Research On Synthesis Of Semiconducting Metal Oxide Nanomaterials And Their Gas Sensing Properties

The internet of things（IOT）also known as sensor network is an important part of the future information technology and an important development stage of the informationization era.The IOT is anything connected to the internet,through the radio frequency identification,infrared sensors,global positioning system,laser scanner,various types of sensing equipment,etc.which according with the contract agreement and exchange information in order to realize intelligent identification,location,tracking and management.The terminal of the IOT is sensors,which connect any objects together.Sensor is a physical device or biological organ,which can detect or feel the outside of the signal,the physical conditions（e.g.light,heat,humidity）or chemical composition（e.g.gas,smoke）and translate the information to other devices or organs.For decades of research and development,metal oxide semiconductor（MOS）gas sensors have been widely applied for their advantages of simple structure,low cost,high sensitivity,rapid response.Development of nanotechnology injected new blood in the research of MOS material microstructure,so the preparation of gas-sensitive materials using nanotechnology is an important way to improve the performance of gas sensor.This paper mainly focuses on the problems of MOS gas sensor in the detection to design and develop efficient and green synthetic strategies for the preparation of micro-nanostructure MOS sensitive material.It is well known that high sensitivity,rapid response,and excellent selectivity are three of most important properties for MOS gas sensors.The main contents are as follows:（1）V₂O₅-decorated a-Fe2O3 composite nanorods were synthesized successfully by electrospinning and environment-friendly soak-calcination method.The BET method is used to demonstrate the increasing of the specific surface area and mesoporous structure of the composites.Gas molecules can easily be adsorbed on the surface of materials by the van der Waals force.The composite showed high selectivity and stability to diethylamine gas as well as ultra fast response times within 2 s to 100 ppm diethylamine gas.（2）Uniform SnO₂-Co₃O₄ hollow nanocubes have been synthesized successfully by an inexpensive and simple way.Due to the hollow structure,the SnO₂-Co₃O₄ hollow nanocubes behave well in gas sensing toward H2S at 180℃.Considering the annealing temperature may affect the sensing performance,we investigated the products annealed at different temperature.As a result,the SnO₂-Co₃O₄ hollow nanocubes dealt with higher annealing temperature,display a higher sensitive and lower recovery time to H2S at operating temperature.X-ray photoelectron spectroscopy（XPS）was using for confirming the existence of CoS₂ in gas sensor during the H2S atmosphere.（3）The SnO₂-ZnO heterogeneous nanofibers have been prepared via an electrospinning method followed by calcination at 500℃ in air.Compare to the traditional gas sensing materials SnO₂ and ZnO nanofibers,SnO₂-ZnO heterogeneous nanofibers sensors showed excellent gas selectivity and good repeatability of H2S gas due to synergies effects,small size effects and n-n junction.The sensitivity of heterogeneous nanofibers sensors exhibited 3.8 times higher than the sensors of SnO₂ nanofibers and 5 times higher than the ZnO nanofiber sensors,and analysed the mechanism of the gas sensing.（4）We have successfully fabricated the novel Fe2（MoO4）3 microspheres which were self-assembled with nanoflakes through a facile,rapid and green microwave heating method.The reaction processes were accomplished by its dual-hydrolysis-assisted liquid precipitation reaction without using any precipitant.And the Fe2（MoO4）3 nanoparticles have also been obtained just via changing the solvent.The response of the Fe2（MoO4）3 microspheres sensor was up to 8.4 for 30 ppm H2S.Nevertheless,the Fe2（MoO4）3 nanoparticles sensor was only 5.2 for 30 ppm H2S.The response time of Fe2（MoO4）3 microspheres sensor was 8 s for 50 ppm H2S.These results demonstrated that microwave irradiation was an effective method to obtain Fe2（MoO4）3 nanomaterials and the Fe2（MoO4）3 microspheres material which were self-assembled with nanoflakes was a potential candidate for the high performance H2S gas sensor.