With the rapid development of industry, the overuse of oil, natural gas and other resources has caused serious pollution of air and environment. The manufacture of gas sensing material for detecting toxic and harmful gases has became a hot research spot. Nano tungsten trioxide used as gas sensing material can be divided into four structures。
（1）Nano tungsten trioxide gas sensing material with zero-dimensional structure
The materials of zero-dimensional structure are mainly nanospheres, nanoparticles and quantum dots. Although the specific surface area of nanocrystallization is improved, the large interface hinders electron to transfer. Therefore, it is necessary to add precious metals to modify it to improve its gas sensing performance. The chemical sensitization of precious metals can increase the amount of oxygen adsorbed, the electron sensitization can increase the electron movement rate, or the Fermi level of nano tungsten trioxide can be changed by catalysis.
（2）Nano tungsten trioxide gas sensing material with one-dimensional structure
In the one-dimensional nano tungsten trioxide structure, such as porous nanowires, the nanofibers have high specific surface area and maintain good chemical and thermal stability. However, simple nano tungsten trioxide can not meet the higher gas sensing requirements. Only by doping other metal oxides to build semiconductor heterojunction, then it can be improved, such as doping p-type semiconductor or n-type semiconductor to promote electron transfer and improve the gas sensing performance.
（3）Nano tungsten trioxide gas sensing material with two-dimensional structure
Typical two-dimensional nano tungsten trioxide structures, such as thin film, nanosheet or nanoplate have high surface activity, surface polarization and abundant oxygen vacancy,which have good gas sensing perfomance.
（4）Nano tungsten trioxide gas sensing material with three-dimensional structure
Three-dimensional nano tungsten trioxide is a hierarchical structure formed by nano particles and nanosheets, with typical shapes such as microspheres and sea urchin-like structures, etc. Its unique morphology and structure make it have large specific surface area, rich porosity, and high gas sensing compare to other gases.
The synthesis of zero-dimensional, one-dimensional, two-dimensional, and three-dimensional nano tungsten trioxide materials, the interface regulation and its modification methods still need to be further studied in order to give full play to their effects.
