Hydrothermal Synthesis And Gas Sensing Properties Of Nanostructured In₂O₃ And Nanocomposites

Gas sensor is a kind of device that detects and monitors all kinds of toxic,hazardous,flammable and explosive gases.It has a very wide range of applications in air environment monitoring and control,smart home,public safety,chemical production and storage,and anti-terrorism/military security.Among them,the metal oxide semiconductor gas sensor as the most widely used sensor,compared with other sensors,it has many advantage,including high sensitivity,light and easy to carry,good stability and low production costs.Among many metal oxides,In₂O₃ as a new type of n-type semiconductor metal oxide,has a wide bandgap,which has attracted wide attention due to its unique physical and chemical properties.It has the extensive applications in gas sensor applications for its excellent performance.But the single component In₂O₃ still has some shortcomings,such as lower sensitivity and higher working temperature,which limits its development.In recent years,studies have shown that heterojunction with In₂O₃ and other metal oxides or noble metals can help to improve the gas sensing performance.In this paper,nanostructured In₂O₃ with different morphologies was prepared by hydrothermal method.Also obtained In₂O₃ nanocomposites which compounded with noble metals,other metal oxides and rGO and tested the gas sensing properties.The main contents of this paper are as follows:1.Hydrothermal method was used to prepare In₂O₃ gas sensing materials with different nanostructures.Several nanostructured In₂O₃ gas sensing materials were prepared by using different amines and adjusting hydrothermal time and temperature.The obtained material was characterized by X-ray diffraction（XRD）,field emission scanning electron microscopy（FESEM）,Brunauer-Emmett-Teller analysis（BET）and transmission electron microscopy（TEM）.The gas sensing performance of the obtained material was tested by WS-30A gas sensor system.2.The noble metal is loaded on the surface of In₂O₃ nanocubes to prepare Au@In₂O₃nanocomposites.A series of characterizations and gas sensitivity tests were performed on the obtained materials.The results showed that the size of In₂O₃ nanocubes prepared was 150-200nm and the size was uniform,and the size of Au anoparticles loaded on the surface was about 15nm.The nanocomposite had good selectivity to formaldehyde.Compared with the pure In₂O₃nanocubes,the nanocomposite not only had greatly increases in the response,but also reduced the optimum working temperature for 40oC.Due to the unique catalytic properties of noble metals,the gas-sensitive properties of the materials are improved.3.Fe₂O₃/In₂O₃ N-N heterojunction nanocomposites were successfully synthesized by hydrothermal method.The obtained composites were characterized and analyzed microstructurally.The results showed that the prepared Fe₂O₃ was rod-shaped and uniformly grown on In₂O₃ nanospheres.The size of the prepared Fe₂O₃/In₂O₃ composite was 2-3μm.The diameter of the Fe₂O₃ rod was 10-15 nm.The results of gas-sensing test showed that the obtained nanocomposite has a seven-fold increase in sensitivity over pure In₂O₃ and has good selectivity for acetone.4.NiO/In₂O₃ P-N heterojunction nanocomposites were prepared.A series of structural characterization and analysis of the obtained composites were carried out.The results showed that the NiO nanosheets were uniformly grow on the surface of In₂O₃ nanospheres with a length of about 100 nm.The size of the prepared NiO/In₂O₃ composite was 0.5-1μm.Gas sensing results showed that although the nanocomposites were increased much,their optimum operating temperature was reduced by 20oC.And had good selectivity towards formaldehyde.5.In₂O₃/rGO nanocomposites were synthesized by hydrothermal method.rGO is a typical two-dimensional material,which has a large specific surface area and unique functional groups for gas-sensing properties to provide the possibility of improvement.In this paper,firstly,the prepared In₂O₃ nanocubes are surface-treated to carry the positive charge,the In₂O₃ were recombined with GO by electrostatic attraction,and the GO is then reduced to rGO in a hydrothermal environment.The gas sensing performance of the gas sensor made of this material was tested at room temperature,which showed good sensitivity to 100 ppm NH₃.With the increase of NH₃ concentration,the response was also increased.