Fabrication And Gas Sensing Properties Of Metal Oxide Semiconductor Micro/Nanostructures

Nowadays, highly sensitive gas sensors have attracted tremendous attentionbecause of their prominent roles in the areas of environmental monitoring, industrialproduction and disease diagnoses. Metal oxide semiconductors based gas sensorshave been intensively studied due to low cost and good gas sensing performances.And the basis of high performance gas sensors is excellent sensing nanomaterials formetal oxide semiconductors based gas sensors. In order to effectively detect toxic andcombustible gases, significant efforts have been focused on exploring variousfunctional materials. However, simple, environmentally friendly and low costfabrication method without stern experiment conditions or the emission of noxiousgas still remains a challenge. In this paper, with the aim of fabricating highperformance gas sensors, various semiconductor nanomaterials with uniquemorphologies and high gas sensing performances are synthesized by simple and facilemethods. In addition, surface modification and component control for purenanomaterials are carried out to improve selectivity, sensitivity and response/recoveryspeed. The main research contents are summarized as follows:(1) Nanoscale single crystalline In2O3nanoparticles with sizes of10-40nm areprepared by annealing room temperature-synthesized In2S3nanoparticles. In2O3nanoparticles present slight aggregation. The room temperature photoluminescence(PL) spectroscopy demonstrates the existence of oxygen vacancies in In2O3nanoparticles. Gas sensors based on the as-synthesized In2O3nanoparticles arefabricated and exhibit favorable gas sensing performances towards acetone, which areattributed to small crystal sizes and the existence of oxygen vacancies. In order tosolve the issue of the aggregation, the irregular ultrathin ZnO nanoplates arefabricated by a facile room temperature solution route and the subsequent annealingtreatment. ZnO nanoplates are about10nm in thickness and their surfaces are rough.Unique morphologies with thin and rough surfaces make ultrathin ZnO nanoplatesexhibit a good selectivity, a superior sensitivity and a fast response speed towardsethanol. (2) In order to improve sensitivity and selectivity, the noble metal is induced toconstruct noble metal-oxide semiconductor hierarchical architectures. NanoscaleAg-loaded sunflower-like In2O3hierarchical nanostructures are fabricated by a simpleand facile route. The gas sensing performances of different Ag contens in thecomposites are investigated. Gas sensing tests indicate that Ag-In2O3hierarchicalnanostructure with an appropriate Ag content shows a better selectivity and a highersensitivity, while more Ag contents in the composites deteriorate gas sensingperformaces. Novel sunflower-like hierarchical architectures with rough surfaces andthe chemical and electronic sensitization effect of Ag nanoparticles endow Ag-loadedIn2O3nanostructures with excellent HCHO gas sensing performances.(3) Hierarchical heterostructures based on two oxide semiconductors aredesigned, fabricated and applied to gas sensors to improve gas sensing performances.In2O3nanoparticle-decorated flowerlike ZnO hierarchical architectures or Pd0.5Pd3O4nanoparticle loaded ZnO hierarchical architectures have been successfully synthesizedby a simple and facile two-step approach, including the room temperature synthesis offlowerlike ZnO and the subsequent decoration with In2O3or Pd0.5Pd3O4nanoparticles.For two hierarchical heterostructures, the results of FESEM, TEMå'ŒHRTEM confirmIn2O3or Pd0.5Pd3O4nanoparticles have successfully grown and are closely attached tothe surfaces of ZnO hierarchical structures. The sensors based on In2O3-ZnOhierarchical architectures show enhanced HCHO gas sensing performances. Thesensors based on Pd0.5Pd3O4-ZnO hierarchical architectures shows excellent methanolgas sensing performances. In addition, the gas sensing performances of differentnanoparticle contents in the composites are investigated. The enhanced gas sensingperformances of two hierarchical heterostructures can be explained by the special3Dhierarchical architectures, the appropriate decoration amount of In2O3or Pd0.5Pd3O4nanoparticle and extra electron depleption layers located at the interfaces between(In2O3or Pd0.5Pd3O4) nanoparticles and ZnO nanoplates.