Preparation Of One-dimensional Modified SnO₂ Composites And Research On NO₂ Gas Sensitivity

In order to efficiently detect and monitor the pollutant NO₂ gas,pristine SnO₂ and modified SnO₂ nanotube materials were prepared by electrospinning combined with high temperature calcination.The morphology and structure of the modified materials were analyzed by XRD,FT-IR and XPS.The gas sensing properties of the modified materials were tested at RT.The gas sensing mechanism was discussed.Firstly,pristine SnO₂ and CeO₂ surface modified SCCTs nanotubes were prepared by electrospinning and high temperature calcination using ethanol and N,N-dimethylamide?DMF?as solvent and polyvinylpyrrolidone?PVP?as the shape regulator.The modified SCCTs have more pores and are composed of smaller particles?12-18 nm?.The test results of NO₂ at RT show that the response of CeO₂ modified material is higher than that of pristine SnO₂ for 100 ppm NO₂.The best sample 2-SCCT response was as high as 8.88,the response time was 1.33 s,and the detection limit was as low as 0.03 ppm.Secondly,Al₂O₃ doped and modified SACTs nanofibers were prepared by high voltage electrospinning.After calcination,a porous tubular structure composed of 10-30nm particles was formed,and the pore diameter was mainly concentrated at 2-50 nm.The study found that the modified materials have significantly improved gas sensitivity.Among them,the best sample 8-SACT can reach 8.79 at 100 ppm NO₂ at RT,the response time is only 2.67 s,the detection limit is up to 10 ppb,and it has good selectivity and repeatability to NO₂.The increase of oxygen vacancies?or oxygen defect structure?in the modified material leads to an increase in p-type conductivity?hole density?,which is favorable for the adsorption of oxygen on the surface of the material and the adsorption of NO₂.Thirdly,PdO functionalized SnO₂ nanotube materials SPCTs were prepared by one-step electrospinning synthesis.SEM or TEM results show that the modified material has a large number of mesopores and many hetero/homomorphic junctions.The gas sensitivity test at RT showed that the best 3-SPCT sample with a molar ratio of SnO2:PdO of 100:3 showed excellent gas-sensitivity response?²0.30?and response time as low as 1.33 s for 100 ppm NO₂.The detection limit is as low as 10 ppb and better selectivity.The reason is that a large number of mesopores in the material provide more channels for gas diffusion and adsorption,which increase the gas adsorption site;the hetero/homojunction can act as an electron transport channel,which accelerates the electron transport rate and improves the NO₂ gas sensitivity.Finally,the best performance ratios of Al₂O₃ doped and PdO functionalized SnO₂nanotubes were selected and combined with the above preparation methods,SAPx nanotubes modified by Al₂O₃ and PdO were prepared.Its surface is rough porous and has many lattice defects.At RT,the modified material SAPx showed high response?²7.22?to 100 ppm NO₂,good stability and excellent selectivity.The improvement in gas sensitivity is attributed to the synergy of Al₂O₃ and PdO.On the one hand,Al₂O₃doping distorts the SnO₂ lattice,promotes the formation of oxygen vacancies,and promotes the rate of surface adsorption of oxygen and electrons.On the other hand,PdO functionalization improves the electronic structure of SnO₂ nanotubes,which is prone to Pd²⁺?Pd⁴⁺transition.PdO/PdO₂ as the active center of NO₂,further improving NO₂ gas sensitivity.