Preparation Of SnO₂-based Composites Through Electrospinning And Study On Gas Sensing Performances

In this paper,Sn O₂ based one-dimensional micro-nano structure with various micro-morphologies composites are prepared via electrospinning technology,including porous and hollow Sn O₂/Ni O fibers,porous and hollow Sn O₂/Zn₂Sn O₄ fibers,hierarchical Sn O₂/In₂O₃structure,and porous and hollow Sn O₂/Cu O fibers.A series of Sn O₂-based 1D structures with adjustable size and controllable morphology can be obtained by effectively constructing the suitable heterojunction,and adjusting the crystal nucleation and growth process.The improvement of gas-sensing performances for target gas caused by the phase composition,micro morphology and surface/interface electron transport are systematically studied,and proposes the novel gas-sensing enhancement mechanism.The results show that more electron-hole pairs are produced under the UV light excitation,in which provides greater carrier concentration and faster surface electron transport efficiency,leading to the significant enhancement of the gas-sensing behaviors of the materials.The main research contents of this paper are listed as follows:1.Porous and hollow Sn O₂/Ni O heterostructures with excellent surface electron transfer properties are successfully prepared by appropriate electrospinning technology.Various micro-morphology can be obtained after high temperature calcination by adjusting the adding amount of Ni component and the crystal nucleation and growth process of Sn O₂ and Ni O.Meanwhile,the evolution mechanism of different microstructure is explored.The results show that the introduction of Ni O crystal phase into Sn O₂ matrix fibers can significantly improve the gas-sensing performance of Sn O₂/Ni O composites to n-butanol gas.For example,all samples show the best response value at 280℃;the response of Sample 3 heterostructure for 100 ppm n-butanol gas at the optimal working temperature can reach up to 199,which is 4.5 times than that of pure Sn O₂ fibers;compared with pure Sn O₂ fibers,the response/recovery time of Sample3 can significantly decrease from 57/16 to 36/10 s;Sample 3 also exhibits better stability and selectivity.The gas-sensing enhancement mechanism is mainly attributed to the formation of Ni O-Sn O₂ p-n heterojunction and hollow and porous 1D structure,which can provide large specific surface area and a large number of active sites,promoting the reaction between n-butanol molecules and oxygen species on the material surface.2.Porous and hollow Sn O₂/Zn₂Sn O₄ composites have been synthesized by adjusting the amounts of ZIF-8 added in the precursor solution through a modified electrospinning technology.Compared with the gas-sensing performances of different samples detected in the normal condition,it is confirmed that the optimal working temperature can be markedly decreased from 260 to 120℃under UV light excitation,along with the substantially improved gas selectivity.For example,under the optimal working temperature of 120℃,Sn O₂/Zn₂Sn O₄heterostructures exhibit a higher response（increases from 1.7 to 2.8）and faster response/recovery times（decreases from 24/154 to 14/42 s）to 100 ppm triethylamine（TEA）than that of the pure Sn O₂.The gas sensor based on Sn O₂/Zn₂Sn O₄ heterostructure shows the application prospect in the field of freshness evaluation of seafood products by effectively detecting the gas released in the process of seafood storing.The improved surface electron migration produced by UV light excitation can enhance the synergistic effect between the formation of n-n heterojunction and tunable surface/interface electron transport behavior,and promote the adsorption and desorption of TEA molecules on the surface of the sensing materials.3.Hierarchical Sn O₂/In₂O₃ heterostructures are successfully fabricated by a facile and easy electrospinning technology.It can be found that the 1D hierarchical structure is made up of matrix fiber and nanoparticles on the surface.The increase of In-MIL-68 addition can increase the number and reduce the average diameter of nanoparticle on the surface,along with the reaction capacity of Sn O₂/In₂O₃ can be enhanced through higher specific surface area.Under the normal conditions without the excitation of UV light,Sn O₂/In₂O₃ exhibits a higher optimal working temperature of 300℃and unsatisfactory selectivity.However,the optimum working temperature of Sn O₂/In₂O₃ observably decreases from 300 to 90℃after introducing UV light excitation with a power of 120 m W/cm².Meanwhile,Sn O₂/In₂O₃display other superior gas-sensing performance,for example,better response for 100 ppm TEA（6.47）,smaller limit value of detection at the optimal working temperature（1.07 ppm）,and excellent selectivity for TEA.The excellent practice ability of the gas sensor prepared based on Sn O₂/In₂O₃is evaluated by detecting the gas released during the storing of prawns.The enhanced TEA-sensing performances of Sn O₂/In₂O₃ composites can be explained that the advantages of the electron migration adjusted by effective n-n heterojunctions and the absorption-desorption process improved by special hierarchical and porous structures are further enhanced under UV light excitation.4.Porous and hollow Sn O₂/Cu O fibers with adjustable morphology are successfully prepared by changing the adding amount of Cu-MOF in electrospinning precursor solution.With the increase of the addition amount of Cu-MOF,the diffraction intensity of（110）crystal plane is significant increase,indicating that Cu-MOF can effectively control the crystal nucleation and growth process of Sn O₂/Cu O composites.For example,Sn Cu 2 displays hollow and porous 1D microstructure with ordered arrangement of nanoparticles.Under the normal conditions without the excitation of UV light,all samples can be detected at 50℃for 50 ppm TEA,but the phenomenon of the low response and the poor resistance stability can be obtained.However,after introducing UV light excitation,all samples show better TEA-sensing performances at room temperature.Among them,Sn-Cu 2 exhibits the best TEA-sensing behavior,for example,better response for 50 ppm TEA（3.5）,compassable desorption of TEA molecules,excellent cycle stability,and smaller attenuation rate of response（0.33%）toward unit relative humidity change.The TEA-sensing enhancement mechanism is mainly attributed to the generation of large number of electron-hole pairs in the material caused by UV light excitation,which effectively regulates the electron transport behavior and carrier concentration on the surface/interface of the material,along with improving the directional transfer process between Cu O-Sn O₂ p-n heterojunctions.And then,more adsorbed oxygen species can be produced by capturing more free electrons from the surface conduction band of the gas sensing material,and the chemical reaction with TEA gas molecules is effectively promoted.In addition,the unique microstructure of the material provides abundant active sites and gas molecule transmission channels for TEA-sensing behavior.