| Gas sensors are widely used in various fields such as medical diagnosis,environmental monitoring,public safety.Therefore,seeking and designing efficient gas-sensitive materials is the key for developing advanced gas sensors.Ordered mesoporous metal oxides with porous structure and high specific surface area are a class of very promising gas-sensing materials.p-type semiconductor metal oxides with ordered mesoporous structures ehxibited relatvely lower gas-sensing response than those of their n-type counterparts and were rarely investigated.In this dissertation,p-type nickel oxide semiconductor was taken as an example to demonstrate the design and synthesis of ordered large-pore mesoporous nickel-based oxides with controlled framework structure and composition by a hard template method and their significantly enhanced gas-sensing performances by metal ion doping and noble metal functionalizing.First,a series of ordered mesoporous nickel oxide materials were synthesized by hard template method using ordered mesoporous silica KIT-6 as the template and nickel nitrate as the precursor at different calcination temperatures(300,400,500,600 and 750?).The resultant products have large pore size(11 nm)and high specific surface area(121?129 m2/g).Their response toward formaldehyde gas increased with the calcination temperature,whose response toward 90 ppm of formaldehyde(Rgas/Rair)is up to 21.2.Second,a series of chromium-doped ordered mesoporous nickel oxide materials were synthesized by a hard template method by using ordered mesoporous silica KIT-6 as template,chromium nitrate and nickel nitrate with different molar ratios(Cr/Ni =0.1,0.15,0.2,0.25,0.3)as mixed precursors.The resultant products maintain an ordered large-pore(11 nm)structure after doping Cr ions,which leads to a decrease in hole carrier concentration and a increase in specific surface area(171?218 m2/g),thus resulting in a significant increase in response to formaldehyde gas.The response of the material to formaldehyde gas is increased with with the increase of chromium doping.The response reach to maximum when the Cr/Ni is up to 0.2,its response(476)to 90 ppm of formaldehyde increased 126 times compared with pure mesoporous nickel oxide.When further increasing Cr/Ni,additional NiCrO4 byproducts appeared and resulted in a decrease in the gas-sensitivity response.Third,a series of Sn-doped ordered mesoporous nickel oxide materials were synthesized by a hard template method using KIT-6 as template,tin tetrachloride and nickel nitrate with different molar ratios(Sn/Ni=0.1,0.15,0.2,0.25,0.3)as mixed precursors.The resultant mesoporous Sn-doped NiO materials retained an ordered large mesoporous(11 nm)structure.The introduction of tin ions led to a decrease in hole carrier concentration and a increase significant increase in specific surface area(171?218 m2/g)in the material,thus leading to a significant increase to the response for formaldehyde gas.When Sn/Ni was increased to 0.25,the response of the material to formaldehyde gas get to the highest,whose response(346)toward 90 ppm of formaldehyde was 91 times higher than that of the pure mesoporous NiO material.When further increasing Sn/Ni,SnO2 byproducts appeared and resulted in a reduced the gas response.Fourth,we also use KIT-6 as a template,chromium nitrate,nickel nitrate,and noble metal salts are mixed precursors to synthesize a series of ordered large-pore mesoporous chromium doped nickel oxides functionalized by different noble metals(Au,Pt,Ag,Pd).The resultant materials exhibited an ordered large pore size(11 nm)structure and a large specific surface area(221?268 m2/g).It was found that the response of the resultant products functionalized by 5 wt%of Au and Pt toward 90 ppm of formaldehyde was 878 and 1069 respectively,which was 1.84 and 2.25 times higher than that of the ordered mesoporous chromium-doped nickel oxide respectively.However,the response of the resultant products functionalized by Ag and Pd toward formaldehyde significantly decreased. |
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