| With the development of industry and the extensively application of motor vehicles,atmosphere pollution problems have been attracted increasing attation.Nitrogen dioxide(NO2),as a common pollutant of the industrial waste gas and automobile exhaust,is a major inducing factor of acide rain,photochemical smog and haze.It seriously threatens the living environment and human being's heath.Therefore,it is increasing significant to develop a sensing material with superior gas sensing properties for NO2 detection.Metal oxide semiconductor nanomaterials were regaded as promising candidates for various toxic/flammable dangerous gases detection due to their high sensitivity,low cost,small dimension and high compatibility with morden electronic devices.However,industrial scale applications of metal oxide-based sensing materials are still hindered because of their poor selectivity and stability,high operating temperature,low response and long response/recovery time to low concentration of NO2.gas.In this paper,the SnO2 and In2O3 based gas sensors with superior NO2 gas sensing performances,such as high sensitivity,superior selectivity,fast response/recovery speed,low operating temperature and good stability,were obtained via the modification of noble metal nanoparticles,the reduction of the metal oxide,construcing the p-n hetero-junction structure and metal ion doping.Besides,the microstructures,electronic structures,chemical compositions and states of sensing materials were analyzed and the enhanced sensing mechanism was further studied.The main contents are summarized as following:(1)The Pt-SnO2 porous nanospheres with different concentrations of Pt nanoparticles were synthesized via the facile solvothermal,pyrolysis,and followed by a chemically reducing process.The Pt-SnO2 porous nanospheres with the size of ca.400-700 nm in diameter exhibit a high specific surface area of 36.3 m2g-1.NO2 gas sensing performances of samples were tested and the infullence of the concentration of Pt nanoparticles on the gas sensing performances was studied.The result shows that the Pt-SnO2 porous nanospheres with an optimized loading amounts of Pt nanoparticles(0.25 wt%Pt-SnO2)display higher sensitivity of 5770 to 5 ppm NO2,and shorter response/recovery time of 30/90 s than pure SnO2 and other reported other sensing materials at a low operating temperature of 80?.Besides,the 0.25 wt%Pt-SnO2 sensor exhibits superior selectivity and good stability to NO2 gas.The sensing mechanism exhibits that the improved NO2 gas sensing performances are contributed to the catalytic function of Pt nanoparticles.The work displays that the modification of noble metal(Pt)nanosparticles is an efficient way to synthesize high-efficiency NO2 gas sensor with superior gas sensing performances at low operationg temperature.(2)In order to investigate the correlation between the electronic structure of the indium oxide and their NO2 gas sensing performances,the In2O3 porous nanospheres with a diameter size of ca.300-500 nm were obtained via facile solvothermal and pyrolysis methods,and the In2O3-x nanspheres with different concentrations of oxygen vacancies were futher synthesized via metallic aluminum reduction at different reducing temperatures in a two-zone tube furnace.NO2 gas sensing performance tests show that the In2O3-x porous nanspheres prepared at the reducing temperature of 300?(Vo-In2O3-300)exhibit high response of 130 to 3 ppm NO2 at 80?,which is almost 2.5-folds as high as the response(55)of the In2O3 porous nanospheres.The sensimg mechanism shows that the improved gas sensing performances are contributed to the increase in surface oxygen vacancies,high electron concentration and mobility,unique porous structure and high specific surface area.The work can provide some instructive thoughts for constructing metal oxide based senismg materials for high-efficient nitrogen dioxide detection.(3)The metal-organic frameworks consisting of metal ion and organic ligands are proved to be an ideal template for synthesizing porous metal oxide nanomaterials.In this work,In2O3 porous microtubes derived from In-MOF were synthesized and then modified by p-type Sb2O3 nanoparticle.Finally,the Sb2O3/In2O3 porous microtubes with an ultrathin wall thickness of ca.20 nm,a big inner diameter of ca.500 nm,and high specific surface area of 100.3 m2g-1 were obtained.NO2 gas sensing property tests display that In2O3 porous microtubes with Sb2O3 loading of 1.5 mol%exhibit high response of 47,short response/recovery time of 80/85 s to 1 ppm NO2 in comparison with reported other sensing materials at 80?.Besides,the 1.5 mol%Sb2O3/In2O3 porous microtubes show superior selectivity and good stability to NO2 gas,and the detection limit of 1.5 mol%Sb2O3/In2O3 porous microtubes toward NO2 is down to 50 ppb.The sensing mechanism investigations reveal that the hetero-junction at Sb2O3/In2O3 interfaces,the catalytic function of Sb2O3,and high specific surface area result in the superior NO2 gas sensing performances of Sb2O3/In2O3 composite materials at a low operating temperature.Therefore,this work provides a promising candidate for the development of high-performance NO2 gas sensors.(4)Transition metal ion doping is an important approach to improve the gas sensing performances of metal oxide-based sensing materials.Combined with the unique structure characters of porous metal oxide nanomaterials,in this work,we have synthesized the Fe-In2O3 porous microrods derived from In/Fe-MIL-68s.The NO2 gas-senisng properties of samples were tested and the influence of the concentration of Fe(?)doping on the NO2 gas-senisng properties of the pure In2O3 was studied.The result displays that the Fe-In2O3 microrods derived from In/Fe-MIL-68s with the Fe(?)content of 5 mol%(Fe(5)-In2O3)exhibit higher response(82)and shorter response/recovery time(70/65 s)towards 2 ppm NO2 at 80? in comparion with their counterparts.Besides,superior selectivity and good stability are observed.The sensing mechanism studies reveal that improved gas sensing performances are attributed to the decrease in gran size,the formation of rich oxygen vacancies and narrow band gaps caused by Fe(?)doping,as well as the porous structure with high specific surface area.Therefore,this work not only demonstrates that the Fe-In2O3 microrods derived from In/Fe-MIL-68s precursors can be a promising candidate for NO2 detection,but also provides significant guidances for constructing high-performance NO2 gas sensors. |
PDF Full Text Request