Metal-Organic-Framework Derived Co-Mo Multimetal Oxide Semiconductors: Selective Trace-Level Hydrogen Sulfide Detection

The development of a highly selective and trace-level gas sensing platform for detecting hydrogen sulfide (H2S) remains a formidable challenge. To solve this problem, Co-Mo multimetal oxide semiconductors are rationally tailored by employing metal organic frameworks (MOFs) as self-sacrificial templates. The MOF-derived Co3O4/β-CoMoO4 based gas sensors displays high sensitivity (Rg/Ra = 22) to 10 ppm of H2S and ultralow limit of detection (10 ppb H2S). The formation of p-p heterojunction and multivalence states of Mo play a crucial role in electron transfer and oxygen adsorption. A sensor array constructed from four Co3O4/β-CoMoO4 materials with different Co/Mo ratios demonstrates a superior selective discrimination of H2S from other VOCs and malodorous gases by principal component analysis (PCA). Besides, a H2S gas sensing and alarming platform was designed for monitoring the environment contaminated with H2S. This finding provides a feasible approach for the discovery of highly efficient gas sensors to monitor environmental H2S concentration.

Achieving Room-Temperature ppb-Level H2S Detection in a Au-SnO2 Sensor with Low Voltage Enhancement Effect

Although semiconductor metal oxide-based sensors are promising for gas sensing, low-power and room temperature operation (24 ± 1 °C) remains desirable for practical applications particularly considering the request of energy saving or net zero emission. In this study, we demonstrate a Au/SnO2-based ultrasensitive H2S gas sensor with a limit of detection (LOD) of 2 ppb, operating at very low voltages (0.05 to 0.5 V) at room temperature. The Au/SnO2-based sensor showed approximately 7 times higher response (the ratio of change in the current to initial current) of ∼270% and 4 times faster recovery (126 s) compared to the pure SnO2-based sensor when exposed to 500 ppb H2S gas concentration at 0.5 V operating voltage at relative humidity (RH) 17.5 ± 2.5%. The enhancement can be attributed to the catalytic characteristics of AuNPs, increasing the number of adsorbed oxygen species on sensing material surfaces. Additionally, AuNPs aid in forming flower-petal-like Au/SnO2 nanostructures, offering a larger surface area and more active sites for H2S sensing. Moreover, at low voltage (<1 V), the localized dipoles at the Au/SnO2 interface may further enhance the absorption of polar oxygen molecules and hence promote the reaction between H2S and oxygen species. This low-power, ultrasensitive H2S sensor outperforms high-powered alternatives, making it ideal for environmental, food safety, and healthcare applications.

Hydrogen Sensing with Palladium-Based Materials: Mechanisms, Challenges, and Opportunities

Palladium morphologies are prominently used in Hydrogen gas sensing applications owing to their unique characteristics and properties. In this review article, Palladium nanoparticles, thin films, and alloys were designated as the scope of Palladium morphologies. The aim of this review article is to explore Hydrogen sensing using Palladium, focusing on the recent advancements in the field.. The principles underlying Hydrogen sensing mechanisms with Palladium are discussed initially, highlighting the unique properties of Palladium that make it a promising material for this purpose. Special attention is given to the surface interactions and structural modifications that influence the sensitivity and selectivity of Palladium-based sensors The study also addresses key challenges and recent innovations in the field which contribute to the enhancement of Palladium-based Hydrogen sensing capabilities. The current state of research is critically examined to identify gaps in knowledge and future research directions are highlighted. The prospects and challenges associated with the use of Palladium for Hydrogen sensing, emphasizing its pivotal role in advancing sensor technologies for Hydrogen detection are also discussed.

Design and Application of Cu2+ Fluorescent Sensor Based on Carbazole Derivatives

A novel fluorescent sensor for the detection of Cu2+ was developed based on carbazole derivatives. After the addition of Cu2+, the sensor exhibited obvious fluorescence quenching phenomenon, and the optical signal variation also enabled the sensor to quantitatively analyze Cu2+ due to the formation of a stable 1:1 metal-ligand complex in a short time. In addition, the sensor possessed chemical reversibility and pH stability. The cell imaging and zebra fish experiments also verified its application value in biological system.

Designing State-of-the-Art Gas Sensors: From Fundamentals to Applications

Gas sensors are crucial in environmental monitoring, industrial safety, and medical diagnostics. Due to the rising demand for precise and reliable gas detection, there is a rising demand for cutting-edge gas sensors that possess exceptional sensitivity, selectivity, and stability. Due to their tunable electrical properties, high-density surface-active sites, and significant surface-to-volume ratio, nanomaterials have been extensively investigated in this regard. The traditional gas sensors utilize homogeneous material for sensing where the adsorbed surface oxygen species play a vital role in their sensing activity. However, their performance for selective gas sensing is still unsatisfactory because the employed high temperature leads to the poor stability. The heterostructures nanomaterials can easily tune sensing performance and their different energy band structures, work functions, charge carrier concentration and polarity, and interfacial band alignments can be precisely designed for high-performance selective gas sensing at low temperature. In this review article, we discuss in detail the fundamentals of semiconductor gas sensing along with their mechanisms. Further, we highlight the existed challenges in semiconductor gas sensing. In addition, we review the recent advancements in semiconductor gas sensor design for applications from different perspective. Finally, the conclusion and future perspectives for improvement of the gas sensing performance are discussed.

Recent Advances of Graphene Quantum Dots in Chemiresistive Gas Sensors

Graphene quantum dots (GQDs), as 0D graphene nanomaterials, have aroused increasing interest in chemiresistive gas sensors owing to their remarkable physicochemical properties and tunable electronic structures. Research on GQDs has been booming over the past decades, and a number of excellent review articles have been provided on various other sensing principles of GQDs, such as fluorescence-based ion-sensing, bio-sensing, bio-imaging, and electrochemical, photoelectrochemical, and electrochemiluminescence sensing, and therapeutic, energy and catalysis applications. However, so far, there is no single review article on the application of GQDs in the field of chemiresistive gas sensing. This is our primary inspiration for writing this review, with a focus on the chemiresistive gas sensors reported using GQD-based composites. In this review, the various synthesized strategies of GQDs and its composites, gas sensing enhancement mechanisms, and the resulting sensing characteristics are presented. Finally, the current challenges and future prospects of GQDs in the abovementioned application filed have been discussed for the more rational design of advanced GQDs-based gas-sensing materials and innovative gas sensors with novel functionalities.

Microfluidic integrated gas sensors for smart analyte detection: a comprehensive review

The utilization of gas sensors has the potential to enhance worker safety, mitigate environmental issues, and enable early diagnosis of chronic diseases. However, traditional sensors designed for such applications are often bulky, expensive, difficult to operate, and require large sample volumes. By employing microfluidic technology to miniaturize gas sensors, we can address these challenges and usher in a new era of gas sensors suitable for point-of-care and point-of-use applications. In this review paper, we systematically categorize microfluidic gas sensors according to their applications in safety, biomedical, and environmental contexts. Furthermore, we delve into the integration of various types of gas sensors, such as optical, chemical, and physical sensors, within microfluidic platforms, highlighting the resultant enhancements in performance within these domains.

Fabrication of conifer-like TiSnO2 nanorods for sensing H2S gas at room temperature

Conifer-like TiSnO2 nanorods mixed metal oxide was synthesized via the one-pot polyol method utilizing ethylene glycol (EG), poly(diallyldimethylammonium chloride) (PDDA), tin(II) chloride dihydrate (SnCl2·2H2O), and titanium(IV)-ethylhexanoate (TE) as precursor materials, aimed at room temperature H2S gas sensing. The effects of polyol duration time and capping agent concentration (PDDA) were examined to explore the morphological, structural, and gas-sensing characteristics, as well as to propose potential growth mechanisms of conifer-like TiSnO2 nanorods mixed metal oxide. The morphology and composition of the synthesized TiSnO2 mixed metal oxide were carried out employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffractometry (XRD). The experimental findings demonstrated a significant influence of polyol duration time and PDDA concentration on the morphological evolution of the synthesized TiSnO2 mixed metal oxide structures. Comparative gas-sensing analysis indicated that the conifer-like TiSnO2 nanorods mixed metal oxide exhibited the highest response (2.45%) towards H2S gas at a concentration of 1 ppm, along with a low detection limit (0.20 ppm) and good linearity (R2 = 0.9865) within the range of 1-15 ppm of H2S gas at room temperature.

Enhancement of H2S sensing performance of rGO decorated CuO thin films: experimental and DFT studies

We demonstrate a highly selective and sensitive Cupric oxide (CuO) thin film-based low concentration Hydrogen sulfide (H₂S) sensor. The sensitivity was improved around three times by decorating with reduced graphene oxide (rGO) nanosheets. CuO thin films were deposited by Chemical Vapor Deposition followed by inter-digital electrode fabrication by a thermal evaporations system. The crystal structure of CuO was confirmed by x-ray diffraction. The sensing response of pristine CuO was found around 54% at 100 °C to 100 ppm of H₂S. In contrast, the sensing response was enhanced to 167% by decorating with rGO of 1.5 mg ml^-1concentration solution. The sensing was improved due to the formation of heterojunctions between the rGO and CuO. The developed sensor was examined under various gas environments and found to be highly selective towards H₂S gas. The improvement in sensing response has been attributed to increased hole concentration in CuO in the presence of rGO due to the Fermi level alignment and increased absorption of H₂S molecules at the rGO/CuO heterojunction. Further, electronic structure calculations show the physisorption behavior of H₂S molecules on the different adsorption sites. Detailed insight into the gas sensing mechanism is discussed based on experimental results and electronic structure calculations.

Selective monitoring of natural gas sulphur-based odorant mixture of t-butyl mercaptan and methyl ethyl sulphide using an array of microfluidic gas sensors

A natural gas (NG) odorization system requires continuous monitoring as well as an optimal injection to satisfy the odorization guidelines, minimize over-odorization, and prevent hazardous gas leaks. NG consists of hydrocarbons such as methane, odorants such as tert-butyl mercaptan, and other sulphur-based VOCs such as hydrogen sulphide; therefore, selectivity is paramount for the reliable and accurate monitoring of odorants. In this study, we developed a portable device integrated with an array of five different sensors to detect a mixture of tert-butyl mercaptan and methyl ethyl sulphide for a concentration range of 1 ppm to 10 ppm. A machine learning model was developed to predict the presence and concentration of NG odorants from the sensor data. The best-performing sensors in the array achieved high sensitivity and selectivity indicators (measured using the Davies-Bouldin index) of 0.3667 (1⁄ppm) and 0.125, respectively. The sensor system achieved a classification accuracy of 98.75% between NG odorants and hydrogen sulphide, with an overall Mean Squared Error (MSE) and R² error (for the regression model) of 0.50 and 95.16%. These results indicate that the developed portable device and the machine learning model have promising applications for the selective monitoring of NG odorants.

Synthesis and H2S-Sensing Properties of MOF-Derived Cu-Doped ZnO Nanocages

Metal–organic framework (MOF)-derived pure ZnO and Cu-doped ZnO nanocages were fabricated by calcining a zeolitic imidazole framework (ZIF-8) and Cu-doped ZIF-8. The morphology and crystal structure of the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). It was found that Cu doping did not change the crystal structures and morphologies of MOF-derived ZnO nanocages. The H2S-sensing properties of the sensors based on ZnO and Cu-doped ZnO nanocages were investigated. The results indicated that the H2S-sensing properties of MOF-derived ZnO nanocages were effectively improved by Cu doping, and the optimal doping content was 3 at%. Moreover, 3 at% Cu-doped ZnO nanocages showed the highest response of 4733 for 5 ppm H2S at 200 °C, and the detection limit could be as low as 20 ppb. The gas-sensing mechanism was also discussed.

Selective detection of VOCs using microfluidic gas sensor with embedded cylindrical microfeatures coated with graphene oxide

Volatile organic compounds (VOCs) are major environmental pollutants. Exposure to VOCs has been associated with adverse health outcomes. The monitoring of hazardous VOCs is a vital step towards identifying their presence and preventing the risk of acute or chronic exposure and polluting the environment. One of the challenges associated with monitoring VOCs is selectivity of the sensor. Microfluidic gas sensors offer selective and sensitive detection capabilities that have been recently applied for detection of VOCs. In this study, we achieve improved selectivity for detection of a range of VOCs by adding micro- and nanofeatures to the microchannel of microfluidic gas sensors. First, microfeatures are embedded into the microchannel and their geometries are optimized using Taguchi design of experiment method. In the next step the microfeatures embedded microchannel is coated with graphene oxide, to increase the surface to volume ratio by introducing nanofeatures to the surfaces. The nano- and microfeatures are characterized by SEM, XPS, and water contact angle measurement. Finally, the changes in the sensor response are compared to plain microfluidic gas sensor, the results show an average of 64.4% and 120.9% improvement in the selectivity of the sensor with microfeatures and both nano- and microfeatures, respectively.

A novel quinoline derivative as a highly selective and sensitive fluorescent sensor for Fe3+ detection

In this research, a novel selective and sensitive fluorescent sensor for detecting Fe³⁺ was designed and synthesized; it revealed an obvious fluorescence quenching effect upon addition of Fe³⁺, and possessed the quantitative analysis ability on account of the formation of a 1 : 1 metal–ligand complex. Furthermore, the density functional theory calculations were utilized to study the molecular orbitals as well as the spatial structure. Simultaneously, the cell experiments and zebra fish experiments verified the application value of the sensor in the biological field.

A novel selective and sensitive fluorescent sensor for detecting Fe³⁺ was designed and synthesized; it revealed obvious fluorescence quenching effect upon addition of Fe³⁺, and possessed the quantitative analysis ability on account of the formation of a 1 : 1 metal–ligand complex.