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In this research, a two-step hydrothermal technique is used to fabricate a NO 2 gas sensor based on MoS 2 nanoflowers with SnO 2 nanoparticles. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) , were used to determine the morphologies, nanostructures, and compositions of the materials. The nanocomposites consisting of MoS 2 /SnO 2 demonstrated a remarkable sensing response (38.6) towards 100 ppm of NO 2. Moreover, the nanocomposites showed a rapid response and recovery time (42/147 S) when exposed to 100 ppm at temperature (250 °C). The MoS 2 /SnO 2 nanocomposites demonstrated exceptional selectivity to NO 2 against CO, NH 3 , and H 2 S, as well as demonstrated good repeatability. The significant gas detection characteristics could potentially be controlled by the distinctive structures of thin layers assembled into flower-like formations of two-dimensional MoS 2. The multi-joint nanostructures promote the process of transferring the electrical charge of the carrier and the response to MoS 2 /SnO 2 and NO 2. The fabricated sensors are considered as potential candidates for the commercial in the nitrogen dioxide gas-sensing applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) gas is a dual menace since it is not only hazardous to human health and the environment, but it is also flammable. Given these crucial considerations, the need for competent gas sensors for H 2 S detection becomes apparent. In this endeavor, an investigation of the gas-sensing prowess inherent in sensors made from assembled nanosheets of ZnO–NiO arranged into intricate flower-like structures. The sensing materials were prepared using a straightforward solvothermal process. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to thoroughly examine the sensor's chemical properties and structural composition. The gas-sensing abilities of the sensing materials were rigorously assessed, which included a close examination of their electrical response to varied concentrations of H 2 S. The efficacy of the sensors may be due to the synergistic interactions between their distinct flower-like design, endowing them with an expansive surface area for optimum gas adsorption, and the significant catalytic impact supplied by the composition of ZnO–NiO. The results show that the ZnO–NiO flower-like sensors have high sensitivity, selectivity, and stability to H 2 S gas. Within the studied range, the response and recovery times were 51.43 s and 38.11 s respectively at 250 °C in 100 ppm H 2 S. This amalgamation of attributes manifests as an enhancement in the sensors' gas-sensing capabilities, highlighting their suitability for such an application. This research complements the explanation offered by first-principles calculations based on Density Functional Theory (DFT) to dive into the fundamentals of this gas-sensing mechanism. [ABSTRACT FROM AUTHOR]

ZIF-8 and ZIF-67 are the most investigated zeolitic imidazolate frameworks (ZIFs) materials that have aroused enormous scientific interests in numerous areas of application including electrochemistry, gas storage, separation, and sensors by reason of their fascinating structural properties. Recently, there is a rapidly growing demand for chemical gas sensors for the detection of various analytes in widespread applications including environmental pollution monitoring, clinical analysis, wastewater analysis, industrial applications, food quality, consumer products, and automobiles. In general, the key to the development of superior gas sensors is exploring innovative sensing materials. ZIF-X (8, 67) based nanostructures have demonstrated great potential as ideal sensing materials for high-performance sensing applications. In this review, the general properties and applications of ZIF-X (8, 67) including gas storage and gas adsorption are first summarized, and then the recent progress of ZIF-X (8, 67) based nanostructures for gas-sensing applications and the structure-property correlations are summarized and analyzed. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) is an odorless gas with a pungent smell that can affect health differently based on exposure and concentration. In this study, indium oxide was decorated with cobalt oxide (In 2 O 3 /Co 3 O 4) flower-like nanocomposites (NFs) as gas-sensitive materials, revealing p-type semiconducting characteristics. The detection of ammonia (NH 3) at low concentrations is a significant challenge for chemoresistive gas sensors. Porous Co 3 O 4 nanoflowers were combined with In 2 O 3 nanoparticles to form p-n heterojunctions for NH 3 detection. The p-n heterojunction effect and the capability of the sub-valent band to hold vacancies within In 2 O 3 nanoparticles effectively inhibit electron-hole recombination and extend the carrier lifetime. The In 2 O 3 /Co 3 O 4 = 0.04 ratio-based gas sensor exhibited excellent selectivity, achieving a low detection limit of 500 ppb for NH 3 at 250 °C. The rapid diffusion of gas within the porous Co 3 O 4 NSs and In 2 O 3 nanoparticles accounted for the high response (7.72) and fast response/recovery time (92 s/51 s) of the In 2 O 3 /Co 3 O 4 -based gas sensor to 10 ppm NH 3. This study presents a method for fabricating NH 3 gas sensors with trace-level detection capabilities by adjusting the band structure of nanoparticles and three-dimensional metal-oxide nanostructures. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) is a colorless toxic acidic gas, so the development of gas sensors that can effectively detect H 2 S in the environment is critical to protecting human health. Metal-organic frameworks (MOFs) are emerging as promising template for semiconductor materials in gas sensor technology, offering unique structural advantages for various sensing applications. This study aimed to understand the properties of Indium-doped ZIF-67 nanoflowers by analyzing their crystal structure, surface morphology, and chemical composition. It also investigated the hydrogen sulfide (H 2 S) gas-sensitive properties of these materials to fully comprehend their capabilities and limitations. It is demonstrated that the Co 3 O 4 sensor doped with 5 % In displays excellent stability, gas selectivity, and responsiveness. Specifically, the Co 3 O 4 sensor doped with 5 % In showed a response of 19–50 ppm H 2 S at an operating temperature of 180 °C, which was significantly higher than that of the pure Co 3 O 4 sensor. This is mainly due to the high content of oxygen vacancy (11.26 %). In the 5 % In doped sample, and the relatively large specific surface area (60.58 m2g-1). [ABSTRACT FROM AUTHOR]

This study reports the synthesis and modification of hexagonal ZnO to face-centered cubic (Fcc) Zn 2 SnO 4 via a single hydrothermal method. We systematically investigated the synthesized materials' structural, morphological, surface area, and sensing properties. X-ray diffraction (XRD) analysis confirmed the Fcc structure of the Sn-modified ZnO samples. X-ray photoelectron spectroscopy (XPS) was employed to elucidate the influence of Sn modified on defect levels in these chemical sensors. Remarkably, Zn 2 SnO 4 exhibited outstanding NO 2 sensing properties, including high response, selectivity, and recovery characteristics. The sensor demonstrated a rapid response time of less than 18s and an optimal operating temperature of 260 °C. Furthermore, the cubic face-centered Zn 2 SnO 4 displayed a wide detection range of 1–100 ppm for NO 2. The synergistic effects of chemical sensitization and catalytic activity are responsible for the enhanced sensing mechanism in Zn 2 SnO 4. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) is one of the most dangerous gases owing to its dual threat, role in global warming, and severe impact on human health. Metal-organic framework (MOF) gas-sensing materials have drawn the interest of many different sectors due to their unique structural characteristics. This study used a solvothermal technique and subsequent annealing to create a hierarchical, yeast-shaped Mo-Co 3 O 4 material from a Co-MOF precursor. The prepared materials have been employed in the development of a CO-detection gas sensor. Gas-sensing experiments revealed that Mo-Co 3 O 4 exhibited significantly improved sensing capabilities compared to pure Co 3 O 4. Notably, at 200 °C, 2 mol% Mo-Co 3 O 4 showed high response levels of about 136 at 100 ppm CO concentrations, approximately 50.4 times higher than pure Co 3 O 4. Furthermore, the Mo-doped material exhibited a low detection threshold, excellent reproducibility, long-term stability, good selectivity, and rapid response and recovery times (78.5/55.3 s). Introducing Mo dopants into the Co 3 O 4 material and the hierarchical yeast-like nanostructure are responsible for these improvements in gas-sensing capability. • Utilizing the solvothermal synthesis, a yeast-like Mo-Co 3 O 4 nanostructure for gas sensors. • Remarkable selectivity and effectiveness in detecting CO gas at 200 °C. • Mo dopants and hierarchical structure contribute to improved gas-sensing performance. • Exceptional stability and low detection limits, ensuring reliable long-term gas sensing performance. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOF)-based gas sensors have garnered significant interest and are highly desirable for monitoring indoor air quality and mitigating various environmental reclamation challenges. Herein, we describe a unique approach for fabricating hydrogen sulfide (H 2 S) gas sensors based on MOF-derived cobalt oxide nanosheets (Co 3 O 4 Ns) nanostructures. The surface morphology and porosity of the fabricated material were confirmed through comprehensive Brunauer-Emmett-Teller (BET) and electron microscopy analyses. Chemical composition and phase purity were identified using Energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The sensor exhibited remarkable sensitivity towards hydrogen sulfide in the range of 0.5–100 ppm, reaching a maximum response of 1702.61 % at an operating temperature of 250 °C for 100 ppm H 2 S gas. Furthermore, the sensor demonstrated a detection limit of 500 ppb with a response rate of 78.22 %. A consistent stability over 30 days was observed, validating its suitability for real-world applications. The response and recovery times of the H 2 S gas sensors were assessed with τ res /τ rec = 63.56/103.34 s, offering valuable insights into their real-world applicability. [Display omitted] • Simple Coprecipitation synthesis technique producing Co 3 O 4 nanosheets for gas sensors. • Co 3 O 4 nanosheets show high selectivity and efficiency in H 2 S gas at 250 °C. • CTAB concentration improves ZIF-67-derived-Co 3 O 4 nanomaterials porous topologies, improving gas sensing properties. • Co 3 O 4 nanomaterials exhibit exceptional stability, ensuring long-term gas sensing reliability. [ABSTRACT FROM AUTHOR]

Designing of semiconductor metal oxide based gas sensors for detection of toxic analytes describes a facile strategy to address the challenges of environmental contamination and human health. Semiconductor Metal Oxides (SMO) gained the interest of contemporary science for their remarkable characteristics like large surface area, tunable chemical properties, controllable size and good redox behaviour. The excellent properties of metal oxides have been widely explored in environmental remediation, medical diagnostics, food industry, communication sector, defense sector etc., SMO shown good prospects in trace contaminant detection of toxic analytes and are been widely used as sensing materials due to their long term stability, cost-effectiveness, simple fabrication and good sensing response. Among various SMO the Indium Oxide (In 2 O 3) is found to be good sensing material and has attracted significant attention due its stable physiochemical properties, high thermal stability and good redox behaviour. In this review, the prospects of In 2 O 3 in detection of various toxic analytes, its interaction with hazardous gases, chemisorption capability of oxygen, have been discussed. Moreover, the protocols related to synthesis of In 2 O 3 nanostructure and possible routes of enhancement of sensing performance have also been discussed. We also discussed the possible interactions between metal-organic frameworks (MOFs) of In 2 O 3 and their excellent gas-sensing performance in detail. Furthermore, the future prospects of In 2 O 3 -based sensors along with consensus recommendations are also discussed. [Display omitted] • Overviews recent studies on indium oxide heterostructure-based gas sensor • Resumes the advantages of properties of indium oxide heterojunctions • Highlight progresses and summarizes the data on indium oxide base gas sensing • Critically proposes paths of future research and application trends in field of gas sensor [ABSTRACT FROM AUTHOR]

The detection of small quantities of hazardous and flammable gases at room temperature is crucial for protecting human health and the environment. In this study, the indium oxide (In 2 O 3) and MXene (Ti 3 C 2) were prepared separately using different techniques and then combined to form a composite through sonication in an ethanol solution. The findings from the gas-sensing performance revealed that the In 2 O 3 /Ti 3 C 2 nanocomposites had very high response values of 3785.01 and 33.84 towards 100 and 10 ppm NO 2 gas at the optimal working temperature (150 °C) respectively. The In 2 O 3 /Ti 3 C 2 -1 composite has a strong linear relation (R2 = 0.9869), it is reproducible and has prolonged detection stability. The occurrence of oxygen vacancies and the creation of Schottky barriers are principally responsible for the outstanding gas-sensing capabilities reported. The computed response and recovery times were 24 and 56 s respectively under 100 ppm NO 2 environment showing strong selectivity toward the gas. This research combines density function theory (DFT) to investigate the room-temperature gas sensitivity of indium oxide-MXene nanocomposites, shedding new light on how to optimize the materials for practical applications in wearable and low-energy consumption devices. [Display omitted] • Facile synthesis of In 2 O 3 @MXens nanosheets for efficient detection of NO 2 gas with ultimate senor stability. • High specific surface area, porosity and multi-metallic ions sustenance with 2D nanostructures. • DFT simulation for adsorption energy to fully understand gas-sensing mechanism. • The fabricated gas sensor proved to be potential practical applicant in low-energy consumption devices. [ABSTRACT FROM AUTHOR]

In an effort to develop a long-lasting gas sensor, this article presents titanium nitride (TiN) as a potential substitute sensitive material in conjunction with (copper(II) benzene-1,3,5-tricarboxylate) Cu-BTC-derived CuO. The work focused on the gas-sensing characteristics of TiN/CuO nanoparticles in detecting H 2 S gas at various temperatures and concentrations. XRD, XPS, and SEM were utilized to analyze the composites with varied Cu molar ratios. The responses of TiN/CuO-2 nanoparticles to 50 and 100 ppm H 2 S gas at 50 °C and 250 °C are 34.8 and 60.0, respectively. The related sensor had high selectivity and stability towards H 2 S, and the response of TiN/CuO-2 is still 2.5–5 ppm H 2 S. The gas-sensing properties as well as the mechanism are fully explained in this study. TiN/CuO might be a choice for the detection of H 2 S gas, opening up new avenues for applications in industries, medical facilities, and homes. [Display omitted] • Synthesis of unique double-shelled hollow MOF based TiN–CuO nanoparticles by a simple method. • High specific surface area, porosity and multi-metallic ions sustenance with clustered nanostructures. • The fabricated sensor exhibits high selectivity and response towards H 2 S gas. [ABSTRACT FROM AUTHOR]

Wurtzite zero dimensional ZnS nanospheres and random-shaped nanoparticles successfully synthesized via a low temperature hydrothermal route. The formation of nanostructures is attributed due to PVP and thiourea and discussed in details. The as-prepared nanostructures were characterized by XRD, EDS, SEM and HRTEM. Based on experimental results, a plausible growth mechanism is also proposed along with crystal structure of ZnS. The gas–sensing properties of as–prepared ZnS products are tested using efficient substrate sensors via an intelligent gas testing system. Both at room and 100–400 °C temperature, high response and selectivity towards formaldehyde than other gases is observed. Comparative studies of ZnS nanostructures for different concentrations of formaldehyde gas and definite sensor-stability for different gases is studied, as well. [ABSTRACT FROM AUTHOR]

Considering that H 2 S is a hazardous gas that poses a significant risk to people's lives, research into H 2 S gas sensors has garnered a lot of interest. This work reports a CuO/ZnO multifaceted nanostructures(NS) created by heat treating Cu2+/ZIF-8 impregnation precursors, and their microstructure and gas sensing characteristics were examined using various characterization techniques (XRD, XPS, SEM, TEM, and BET). The as-prepared hollow CuO/ZnO multifunctional nanostructures had a high gas response value (425@50 ppm H 2 S gas), quick response and recovery times (57/191s @20 ppm), a low limit of detection (1.6@500 ppb H 2 S), good humidity resistance and highly selective towards H 2 S gas. The hollow CuO/ZnO multifaceted nanostructures possessed enhanced gas sensing capabilities which may be related to their porous hollow nanostructures, the manufactured p-CuO/n-ZnO heterojunctions, and the spillover effect between CuO and H 2 S. [Display omitted] • Facile synthesis of multifaceted Cu2+/ZIF-8 nanostructures for efficient detection of H 2 S gas with ultimate senor stability. • High specific surface area, porosity and bi-metallic ions sustenance with polyhedral nanostructures. • Heterojunction aided high selectivity and response of fabricated sensor towards reducing gas H 2 S. [ABSTRACT FROM AUTHOR]

The detection of hydrogen sulfide (H 2 S) is critical because of its potential harm and widespread presence in the oil and gas sectors. The zeolitic imidazolate framework-8 (ZIF-8) derived ZnO nanostructures manufactured as gas sensors have exceptional sensitivity and selectivity for H 2 S gas. In/Zn-ZIF-8 template material was synthesized by a simple one-step co-precipitation method followed by thermal annealing in air. The heat treatment resulted in In 2 O 3 / ZnO nanostructures with mixed heterostructures. The crystal structure (XRD), morphology (SEM/TEM), chemical state (XPS), surface area (BET), etc were investigated to ascertain the nature of the as-prepared material. SEM imagery revealed that the as-prepared In 2 O 3 / ZnO sensitive material had a microstructure of porous hollow nanocages with an average particle size of about 200 nm, which is beneficial to the diffusion and adsorption of gas molecules. The gas sensing performance test results of the In 2 O 3 / ZnO hollow nanocages show that their response to H 2 S gas is significantly improved 67.5 @50 ppm H 2 S (about 11 times that of pure ZnO nanocages) at an optimal temperature of 200 °C, better selectivity, lower theoretical detection limit and good linearity between gas concentration and response values. The enhanced gas sensing feat to H 2 S gas is mainly attributed to the formation of n-n heterojunction and the wide surface area of the newly formed In 2 O 3 / ZnO porous hollow nanocages. [Display omitted] • One-step self-sacrificing template synthesis of In 2 O 3 /ZnO nanocages with high stability for effective detection of H 2 S gas. • The porous hollow nanostructures provide high specific surface area, porosity, and abundant active sites. • For H 2 S gas at lower ppm, the sensor demonstrated higher responsiveness, selectivity, and stability. [ABSTRACT FROM AUTHOR]

Indium oxide (In 2 O 3) gas sensors are regarded as one of the potential materials for detecting and quantifying hazardous gases for monitoring systems and public safety assurance to address the severe environmental problems plaguing our civilization. In this work, In 2 O 3 /PANI composites were synthesized using the hydrothermal technique to explore nitrogen dioxide (NO 2) sensing capabilities. The scanning electron micrographs (SEM), crystal structures (XRD), energy dispersive X-ray analysis (EDS), and the gas sensing properties were investigated to ascertain the morphology, purity, response/recovery time, optimal temperature, and recyclability. The samples displayed a gas-accessible structure with stacks of several porous nanosheets. The as-synthesized In 2 O 3 /PANI-1 sensors have extremely high responses (341.5 @ 30 ppm, 12.8 @ 3 ppm) to NO 2 gas at a working temperature (250 °C), quick response times (24 s @ 30 ppm, 47 s @ 3 ppm) and recovery times (53 s @ 30 ppm, 74 s @ 3 ppm), and a low detection limit (300 ppb). Following a series of testing, high repeatability and selectivity were obtained. Furthermore, the In 2 O 3 /PANI sensor's fundamental detecting mechanism for NO 2 gas was completely discussed. In addition, a developed mechanism defining the performance of the nanosheet-based sensors in NO 2 gas is shown, which is backed by density functional theory (DFT) calculations to investigate the electrical characteristics of In 2 O 3 /PANI composites. This work offers an intriguing perspective as well as a useful strategy for fabricating long-lifetime In 2 O 3 -based nanosheets using the hydrothermal process. [Display omitted] • Synthesis of unique hollow In 2 O 3 /PANI Nanosheets Clusters by a simple method. • High specific surface area, porosity and synergistic benefit sustained with clustered nanostructures. • Detailed DFT calculations for gas sensing mechanism in adsorptions. • The fabricated sensor exhibits high selectivity and response towards NO 2 gas. [ABSTRACT FROM AUTHOR]

Regular hexagonal embedded ZnO nanorods were successfully prepared by a simple hydrothermal method. The addition of urea as a homogeneous precursor was found to play a vital role in the embedding of secondary nanorods. The nanostructures were characterized by XRD, SEM, and EDS. The gas-sensing properties of secondary grown embedded nanorods were reported for formaldehyde, ethanol, methanol, acetone, and ammonia at different concentrations and temperatures. A higher response and greater selectivity toward formaldehyde than other gases was observed. A sharp response with the best recovery time was achieved at an optimum temperature of 200 °C. [ABSTRACT FROM AUTHOR]

ZnO nanodisks exhibiting regular hexagonal structures were successfully synthesized using two surfactants via a hydrothermal method. The surfactants, namely, cetyltrimethylammonium bromide and sodium dodecyl sulfate, had vital functions in the formation of nanodisk structures. The fabricated ZnO nanodisk-based sensor was exposed to reductive gases. The performance of the developed gas sensor to formaldehyde was superior than that to ethanol. The highest sensitivity values for formaldehyde and ethanol (150 ppm) were 81.6 and 43.2, respectively, at an optimal temperature of 300 °C. [ABSTRACT FROM AUTHOR]

Abstract: Hexagonal ZnO nanocones were successfully prepared using a controlled hydrothermal method with the assistance of double anionic surfactants. The products were characterized using X-ray powder diffraction. The morphologies of ZnO nanostructures were characterized using field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The effects of the addition of one anionic to another anionic reagent in the crystal structure formation were discussed in detail. The gas sensing properties were measured for formaldehyde. [Copyright &y& Elsevier]

Abstract: Morphological transformation was achieved from ZnO hexagonal needle-like rods to hexagonal flower-like rods by varying the reaction growth time using the hydrothermal method. Optical bandgap energies were calculated from the absorption spectra using UV‐vis spectroscopy. Gas sensing properties of flower-like hexagonal ZnO structures at 50ppm for ethanol (C2H5OH) and nitrogen dioxide (NO2) at different temperatures were analyzed. The sensor showed a higher response toward C2H5OH than NO2 gas at 350°C. [Copyright &y& Elsevier]

We have successfully reported a new diamond-like morphology of zinc oxide (ZnO) structures via a simple hydrothermal method and discussed its probable growth mechanism. Compared with other morphologies of ZnO structures (microrods and nanosheets), nanodiamonds have excellent gas-sensing property owning to its large specific surface area, holding the perfect promise for ZnO powders as underlying gas-sensing materials. Furthermore, the as-prepared nanosheets assisted with the sodium citrate as an additive were found to show better gas-sensing property due to the smaller size than microrods. We found the positive role of the sodium citrate and reaction time in the growth of nanosheets and nanodiamonds respectively and the corresponding influences on growth mechanism were discussed. [ABSTRACT FROM AUTHOR]

The structure of metal oxide thin films can greatly affect their gas sensing properties. However, the structure-property relationship has not been fully established for the NO 2 sensing properties of WO 3 thin films. In this study, WO 3 thin films with two distinct structures have been prepared by the sol-gel technique via employing two different precursor sols. Dense and porous WO 3 thin films were successfully prepared as tungsten and WCl 6 was used as the precursor source, respectively. Both WO 3 thin films are exclusively sensitive to NO 2 as low as 80 ppb. Porous WO 3 thin films exhibit higher response toward NO 2 but slower response/recovery kinetics as compared to the dense ones. Hall measurement and electrochromic coloration confirm the higher carrier mobility in the porous WO 3 thin films. The response/recovery kinetics is found to be determined by the gas-solid reaction (receptor function), which is combinedly influenced by the porosity and grain size of the WO 3 thin films. [ABSTRACT FROM AUTHOR]

Nanomaterials offer a wide range of applications in environmental nanotechnology. Hazardous pollutants in the environment are needed to be detected and controlled effectively to avoid human health risks. In this paper, we described the fine-controlled growth of In 2 O 3 nanoparticles embedded on GO nanosheets by a facile precipitation method. The In 2 O 3 @GO nanocomposites exhibited outstanding gas sensing performance as compared with pure In 2 O 3 nanoparticles towards NO 2. At 225 °C, the sensor displayed high selectivity, best response (78) to 40 ppm NO 2 , quick response, and recovery times of 106s/42s. The improved sensing performances of the nanocomposite were attributed to large surface area, high gas adsorption-desorption capability, and the formation of p-n heterojunctions between In 2 O 3 nanoparticles and GO nanosheets. The excellent gas detecting activities validate In 2 O 3 @GO nanocomposites as a promising candidate in the NO 2 gas sensor industry. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO 2) exposure can have several adverse health impacts on people, especially the respiratory system. Low selectivity, a lack of long-term stability, and structural and morphological optimization are some challenges associated with using ZnO for NO 2 gas sensing. Therefore, we intended copper (Cu) doping in ZnO to alter its shape and gas-sensing characteristics. This study explores the synthesis, properties, and gas-sensing capabilities of bitter gourd-shaped Cu-doped zinc oxide (ZnO) nanostructures for the detection of nitrogen dioxide (NO 2). A facile hydrothermal synthesis method was employed to synthesize bitter gourd-shaped Cu-doped ZnO nanostructures and comprehensively characterized by several techniques. Comprehensive characterizations of our produced Cu-doped ZnO nanomaterial demonstrated by X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS), and different energy spectrum. The material was annealed at 400 °C in a controlled dry air environment to improve its suitability for gas sensor applications. A series of temperature-ranging experiments were conducted to get gas-sensing readings from 25 °C to 300 °C. The resulting sensor, founded upon the distinctive morphology of Cu-doped ZnO structures reminiscent of the intricate shape of bitter gourd, unveiled good selectivity with a pronounced affinity for detecting NO 2 gas. Notably, the zenith of its performance was attained at an operating temperature of 200 °C, where its selectivity and sensitivity were most pronounced. Even at a low concentration of 1 ppm, the sensors displayed a maximum response of 3.7, highlighting their high sensitivity. The sensors demonstrated excellent reproducibility, selectivity, and a low detection limit. These findings position bitter gourd-shaped Cu-doped ZnO nanostructures as promising candidates for NO 2 sensing applications across diverse environments. [ABSTRACT FROM AUTHOR]

Timely detection of harmful, poisonous and air pollutant gases is of vital importance to the protection of human beings from exposure to rigorous gases. The development of gas-sensing devices based on sphere-like porous SnO 2 /ZIF-8 nanocomposites is required to overcome this challenge. Nanostructures with high surface area, more porosity and hollow interior provide plenty of active cites for high responses in metal oxide gas sensors. The engineered gas sensors have excellent sensing sensitivity (164), rapid response and recovery times (60, 45 s), and favorable selectivity for NO 2 gases under 300 °C. Consequently, NO 2 gas sensors based on core-shell SnO 2 /ZIF-8 nanospheres are regarded viable capacity industrial applicants. [Display omitted] • Synthesis of Core-shell SnO2/ZIF-8 nanostructures by a via solvothermal method. • High specific surface area, porosity and bimetallic ions sustenance enrich sensing. • ZIF-8 MOF sensor exhibits high selectivity and response towards NO2 gas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Theoretically screening MoSe 2 /Co 3 O 4 system based on the interfacial binding and band edge. • The as-fabricated MoSe 2 /Co 3 O 4 heterostructure exhibits good sensitivity to NO 2 at RT. • Enhanced charge-separation efficiency contributes to the excellent gas sensitivity. • Combining simulations and experiments promises candidate selection for gas sensors. Heterogeneous engineering is an efficient method to overcome the poor adsorption performance of MoSe 2 materials. In this work, the screening process for a suitable transition metal oxide semiconductor with 3 d orbital (3 d –TMOS) was performed based on the work of adhesion and band edges positions with reference to the MoSe 2 material. Then, the gas sensor performance of the suitable composite system was further tested and discussed. The results show that the Cr 2 O 3 , Fe 2 O 3 and Co 3 O 4 surface present good interfacial binding strength with MoSe 2 compared with other 3 d –TMOSs. And the MoSe 2 /Co 3 O 4 system was selected considering the suitable band edges positions. The as-fabricated MoSe 2 /0.5–Co 3 O 4 nanocomposite exhibits excellent sensitivity to NO 2 at room temperature. Moreover, the MoSe 2 /0.5–Co 3 O 4 nanocomposite exhibits excellent linear response (R 2 = 0.985), selectivity, repeatability, and long–term stability to NO 2. The improvement mechanism of gas sensor performance can be mainly attributed to the fast charge extraction rate of type-II heterojunction and greatly sensitive of built-in potential barrier to the carrier density in the MoSe 2 /0.5–Co 3 O 4 nanocomposite. This research provides a promising method to select the candidates for gas sensor using the combined DFT calculations and experiments. [ABSTRACT FROM AUTHOR]

The rapid increases in environmental hazardous gases have laid dangerous effects on human health. The detection of such pollutants gases is mandatory using various optimal techniques. In this paper, porous multifaceted Co 3 O 4 /ZnO nanostructures are synthesized by pyrolyzing sacrificial template of core-shell double zeolitic imidazolate frameworks (ZIFs) for gas sensing applications. The fabricated exhibit superior gas sensor response, high selectivity, fast response/recovery times, and remarkable stability and sensitivity to H 2 S gas. In particular, the multifaceted Co 3 O 4 /ZnO nanostructures show a maximum response of 147 at 100 ppm of H 2 S under optimum conditions. The remarkable gas sensing performances are mainly ascribed to high porosity, wide surface area multifaceted nanostructures, presence of heterojunctions and catalytic activity of ZnO and Co 3 O 4 , which are beneficial for H 2 S gas sensors industry. [Display omitted] • Multifaceted Co 3 O 4 /ZnO nanostructures were prepared via MOF template. • A maximum response was147 at 250 °C for 100 ppm of H 2 S gas. • Sensor exhibited superior response, selectivity and stability for H 2 S gas. [ABSTRACT FROM AUTHOR]

The remarkable electrical conductivity, abundance of surface functional groups, and large specific surface area make 2D MXenes-based heterostructures highly promising for room temperature gas sensing applications. However, these MXenes-based heterojunctions composed of different materials may suffer from issues, such as crystal incompatibility and bandgap mismatch. Herein, the {001}TiO 2- x /Ti 3 C 2 T x composite was prepared in situ by hydrothermal process and subsequent annealing. The {001} facets of TiO 2 and oxygen vacancies that provide a heightened exposure of active sites in the composite and more gas diffusion channels, as well as the formation of Schottky barriers between {001}TiO 2 nanosheets and Ti 3 C 2 T x , can synergistically enhance the gas performance. The experimental results show that the {001}TiO 2- x /Ti 3 C 2 T x composite exhibits 1.9 and 27.5 times higher than the {001}TiO 2 /Ti 3 C 2 T x composite and pristine Ti 3 C 2 T x to 10 ppm NO 2 at room temperature, respectively. Moreover, the {001}TiO 2- x /Ti 3 C 2 T x composite presents the great linear response (R2 = 0.99509), selectivity, repeatability and long-term stability to NO 2. Density functional theory (DFT) calculations reveal the strong interactions between the {001}TiO 2- x /Ti 3 C 2 T x and NO 2 , indicating excellent sensitivity and selectivity of the composite material towards NO 2. This work provides an effective way to construct a series of oxygen-defective Ti 3 C 2 T x -based composites with exposed high-energy facets for enhanced gas sensing performances. • First synthesis of {001}TiO 2- x /Ti 3 C 2 T x composite. • Room-temperature and light-activation-free detection of ppb-level NO 2. • Synergistic effects of high energy facets, oxygen vacancy and Schottky barrier. • Outstanding gas-sensing performance towards NO 2. [ABSTRACT FROM AUTHOR]

In this comprehensive study, Ce-doped ZnO nanostructures were hydrothermally synthesized with varying Ce concentrations (0.5%, 1.0%, 1.5%, and 2.0%) to explore their gas-sensing capabilities, particularly towards NO 2. Structural characterization revealed that as Ce doping increased, crystal size exhibited a slight increment while band gap energies decreased. Notably, the 0.5% Ce-doped ZnO nanostructure demonstrated the highest NO 2 gas response of 8.6, underscoring the significance of a delicate balance between crystal size and band gap energy for optimal sensing performance. The selectivity of the 0.5% Ce-doped ZnO nanostructures to NO 2 over other gases like H 2 , acetone, NH 3 , and CO at a concentration of 100 ppm and an optimized temperature of 250 °C was exceptional, highlighting its discriminatory prowess even in the presence of potential interfering gases. Furthermore, the sensor displayed reliability and reversibility during five consecutive tests, showcasing consistent performance. Long-term stability testing over 30 days revealed that the gas response remained almost constant, indicating the sensor's remarkable durability. In addition to its robustness against humidity variations, maintaining effectiveness even at 41% humidity, the sensor exhibited impressive response and recovery times. While the response time was swift at 11.8 s, the recovery time was slightly prolonged at 56.3 s due to the strong adsorption of NO 2 molecules onto the sensing material hindering the desorption process. The study revealed the intricate connection between Ce-doping levels, structure, and gas-sensing. It highlighted the 0.5% Ce-doped ZnO nanostructure as a highly selective, reliable, and durable NO 2 gas sensor, with implications for future environmental monitoring and safety. [Display omitted] • Pure ZnO and Ce-doped ZnO nanostructures were hydrothermally synthesized and characterized. • 0.5% Ce-doped ZnO demonstrated superior NO 2 gas response, emphasizing critical doping levels for optimal sensing. • High gas response of 8.6–100 ppm NO 2 at optimal temperature of 250 °C with fast response and recovery times. • Consistent performance over five tests and stability over 30 days highlighted the gas sensor's reliability. • Robust against humidity, effective at 41%, emphasizing practical applicability. [ABSTRACT FROM AUTHOR]

A new NiO/CdS-CdO composite-based chemiresistive gas sensor for NO 2 detection exhibits temperature-driven adsorption switching. In-situ CdS nanoparticle growth on Ni-based metal-organic framework (MOF) spheres produced Ni-MOF/CdS, and then calcinating the Ni-MOF/CdS in air yielded NiO/CdS-CdO composite. The composite's NO 2 sensing characteristics were examined at 25–350 °C, demonstrating that the NiO/CdS-CdO composite switches from n- to p-type above 200 °C with strong NO 2 sensitivity and selectivity. Adsorption switching allows the NiO/CdS-CdO composite to serve as a dual-mode sensor, where NiO and CdS-CdO dominate at higher temperatures (>200 °C) and lower temperatures (≤200 °C) with realistic detection ability, respectively. This switching is mainly caused by variations in charge carrier concentration and NO 2 adsorption/desorption behavior on the composite surface. At 150 °C, NiO/CdS-CdO sensors have a low detection limit of 100 ppb, high response (R g /R a , ∼215), quick response time (∼47 s), and recovery time (∼66 s) at 100 ppm. FTIR analysis, estimation of activation energies, and a qualitative comparison of n- to p-type transition with a typical full-wave rectification process explain the adsorption switching phenomenon. Adsorption switching in NiO/CdS-CdO-based gas sensors with great repeatability, stability, and fast response may be a promising route for high-performance gas sensing applications. [Display omitted] • Synthesis of a novel hybrid NiO/CdS-CdO composite for NO 2 detection. • Temperature-driven adsorption switching behavior leads to n- to p-type transition. • Superior gas sensing performance over a wide temperature range. • Valuable insights for the development of advanced dual-mode NO 2 gas sensors. [ABSTRACT FROM AUTHOR]

Highly selective and sensitive detection to toxic and hazardous gases with low concentrations is important, but difficult to detect ppb-level NO 2 or slow response & recovery hinders the practical applications of the In 2 O 3 -based composites in the detection of NO 2 to a great extent. In this work, we synthesized the pristine In 2 O 3 and Au-decorated In 2 O 3 (Au-In 2 O 3) microcubes by hydrothermal method using F-127 as a template agent. The experimental results reveal that the Au-In 2 O 3 -0.5 sample exhibits the best /Auresponse of 26.5 to NO 2 of 2 ppm at the optimum test temperature of 200 °C, with respective response and recovery time of 50 and 52 s. Moreover, the lowest detection concentration (LDC) arrives at 10 ppb. In particular, the low concentrations of NO 2 can be detected at room temperature. Moreover, the Au-In 2 O 3 sample presents excellent linear response (R2 =0.99015), selectivity, reproducibility, and stability to NO 2. The improvement mechanism of gas sensitivity is also briefly discussed, which can be mainly ascribed to the spillover effect from Au nanoparticles and the surface reaction. This research provides a promising candidate gas sensing material sensitive to NO 2 with low concentration. [Display omitted] • First synthesis of Au-In 2 O 3 microcubes by hydrothermal method using F-127 as a template agent. • Good overall gas-sensing performance. • Room-temperature detection of ppb-level NO 2. • Demonstration of good sensitivity and selectivity by experiments and DFT calculations. [ABSTRACT FROM AUTHOR]

Hierarchical three dimensional MoS 2 nanostructures composed of small sheet-like nanostructures are successfully prepared using a simple two-step hydrothermal process with sodium dodecyl sulfate (SDS), as a surface modifier. The as-preparedMoS 2 nanospheres are characterized by XRD, BET, XPS, EDS, SEM and HRTEM. The gas–sensing properties of as–prepared MoS 2 nanostructures are tested at 175–230 °C temperatures for 50–500 ppm concentration range, using an efficient ceramic-tube sensor system via an intelligent gas testing system. A high response and selectivity towards carbon monoxide than other gases is observed. Comparative studies of MoS 2 nanostructures for different concentration of carbon monoxide gas and definite sensor-stability for different gases are studied, as well. The sensor fabrication and sensing mechanism is discussed as well. [ABSTRACT FROM AUTHOR]

Realizing room-temperature detection to low concentrations of hazardous gases can not only contribute to the long-term stability and low power consumption of gas sensors, but also benefit the life and health of human being. In this work, we firstly fabricated mulberry-like Cu 2 O/CuO composites by one-pot hydrothermal method. The optimized Cu 2 O/CuO nanocomposite exhibits the outstanding room-temperature sensitivity to NO 2 , such as the higher response, shorter response & recovery time, and lower detection threshold. Specifically, the room-temperature responses (ΔR/Ra) arrive at 19.3%, 62.3%, 70.9% and 82.0% to 0.01, 0.1, 1 and 10 ppm NO 2 , and the response & recovery time are 58 and 250 s while employing 0.1 ppm NO 2 , respectively. Furthermore, the optimized Cu 2 O/CuO composite presents excellent selectivity and reproducibility, good long-term stability to NO 2 , and non-monotone humidity dependence of response. Specifically, the fluctuations of response are less than 1.5% to 0.1 – 1 ppm NO 2 after five cycles, and ∼2% and 3% to 0.1 and 0.5 ppm NO 2 for 30 consecutive days, respectively. Finally, the gas sensing mechanism is also proposed based on the microstructure and microchemistry of the optimized Cu 2 O/CuO composite, the redox reactions on the surface, and the formation of p-p heterojunction. This work provides a promising candidate material for room-temperature detection of NO 2. [Display omitted] • First synthesis of mulberry-like Cu 2 O/CuO composites. • In-situ formation of p-p heterojunction. • Outstanding room-temperature sensitivity to NO 2. • Excellent selectivity, reproducibility and long-term stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • First synthesis of ZnO 1-X /Ti 3 C 2 composite with rich oxygen vacancies. • Room-temperature detection of ppb-level NO 2. • Synergistic effects of oxygen vacancy and Schottky barrier. • Outstanding gas-sensing performance towards NO 2. Room-temperature detection of low concentrations of toxic and harmful gases is of great significance for the health and life of human being and contributes to long-term stability and low power consumption of gas sensors. In this work, we firstly prepared a ZnO 1- x /Ti 3 C 2 composite with rich oxygen vacancies by a hydrothermal process and subsequent annealing in hydrogen atmosphere. The experimental results reveal that the ZnO 1- x /Ti 3 C 2 composite exhibits very high responses (ΔR/R a) of 0.03, 0.21 and 2.28 to 0.01, 1 and 10 ppm NO 2 at room temperature, among which the response to 10 ppm NO 2 is 2.3 and 14.2 times higher than those of ZnO/Ti 3 C 2 composite and pristine Ti 3 C 2 , respectively. Moreover, the ZnO 1- x /Ti 3 C 2 composite presents good linear response (R2 = 0.99509), reproducibility and long-term stability to NO 2. The outstanding NO 2 sensing properties of ZnO 1- x /Ti 3 C 2 composite are mainly attributed to the presence of abundant oxygen vacancies and the formation of ZnO 1- x /Ti 3 C 2 Schottky barrier. Both the gas responses and calculated adsorption energies of ZnO 1- x /Ti 3 C 2 and ZnO/Ti 3 C 2 composites to NO 2 , NH 3 , CO, HCHO and acetone demonstrate the high selectivity of the ZnO 1- x /Ti 3 C 2 composite to NO 2. This work provides a new perspective on enhancing the room-temperature gas sensitivity of MOS-containing composites by constructing oxygen vacancies and heterojunction. [ABSTRACT FROM AUTHOR]

We report synthesis of hierarchical SnO 2 nanostructures by a facile hydrothermal method. Extensive structural characterizations demonstrate that the well-defined hierarchical nanostructures are composed of numerous one-dimensional nanorods, the diameter and density of which can be precisely tailored by adjusting the dosage of NaOH. Interestingly, with more NaOH added, smaller and denser nanorods are formed, which is consistent with the assumption. We proposed that the nucleation process was facilitated in such case leading to all-direction rapider growth. Moreover, the nucleation process could be started by the decomposition of preformed ZnSn(OH) 6 induced by alkali etching. Based on the comparative experiments, a possible growth mechanism for hierarchical SnO 2 nanostructures has been proposed and discussed in detail. The gas sensing properties of the as-prepared hierarchical SnO 2 nanostructures were all tested. It was found that the S3 sample which assembled with smallest and densest nanorods showed the excellent sensitivities toward ethanol. [ABSTRACT FROM AUTHOR]

Novel urchin-like SnO 2 nanostructures were prepared by a facile hydrothermal process. The well-defined nanostructures were composed of numerous one-dimensional nanowires with a diameter of ∼8–10 nm. Based on comparative studies, a possible formation mechanism was proposed in detail. It was believed that the nucleation was initiated by formation of ZnSn(OH) 6 . Furthermore, gas-sensing measurement indicated that the urchin-like SnO 2 nanoflowers showed excellent gas-sensing properties. [ABSTRACT FROM AUTHOR]

Here, we firstly synthesized SnO 2 /Ti 3 C 2 composites with Schottky and surface heterojunctions via a hydrothermal oxidation process to lower the operation temperature of SnO 2 -based gas sensors and increase the response of Ti 3 C 2 -based gas sensors simultaneously. The SnO 2 nanoparticles are mainly surrounded by {221} and {110} facets by controlling the HCl content, and a surface heterojunction is formed inside SnO 2 due to the difference in energy band structure between {221} and {110} facets. The synergistic effect of the SnO 2 /Ti 3 C 2 Schottky heterojunction and SnO 2 {221}/{110} surface heterojunction can accelerate electron transport and thus enhance sensitivity to NO 2. Under a moderate pulse heating (100 °C) during desorption process, the optimal SnO 2 /Ti 3 C 2 composite presents the outstanding responses (ΔR/R a) of 0.02, 0.83 and 1.57 to 0.05, 5 and 10 ppm NO 2 at room temperature, respectively. Moreover, the optimal SnO 2 /Ti 3 C 2 composite exhibits the excellent linear response (R2 = 0.99729) and good recycling performance and selectivity to NO 2. This work provides an idea for synergistically improving the gas-sensing performance of MXene by in-situ constructing double heterojunctions. • First synthesis of SnO 2 /Ti 3 C 2 composites with Schottky and surface heterojunctions. • Tuning the SnO 2 {221}/{110} surface heterojunction by altering HCl content. • Enhancing room-temperature NO 2 -sensing performance by the synergistic effect. • To restore the desorption process by a moderate pulse-heating treatment. [ABSTRACT FROM AUTHOR]

Monodisperse WO 3 ·H 2 O square nanoplates were controlled synthesized under hydrothermal conditions with the adding of malic acid. The powders obtained under two different hydrothermal reaction times were characterized by X-ray powder diffraction (XRD) field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The thickness of the nanoplates would increase due to the prolongation of reaction time. In addition, the differences of exposure of crystal facets of this orthorhombic WO 3 ·H 2 O square nanoplates were researched and its influence on the gas sensing properties were also discussed. Gas sensor based on the two obtained WO 3 ·H 2 O square nanoplates powders was prepared and the gas responses to serious concentrations of C 2 H 5 OH gas were carried out. These kinds of nanoplates show excellent ethanol gas sensing and it can be influenced by the crystal facet percentage in nanoplates. This works show great significance to the control synthesis of semiconductor metal oxides and their applications in gas sensor research. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, sub-micron porous WO3 spheres with uniform size were firstly prepared by the hydrolysis of WCl6 using carbon microspheres as templates in the hydrothermal system and the following heating treatment. The carbon template, precursor, and the final products were characterized by XRD, SEM, TEM and BET analysis. The as-prepared sub-micron porous WO3 spheres had a large diameter of about 200nm, which is critically determined by the size of carbon templates and WO3·H2O/C precursor. In addition, these porous spheres have a large porosity and exhibit high gas sensitivity to alcohol in different concentrations. The facile preparation method and the improved properties derived from the porous spheres structures are significant in the synthesis and future applications of functional nanomaterials. [Copyright &y& Elsevier]

Abstract: Materials with hierarchical and porous architectures often take on novel functional features. Here, we fabricate successfully the Zn4(OH)6CO3·H2O (ZCHH) microspheres which consist of the nanoflakes by using a simple hydrothermal process, and demonstrate that the ZCHH precursor can be transformed utterly to ZnO porous microspheres after calcination. Further comparative studies reveal that both urea and MEA play a critical role in producing such unique porous microspherical architecture. The likely formation mechanism of the porous microspheres is proposed based on the time-dependent experiments. As a consequence of the unique hierarchical and porous architecture, the microspheres show a large specific surface area due to the remarkable amount of petals and pores on them and therefore excellent gas-sensing properties. [Copyright &y& Elsevier]