H2S Sensing Research Articles

In Situ Generatable and Recyclable Oxygen Vacancy-Modified Fe2O3-Decorated WO3 Nanowires with Super Stability for ppb-Level H2S Sensing.

Detecting hydrogen sulfide (H2S) odor gas in the environment at parts-per-billion-level concentrations is crucial. However, a significant challenge is the rapid deactivation caused by SO42- deposition. To address this issue, we developed a sensing material comprising Fe2O3-decorated WO3 nanowires (FWO) with strong interfacial interaction. During the H2S sensing process, important oxygen vacancies (OVs) are generated in situ and are recyclable on the surface of the Fe2O3 cluster. This sensor achieves a response of 140 (Ra/Rg) toward 50 ppm of H2S at 250 °C, with an experimentally measured detection limit of 1 ppb. It also exhibits remarkable stability, with no significant change observed over a long period of 150 days. Based on a combination of in situ DRIFT and DFT calculations, we have identified that the overactivation of O2 is the key step in the formation of SO42-. This overactivation can be partially modulated by the synergistic effect of Fe2O3 decoration and the in situ generated OVs, regulating the oxidation product to SO2 rather than the toxic SO42-. Furthermore, the continuous generation of OVs compensates for the loss of active sites pertaining to SO42- deposition, thereby contributing to the excellent stability of the sensor. This study underscores the beneficial impact of in situ OV generation in FWO for H2S sensing, offering a dynamic strategy to enhance sensor performance, particularly in terms of stability.

In Situ Synthesis of Hierarchical Co(CO3)0.5(OH)·0.11H2O@ZIF-67/WO3 With High Humidity Immunity and Response to H2S Sensing.

H2S gas sensors with facile preparation, low detection limits, and high selectivity are crucial for environmental and human health monitoring. However, it is difficult to maintain a high response of H2S gas sensors under high humidity in practical applications. To face this dilemma, a layer-by-layer growth method is applied to in situ prepare a nanostructured Co(CO3)0.5(OH)·0.11H2O/WO3 coated by a hydrophobic hierarchical ZIF-67 as the H2S sensor. This novel composite exhibits excellent humidity immunity without sacrificing the excellent sensitivity and selectivity of H2S. At a low operating temperature of 90°C, a remarkable response value of 1052.3 to 100ppm H2S has been achieved, which is 779 and 9.36 times higher than that of pure WO3 and Co(CO3)0.5(OH)·0.11H2O/WO3, respectively. More importantly, an 82.2% relative response value remains at a high humidity of 75%RH. The sensing mechanisms are investigated using gas chromatography-mass spectrometry (GC-MS), which revealed that the reaction products are H2O and SO2. The high humidity immunity and fast response of the Co(CO3)0.5(OH)·0.11H2O@ZIF-67/WO3 demonstrate the layer-by-layer in situ synthesis method holds the potential application for the development of high-performance WO3-based H2S sensors.

Lab-on-Device Synthesis of Hierarchical Macro/Mesoporous WO3 Semiconducting Films for High-Performance H2S Sensing.

The performance consistency of the gas sensor is strongly dependent on the interface binding between the sensitive materials and the electrodes. Traditional powder coating methods can inevitably lead to differences in terms of substrate-film interface interaction and device performance, affecting the stability and lifetime. Thus, efficient growth of sensitive materials on device substrates is crucial and essential to enhance the sensing performance, especially for stability. Herein, hierarchically ordered macro/mesoporous WO3 films are in situ synthesized on the electrode via a facile soft/hard dual-template strategy. Orderly arrayed uniform polystyrene (PS) microspheres with tailored size (ca. 1.2µm) are used as a hard template, and surfactant Pluronic F127 as a soft template can co-assemble with tungsten precursor into ordered mesostructure in the interstitials of PS colloidal crystal induced by solvent evaporation. Benefiting from its rich porosity and high stability, the macro/mesoporous WO3-based sensor shows high sensitivity (Rair/Rgas = 307), fast response/recovery speed (5/9 s), and excellent selectivity (SH2S/Smax > 7) toward 50ppm H2S gas (a biomarker for halitosis). Significantly, the sensors exhibit an extended service life with a negligible change in sensing performance within 60 days. This lab-on-device synthesis provides a platform method for constructing stable nanodevices with good consistency and high stability, which are highly desired for developing high-performance sensors.

Gadolinium-Doped CeO2 Gas Sensor for H2S Sensing

Dihydrogen sulfide (H2S) gas has a flammable nature and is one of the most toxic and dangerous gases. Even small concentrations can be fatal to humans. Herein, we investigated the H2S gas-sensing features of commercial pristine cerium oxide (CeO2 ) and gadolinium (Gd)-doped CeO2 (GDC) nanoparticles. First, the sensing materials were well-characterized using various methods including X-ray photoelectron spectroscopy, transmission electron microscopy and X-ray diffraction to gain insight into their chemical composition, morphology, phases, and crystallinity, respectively. In the next step, gas sensors were fabricated using a top electrode (Au/Ti) configuration. Preliminary H2S-gas-sensing studies revealed that GDC gas sensor had a superior gas response to H2S gas than the pristine CeO2 gas sensor at 350°C. The responses of the pristine CeO2 gas sensor to 20 ppm H2S gas was 1.542, while the response of the GDC gas sensor to the aforementioned H2S concentration was 3.489. In addition, the GDC sensor exhibited good selectivity to H2S gas among C2H5OH, C7H8 and NH3 gases. Also, we investigated the response of the sensor in up to 60% relative humidity. The enhanced response of the GDC gas sensor to H2S gas was mainly related to the formation of oxygen defects as a result of Gd-doping in CeO2 . Also, good selectivity to H2S was related to the sensing temperature, the higher reactivity of H2S relative to other gases and the small bond energy of H-SH. This study demonstrates the promising ability of Gd-doping to enhance the H2S gas-sensing characteristics of CeO2 , which can be applied to other similar systems based on semiconducting metal oxides.

Pore Size Modulation in Flexible Metal-Organic Framework Enabling High Performance Gas Sensing.

Pore size plays a critical role in determining the performance of metal-organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore-size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent-coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL-88B. Pore-size-dependent gas sensitivity and selectivity were studied for the first time in the MIL-88B samples. The optimized MIL-88B-20 % sample showed one of the best sensing performances among all the reported MOF-based H2 S-sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore-size and properties, but also may inspire the development of high-performance gas sensing materials.

Feasible H2S Sensing in Water with a Printed Amperometric Microsensor.

Concern over pollution has led to an increase in wastewater treatment systems, which require constant monitorization. In particular, hydrogen sulfide (H2S) is a toxic gas, soluble in water, commonly found in industrial and urban effluents. For proper removal control, fast, durable, and easy-to-handle analytical systems, capable of on-line measurements, such as electrochemical sensors, are required. Moreover, for a proper monitoring of said treatment processes, analysis must be carried out through all steps, thus needing for an economic and highly reproducible method of sensor fabrication. Digital printing have risen in the last few years as technologies capable of mass producing miniaturized electronical devices, allowing for the fabrication of amperometric sensors. Here, a 2 mm2 graphite (Gr) electrode, modified with different dispersions of single-walled carbon nanotubes (SWCNTs), poly(vinyl alcohol), poly(diallyl dimethylammonium chloride), and polylactic acid (PLA), is presented as a H2S sensor. SWCNTs allow for lower oxidation potentials, higher sensitivity, and a reduced rate of sulfur poisoning, while polymer dispersion of PLA increases mechanical stability and as a result, electrochemical performance. This microsensor presents an optimal pH working range between 7.5 and 11.0, a limit of detection of 4.3 μM, and the capacity to operate on complex matrices for H2S contamination detection.

Colorimetric Sensor Based on Ag-Fe NTs for H2S Sensing.

Meat waste is widely associated with spoilage caused by microbial growth and metabolism. Volatile compounds produced by microbial growth such as volatile sulfides could directly indicate the freshness of meat during distribution and storage. Herein, silver-iron nanotriangles (Ag-Fe NTs) for hydrogen sulfide (H2S) detection were developed via one-pot facile reflux reactions. The Ag-Fe NTs were integrated into food packaging systems for the rapid, real-time, and nondestructive detection of the freshness of chilled broiler poultry. The principle of color development is that an increase in the volatile sulfide content leads to a change in the absorption wavelength caused by the etching of the Ag-Fe NTs, resulting in a color change (yellow to brown). The minimum H2S concentrations detected by the naked eye and UV-vis spectrophotometer were 4 and 2 mg/m3, respectively. This label is economical and practical and can monitor the spoilage of chilled broiler meat products in real-time.

Effects of Electrode Structure on H2S Sensing and Low-Frequency Noise Characteristics in In2O3-Based Resistor-Type Gas Sensors

Most studies on gas sensors are focusing on improving the response of the sensor. However, noise characteristics should also be considered for the design of gas sensors with optimal performance. This paper investigates the effects of electrode structure on H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas sensing and low-frequency noise (LFN) characteristics in In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> resistor-type gas sensors. We mainly analyze the response and noise performances of the interdigitated electrode (IDE) sensors with different combinations of spacing between the fingers ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}$ </tex-math></inline-formula> ) and the number of electrode fingers ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}_{\mathrm{f}}$ </tex-math></inline-formula> ). Parallel electrode (PE) sensors are also compared as a reference. For the IDE sensors, the response increases as the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}$ </tex-math></inline-formula> decreases (or N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> increases), while the PE sensors show constant response regardless of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}$ </tex-math></inline-formula> . The gas response characteristics of the IDE and PE sensors are further analyzed using the gas sensing results of a transmission line method (TLM) pattern. It is shown that the contributions of bulk and contact to the overall gas response differ depending on electrode spacing. The normalized LFN of the IDE sensors is at least 100 times smaller than that of the PE sensors since <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}$ </tex-math></inline-formula> greatly affects the noise characteristics. The limit of detection (LOD) of the sensor for H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas can be improved from 8380 ppb ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}= 100\,\,\mu \text{m}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}_{\mathrm{f}} = 2$ </tex-math></inline-formula> ) to 6.42 ppb ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}= 2\,\,\mu \text{m}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}_{\mathrm{f}} = 30$ </tex-math></inline-formula> ) by adopting a shortly spaced interdigitated electrode structure. The results provide an electrode design guidance for the resistor-type gas sensors that show optimal performance considering both the noise and gas response.

Highly Selective H2s Sensing of Co12 Cluster and Zno/Co12 Composites Based Mems Sensors

Highly Selective H2s Sensing of Co12 Cluster and Zno/Co12 Composites Based Mems Sensors

Effect of moisture and molecular weight of polyaniline on H2S sensing characteristics

Chemical behavior of some gases, such as H2S, changes with presence of moisture. Sensing of H2S by polyaniline (PANI) has been studied; the sensing characteristics depend upon the specific surface area, concentration of active surface sites, pore size, and surface heterogeneity controlled by the chain configuration, which is further governed by the molecular weight. However, effects of moisture in the environment and molecular weight of PANI on H2S sensing characteristics have not been studied, and this is the motivation of the present work. Here we have studied the H2S sensing by PANI of different molecular weights in the same environment (N2) with different moisture (dry and humid) conditions, and in different environments (N2 and compressed air) at the same humidity level. It was observed that regardless of the environment, (i) with increasing concentration of H2S gas, the resistance of the sensors increased in dry atmosphere and decreased in presence of moisture, and (ii) the response time was lower in moist conditions. The sensitivity and response were non-monotonous with respect to the molecular weight. However, response time decreased monotonically with increase in band gap of PANI. New correlations were developed to get surface site kinetics from the response data.

Hierarchical Sphere-Like ZnO–CuO Grown in a Controlled Boundary Layer for High-Performance H2S Sensing

Hierarchical Sphere-Like ZnO–CuO Grown in a Controlled Boundary Layer for High-Performance H2S Sensing

Exposed Mo Atoms Induced by Micropores Enhanced H2s Sensing of Moo3 Nanoflowers

Exposed Mo Atoms Induced by Micropores Enhanced H2s Sensing of Moo3 Nanoflowers

Controllable Synthesis of Zn-Doped α-Fe2O3 Nanowires for H2S Sensing.

One-dimensional Zn-doped α-Fe2O3 nanowires have been controllably synthesized by using the pure pyrite as the source of Fe element through a two-step synthesis route, including the preparation of Fe source solution by a leaching process and the thermal conversion of the precursor solution into α-Fe2O3 nanowires by the hydrothermal and calcination process. The microstructure, morphology, and surface composition of the obtained products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was found that the formation process of α-Fe2O3 is significantly influenced by the introduction of Zn2+. The gas sensing measurements indicated that the sensor based on 1% Zn-doped α-Fe2O3 nanowires showed excellent H2S sensing properties at the optimum operating temperature of 175 °C. Notably, the sensor showed a low H2S detection limit of 50 ppb with a sensor response of 1.5. Such high-performance sensing would be ascribed to the one-dimensional structure and high specific surface area of the prepared 1% Zn-doped α-Fe2O3 nanowires, which can not only provide a large number of surface active sites for the adsorption and reaction of the oxygen and H2S molecules, but also facilitate the diffusion of the gas molecules towards the entire sensing materials.

Synthesis of Cu₂O/CuO Nanocrystals and Their Application to H₂S Sensing.

Semiconducting metal oxide nanocrystals are an important class of materials that have versatile applications because of their useful properties and high stability. Here, we developed a simple route to synthesize nanocrystals (NCs) of copper oxides such as Cu2O and CuO using a hot-soap method, and applied them to H2S sensing. Cu2O NCs were synthesized by simply heating a copper precursor in oleylamine in the presence of diol at 160 °C under an Ar flow. X-ray diffractometry (XRD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) results indicated the formation of monodispersed Cu2O NCs having approximately 5 nm in crystallite size and 12 nm in colloidal size. The conversion of the Cu2O NCs to CuO NCs was undertaken by straightforward air oxidation at room temperature, as confirmed by XRD and UV-vis analyses. A thin film Cu2O NC sensor fabricated by spin coating showed responses to H2S in dilute concentrations (1–8 ppm) at 50–150 °C, but the stability was poor because of the formation of metallic Cu2S in a H2S atmosphere. We found that Pd loading improved the stability of the sensor response. The Pd-loaded Cu2O NC sensor exhibited reproducible responses to H2S at 200 °C. Based on the gas sensing mechanism, it is suggested that Pd loading facilitates the reaction of adsorbed oxygen with H2S and suppresses the irreversible formation of Cu2S.

H₂S Sensing by Hybrids Based on Nanocrystalline SnO₂ Functionalized with Cu(II) Organometallic Complexes: The Role of the Ligand Platform.

This paper deals with the functionalization of nanocrystalline SnO2 with Cu(II) complexes with organic ligands, aimed at the improvement of sensor selectivity towards gas molecules. For the synthesis of metalorganic/SnO2 hybrid material complexes of Cu(II) with phthalocyanine, porphyrinines, bipyridine and azadithiacrown etherwere used. The analysis of gas sensor properties showed the possibility of increasing the sensitivity and selectivity of hybrid materials in H2S detection due to the electron transfer from SnO2 to an adsorbed organic molecule, which changes during the interaction between H2S and Cu(II) ions.