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Portable and sensitive mixed-potential type solid-state electrolyte (MPSE) gas sensors can detect exhaled biomarkers in a noninvasive and inexpensive way, which is significant for convenient disease diagnosis and saving medical resources. However, high working temperature is still one of the main bottlenecks for hindering MPSE gas sensors' applications in disease diagnosis. Here, we, for the first time, developed and fabricated new room-temperature MPSE gas sensors utilizing K2Fe4O7 electrolyte and Ni/Fe-MOF (Ni/Fe clusters are coordinated with 1,4-H2BDC) sensing electrodes (SEs) for the detection of ppb-level NO. Among different MOF SEs, the sensor attached with the Ni-MOF SE presents the highest NO sensitivities. This is attributed to a reducing oxygen reduction reaction activity and enhancing NO electrochemical catalytic reaction activity, verified by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests. In addition, the presented sensor also shows a low detection limit (20 ppb), fast response/recovery characteristic (17 s/6 s to 50 ppb NO), excellent selectivity, acceptable repeatability, and long-term stability of 34 days to NO at 25 °C and 60%RH. Simultaneously, the mechanism of humidity effect on the sensing performance was investigated by EIS and CV tests. Our work provides new insight into the development of room-temperature solid-state electrolyte gas sensors based on the mixed-potential mechanism and enlarges the potential application domain.

Yttrium-stabilized zirconia (YSZ)-based mixed potential-type NOx sensors have broad application prospects in automotive exhaust gas detection. Great efforts continue to be made in developing high-performance sensitive electrode materials for mixed potential-type NO2 gas sensors. However, only five kinds of new sensing electrode materials have been developed for this type of gas sensor in the last 3 years. In this work, four different tree-based machine learning models were trained to find potentially sensitive electrode materials for NO2 detection. More than 400 materials were selected from 8000 materials by the above machine learning models. To further verify the reliability of the model, 13 of these materials containing unexploited elements were selected as sensitive electrode materials for making sensors and testing their gas-sensing performances. The experimental results showed that all 13 materials exhibited good gas-sensing performance for NO2. More interestingly, an electrode material BPO4, which does not contain any metal elements, was also screened out and showed good sensing properties to NO2. In a short period of time, 13 new sensitive electrode materials for NO2 detection were targeted and screened, which was difficult to achieve by a trial-and-error procedure.

Lipid droplets (LDs) are important cellular organelles associated with many physiological processes. To visualize and study LDs, particularly the nascent LDs (diameters of 30–60 nm), super-resoluti...

A series of different facile modification layers (MLs) was designed to gradually increase the electrochemical sensing performance of glassy carbon electrode (GCE) for simultaneously detecting Pb2+ and Cu2+. ML designs were mainly a different combination of ZIF-67, MWCNT and Nafion, and their different electrochemical sensing performances were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave stripping voltammetry (SWSV) and chronocoulometry. The fabricated sensor, which modified with ZIF-67/MWCNT and Nafion layer, exhibited the biggest response peak current to Pb2+ and Cu2+. In addition, it displayed a wide linear detection range of 1.38 nM–5 μM for Pb2+ and 1.26 nM–5 μM for Cu2+, a detection accuracy of about 1 nM for both Pb2+ and Cu2+, and an excellent stability for both Pb2+ and Cu2+. We also analyzed the real water sample taken from Changchun’s Sanjia Lake and Yan Lake. We believe this ML design provides instruction for building high-performance electrochemical sensing systems.

Portable and sensitive mixed-potential type solid-state electrolyte (MPSE) gas sensors can detect exhaled biomarkers in a noninvasive and inexpensive way, which is significant for convenient disease diagnosis and saving medical resources. However, high working temperature is still one of the main bottlenecks for hindering MPSE gas sensors' applications in disease diagnosis. Here, we, for the first time, developed and fabricated new room-temperature MPSE gas sensors utilizing K

Yttrium-stabilized zirconia (YSZ)-based mixed potential-type NO

In this work, the mixed-potential-type gas sensor based on NASICON solid electrolyte and MMnO3 (M: Gd, Sm, La) sensing electrode (SE) was developed and fabricated aiming at the low-concentration triethylamine (TEA) detection. The research point of the fabricated sensors mainly concentrated on the effect of different A-site elements in MMnO3-SE (M: Gd, Sm, La) on TEA sensing characteristics. The result reveals that the highest response value (−217.5 mV) towards 50 ppm TEA was observed for the device utilizing SmMnO3-SE. The highest electrochemical catalytic activity of the fabricated sensors attached with SmMnO3-SE was further authenticated by the polarization curve measurement. Moreover, the response value displays a segmentally linear relationship with TEA concentrations and the logarithm of TEA concentrations, and the slopes are −49 mV/ppm and −105 mV/decade at the ranges of 0.05–0.5 ppm and 1–50 ppm TEA, respectively. The device could also produce an acceptable response value (−5.6 mV) towards 50 ppb TEA. Moreover, it also displays good repeatability and selectivity, along with steady response signals towards 5 ppm and 50 ppm TEA for 15 days and 1 ppm TEA at different humidity levels.

Here, the porous SnO2/Zn2SnO4 sensing electrode material prepared by facile hydrothermal method was applied to fabricate the mixed-potential-type gas sensor based on yttrium-stabilized zirconia (8 mol% Y2O3-doped ZrO2) solid electrolyte plane substrate for effectively detecting acetylene (C2H2) at 700 °C. In terms of the sensing characteristics of the C2H2 gas sensor, the response value toward 100 ppm C2H2 was -82.3 mV, and the detection limit of C2H2 was lowered to 500 ppb. The ΔV of the sensing device varied piecewise linearly with the logarithm of C2H2 concentration gradient range of 0.5–2 and 5–1000 ppm, with sensitivities of -12 and −56 mV/decade, respectively. In addition, the sensor exhibited good humidity stability, long stability, and selectivity to C2H2 at 700 °C. More interestingly, after high-temperature measurement (700 °C) for 20 consecutive days, the sensor continued to present good response transients, sensitivity, and reproducibility to C2H2. Furthermore, the sensing mechanism of the mixed-potential-type sensor was verified by measuring the polarization curves and complex impedance curves.

Spinel-type oxides have attracted a broad interest in sensing materials research owing to their high catalytic activity and flexibly tunable chemical properties. Here, we report the synthesis of superfine porous NiFe2O4 microspheres by one-step solvothermal approach, in order to fabricate ultra-sensitive acetone sensors for real-time monitoring, relying on the high catalytic activity of NiFe2O4 and effective mass transfer property of porous microspheres structure. The porous NiFe2O4 sensors displayed high selectivity to acetone against other interfering gases, giving a high sensitivity (27.4), fast response time (2 s) towards 100 ppm acetone and low detection limit (200 ppb) at 250 °C. This paper proposed a general approach for fabricating highly sensitive gas sensor based on spinel-type oxides in monitoring volatile organic pollutants.

The development of room temperature NH3 sensors with flexible substrate can fulfill the future demands of high NH3 sensing performance under the premise of lower energy consumption and safety circumstance in wearable electronics field. The polyaniline and a serious of WO3 hollow spheres@ polyaniline hybrid were successfully synthesized via a combined route of simple hydrothermal method and in-situ chemical oxidative polymerization. The room temperature NH3 sensors were fabricated by assembling WO3 hollow spheres@ polyaniline hybrid on flexible polyethylene terephthalate (PET) films. The NH3 sensing properties of the fabricated devices demonstrated that the device utilizing 10 mol% WO3 hollow spheres@ polyaniline (PAWHs 10) hybrid exhibited the best sensing performance to 100 ppm NH3 (response value at 25) at 20 °C. Moreover, the PAWHs10 hybrid sensor also achieved excellent NH3 selectivity, ppb-level detection limit (1.67–500 ppb NH3), and good response/recovery rates (136 s/130 s) at 20 °C. The enhanced sensing performance of incorporation of polyaniline and WO3 hollow spheres was mainly attributed to the hollow structure of WO3 and the formation of p-n heterojunction between PANI and WO3 hollow spheres.

The polycrystalline perovskite SmMO3 (M = Al, Cr, Co) sensing electrode was synthesized by the sol-gel method, and the NASICON-based sensors attached with SmMO3 were designed and fabricated for triethylamine (TEA) detection. This study investigated the effects of different M3+ ions in SmMO3 and various calcination temperatures of the sensing material on TEA sensing properties. The results reveal that compared with the other devices, the sensor attached with SmCrO3 sintered at 800 °C displays a higher response value (−108.2 mV) towards 100 ppm TEA, and that the sensor even detects 2 ppm TEA with an acceptable value (−6 mV). The sensor utilizing SmCrO3 (800 °C) also exhibits pretty swift response and recovery times of 2 and 22 s, respectively, toward 20 ppm TEA. A linear relationship exists between the response values and the logarithm of TEA concentrations, and the sensitivity is −64 mV/decade. At the same time, good repeatability, selectivity, and long-term stability of the sensor are also observed. Furthermore, the sensing mechanism related to the mixed potential model is demonstrated by the polarization curve measurements.

In this study, Sr2MMoO6 (M: Fe, Mg and Ni) were prepared successfully by sol-gel method and used as sensing electrode materials for CeO2-based mixed potential type acetone sensors. Results indicated that the sensor attached with Sr2FeMoO6 sensing electrode exhibited the best sensing characteristic to acetone among all the other sensors in this study, which showed the maximum response value of −147 mV to 100 ppm acetone at 590 °C and the typical 90% response time was about 13 s. The sensitivity of the sensor using Sr2FeMoO6-SE was the largest towards acetone at the range of 5–200 ppm, and the slope of which was −100 mV/decade. Moreover, the sensor could also detect 0.5 ppm acetone with an acceptable value. In addition, the device also exhibited excellent repeatability and humidity stability, good selectivity and stability during 25 days. Besides, the sensing mechanism of the mixed potential type acetone sensor was explained clearly in this study.

Rapid and precise profiling of acetylcholine (ACh) has become important for diagnosing diseases and safeguarding health care because of its pivotal role in the central nervous system. Herein, we developed a new colorimetric sensor based on protein-inorganic hybrid nanoflowers as artificial peroxidase, comprising a test kit and a smartphone reader, which sensitively quantifies ACh in human serum. In this sensor, ACh indirectly triggered the substrate reaction with the help of a multienzyme system including acetylcholinesterase, choline oxidase, and mimic peroxidase (nanoflowers), accompanying the enhancement of absorbance intensity at 652 nm. Therefore, the multienzyme platform can be used to detect ACh via monitoring the change of the absorbance in a range from 0.0005 to 6.0 mmol L-1. It is worth mentioning that the platform was used to prepare a portable agarose gel-based kit for rapid qualitative monitoring of ACh. Coupling with ImageJ program, the image information of test kits can be transduced into the hue parameter, which provides a directly quantitative tool to identify ACh. Based on the advantages of simple operation, good selectivity, and low cost, the availability of a portable kit for point-of-care testing will achieve the needs of frequent screening and diagnostic tracking.

In this work, hierarchucal porous SnO2/Zn2SnO4 nanospheres were succesfully prepared via a facile one-step hydrothermal method with subsequent calcination process. Scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed in order to investigate the structural and morphological properties of the as-prepared composites. The results showed that the SnO2/Zn2SnO4 composites were cpmposed of many porous nanospheres with a uniform diameter of about 500 nm. Moreover, the as-prepared products were used as sensing material for the fabrication of gas sensor. The sensing performance of the sensor was systematically evaluated, and the sensor exhibited excellent ethanol-sensing property. The optimum operating temperature was 250 °C with a reponse of 30.5 toward 100 ppm ethanol. Also, the sensor showed good selectivity, stability and a low detection limit of 0.5 ppm (response 1.4). The good sensing performance of SnO2/Zn2SnO4 nanospheres can be attibuted to the porous structure as well as the heterojunction formed between SnO2 and ZnSn2O4.

Hedgehog-like titanium dioxide (TiO2) architectures composed of hundreds of one-dimensional (1D) nanorods and silver (Ag) loaded TiO2 with different amounts (0.2 at%, 0.5 at% and 1 at%) were successfully prepared by facile hydrothermal process and simple isometric impregnation route. The high electron mobility of 1D nanorods on the surface of TiO2 and the high porosity of Ag loaded hedgehog-like TiO2 architectures enable the sensor with fast responsive and recovered properties. TiO2 loaded with 0.5 at% Ag exhibited the highest response to xylene with low response/recovery time at the operating temperature of 375 °C. In addition, the sensitivity and selectivity of the TiO2 sensor were enhanced markedly with Ag loading.

In this work, a novel branched heterostructural composite composed of nanorods ZnO backbone and SnO2 branches was prepared via a facile one-step hydrothermal method. The morphology, structure and component of the SnO2/ZnO composite was characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and elemental mapping analysis. The evolution process of the SnO2/ZnO composite was observed by SEM that the SnO2 branches gradually grow on ZnO backbones. The composite with novel heterostructure was applied as the sensing material for the fabrication of gas sensor, and their gas sensing properties were tested for response to various gases. Compared to pure ZnO gas sensors the branched SnO2/ZnO gas sensor exhibited enhanced gas sensing properties toward ethanol, giving a response of 18.1–100 ppm.

In this work, the highly selective and stable mixed potential type stabilized zirconia (YSZ) based gas sensor using Cd2V2O7 sensing electrode (SE) synthesized via simple coprecipitation method was fabricated and developed for effective detection of NH3 at 650 °C. The as-prepared Cd2V2O7 sensing material was characterized by X-ray diffraction (XRD), Raman spectrum, X-ray photoelectron spectroscopy (XPS) and Field-emission scanning electron microscopy (FESEM). The results of gas sensing measurement indicated that the sensor attached with Cd2V2O7- SE displayed the response value of −68 mV and rapid response rate of 5 s to 100 ppm NH3 at 650 °C. The present device also exhibited the low detection limit of 1 ppm and the piecewise sensitivities of −6 and −66 mV/decade to NH3 in the concentration ranges of 1–10 ppm and 10–200 ppm, respectively. Moreover, the fabricated sensor showed good reproducibility, excellent selectivity, stability to oxygen concentration, relative humidity and 30 days continuous aging of high temperature at 650 °C. And the complex impedance and polarization curves were performed to explain the selectivity and verify the sensing mechanism involving mixed potential model.

Acetone sniffer, because of its ability of continuous non-invasive monitoring, is recognized as a potential method for the diagnosis of diabetes. In this study, mixed potential electrochemical sensors based on YSZ and K2NiF4 -type oxides Sm2-xSrxNiO4 (x = 0.4, 0.6 and 0.8) sensing electrode were fabricated as bio-sniffer for diagnosis of diabetics by detecting acetone concentration in exhaled breath. The results showed that when Sm1.4Sr0.6NiO4 was used as sensing material, the fabricated sensor exhibited the best performance in comparison with other sensors, the present device also exhibited prominent reliability, excellent humidity resistance and good stability over 30 days. What’s more, the low detection limit of sensor to acetone was 300 ppb, indicating that the sensor had ability for acetone detection in exhaled breath. The exhaled breathes of the diabetics with ketosis were used for detection and results showed that the sensor had a manifest and stable signal. Besides, the response and recovery time were also acceptable to real-time detection. In addition, the relationship of the blood ketone level and the acetone concentration in exhaled breath was given in the paper. Above all, the fabricated sensor has enormous potentiality for the diabetes monitoring through breath analysis.

Urchin-like hierarchical Zn doped CdS powders were successfully synthesized via simple one-pot hydrothermal process. Their SEM and TEM images indicated that the hierarchical structure were assembled by single crystal nanorods with the hexagonal wurtzite phase. EDS element mapping verified that Zn ions were homogeneously distributed among the hierarchical microstructure. The performances of gas sensors based on pure and Zn doped CdS were measured and compared. The results indicated that Zn doping could enhance their responses to some volatile organic compounds and improve its selectivity to ethanol and toluene as well. The possible reasons for this enhancement were investigated. In addition, the sensor based on Zn doped CdS exhibited the ultrafast response and recovery to ethanol ( τ response 1 , τ recovery = 8 s ), indicating that the Zn doped CdS could be a promising gas sensing candidate for online monitoring of ethanol.

Mulberry-shaped tin oxide (SnO2) hierarchical architectures and samarium oxide (Sm2O3) loaded tin oxide with different amounts (0.5, 1, 2.5, and 4 mol% Sm2O3) were successfully synthesized by facile hydrothermal synthesis method and simple isometric impregnation method. The gas sensing performance of the sensors based on pure SnO2 and Sm2O3 loaded SnO2 materials were systematically investigated. The results indicated that Sm2O3 loading considerably affected the improvement of the sensing performance of the SnO2 sensor. The 2.5 mol% Sm2O3/SnO2 exhibited the highest response (41.14) to 100 ppm acetone, the response was 2.29 times higher than that of pure SnO2 (18). In addition, with 2.5 mol% Sm2O3 loading, the low detection threshold of the sensor dropped from 500 ppb to 100 ppb. The enhanced gas sensing performance was mainly bacause of the increased oxygen vacancies created by the substitution of samarium in the SnO2 lattice, which enhanced the adsorption of oxygen and the exceptional catalytic effect of Sm2O3.

The undoped and 1.0–5.0 mol% La–doped In2O3 hollow microspheres have been successfully synthesized via a simple hydrothermal method without template and gas sensor have been fabricated basing on them. The nanostructures and morphologies of the maintained hollow spheres were characterized by various experimental techniques. The gas sensing properties of these hollow microspheres were investigated systematically. The results indicated that among all the samples (pure, 1.0, 3.0 and 5.0 mol% La–doped In2O3), 3.0 mol% La–doped In2O3 exhibited the highest response toward 10 ppm hydrogen sulfide (H2S) at 200 °C, having a response value of 17.8, approximately 4.8 times higher than pure In2O3. Furthermore, excellent selectivity, good repeatability and outstanding long-term stability were also achieved. The significantly enhanced sensing properties to H2S could be attributed to the changes in distribution of different oxygen components, crystallite size and specific surface area caused by La doping.

In order to obtain high-performance CeO2-based mixed potential type acetone sensors, MFeO3 (M: Bi, La and Sm) sensing electrode materials were prepared by sol-gel method. The present study mainly focused on the effect of sensing electrode material and sintering temperature on sensing performance of sensors. The results showed that the sensor used BiFeO3-SE sintered at 800 °C presented the best sensing characteristic to acetone at 600 °C, which can detect even 1 ppm acetone with an acceptable response value. The response value (ΔV) of the sensor changed proportionally with the logarithm of acetone concentration at the ranges of 1–5 ppm and 5–200 ppm, and the slopes of which were −7 and −75 mV/decade, respectively. The sensor also showed excellent repeatability, relatively good selectivity, resistance to humidity and good long-term stability. The high-sensing characteristics of the sensor attached with BiFeO3-SE sintered at 800 °C to acetone were explained in terms of morphology and electrocatalytic activity of sensing electrode, which are validated by SEM, BET, XPS, polarization curves and complex impedance.

An ultrafast-response yttria stabilized zirconia (YSZ)-based mixed potential type gas sensor utilizing molybdate CoMoO4 sensing electrode was developed to realize the effective detection of triethylamine (TEA) at 600 °C. The gas sensing characteristic of the fabricated sensor was optimized by changing the calcination temperature of CoMoO4 sensing material and results indicated that the device attached with CoMoO4-SE sintered at 1000 °C exhibited the highest response value (−102 mV) to 100 ppm TEA and low detection limit of 100 ppb at 600 °C. Interestingly, the response and recovery times of the present sensor to 100 ppm TEA were 1 s and 10 s, which signified the ultra-fast response rate. The response value of fabricated sensor displayed the piecewise linear function to logarithm of TEA concentrations and the sensitivities were −14 mV/decade (0.1–5 ppm) and −53 mV/decade (5–200 ppm), respectively. More importantly, the present sensor also exhibited good repeatability, selectivity, slight effect of humidity and long-term stability of 20 days, indicating a great candidate for use in detection of TEA. Furthermore, the device based on mixed potential mechanism was proposed and further verified using polarization curve.

Flower-liked ZnO architectures and Ce doped ZnO materials with different amounts (0.2, 0.5, 1.2 and 2 at% Ce) were successfully synthesized by a simple room-temperature precipitation route. As the gas sensing materials, their sensing performance were investigated systematically. The results indicate that Ce doping can improve the performance of ZnO sensor. The ZnO doped with 0.5 at% Ce exhibited the highest response to ethanol at the operating temperature of 300 °C, and the response value was about 72.6–100 ppm ethanol. With Ce doping, the proportions of oxygen vacancy and chemisorbed oxygen species were increased obviously, which could greatly promote the gas sensing properties of surface resistance-type metal oxide semiconductors. Thus, the doping of flower-liked ZnO with Ce should be a promising approach for designing and fabricating the high performance gas sensor.

Porous CuFe2O4 nanospheres were successfully prepared via a facile solvothermal method with subsequent calcination treatment. Various techniques were employed to investigate the structural and morphological characteristics of the as-synthesized product. The results revealed that the hierarchical CuFe2O4 porous nanospheres with a diameter of about 200 nm were composed of many nanoparticles. In addition, gas sensors were fabricated with the as-prepared samples, and their gas sensing performances were systematically investigated. Compared with pure CuO and Fe2O3 nanoparticles, the CuFe2O4 nanostructure exhibited superior gas sensing properties toward acetone at the operating temperature of 250 °C, including high response, outstanding selectivity, and excellent response-recovery property.

Carbonization followed by calcination in air has been developed to synthesize porous SnO2 based nanofibers. The precursor nanofibers were synthesized through electrospinning. The optimal synthesized condition was investigated according to the gas sensing properties of pure SnO2 nanofibers through adjusting the heating rate in air. Gas sensors based on 1% Pd doped SnO2 nanofibers under this optimal synthesized condition were fabricated, and the gas sensing properties was systematically investigated. The experimental results indicate that all the carbonized nanofibers have a porous microstructure. For the pure SnO2 nanofibers, carbonized nanofibers also have a hollow structure. At the optimal synthesized condition, the sensor based on the carbonized SnO2 nanofibers Exhibits 2.6 times higher response (20.4) than pristine pure SnO2 nanofibers (7.7) toward 100 ppm ethanol. However, the selectivity is almost unchanged. For the Pd doped SnO2 nanofibers, the gas response is improved from 10 to 24.6 to 100 ppm toluene at optimum operation temperature under the carbonization process. The sensors also exhibit a low detecting limit (1.6–500 ppb toluene) and a short response time (∼3 s). The evolution process and the formation mechanism were also discussed.

In this article, CeO2-based mixed potential type gas sensor attached with sensing electrodes (SEs) consisting of perovskite-type La1-xSrxCoO3 (x = 0.1, 0.2, 0.3 and 0.5) composite oxides has been developed for acetone detection. The effect of different Sr2+ doping content in La1-xSrxCoO3 oxide material and calcination temperature on acetone sensing characteristics was investigated. It was seen that the sensor using La0.8Sr0.2CoO3 calcined at 1000 °C as SE gave the largest sensing signal to acetone in the concentration range of 1–50 ppm at 600 °C among these sensors. The response value (ΔV) of the sensor was sectionally linearly changed with the logarithm of acetone concentration within the ranges of 1–5 ppm and 5–50 ppm, and the sensitivities were −26 and −49 mV/decade, respectively. In addition, it is noteworthy that the response of the sensor to 1 ppm acetone was approximately −8.7 mV. The sensor also exhibited consistent response and recovery characteristics in five cycles, indicating the sensing device had good reproducibility. Besides, the sensor exhibited the highest response to 10 and 50 ppm acetone and less effective response to other tested gases, it indicates that the sensor has good selectivity. Furthermore, the long-term stability for the sensor to 20 ppm acetone was good because that only a slight attenuation in the sensing response was observed during 30 days. The sensing characteristics of the sensor attached with La0.8Sr0.2CoO3-SE sintered at 1000 °C to acetone were explained in terms of electrocatalytic activity changes induced by effects of doped Sr divalent cation.

Hierarchical NiO nanomaterials doped by 0.5, 1.0, 1.5 and 2.0 at% Sn2+ ions were synthesized through a facial hydrothermal route. The isovalent Sn2+ ions were selected as dopants and occupied the interstitial spaces of NiO lattice. Such obtained NiO specimens were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) etc. and used as sensing materials for gas sensors. The comparative sensing property tests among these Sn2+ doped NiO sensors demonstrated that 1.5 at% Sn2+-NiO microspheres showed the highest response (∼25.2 ± 10%) to 200 ppm xylene, which was about 14-fold higher than that of the pure NiO. Moreover, the humidity-independent performance of the 1.5 at% Sn2+-NiO sample was excellent, such as low detection limit (1.1-500 ppb) and good selectivity toward xylene at high relative humidity (90% RH). The gas sensing mechanisms for the improved sensing performance were also discussed.

Pure α-Fe2O3 nanotubes and a series of Al2O3/α-Fe2O3 composite nanofibers were synthesized via facile electrospinning and subsequent calcination at 500 °C in air for 2 h. The morphologies and nanostructures of these samples were characterized through various experimental techniques. It was found that the composite samples were composed of crystal α-Fe2O3 and amorphous Al2O3. The composite Al2O3/α-Fe2O3 nanofibers have smaller grain size than that of pure α-Fe2O3 nanotubes prepared by the same process. Furthermore, comparative gas sensing investigation between Al2O3/α-Fe2O3 composite nanofibers and pure α-Fe2O3 nanotubes was performed to show the superior sensing properties of the composite samples. When the mass ratio of Al source and Fe source was 1:4, the sensor exhibited the highest response to 100 ppm triethylamine at 250 °C. It is worth noting that the response times were no more than 2 s at operating temperatures ranged from 175 °C to 300 °C. Finally, the related mechanism of gas sensing and the role of Al2O3 in the composite nanofibers were discussed in this paper.

In this work, hierarchical porous SnO2/Zn2SnO4 composites were synthesized via a facile one-step hydrothermal method with subsequent heat treatment. Many methods were performed to investigate the crystalline and morphological characterization of the as-prepared composite. The gas sensors based on the porous SnO2/Zn2SnO4 composite were fabricated and their gas sensing performance was systematically investigated. Significantly, compared with the pure SnO2 and Zn2SnO4 solid particles, the hierarchical SnO2/Zn2SnO4 porous spheres exhibited excellent gas sensing properties toward triethylamine (TEA). The response value was 48 toward 100 ppm TEA, and the detection limit could be down to 500 ppb with a response value of 1.4. The excellent gas sensing properties are contributed to the porous nanostructure and the heterojunction between SnO2 and Zn2SnO4 composite.