S Gas Sensor

In this study, Cu2ZnSnS4 (CZTS) nanostructure are successfully synthesized by using hydrothermal method. Structural, morphology, optical properties have been studied for thin films (CZTS) deposited via spin-coating method. X-ray diffraction show that the films have pure tetragonal-kesterite structure preferred orientation along (112) . The FE- SEM shows that (CZTS) have a nano-sphere like structure, consist with diameters less than 35 nm. UV-Vis spectroscopy measurement showed that absorption coefficient (α <104 cm−1) and the band gap energy is equal to 1.42 eV. The Sensitivity properties of (CZTS) samples for H2S gas was tested at various operating temperature and found that the highest sensitivity is (83.63 %) at T=150 ºC.

Sub-ppb Sensing Level Hydrogen Sulphide at Room Temperature Using Doped Indium Oxide Gas Sensors

Hydrogen sulfide (H2S) is a highly corrosive, harmful, and toxic gas. Whereas 130 ppb is the threshold for maximum safety exposure level. Thus, it has become mandatory to develop highly sensitive sensors operating at room temperature to detect low levels of H2S. Sensors based on electrochemical measurement principles, semiconducting metal oxides or p–n heterojunctions have showed promising results to detect H2S gas. To date, drawbacks have boon reported due to their extended response times, high operating temperatures, limited selectivity to the gas and/or sensitivity to humidity changes. Efforts have been made to develop sensors based on metal oxides operable at room-temperature for H2S detection.Here, we describe novel flexible H2S gas sensors based on optimized composite mixture of indium oxide (In2O3), copper acetate (CuAc), graphite (Gt) and polystyrene (PS). While we employed Gt in sensor’s structure to reduce sensor’s resistance to ~ 0.5 MΩ, we used PS and enhance sensor’s integrity as well as the adhesiveness of the sensing layer on the top of carbon electrodes. Whereas we applied In2O3 as the active material in sensors due to its promising performance to detect ~ 100 ppb gas concentration. We used CuAc as activator when it converts to the form of copper sulfide (CuS) due to its high conductivity (10 S/cm). Hypothetically, upon exposing sensors to the H2S gas, In2O3 converts spontaneously to the metallic form In2S3 (eq.1). Alternately, CuAc plays two critical roles in the sensor composition. First, CuS formation drops sensor’s resistance significantly due its high conductivity (eq.2). At this point, In2S3 and CuS can form a continues metallic layer, thus it increases sensor’s conductivity. Second, CuS may play a similar role as same as noble metals, which can cause the formation the structure of noble-doped metal oxide and ease oxygen molecules adsorption/ionization on sensor’s surface (eq.3,4). This may facilitate oxidizing and/or adsorption H2S on the sensor’s surface (eq.5,6), which consists of releasing electrons to sensors and reduce sensors resistance dramatically. The developed sensors have showed high selectivity toward H2S gas, high sensitivity to H2S concentration of less than 100 ppb, fast detection time less than 60 seconds, and high resistivity to humidity changes. Figure 1

Hydrogen Sulfide Detection for Medical Breath Analysis with Surface Functionalized ZnO Nanowires

Over the past decade, the medical role of hydrogen sulfide (H2S) for therapeutic applications and diagnostics was extensively investigated and revealed the importance of H2S for medical breath analysis.It was suggested that decreased production of the endogenous gaseous mediator H2S in tissues of the human respiratory system can be interpreted as an early detection biomarker for inflammatory diseases like asthma etc. In order to detect the H2S concentration levels of interest, a reliable selective device sensitive to H2S in the very low parts per billion (ppb) range is needed.The main goal of our project is the development of such a highly sensitive, reproducible and reliable H2S gas sensor, acting as a future integrated component of a multiple-sensor array in an “electronic nose” type device for medical applications or for detecting trace concentrations in chemical industry.We present here a planar resistive gas sensor design based on the gas sensing mechanism of a chemical field effect transistor (ChemFET) made from very high quality zinc oxide (ZnO) nanowires (NW) with gas sensitive open gate. The open gate operates as a transducer between adsorption/desorption of the ambient target gas and a measurable resistivity change in the NWs. This resistivity change results from the band bending effect of metal oxide surface exposed to different gas atmospheres and is analyzed by current-time (I-t) measurements.To improve the selectivity of our ZnO NW sensor towards a certain target gas, we investigated the impact of surface modification by addition of catalytic metal layers on the detection limit of our ZnO NWs towards H2S. In particular, we studied the chemical affinity between gold (Au) and sulfur (S) which leads to catalytic effects between the sputtered gold nanoparticle layer and the target gas H2S. Accordingly, H2S molecules are expected to adsorb more efficiently on Au modified ZnO NWs and drastically improve the overall sensor performance towards H2S. Our modified ChemFETs showed higher signal-to-noise ratio (SNR), improved sensitivity, faster response time, and an exceptionally low detection limit of less than 10 ppb for H2S diluted in synthetic air at room temperature.

A one-pot hydrothermal-induced PANI/SnO2 and PANI/SnO2/rGO ternary composites for high-performance chemiresistive-based H2S and NH3 gas sensors

We have fabricated the PANI/SnO2 and PANI/SnO2/rGO ternary composites by facile one-step hydrothermal approach followed by polymerization method. The hybrid nanocomposites were scientifically investigated for their structural, morphological and elemental composition through XRD, TEM, EDAX, FTIR and EPR analysis. The tetragonal rutile phase with nanospherical morphology sizes in the range of 25–35 nm was investigated by XRD and TEM results. The N2 adsorption–desorption measurement showed that ternary PANI/SnO2/rGO composite showed huge specific surface area (114.51 m2/g) and pore size (17–21 nm), which is higher than the bare SnO2 (surface area = 83.51 m2/g; pore size = 33–37 nm). The chemiresistive-type gas sensor was fabricated and the designed sensors were investigated by their sensing responses towards different gases (ethanol, methanol, carbon monoxide, oxygen, H2S and NH3). The results exposed that the ternary PANI/SnO2/rGO showed high sensing response (56%), fast response (35 s) and recovery time (40 s) towards H2S gas than other gases. The improved gas-sensing mechanism was also proposed.

Low-temperature and highly sensitivity H2S gas sensor based on ZnO/CuO composite derived from bimetal metal-organic frameworks

The bimetallic metal-organic frameworks (MOF) Zn/Cu-BTC were prepared by a facile solvothermal method in one step and used as a self-sacrificed template to obtain the ZnO/CuO composites. The composites with different Cu/Zn molar ratios were characterized by XRD, FESEM, and XPS. The ZnO/CuO composite exhibited an octahedral structure, and a p-n heterojunction may be formed between p-type CuO and n-type ZnO. To prove its functional characteristics, the ZnO/CuO composite was used as a sensing material to test its gas sensitivity. The effect of Cu/Zn molar ratios was examined, and the results showed that the optimized ZnO/CuO (1: 0.33) composite based gas sensor exhibited reasonable selectivity to 10 ppm H2S, operated at 40 °C. The sensitivities were improved by 17.1 times and 327.8 times compared with the pristine CuO and ZnO based gas sensors, respectively. Moreover, the detection limit to H2S of such sensors could be reduced as low as 300 ppb. The sensing mechanism has been thoroughly studied and such ZnO/CuO composite is an ideal candidate for highly sensitive detection for H2S with low power consumption in the real application.

The blue luminescence of p-type NiO nanostructured material induced by defects: H2S gas sensing characteristics at a relatively low operating temperature

The detection of hazardous and toxic gases in homes and corporate world, with highly sensitive and selective manner continues to be of great interest. Therefore, we report on the gas sensing characteristics of NiO nanostructures with crystallite sizes of approximately 10–17 nm prepared by a co-precipitation method using various reaction times ranging from 2 to 24 h. The physical variation of the colour from green to black after heat treatment was observed due to non-stoichiometric property of NiO revealing blue emission, which was assigned to oxygen and/or nickel vacancies. The diffuse reflectance spectra revealed a wide direct band gap in the range of 3.4–3.6 eV. The high BET surface area ranging from 46 to 84 m2/g was witnessed. The NiO-8 h sensor revealed an excellent response of 74 towards 60 ppm of H2S at 75 °C in dry air. The detection limit of 0.013 and 1.6 ppm was observed for NiO-8 h based sensor in dry air and RH-40%, respectively. These findings specify that the NiO-8 h sensor has pronounced potential for applications in high-performance H2S gas sensor operating at low temperature. The underlying mechanism for the improved NiO-8 h sensing performance is debated.

Ultrasensitive and low temperature gas sensor based on electrospun organic-inorganic nanofibers

Abstract Organic-inorganic hybrid material is one of the most promising materials for high performance gas sensors due to its improved properties like high sensitivity, selectivity, fast response time, flexibility and low power consumption. This work presents ultrasensitive, selective and low operating temperature H2S gas sensor. It is based on metal-oxide nanoparticles (NPs) embedded in organic semiconductor polymeric nanofibrous (NFs) membrane containing an ionic liquid (IL). In this context, high surface area Tungsten(VI) oxide- Polyvinyl alcohol (WO3-PVA) nanofibrous composite sensor material with average diameter of 130 ± 20 nm were synthesized with controlled morphology and interconnectivity through an electrospinning technique. The obtained WO3 NPs-containing PVA nanofibrous sensing material was evaluated for its ability as a potential sensor for H2S gas at different operating temperatures and gas concentrations. Results demonstrated that the fabricated sensor is ultrasensitive and selective for H2S gas and exhibit an excellent reproducibility, and long-term stability. Furthermore, the sensor showed adequate response in a humid environment. It was also shown that nanofibers' membrane porosity and thickness control the sensing performance. The optimum operating temperature of 40°C with a detection threshold as low as 100 ppb with a response time of 16.37 ± 1.42 s were achieved. This combined high sensitivity, fast response time and low operating temperature (low-power consumption) provides clear evidence of the sensor's potential to outperform existing devices, which could pave the way for a commercial exploitation.

Low power consumption and fast response H2S gas sensor based on a chitosan-CuO hybrid nanocomposite thin film

In this work, a novel selective and low temperature H2S gas sensor was fabricated based on copper (II) oxide nanoparticles (CuO NPs) in different concentrations, embedded in a conductivity-engineered organic (glycerol ionic liquid-doped chitosan) membrane/film. The sensing membranes of organic-inorganic nanocomposites (CS-IL-CuO) were prepared by casting method and were tested against H2S gas with reference to time at different temperatures and H2S gas concentrations. The fabricated sensor showed a fast response (14 s) and good sensitivity (15 ppm) towards H2S gas at a low temperature of 40 °C. Moreover, the sensor showed a high reversibility and less humidity dependence at 40 °C. Moreover, this type of hybrid nanocomposites sensor is easy and inexpensive to manufacture and is energy efficient. Thus, it has potential to be used for industrial applications in harsh environments.

Amperometric H2S sensor based on a Pt-Ni alloy electrode and a proton conducting membrane

In this work, carbon fiber carrying platinum-nickel alloy is used as a sensing electrode material to develop a H2S gas sensor based on Nafion proton membrane. Characterizations of the material by X-ray diffraction (XRD), scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS) reveal that the structure and morphology of the particles change with the ratio of the alloy. The electrochemical specific area (ECSA) of the material is calculated by cyclic voltammetry, which further proves the influence of alloy formation on the catalytic performance of the materials. When the ratio of platinum to nickel is 1:1, the material is uniformly loaded and its catalytic performance is optimal. Thus, the device made with it has the highest sensitivity. The sensor's low detection limit is 0.2 ppm. For the incorporation of nickel, the sensitivity is increased to -0.306 μA/ppm, which is 18 % higher than before. Not only does the sensor have good repeatability and short response recovery time, the presence of oxygen and water vapor does not have much effect on the sensor. Therefore, it has a great application potential in the field of gas detection at room temperature.

Cellulose-Copper Oxide hybrid nanocomposites membranes for H2S gas detection at low temperatures

We report on novel, sensitive, selective and low-temperature hydrogen sulfide (H2S) gas sensors based on metal-oxide nanoparticles incorporated within polymeric matrix composites. The Copper-Oxide (CuO) nanoparticles were prepared by a colloid microwave-assisted hydrothermal method that enables precise control of nanoparticle size. The sodium carboxymethyl cellulose (CMC) powder with 5% glycerol ionic liquid (IL) was prepared and mixed with different concentrations of CuO NPs (2.5–7.5 wt.%) to produce flexible and semi-conductive polymeric matrix membranes. Each membrane was then sandwiched between a pair of electrodes to produce an H2S gas sensor. The temperature-dependent gas sensing characteristics of the prepared sensors were investigated over the temperature ranges from 40 °C to 80 °C. The sensors exhibited high sensitivity and reasonably fast responses to H2S gas at low working temperatures and at a low gas concentration of 15 ppm. Moreover, the sensors were highly selective to H2S gas, and they showed low humidity dependence, which indicates reliable functioning in humid atmospheres. This organic-inorganic hybrid-materials gas sensor is flexible, with good sensitivity and low power consumption has the potential to be used in harsh environments.

Ultrasensitive ppb-level H2S gas sensor at room temperature based on WO3/rGO hybrids

Gas sensors with high performance and low energy consumption are necessary for system integration in the environment monitoring of explosives. High-performance room-temperature hydrogen sulfide (H2S) gas sensors were fabricated based on the hybrids of tungsten oxide (WO3)/reduced graphene oxide (rGO). WO3 nanocubes modified with different contents of rGO were synthesized by acid-based hydrothermal method. The optimal amount of rGO in the composite is 5 wt%, at which the room-temperature operating sensor presents the highest sensitivity of approximately 32.7 to 500 ppb H2S, a fast recovery time of ~ 180 s, as well as an excellent sensing selectivity. The overall improvement in sensing performances demonstrated an important progress made in H2S sensor fabrication for portable and real-time gas detection. The improved gas-sensing performance is attributed to the large specific surface area of the WO3 nanocubes, the formation of WO3/rGO heterojunctions, and the enhanced electron transfer efficiency.

Metal-Organic frameworks-derived bamboo-like CuO/In2O3 Heterostructure for high-performance H2S gas sensor with Low operating temperature

Hydrogen sulfide (H2S) sensors with excellent response and selectivity are in great demand to monitor its concentration changes in the real environment, especially at an ultra-trace level. This work presents a metal-organic framework (MOF)-derived metal oxide prepared via the solvothermal method and the developed sensors based on such materials exhibits enhanced gas-sensing performance. The bamboo-like CuO/In2O3 derived from Cu2+-impregnated CPP-3 were investigated through structural analyses, and it confirms that the n-type In2O3 and p-type CuO were successfully combined and heterojunctions were formed at CuO/In2O3 interfaces. The gas-sensing properties of CuO/In2O3 towards H2S were evaluated, and the sensor based on CuO/In2O3 with 3.5 wt% of Cu to CPP-3(In) is found to exhibit excellent H2S response (Rair/Rgas = 229.3–5 ppm), which are 8.5 times higher than that of with pristine In2O3. It also discloses low detection limits (200 ppb), low operating temperature (70 °C) and superior selectivity against other interfering gases. The gas sensing mechanism is thoroughly discussed and CuO/In2O3 could be considered as a novel and promising material for the practical application to selectively detect H2S at low operating temperature.

Enhanced H2S gas-sensing performance of α-Fe2O3 nanofibers by optimizing process conditions and loading with reduced graphene oxide

We systematically investigated the effects of process conditions and reduced graphene oxide (RGO) loading on the H2S gas-sensing performance of the α-Fe2O3 nanofibers (NFs) fabricated via on-chip electrospinning. The annealing temperature and precursor solution contents strongly influenced on the morphology and structure of the α-Fe2O3 NFs that accordingly affected on the gas-sensing performance. The optimum process conditions with the annealing temperature of 600 °C and the precursor solution contents of 11 wt% PVA and 4.0 wt% Fe(NO3)3.9H2O led to the α-Fe2O3 NF sensors having a high response of ∼6.1 at 1 ppm H2S gas. The RGO loading further improved the gas response, increasing the response to 1 ppm H2S gas up to ∼9.2. Also, the RGO-loaded α-Fe2O3 NF sensors enhanced their selectivity and detection limit as compared with pure α-Fe2O3 NF sensors. The enhanced gas-sensing performance was attributed to the presence of nanograins, the increase of surface-to-volume ratio and the formation of potential barriers at nanograin homojunctions and RGO/α-Fe2O3 heterojunctions.

Fabrication of H2S Gas Sensor Based on Ppy/CuO and Ppy/SnO2 Nanocomposites at Room Temperature

The existence of Hydrogen sulfide (H2S) during the petroleum production and its high risks is the main reason to develop a smart, cheap and flexible device for H2S monitoring. This article is focusing on developing electrochemical sensors, which seems to have a promising potential. Polypyrrole (Ppy) and its two composites were prepared; Ppy doped with Cupper oxide (CuO) nanoparticles (Ppy/CuO) and Ppy doped with Tin oxide (SnO2) nanoparticles (Ppy/SnO2) via in-situ polymerization approach. The characterizations of these nanocomposites were confirmed by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), Dynamic Light Scattering (DLS) and High-Resolution Transition Electron Microscopy (HR-TEM). The testing of these nanocomposites towards the monitoring of H2S gas at different concentrations was carried out in the term of electrical resistance changes. From the data; it was found that the response at 1000 ppm H2S gas concentration was ranked as; Ppy 0.12 %. Ppy/CuO 4.7 %. Ppy/SnO2 53.2 %.

H2S gas sensor based on integrated resonant dual-microcantilevers with high sensitivity and identification capability

Detection of trace-level hydrogen sulfide (H2S) gas is of great importance whether in industrial production or disease diagnosis. This research presents a novel H2S gas sensor based on integrated resonant dual-microcantilevers which can identify and detect trace-level H2S in real-time. The sensor consists of two integrated resonant microcantilever sensors with different functions. One cantilever sensor can identify H2S by outputting positive frequency shift signals, while the other cantilever sensor will detect H2S as a normally used cantilever sensor with negative frequency shifts. Combined the two cantilever sensors, the proposed gas sensor can distinguish H2S from a variety of common gases, and the detection limit to H2S of the sensor is as sensitive as below 1 ppb.