Study On Regulation Of The Selectivity Of SnO₂ Based Materials

With the improvement of people's live and the increasing emphasis on environmental protection,higher requirements have been imposed on the monitoring of various toxic and harmful polluting gases in the atmosphere,and the detection of food safety and indoor air quality.Metal oxide gas sensors have become the first choice for toxic and harmful gas detection due to their many advantages such as high sensitivity,response quickly,easy miniaturization and easy integration.Due to the characteristics of the broad-spectrum response of metal oxides,selectivity has become an important factor restricting the development of metal oxide gas sensors.Gas sensing process includes:diffusion,adsorption,surface competition reaction,desorption,and diffusion.Factors that affect gas sensitivity and selectivity include:the diffusion of gas molecules on the surface of metal oxides,the adsorption of gas molecules on the surface of metal oxides and the competitive reaction on the surface of metal oxides.In this paper,surface defects are increased by metal ion substitution doping,so that more active sites are formed on the surface of the metal oxide,and the reactivity of adsorbing oxygen on the surface is changed,thereby improving the gas sensitivity selectivity of the metal oxide.Sn O₂ was used as the matrix material,and Nb⁵⁺with different concentrations were doped.The gas sensingproperties of Sn O₂ sensors with different concentrations of Nb⁵⁺to ethanol,acetone,formaldehyde,and xylene were studied.It was found that Nb⁵⁺doping can effectively improve the response to different VOCs,especially 5 mol%Nb doped Sn O₂ can significantly improve the sensitivity and selectivity to acetone.Secondly,the active catalytic sites on the metal oxidation surface are increased by supporting noble metals,and different surface reactions are catalyzed to increase selectivity.At the same time,combined with the selective permeability of the porous filter membrane,the selectivity is improved by depositing a porous membrane on the surface of the metal oxide.Pt-modified Sn O₂(Pt-Sn O₂),Pd-modified Sn O₂(Pd-Sn O₂),Pt-modified WO₃(Pt-WO₃),and Pd-modified WO₃(Pd-WO₃)gas sensing film was made by ball milling and screen printing.Then,Si O₂ filter membrane was deposited in situ by spray pyrolysis.The gas sensing performance test of H₂,CO,NO,and NO₂ gas shows that Pt-Sn O₂,Pd-Sn O₂,Pd-WO₃,and Pt-WO₃ after the deposition of Si O₂ filter filmshowed selectivity to CO,NO,NO₂ and H₂ at their optimal working temperature,respectively.Finally,in order to study the competitive reaction on the surface of metal oxides in the presence of multi-component gases,Sn O₂and Pt-Sn O₂,which have better selectivity to NO at low temperature,were selected to study the interference of VOCs to the selectivity of NO at low temperature.Comparing the response of two sensors to different VOCs at 150?in air background and in1ppm NO background,it was found that the presence of NO can significantly improve the response of Pt-Sn O₂ to VOCs at low temperature,and this experimental result breaks the traditional definition of selectivity under single-component gas test.the selectivity was redefined by defining the response of VOCs under the multi-component gas test with the interference was considered.