| With the rapid development of modern technology and industry,the detection of VOCs gases has become one of research focus around the world.Due to good performance,low cost and convenient to use,gas sensors based on metal oxide have received more and more concern from researchers.To meet the urgent need of modern industrial production and people's life health,developing materials with good permeability,controlling the morphology,specific surface area and element content of materials,proper choice for dopant or catalyst could improve the performances of gas sensors effectively.This dissertation was devoted to the design and development of SnO2 nanostructures,the research of modifying or catalytic methods,the theoretical studying and simulating calculation of gas sensing mechanism.Firstly,SnO2 nanoparticle material with rutile structure has been prepared through a sol-gel synthetic method,a positioning method guided by droplets has been developed to fabricate low-power MHP-based sensors.SnO2/TiO2 composites exhibited higher response to ethanol,for electrons migrated from TiO2 to SnO2 and an electron accumulation layer was formed on the surface of SnO2 due to the height difference of Fermi level,this facilitated the adsorption and ionization of atmospheric oxygen on materials surface,and hence the resistance of material in air increased.When reductive target gas reacted with adsorbed oxygen,electrons would be released back to material surface,surficial electrons became more and migrated into the interior of material,the resistance was reduced and therefore the response value increased.The gas sensing enhanced mechanism of SnO2/CNT composites was owe to the porous pipeline nanostructure and the catalytic "spillover" effect,which could further facilitate the adsorption and dissociation of oxygen molecule in air and improve the gas sensitivity finally.Density Functional Theory has been used to calculate the surface structure and physical properties of SnO2 bulk material and its(110)surface,the adsorption of oxygen on ideal SnO2(110)surface and SnO2(110)surface with oxygen vacancy.The adsorption of typical target gases on SnO2(110)reductive surface with pre-adsorbed oxygen have also been calculated and the results showed that the average adsorption energy,the charge transferred and the change of band gap in the case of ethanol were the most in quantity,so the selectivity to ethanol was the best,which was in good agreement with the experimental phenomena.To maintain the advantages of nanoparticles and avoid the agglomeration phenomenon in the meantime,a method using carbon spheres as templates was developed to synthesize CuO/SnO2 hollow microspheres.The prepared porous CuO/SnO2 composites exhibited better sensing properties to ethanol than other gases.The contribution of porous hollow microsphere structure and the obvious change of material conductivity caused by the p-n heterostructure between CuO and SnO2 particles could be ascribed to the enhancement of ethanol sensing performances.The adsorption of O2 molecule on SnO2(110)reductive surface,the adsorption of target gases on Cu doped and O2 pre-adsorbed SnO2(110)reductive surface were calculated.The results showed that O2 molecule could be chemically adsorbed on SnO2(110)reductive surface and electrons could be transferred between the two.When O2 molecule was placed above Cu vertically or parallelly with OA axis,and ethanol molecule was placed above the pre-adsorped oxygen vertically,the adsorption energy and electron transferred of ethanol were both the most and this explained the selectivity to ethanol of CuO/SnO2 composites.Porous SnO2 hollow microspheres were synthesized through a synthetic method combined with sol-gel/carbon sphere template and Ag nanoparticles were modified onto SnO2 microspheres through the reduction reaction of AgNO3.Ag/SnO2 composites showed excellent sensitivity and good selectivity tomethoxy propanol,the improved gas sensing mechanism could be due to the porous structure and the catalysis of Ag nanoparticles.Adsorption of oxygen molecule and target gases including methoxy propanol on Ag decorated SnO2(110)surface were calculated.The results showed that when Ag was decorated above Sn atom and oxygen molecule was placed above Ag atom vertically,the adsorption energy and charge transferred were both the most in quantity,and then the influence to conductivity of material was the most.The calculation results verified the catalytic effect of Ag to the improvement of methoxy propanol sensitivity of Ag/SnO2 composite in experiments.Hierarchical and self-assembly nanomaterials are advantageous to the transport and adsorption of gases.Biomimetic materials were prepared using loofah sponge and eggshell membrane as templates respectively,which could offer developed gas transport channels on different scales such as micron,submicron and nanometer.This synthesized material showed good gas sensing performances to ethanol and then has potentials in the field of gas detection.In brief,this paper focuses on the application of mental oxide materials in gas sensor,the design and development of microstructure for SnO2 nanomaterial,the modifying or catalytic methods,the research of gas sensing mechanism and the simulating calculation of physical properties and gas adsorption of SnO2(110)surface are the four main tasks of' this research. |
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