Preparation And Gas-sensitive Properties Of Polyoxometalates/Semiconductor Three-layered Coaxial Nanofibers

Inorganic semiconductor is one of the most important gas sensing materials.However,the single semiconductor gas-sensitive materials have higher carrier recombination rate,which limits their development in gas sensitive field.The band structure of Polyoxometalates（POMs）is similar to that of semiconductor materials and can act as electron acceptors to promote carrier migration in semiconductor materials.At present,there is no report about the application of Polyoxometalates/semiconductor with tandem heterojunction materials in the field of gas sensing.Therefore,it is of great significance to construct Polyoxometalates/semiconductor three-layer coaxial nanofibers to form Polyoxometalates/semiconductor tandem heterojunction,and using such materials to the exploration of gas sensitive properties.In this study,a series of one-dimensional Polyoxometalates/semiconductor composite nanomaterials were prepared by electrospinning technology.The structure,morphology and gas sensing performance of the nano-materials were studied,and the sensing mechanism was proposed.The main results are as follows:1.The Sn O₂@PW₁₂@WO₃three-layer coaxial nanofibers containing different mass fractions of Polyoxotungstic acid(PW₁₂)were successfully constructed by coaxial electrospinning technology,and their gas-sensitive properties were investigated.It wans found that the optimized sample has the highest response to ethanol gas,with a response value of 8.8.Moreover,it has good selectivity and sensitivity.The main reason for the improvement of the gas sensing performance is that two n-n tandem heterojunctions are formed between Sn O₂/PW₁₂and PW₁₂/WO₃,which can effectively promote carrier migration in gas sensitive materials and improve the sensing performance.2.The three classical Keggin-type Polyoxometalates of PMo₁₂,PW₁₂and Si W₁₂have obvious differences in their central/coordination atoms,which may have different effects on the gas sensitive properties.Therefore,In order to explore the difference of gas sensing performance of different Polyoxometalates,Sn O₂@POMs@WO₃three-layer coaxial nanofibers with these three Polyoxometalates as middle layers were constructed.The structure-activity relationship of gas sensing performance parameters between different Polyoxometalates was systematically studied.3.In order to explore the influence of Polyoxometalates on the properties of In₂O₃gas sensitive material,In₂O₃/PW₁₂composite nanofibers were fabricated by electrospinning way.The photoconductivity and gas sensing properties were investigated.The results show that the photoconductivity and gas sensing performance of In₂O₃/PW₁₂composite nanofibers were improved obviously.The reasons for the performance improvement are as follows:In the competition of photoelectron separation and migration in In₂O₃,the introduction of PW₁₂promotes the separation of photocarriers and accelerates their migration,which process has weakened photoproduction electron-hole pair recombination and increase the utilization of electrons,thus improving the gas sensitive performance.4.The In₂O₃@PW₁₂@Sn O₂three layered coaxial nanofibers were constructed by one-step coaxial electrostpinning technology using the properties of Polyoxometalates electron acceptor.The gas sensing properties of the nanofibers were also explored.The response of the best sample to 100 ppm ethanol can reach 22.6 at 320°C,and the response time is only 1 s.The sample has good selectivity to ethanol,showing good gas sensing performance.Four kinds of Polyoxometalates/semiconductor gas sensors performances prepared by electrospinning way were improved significantly.It is mainly due to introduction of POMs as electron acceptor,the formation of tandem heterojunction and the one-dimensional nanostructures,which can play a synergistic role to promote the free electrons directional migration in the semiconductor,and finally show the improvement of gas sensitive performance.The results of this dissertation provide a new idea for the development of high-performance gas sensors and a theoretical basis for the development of Polyoxometalates gas sensors.