Preparation Of Multi-stage Structure Tin Dioxide-based Mesoporous Microtubes And Gas Sensing Properties Of Formaldehyde

Formaldehyde(HCHO),as a colorless pungent odor gas,can induce a lot of diseases.The formaldehyde concentration in China's indoor environment allows should be less than 60 ppb,therefore,simple and effective detection of formaldehyde in the surroundings is necessary.SnO2 is one of the most important N-type wide band gap metal oxide semiconductors,which can detect HCHO.However,the relatively high working temperature(>100?)and detection limit(>100 ppb)of these sensors still need to be further promoted in order to detect ppb-level of HCHO in the surrounding environment.In this paper,the SnO2 mesoporous nanotubes with hierarchical structure were fabricated through solvothermal synthesis.The XRD,SEM,TEM,BET,XPS and other characterization methods were used to analyze the structure and morphology of mesoporous microtubes,and their thick film gas sensor were applied to the to test the gas sensitivity of HCHO and common toxic and harmful gases.The main contents of the thesis are as follows:(1)SnO2 microtube precursors with hierarchical structure were synthesized via solvothermal method,by using EDTA as inducer,three phenyl tin chloride as raw material,deionized water and ethanol as mixed solvent,hydrogen peroxide as oxidant and sodium hydrate to adjust the pH value for the neutral environment.After 500? of heat treatment in air,SnO2 mesoporous microtubes were obtained with smooth surface.The tubes are tetragonal microtubes with the side length of?500 nm,in which the tube length is?4 um and the wall thickness is?50 nm.The tube wall is composed of 5?10 nm nanoparticles,the pore size between particles is about 5?15 nm.The SnO2 microtube sensor has excellent selectivity and sensitivity to formaldehyde gas.The response to 10 ppm HCHO is 6.7 at the optimum temperature of 92?,the response time is 16 s and the lowest detection limit is 10 ppb.(2)Similar CdO/SnO2 microtubes with different mole ratio were obtained via one-pot solvothermal synthesis method.The tubes are also composed of nanoparticles and the nanopore size is about 10 nm.Based on the HCHO sensing measurements,it is found that 2.23 at%CdO/SnO2 microtubes sensors show the best sensing properties.The optimal working temperature rises to 133 0C.The response of CdO/SnO2 sensor to 10 ppm HCHO is 6.04.The response time is decreased to 6 s and the detection limit is lowered down to 1 ppb.(3)similar ZnO/SnO2 microtubes with different mole ratio were obtained via one-pot solvothermal synthesis method.The tubes are also composed of nanoparticles and the nanopore size is about 13 nm.Based on the HCHO sensing measurements,it is found that 2.51 at%ZnO/SnO2 microtubes sensors show the best sensing properties.The optimal working temperature rises to 133?.The response of ZnO/SnO2 sensor to 10 ppm HCHO is 5.61.The response time is decreased to 6.1 s and the detection limit is lowered down to 0.5 ppb.(4)The HCHO sensing mechanism of SnO2,CdO/SnO2,ZnO/SnO2 materials were discussed based on the XPS and GC analysis before and after the sensor expose to the test HCHO gas.The redox reaction of HCHO is taken place on the surface of sensing materials with chemical adsorbed oxygen(O2-)and the final products are CO2 and H2O.