Hierarchical Radial Co3O4 Microcrystal and Application in Gas Sensor

Three-dimensional （3D） hierarchical Co3O4 microcrystal with radial dendritic morphologies was prepared through hydrothermal reactions followed by subsequent annealing treatment. Structural and morphological characterizations were performed by X-ray diffraction, scan-ning electron microscopy and transmission electron microscopy. The gas sensing properties of the as-obtained microcrystal were investigated at 110 oC, which revealed that the 3D hierarchical porous Co3O4 microcrystal exhibited high sensitivity to ammonia, as well as a short response time of 10 s. The response characteristic indicates that the sensor has a good stability and reversibility. Detections of toxic and flammable gases, such as ethanol, acetone and benzene were also carried out at a relative low temperature. The results indicate that such hierarchical Co3O4 microcrystal would be a potential material in the field of gas sensing.

SnO_(2)/Co_(3)O_(4)nanofibers using double jets electrospinning as low operating temperature gas sensor

SnO_(2)/Co_(3)O_(4)nanofibers(NFs)are synthesized by using a homopolar electrospinning system with double jets of positive polarity electric fields.The morphology and structure of SnO_(2)/Co_(3)O_(4)hetero-nanofibers are characterized by using field emission scanning electron microscope(FE-SEM),transmission electron microscope(TEM),x-ray diffraction(XRD),and x-ray photoelectron spectrometer(XPS).The analyses of SnO_(2)/Co_(3)O_(4)NFs by EDS and HRTEM show that the cobalt and tin exist on one nanofiber,which is related to the homopolar electrospinning and the crystallization during sintering.As a typical n-type semiconductor,Sn O_(2)has the disadvantages of high optimal operating temperature and poor reproducibility.Comparing with Sn O_(2),the optimal operating temperature of SnO_(2)/Co_(3)O_(4)NFs is reduced from 350℃to 250℃,which may be related to the catalysis of Co_(2)O_(2).The response of SnO_(2)/Co_(3)O_(4)to 100-ppm ethanol at 250℃is 50.9,9 times higher than that of pure Sn O_(2),which may be attributed to the p–n heterojunction between the n-type Sn O_(2)crystalline grain and the p-type Co_(2)O_(2)crystalline grain.The nanoscale p–n heterojunction promotes the electron migration and forms an interface barrier.The synergy effects between Sn O_(2)and Co_(2)O_(2),the crystalline grain p–n heterojunction,the existence of nanofibers and the large specific surface area all jointly contribute to the improved gas sensing performance.

Improvement of the Sensitivity of ZnGa_2O_4 Gas Sensors by Electron Beam Irradiation

In the present paper,the electron beam irradiation was used to improve gas sensing properties of ZnGa_2O_4 gas sensors.The effects of electron beam irradiation on the performance of ZnGa_2O_4 gas sensors were reported.Results show that the sensitivity of ZnGa_2O_4 gas sensors to various gases increased after electron beam irradiation,and the optimal working temperature decreased.The effect of irradiation dose and the reaction mechanism were discussed.

Methane Gas Sensor Based on Microstructured Highly Sensitive Hybrid Porous Core Photonic Crystal Fiber

We have demonstrated and analyzed the methane gas sensor based on octagonal cladding and hexagonal hybrid porous core photonic crystal fiber (HPC-PCF) for gas detection purpose. The proposed design of HPC-PCF has been numerically investigated by COMSOL Multiphysics software through utilizing the full vectorial finite element method (FEM). The optical characteristics of HPC-PCF as well as confinement loss, relative sensitivity and refractive index, effective area, nonlinearity and numerical aperture are optimized properly by changing the geometrical parameters as well as air filling ratio, air hole diameter, pitch constant of cladding and porosity of the core. In this simulation work, we have achieved optimum relative sensitivity of 21.2%, and confinement loss of 0.000025 dB/m at 3 μm pitch, 0.7 air filling ratio of the cladding and 29% porosity of the core for 3.5 μm absorption wavelength of CH4 gas. This proposed design of HPC-PCF will keep exclusive contribution for detecting the CH4 gas accurately.

Gas Sensing Characteristics of SnO_2 Whiskers Prepared from SNC_2O_4

SnO_2 whiskers were prepared from the decomposition of whisker-like SnC_2O_4,which was precipitated by a reaction between an aqueous SnCl_2 and oxalic acid solution at high solution temperatures (80℃).After the decomposition of SnC_2O_4 at 450℃,SnO_2 whiskers containing both of rutile and metastable orthorhombic phases were obtained with the content of the orthorhombic phase decreasing with increasing heat-treatment temperature and time.The effect of orthorhombic phase upon CO gas sensitivity was investigated by measuring the evolution of the primary particle size and the CO sensitivity with repeating heat treatment at 450℃.The 50μg/g CO sensitivity increased with decreasing concentration of the orthorhombic phase despite particle coarsening,which suggests that the orthorhombic phase is detrimental to the CO gas sensitivity.

一种智能多功能车库的设计

阐述了基于STM32微控制器的多功能车位的设计与实现方法。从传统智能车库的不足出发,详细讨论了多功能车库的硬件组成并给出了软件设计的方法。该系统主要由STM32微控制器、定位系统、烟雾传感器、灭火装置和洗车装置等组成。STM32微控制器作为核心控制单元,负责实现各项功能的协调与控制。实现了车主自动定位车辆所在位置及自动灭火、洗车的功能。同时,在软件设计方面,我们采用了先进的算法和控制策略。经过实践验证,本设计的功能已经得到有效实现,车辆自动定位及灭火中的烟雾检测基本达到了标准的同时,也降低了系统成本,可靠性较高,人机交互便利。

A 1.65μm three-section distributed Bragg reflector(DBR) laser for CH_4 gas sensors

A 1.65μm three-section distributed Bragg reflector （DBR） laser for CH4 gas sensors is reported. The DBR laser has a wide tunable range covering the R3 and R4 methane absorption line manifolds. The wavelength tunability properties, temperature stability and laser linewidth are characterized and analyzed. Several advantages were demonstrated compared with traditional DFB lasers in harmonic detection.

UV light driven high-performance room temperature surface acoustic wave NH_(3) gas sensor using sulfur-doped g-C_(3)N_(4) quantum dots

Nanomaterials integrated surface acoustic wave(SAW)gas sensing technology has emerged as a promising candidate for realtime toxic gas sensing applications for environmental and human health safety.However,the development of novel chemical interface based on two-dimensional(2D)sensing materials for SAW sensors for the rapid and sensitive detection of NH_(3)gas at room temperature(RT)still remains challenging.Herein,we report a highly selective RT NH_(3)gas sensor based on sulfur-doped graphitic carbon nitride quantum dots(S@g-C_(3)N_(4)QD)coated langasite(LGS)SAW sensor with enhanced sensitivity and recovery rate under ultraviolet(UV)illumination.Fascinatingly,the sensitivity of the S@g-C_(3)N_(4)QD/LGS SAW sensor to NH_(3)(500 ppb)at RT is dramatically enhanced by~4.5-fold with a low detection limit(~85 ppb),high selectivity,excellent reproducibility,fast response/recovery time(70 s/79 s)under UV activation(365 nm)as compared to dark condition.Additionally,the proposed sensor exhibited augmented NH_(3)detection capability across the broad range of relative humidity(20%–80%).Such remarkable gas sensing performances of the as-prepared sensor to NH_(3)are attributed to the high surface area,enhanced functional groups,sulfur defects,UV photogenerated charge carriers,facile charge transfer in the S@g-C_(3)N_(4)QD sensing layer,which further helps to improve the gas molecules adsorption that causes the increase in conductivity,resulting in larger frequency responses.The gas sensing mechanism of S@g-C_(3)N_(4)QD/LGS SAW sensor is ascribed to the enhanced electroacoustic effect,which is supported by the correlation of resistive type and COMSOL Multiphysics simulation studies.We envisage that the present work paves a promising strategy to develop the next generation 2D g-C_(3)N_(4)based high responsive RT SAW gas sensors.

Fiber-optic dual Fabry-Pérot interferometric carbon monoxide sensor with polyaniline/Co3O4/graphene oxide sensing membrane

An optical fiber dual Fabry-Perot interferometric carbon monoxide gas sensor based on PANI/Co3 O4/GO(PCG)sensing membrane coated on the end face of the optical fiber is proposed and fabricated.One end face of photonic crystal fiber(PCF)without cut-off wavelength is fused with a single-mode fiber(SMF),and the other end face of the PCF is coated with PCG sensing membrane.The collapsed layer formed during the air hole fusion of PCF is used as the first reflector,the interface between PCF and sensing membrane is used as the second reflector,and the interface between the sensing membrane and the air is used as the third reflector,thus the dual Fabry-Pe rot structure sensor is formed.The results show that the sensor has excellent sensitivity and selectivity to carbon monoxide.With the increasing concentration of carbon monoxide gas in the range of 0-60 ppm,the intensity of interference spectrum decreases.The sensitivity of the sensor is 0.3473 dB m/ppm,and its linearity is good.The response time and recovery time are 68 s and 106 s,respectively.The sensor has the advantages of the compact size,low cost,high sensitivity,strong selectivity and simple structure.It is suitable for the sensing detection of low concentration carbon monoxide gas.

Design of a Methane Monitoring System for Landfill and Duct Emissions

Methane is released from waste disposal areas as a result from anaerobic decay of food. Methane causes more greenhouse effects than carbon dioxide so a methane monitoring system is required to warn its release from gas emitting environments. The low explosive limit of methane is 5% in ambient air, so gas leakage is dangerous and can produce explosions. An entire head monitoring system was built around a MQ-4 methane gas sensor as it is cheap and reliable. The design proves to be flexible enough as it can measure CH4 emissions in ducts, CH4 in landfills at different depths and even in cattle barns. The measuring system head consists of a suction pump, solenoids, and a methane sensor. Measurements are taken 13 seconds after methane gas sucking. A timing of 100 seconds is required for purging the chamber before the second solenoid is turned-on. Devices temperature during operation was sampled with a thermal Flir-One camera and solenoid coil temperature was of 24.9˚C after a continuous operation of 30 seconds. As hoses for emission sampling become larger time for sampling increases as well as energy consumption.

Sensing properties and mechanisms of LaF_(3)-Co_(3)O_(4) nanorods for low-concentration methanol detection

Methanol is one of the characteristic gases that distinguish between healthy individuals and lung cancer(LC)lesions in exhaled human breath.Its concentration in exhaled breath is generally below one part per million(1×10^(-6)).The second-phase composite is widely regarded as one of the methods to improve the gas-sensing perfor-mance of metal oxide semiconductor(MOS)materials.In this study,LaF_(3)-Co_(3)O_(4) was synthesized by a simple hydrothermal method to enhance its low-concentration methanol gas-sensing performance.5 at%LaF_(3)-Co_(3)O_(4) nanorods exhibited excellent methanol detection performance,including a wider linear detection concentration range(0.2×10^(-6)~5×10^(-6)),a response value exceeding 4.0 for 1×10^(-6)methanol at 275°C and 75%relative humidity(RH),long-term stability(maximum deviation within 15%over 2 weeks),and excellent selectivity.The mechanism of performance enhancement was studied using various techniques,and density functional theory.The special spinel structure of Co_(3)O_(4),the high ionic migration of F-in LaF_(3),the larger specific surface area of 5 at%LaF_(3)-Co_(3)O_(4) nanorods,and the generated crystal defects all explain the excellentmethanol gas-sensing property.This work provides a novel route to prepare MOS composite materials for low-concentration methanol gas detection.

Well-designed g-C_(3)N_(4)nanosheet incorporated Ag loaded Er_(0.05)La_(0.95)FeO_(3)heterojunctions for isoamyl alcohol detection

Because the volatile content of isoamyl alcohol increases sharply on the seventh day of wheat mildew infection,isoamyl alcohol can be used as an early biomarker of wheat mildew infection.Currently,only a few sensors for isoamyl alcohol detection have been reported,and these sensors still suffer from low sensitivity and poor moisture resistance.Herein,the isoamyl alcohol sensitivity of 5 at%Er@LaFeO_(3)(ELFO)was enhanced by loading Ag nanoparticles on the surface of the ELFO microspheres,while the optimal operating temperature was reduced.The moisture resistance of Ag/ELFO was improved by the incorporation of g-C_(3)N_(4)nanosheets(NSs)on the surface of Ag/ELFO through electrostatic self-assembly.Given the requirements for practical applications in grain granaries,the sensing behavior of a Ag/ELFO-based sensor incorporating g-C_(3)N_(4)NSs at 20%relative humidity(RH)was systematically studied,and the sensor demonstrated excellent repeatability,long-term stability,and superior selectivity(791 at 50 ppm)for isoamyl alcohol with a low limit of detection(LOD=75 ppb).Furthermore,the practical results obtained for wheat at different mildew stages further confirmed the potential of the g-C_(3)N_(4)/Ag/ELFO-based sensor for monitoring the early mildew stage of wheat.This work may offer guidance for enhancing the moisture resistance of gas-sensitive materials through the strategy of employing composite nanomaterials.

Hierarchical flower-like NiFe2O4 with core-shell structure for excellent toluene detection

The extensive use of toluene stimulates the effective detection by sensitive gas sensors based on unique materials.Here,hierarchical flower-like NiFe_(2)O_(4) with core-shell architecture was synthesized by a facile hydrothermal method in the presence of urea and NH4 F.The controllable experiments indicated that the burr spheres and football-like samples were produced with individual urea or NH4 F.The flower-like NiFe_(2)O_(4) sensor exhibited outstanding sensitivity of 19.95 to 100×10^(-6) toluene with low detection limit(1×10^(-6)).Furthermore,the sensor showed superior sensing selectivity and longterm stability to toluene.The excellent sensing properties could largely arise from a combination of high surface area,numerous active sites,porous structures,and the native catalytic characteristics of NiFe2 O4 to facilitate toluene molecules adsorption,diffusion,and reaction.

Sulfur dioxide sensing properties of MOF-derived ZnFe_(2)O_(4) functionalized with reduced graphene oxide at room temperature

In this paper,ZnZnFe_(2)O_(4) nanorods were prepared using Zn/Fe metal organic framework(MOF)as precursors,and ZnZnFe_(2)O_(4)/reduced graphene oxide(rGO)was prepared by hydrothermal method.The morphology and composition of the ZnZnFe_(2)O_(4)/rGO nanocomposite were characterized,and the results showed that the MOF-derived ZnZnFe_(2)O_(4) nanorods are uniformly modified on the surface of rGO.The ZnZnFe_(2)O_(4)/rGO nanocomposite exhibits better SO_(2) gas sensing performance than the single ZnZnFe_(2)O_(4) nanorods at room temperature.The sensing characteristics of single ZnZnFe_(2)O_(4) film sensor,single rGO film sensor and ZnZnFe_(2)O_(4)/rGO composite film sensor at SO_(2)gas concentration(1×10^(-6)-100×10^(-6))were tested.The response of ZnZnFe_(2)O_(4)/rGO composite sensor can reach 18.32%at room temperature.Compared with single ZnZnFe_(2)O_(4) and rGO film sensors,the ZnZnFe_(2)O_(4)/rGO composite sensor has better transient response,good sensitivity and selectivity.In this work,the improvement of the sensor performance is not only due to the p-n heterostructure between ZnZnFe_(2)O_(4) nanorods and rGO nanosheets,but also to the excellent electrical properties of rGO.It provides a new idea for the detection of SO_(2) at room temperature.

Hollow Fe_(2)O_(3)/Co_(3)O_(4)microcubes derived from metal-organic framework for enhanced sensing performance towards acetone

In this work,hollow Fe_(2)O_(3)/Co_(3)O_(4)microcubes have been successfully synthesized through a hydrothermal method followed by an annealing process using metal-organic framework of Prussian blue as a soft template.The morphologies,microstructures,surface area and element compositions have been carefully characterized by a series of techniques.Meanwhile,compared with that of pure Fe_(2)O_(3)and Co_(3)O_(4),the gas sensor based on the hollow microcubes exhibits enhanced sensing performances towards acetone,e.g.,a higher response of 21.2 and a shorter response time of 5 s towards 20 ppm acetone at a relatively low working temperature of 200℃.Moreover,the hollow microcubes-based gas sensor still shows perfect long-term stability,excellent repeatability and the ability of sub-ppm level detection,which provides a possibility for its application in real life.The enhanced gas sensing performances can be attributed to the hollow structure with a high surface area and the formed p-n heterojunctions within the microcubes.

DFT calculation on p-xylene sensing mechanism of (C_(4)H_(9)NH_(3))_(2)PbI_(4) single crystal based on physisorption

P-xylene(p-C_(8)H_(10))is extremely harmful and dangerous to human health due to high toxicity and strong carcinogenicity.Exploring sensitive material to effectively detect p-xylene is of importance.In this paper,perovskite single crystal(C_(4)H_(9)NH_(3))_(2)PbI_(4) has been successfully synthesized via solution method.The obtained product was analyzed by single crystal X-ray diffraction.With the space group Pbca,orthorhombic(C_(4)H_(9)NH_(3))_(2)PbI_(4) layered perovskite structure consists of an extended two-dimensional network of corner-sharing PbI_(6) octahedron.Single layer perovskite sheets of distorted PbI_(6) octahedron alternated with protonated n-butylammonium cation bilayers,which offers many advantages and provides the possibility of forming a gas sensor device based on the change of resistances.Density functional theory(DFT)simulations regarding the adsorption energy revealed that this organicinorganic hybrid perovskite compound has excellent selectivity toward p-xylene compared with other gases including C_(2)H_(5)OH,C_(6)H_(6),CH_(2)Cl_(2),HCHO,CH_(3)COCH_(3) and C_(7)H_(8).The calculation of electron density,density of states and electron density difference showed the sensing mechanism of p-C_(8)H_(10) is mainly derived from physical adsorption-desorption in view of electron transfer.

Dual-selective detection of CO and CH_(4) based on hierarchical porous In_(2)O_(3) nanoflowers with Pd modification

The timely and effective detection of CO and CH_(4) is critical as the explosion and poisoning of them can bring serious potential risks to coal mining.In this study,combining metal oxide semiconductors with noble metals offers a promising route to achieve this target.Hierarchical porous Pd modified In_(2)O_(3) nanoflowers were prepared via two-step hydrothermal method and exhibited dual detection of CO and CH_(4) at different temperatures.The material has been characterized by a number of advanced techniques and the results indicate that Pd modified In_(2)O_(3) are hierarchical porous nanoflowers structure consisting of pores of approximately 1.8 nm in size.The sensing properties results show that the Pd modified In_(2)O_(3) based sensor exhibits temperature-dependent dual selectivity detection of CO at 280℃ and CH_(4) at 340℃.In addition,the Pd modified In_(2)O_(3) sensor display higher sensing response of CO(5.824 for 100 ppm)and CH_(4)(1.162 for 1000 ppm),fast response and recovery time,as well as good repeatability,which demonstrating the great potential for practical application.Such good gas-sensing performance are mainly attributed to the unique flower-like structure,the presence of porosity on the sample surface,and the catalytic effect of Pd.

Hierarchical NiCo2O4 microspheres assembled by nanorods with p-type response for detection of triethylamine

The morphological and structural design provides an efficient protocol to optimize the performance of gas sensing materials.In this work,a gas sensor with high sensitivity for triethylamine(TEA)detection is developed based on p-type NiCo2 O4 hierarchical microspheres.The NiCo2 O4 microspheres,synthesized by a hydrothermal route,have a three-dimensional(3 D)urchin-like structure assembled by nanorod building blocks.The structure-property correlation has been investigated by powder X-ray diffraction,X-ray photoelectron spectroscopy,transmission electron microscope,scanning electron microscope,N2 adsorption-desorption tests and comprehensive gas sensing experiments.The influence of calcination temperature on the morphological structure and sensing performances has been investigated.Results reveal that the material annealed at 300℃has a very large specific surface area of 125.27 m2/g,thereby demonstrating the best TEA sensing properties including high response and low limit of detection(145 ppb),good selectivity and stability.The further increase of the calcination temperature leads to the collapse of the 3 D hierarchical structure with significantly decreased surface area,which is found to decline the sensing performances.This work indicates the promise of ternary p-type metal oxide nanostructures for application in highly sensitive gas sensors.