| Inorganic gases such as H2S,Cl2,and nitrogen oxides(NO2,NO)are the main pollutants that lead to soil and water acidification,as well as environmental disasters,e.g.acid rain and haze.Meanwhile,contacting with these gases can cause eye irritation,respiratory,cardiovascular and neurological diseases,even life danger.Hence,rapid and accurate detection of above inorganic gases have important practical significance for environmental protection and human health.At present,as the earliest commercially available semiconductor sensing material,SnO2 has shown good application potential in real-time monitoring of harmful inorganic gases due to its advantages of low cost,high sensitivity,fast response-recovery,portability and integration.However,most reported gas sensors have not achieved good comprehensive sensing performance so far,and still have the defects of high energy consumption,low sensitivity,slow response-recovery and large detection limit.Meanwhile,the traditional chemical methods for synthesizing mesoporous SnO2 hierarchical structures also have some shortcomings,such as complex operation,poor repeatability and low yield.Even the usage of massive reagents results in environmental pollution and noble metal sensitization also increase the production cost.Accordingly,this thesis explores a simple,low-cost and green template method.That is,waste biomasses were employed as biotemplate to controllable synthesize SnO2 mesoporous hierarchical structures with different biomorphic forms through simple tin salt solution immersion and air calcination,and the fabricated sensors realize the low temperature,high sensing and selective detection of H2S,Cl2,NO2 and NO gases.The main research contents and results include the following parts:1.Waste scallion roots(SR)were employed as biotemplate and immersed in tin chloride solution.Then,SnO2(SR)-600 mesoporous hierarchical structure was simply and controllably prepared by calcining the immersed precursors at 600℃,which realizes the accurate detection of ppb-level H2S under high humidity condition(85 RH%).At low operating temperature of 92℃,SnO2(SR)-600 sensor has a high response value of 106.9 towards 100 ppm H2S,and the actual detection limit is as low as 0.5 ppb.During the concentration range of 0.5～1000 ppb,this sensor shows a good linear relationship and fast response-recovery characteristics.Simultaneously,it also presents satisfactory results in practically monitoring the exhaled breath of human and the decay process of fresh pork in 72 h.2.Treated cabbage leaves(CL)were selected as biotemplate and simply immersed in tin chloride solution.Subsequently,SnO2(CL)-650 wrinkled nanosheets were controllably prepared by air calcining the immersed precursors at 650℃.The fabricated SnO2(CL)-650 sensor exhibits a ultra-high response value of 2460 towards 10 ppm Cl2 at near room temperature.At 92℃,the sensor can quickly recover to initial Ra value and shows a high sensing response to the same concentration of Cl2(S=611),which is 11.8 times higher than that of template-free SnO2-TF-1 sample.Meanwhile,it also has good selectivity,low detection limit and other comprehensive sensing performance.3.Waste bamboo shoot skins(BSS)were employed as biotemplate and immersed in tin chloride solution.Then,SnO2(Bss)-600 mesoporous squama-wrapped hierarchical tubes were controllably prepared by calcining the immersed precursors at 600℃.At 92℃,the response value of SnO2(BS)-600 sensor towards 10 ppm NO2 reaches up to 1300,and the recovery time is shortened to 20 s,both of which are significantly better than most reported metal oxide-based sensors.Meanwhile,it has good selectivity,satisfactory long-term stability and humidity resistance.4.Waste tung seed shell(TSS)and wood hydrangea petals(WHP)were used as biotemplates to synthesize two types of SnO2 mesoporous nanoparticle sheets-wrapped hierarchical tubes(SnO2(TSS)-600 and GC/SnO2(WHP)-600)by simple tin salt immersion and air calcination at 600℃.The SnO2(TSS)-600 sensor has a response value of 107 towards 1 ppm NO at 92℃,while graphitic carbon doped GC/SnO2(WHP)-600 sensor has a high response value of 256.3 to 1 ppm NO at a lower temperature of 50℃.This is also the first time to realize highly sensing detection of SnO2-based sensors to trace NO at near room temperature.Meanwhile,they also have fast recovery characteristics,good selectivity and ppb-level practical detection limit.5.The compositions,microstructures,and oxygen vacancy defects of above SnO2 sensing materials prepared from waste biomass templates were characterized in detail.Meanwhile,XPS and O2-TPD techniques were used to analyze the elemental valence states,changes in content and type of surface adsorbed oxygen species in sensing materials before and after contacting with H2S,Cl2,NO2 and NO gases.Combined with the resistance and response of SnO2(CL)-650 sensors in air and high-purity N2,the sensing mechanism of fabricated SnO2 sensors to corresponding harmful inorganic gases were explored in depth. |
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