Construction Of Ordered Porous Nano-SnO₂ Based Gas Sensor And Its Performance Study

The emission of toxic gases and soot into the atmosphere from industrial production has caused serious air pollution and is a serious threat to the human environment.Oxide semiconductor gas sensors have the advantages of high reliability,integration and stability,and have been a hot spot for research in the field of gas sensors.Tin dioxide,as an n-type semiconductor oxide,has the advantages of abundant raw materials and low price,so tin dioxide is finally chosen as the gas-sensitive material for research.For SnO2-based sensors,the change in electron concentration in the SnO2 material is a result of chemisorption on the gas surface,and its gas-sensitive properties are closely related to the surface properties of the material.Conventional SnO2 materials are not conducive to gas adsorption due to overly dense particle agglomerates,resulting in defects such as low sensitivity,long response and recovery times,and high power consumption.Therefore,to improve their sensitivity performance,future research on SnO2 semiconductor materials will be directed towards multi-dimensionality,layering and multi-vacancy,and secondly,doping with elemental noble metal elements is also one of the development directions.Therefore,in this thesis,SnO2 nanomaterials are used as gas-sensitive materials,and their surface morphology is modulated to construct three-dimensional ordered porous micro-nano-structures,which improve the utilization of the gas to be detected.At the same time,the doped elements are modified to optimize the response function of the sensitive material and to enhance the sensitivity of the gas sensor.The specific study consists of the following three parts:(1)This paper reports the preparation of 3D ordered porous SnO2 with different diameters(103 nm,546 nm,1030 nm)by a simple template method.Scanning electron microscope(SEM)images proved the successful synthesis of uniform distribution of 3D ordered porous SnO2 nanostructures,at the same time using the X-ray powder diffraction(XRD)and energy dispersive spectrum(EDS)and X-ray photoelectron spectroscopy(XPS)was carried out on the material of crystal structure and elements of characterization analysis confirmed that the synthesis of the pure SnO2 nanomaterials.We find that 103 nm porous SnO2 nanomaterials have the highest response(30)and fastest response/recovery time(3/10 s)towards 100 ppm HCHO compared with 546 nm(24,3/17 s)and 1030 nm(10,6/20 s)porous SnO2 nanomaterials at low working temperature(220℃).All three sensors show good long-term stability,repeatability,and linearity.The results show that lessening the diameter of the porous SnO2 materials could increase gas-sensitive performance to HCHO effectively.The enhancement of gas sensitivity is attributed to the ordered porous structures,large specific surface area,and more oxygen vacancies on the surface.(2)Pure and Ga-doped 3D ordered porous SnO2(3DOPS)nanomaterials were synthesized by a simple template method,and SnO2 nanoparticles(NPs)were prepared by an annealing process.SEM images proved that the 3D-ordered porous SnO2 nanostructure was successfully synthesized.The presence of Ga in 3DOPS was determined by XRD,EDS,and XPS.The surface areas of the porous structure were measured by the BET method using a middle-high pressure physical gas adsorption instrument.Due to the porous structure and dopant effects on the SnO2 nanomaterials,3 at%Ga-doped 3DOPS has the largest specific surface area(61.58 m2/g)compared with pure particle tin dioxide(38.60 m2/g).The 3 at%Ga-doped 3DOPS-based sensor exhibits a lower detection limit(2/0.1 ppm)and improved sensitivity(55/50 ppm)to formaldehyde(HCHO)at a low temperature(210℃),and the response is 6.5 times higher than that of the pure SnO2 NP-based sensor(8.5/50 ppm).However,the response of pure 3DOPS(18/50 ppm)is only twice as high as that of the pure SnO2 NP-based sensor.In addition,the 3.0 at%Ga-doped level of the SnO2 sensor showed a fast response time(2 s)and excellent selectivity.The high sensitivity of SnO2 can be explained by the increase in the specific surface area and porosity brought by the 3D ordered porous structure and the modified surface structure by precious metals(3)The pure and Yb-doped 3D ordered porous SnO2 with a controllable pore diameter(around 50 nm,800 nm,and 1200 nm)were prepared by a simple template method.3 at%Yb-doped 51.3 nm ordered porous SnO2(51.3 nm SnO2/3%Yb)showed the largest specific surface area(70.08 m2/g)and the biggest oxygen vacancy in nitrogen adsorption-desorption and XPS analysis.The response of 51.3 nm SnO2/3%Yb is 95 against 50 ppm HCHO at 108℃,which is 3.7 times higher than 1228.0 nm SnO2/3%Yb(27),2.1 times higher than 806.0 nm SnO2/3%Yb(45),and 2.4 times higher pure 57.3 nm SnO2(40).However,the response of pure 57.3 nm SnO2(40)is only 2.9 times higher than pure 1231.0 nm SnO2(13.5),and 1.2 times higher than pure 832.1.0 nm SnO2(30).Especially,the detectable formaldehyde(HCHO)of 51.3 nm SnO2/3%Yb minimum limit has been reduced to 50 ppb and the relevant response is 3.5.Besides,51.3 nm SnO2/3%Yb also exhibited high linearity(50 ppb-200 ppm),a fast response time(2 s),and excellent selectivity toward HCHO.Above all,for the same kinds of SnO2 nanomaterials,the smaller the pore size is,the stronger sensitivity it will be,and under the effect of Yb doping,the gas sensitivity is enhanced more significantly with the decrease of the pore size.Besides,for the same kinds of SnO2 nanomaterials that have the same pore size,the gas-sensitive property is also significantly enhanced due to the doping of Yb.