Effect of Sm on Gas-Sensing Properties of SnO_2with Different Oxygen Vacancy Concentrations

The SnO2-x. with different oxygen vacancy concentrations was modified by addling Sm. The modified SnO2-x was investigated by means of X-ray diffraction, X-ray photoelectron spectroscope, and scanning electron microscopy. Its gas-sensing properties to C2H6, C6H14, C2H5OH, CO, and H2 were studied too. The experiment results show that the gas-sensing properties of Sm/SnO2-x depend upon the amount of oxygen vacancies, therefore it is possible to improve gas-sensing properties of doped SnO2 by controlling its concentration of oxygen vacancy.

The Preparation and Gas-sensing Property of Nanosize γ-Fe_2O_3/SiO_2

Nanostructured γ-Fe2O3/SiO2 complex oxide was prepared by sol-gel method with tetraethoxysilane and iron nitrate as precursors. The particle size distribution, thermal and phase stabilities and gas sensing properties were systematically characterized by TEM, granularity distribution, TG-DTA, XRD and gas sensitivity measurements. The particle size is about 10 nm and size distribution is very narrow. The sensitivity of the sensing element to CO, H2, C2H4, C6H6 and the effects of calcination temperature on the sensitivity and conductance of gases were examined. The combination of excellent thermal stability and tunable gas sensing properties through careful control of the preparation and judicious selection of material compositions gives rise to novel nanocomposites, which is attractive for the sensitive and selective detection of reducing gases and some hydrocarbon gases.

Gas concentration monitoring system for small and medium-sized coal mines based on gas-sensing detection and single-chip control

This paper is aimed at the actual conditions of disaster caused by gas in small and medium-sized coal mines. A new gas concentration monitoring system for coal mines is developed on the basis of gas-sensing detection and single-chip control. The monitoring system uses the tin oxide as the main material of N-type semiconductor gas sensors, be- cause it has good sensitive characteristics for the flammable and explosive gas （ such as methane, carbon monoxide）. The QM-N5-semiconductor gas sensor is adopted to detect the output values of the resistance under the different gas con- centrations. The system, designedly, takes the AT89C51 digital chip as the core of the circuit processing hardware structure to analyze and judge the input values of the resistance, and then achieve the control and alarm for going beyond the limit of gas concentration. The gas concentration monitoring system has man）, advantages including simple in struc- ture, fast response time, stable performance and low cost. Thus, it can be widely used to monitor gas concentration and provide early wamings in small and medium-sized coal mines.

Preparation and Gas-Sensing Properties of NdFeO_3 Nanocrystalline

With the Nd_2O_3, Fe(NO_3)_3·9H_2O, nitric acid(1∶1 vloume fraction) for the starting materials, rare earth composite oxide NdFeO_3 with the structure of perovskite type was synthesized by sol-gel method in the system of citric acid. Structural characteristics were characterized by XRD and TEM which indicate that the sample is nanocrystallite with uniform grain size distribution and the average grain size is about 28 nm. Moreover, the gas sensing properties of the material were tested. The results show that NdFeO_3 sensors have high sensitivity, excellent selectivity and quick response and recovery behavior to H_2S, hence, this gas sensing material has a better prospects in industrial practice.

Synthesis and Gas-sensing Performance of Nanosized SnO_2

Nanosized tin dioxide particles were prepared by sol-gel dialytic processes with tin(Ⅳ) chloride and alcohol as start materials. The nanoparticles of tin dioxide were charactered by thermogravimetry and differential thermal analysis(TG-DTA), X-ray diffraction(XRD), transmission electron microscopy (TEM) and BET. The results show that the average diameter of tin dioxide particles dried at 353 K was about 2 nm. Even if the tin dioxide particles were calcined at 873 K, the average diameter of particles was less than 10 nm. The removal of Cl- was solved by using this kind of method. The mechanism of the formation of tin dioxide nanosized particles was proposed and analyzed in this paper. We also measured the sensitivity of the sensor based on the tin oxide powder calcined at 673 K to NH 3, alcohol, acetone, hexane and CO. The gas-sensing performance results indicate that this sensor has a higher sensitivity to alcohol and acetone, and selectivity for NH 3, hexane and CO at an operating temperature of 343 K.

Preparation and Gas-sensing Characteristics of Na^+-doped ZnO Single Crystals

ZnO single crystals were grown by vapor phase reaction of Zno powder with active carbon powdei at an elevated temperature The typical crystals were colorless and transparent with maximum size o4 0.1 mm in diameter and 25 mm in length, The gas-sensing characteristics of Na+-doped anc undoped single crystals were investigated in 1 %H2. Co and CH, in air between 1 50 and 600℃. It was found that the undoped ZnO single crystals showed little gas sensitivity in air. and Na+-doping can greatly enhance the senstivity by increasing the resistivities. The maximum sensitivity of the samples is 22 (Ra/ Rg) for H2. 1 2 for CO and 4 for CH4

Facile Synthesis of Rose-Like NiO Nanoparticles and Their Ethanol Gas-Sensing Property

In this study, rose-like nickel oxide （NiO） nanoparticles with diameters of 400-500 nm are prepared on ITO glass substrates by simple electrodeposition in NiSO46H20 solution at room temperature followed by oxidation in air. Scanning electron microscopy, x-ray diffraction and a transmission electron microscope are used for analyses of the NiO nanoparticles. The ethanol gas sensitivity of these nanoparticles is studied. The results indicate that the rose-like NiO nanoparticles could be used for the fabrication of ethanol gas sensors to monitor the low concentration of ethanol gas in air. Furthermore, at 5 ppm, the NiO nanorose-based sensors show a high response to ethanol （Rg/Ra = 8.4）.

Preparation and gas-sensing performance of SnO2/NiO composite oxide synthesized by microwave-assisted liquid phase deposition

We synthesized SnO2/NiO composite oxides by microwave-assisted liquid phase deposition to improve their surface physico-chemical properties and gas-sensing selectivity,and we investigated how the molar ratio of Ni^2+to Sn^4+and the microwave power affected their gas-sensing performance.The microstructure,surface physico-chemical states,and morphology of the samples were characterized by X-ray diffraction,X-ray photoelectron spectroscopy,and scanning electron microscopy,respectively.Nitrogen adsorption-desorption isotherms were used to characterize the specific surface areas of the samples.Our results showed that microwave-assisted liquid phase deposition increased the surface-adsorbed oxygen content and the specific surface area of the SnO2/NiO composite oxide from about 22to 120m2/g.When the molar ratio of Ni^2+to Sn^4+was 0.1,the gas response to 1000ppm ethanol gas reached 84.7at a lower working voltage of 3.5V.However,the optimum working voltages for methanol and acetone gas were 4.5and 4.0V,respectively.Thus,a new method was found to improve the selectivity of the gas sensor.Moreover,at a working voltage of 4.0V,the gas response of a SnO2/NiO gas sensor synthesized by microwave-assisted liquid phase deposition with the optimum radiation power of 450W to 1000ppm acetone gas was 49.7,twice that of a sensor synthesized by traditional liquid phase deposition.

Revisiting traditional and modern trends in versatile 2D nanomaterials: Synthetic strategies, structural stability, and gas-sensing fundamentals

Two-dimensional nanomaterials(2DNMs)have attracted significant research interest due to their outstanding structural properties,which include unique electrical nanostructures,large surface areas,and high surface reactivity.These adaptable materials have outstanding physicochemical characteristics,making them useful in a variety of applications such as gas-sensing,electronics,energy storage,and catalysis.Extensive research has been conducted in the pursuit of high performance room-temperature(RT)gas sensors with good selectivity,high sensitivity,long-term stability,and rapid response/recovery kinetics.Metal oxides,transition metal chalcogenides,MXenes,graphene,phosphorene,and boron nitride have all been discovered as 2DNMs with strong potential for gas sensors.This review presents an in-depth analysis of current advances in 2DNM research.It includes synthetic techniques,structural stabilities,gas-sensing mechanisms,critical performance parameters,and factors influencing gas-sensing capabilities of 2DNMs.Furthermore,the present study emphasizes structural engineering and optimization methodologies that improve gas-sensing performance.It also highlights current challenges and outlines future research directions in the domain of tailoring 2DNMs for advanced RT gas sensors.This systematically designed comprehensive review article aims to provide readers with profound insights into gas detection,thereby inspiring the generation of innovative ideas to develop cutting-edge 2DNMs-based gas sensors.

SnO_(2)nanostructured materials used as gas sensors for the detection of hazardous and flammable gases:A review

SnO_(2)has been extensively used in the detection of various gases.As a gas sensing material,SnO_(2)has excellent physical-chemical properties,high reliability,and short adsorption-desorption time.The application of the traditional SnO_(2)gas sensor is limited due to its higher work-temperature,low gas response,and poor selectivity.Nanomaterials can significantly impact gas-sensitive properties due to the quantum size,surface,and small size effects of nanomaterials.By applying nanotechnology to the preparation of SnO_(2),the SnO_(2)nanomaterial-based sensors could show better performance,which greatly expands the application of SnO_(2)gas sensors.In this review,the preparation method of the SnO_(2)nanostructure,the types of gas detected,and the improvements of SnO_(2)gas-sensing performances via elemental modification are introduced as well as the future development of SnO_(2)is discussed.

Preparation and Characterization of Nanosized Titania Sensing Film

Nanosized titania sensing films were prepared by sol-gel process and the microstructure was characterized. Influence of various factors on the morphologies of the films were studied in details.In order to obtain films with high surface area,Y^(3+),Ce^(3+) and Fe^(3+) were doped in the titania sol.Also titania sol was dispersed in a polymeric solution to get nanosized and porous films.Scanning electron microscope (SEM),atom force microscope (AFM),and x-ray diffraction (XRD) were used to characterize the titania films.SEM,AFM figures indicated that the grain size decreased from about 150 nm to 20 nm when the concentration of additions changed from 0 at% to 55 at% and the film was porous with the grain size less than 30 nm when the titania sol was dispersed in a polymeric solution even when the calcination temperature increased up to 850℃.

Effects of Annealing Temperature on Microstructure and Sensing Properties to Alcohol for Nano-La_(0.68)Pb_(0.32)FeO_3

La_(0.68)Pb_(0.32)FeO_3 samples annealed at different temperature were prepared using citrate sol-gel method. With increasing of annealing temperature from 200 to 1000 ℃, the samples crystallize to have single-phase perovskite structure. However, the sensitivity increases at first due to the improvement of crystallization of the perovskite phase, and finally drops attributed to the larger grain size. The optimal sensitivities for La_(0.68)Pb_(0.32)FeO_3 samples annealed at 400, 600, 800, and 1000 ℃ are 12.14, 14.77, 51.07, and 34.55, respectively.

Solvothermal Synthesis of α-Fe2O3 Porous Nanobelts and Their Enhanced Acetone-sensing Properties

Porous α-Fe2O3 nanobelts have been prepared via a solvothermal route and subsequent calcination. The as-prepared nanostructure was characterized by XRD, FESEM, TEM, N2 adsorption-desorption isotherms, etc. The α-Fe2O3 nanobelts presented obvious porous structures with the length of ca. 1~2μm, width of ca. 200~350 nm and thickness of ca. 30~60 nm. It was found that the assistance of inorganic additives played an important role in the shape control of α-Fe2O3 nanostructure. The gas-sensing performance of the fabricated sensor based on α-Fe2O3 nanobelts sample was also investigated, and the response towards 1000 ppm acetone can reach 24.4. In addition, the gas-sensing conductive mechanism of the sensor was also proposed.

Two-dimensional transition metal MXene-based gas sensors:A review

As an emerging star in the family of two-dimensional(2D)materials,2D transition metal carbides,carbonitrides and nitrides,collectively referred to as MXenes,have large specific surface area,rich active sites,metallic conductivity and adjustable surface chemical properties.These features make MXenes promising candidates for gas-sensing materials.For the past few years,MXene-based sensors have drawn increasing attention due to their enhanced sensor performance.Based on this,this review systematically represents the structure,synthesis methods and properties of MXenes,and summarizes their applications in gas sensors.Firstly,the types,structure,main synthesis methods and properties of MXenes are introduced in a comprehensive way.Next,the corresponding design principle and working mechanism of MXene-based gas sensor are clarified.Subsequently,the sensing performances of pristine MXenes and the MXene-based nanocomposite are discussed.Finally,some future opportunities and challenges of MXene-based sensors are pointed out.

Strategies and challenges for enhancing performance of MXene-based gas sensors:a review

With the advantages of metal conductivity,large specific surface area,and rich surface functional groups,two-dimensional(2D)MXenes have shown great potential in the field of gas sensing.However,gas sensors fabricated with pristine MXenes generally suffer from several problems such as low sensitivity,poor selectivity,significant baseresistance drift,and poor environment stability.Therefore,many efforts have been devoted to overcoming these problems.In this review,we review the progress on MXenebased gas sensors and summarize several efficient strategies(including structural design,surface modification,inorganic Schottky j unction/heterojunction sensitization,polymer addition,and metal-ion intercalation)to promote the gassensing performance.In addition,the major challenges and future development directions of MXene-based gas sensors are also outlined in the present review.