The Effect Of Doping And MWCNTs On The Hydrogen Sensing Properties Of SnO₂

In this paper, we attain Fe ion doping into SnO₂, prepare SnO₂ nanocrystals coated multi-walled carbon nanotubes by a polyol process, which is a general method used to fabricate the nano-structural metal oxide semiconductor. On the basis of these material prepared, we used the polyol process as well to successfully synthesize the Fe-doped SnO₂ nanocrystals coating MWCNTs for the first time. These materials were characterized by XRD, EDS, SEM, TEM, thermal analysis, Raman spectrum and ICP. And we studyed the hydrogen sensing properties of the SnO₂ nanocrystals, SnO₂ nanocrystals coated multi-walled carbon nanotubes and Fe-doped SnO₂ nanocrystals coating MWCNTs.Ethylene glycol (EG), which is used in the polyol process, is not only a medium for the reaction happened in, but also acts as one of reactant to form poly-glycolate. Results show that poly-glycolate precursors can be dissolved in EG, and can be hydrolyzed in hot water, then converting into metal oxides.Comparing the reaction products obtained from In2(C2O4)3 and SnC2O4 mixing into boiling EG, we find that, if a cation doping into SnO₂ lattice is needed to be synthesized, the oxalate of this cation must be capable of forming poly-glycoate with EG. Because In2(C2O4)3 do not reacts with EG to form corresponding poly-glycoate, we failed to attain lattice doping of In into SnO₂.As to the research works on hydrogen sensing properties, some interesting results were obtained. The SnO₂ nanocrystals show the hydrogen sensitivity to 1000 ppm hydrogen atmosphere at room-temperature. After H2/N2 mixture gas in, the resistance decreases. The sensitivity gradual reduces when the voltage between two electrodes decrease. By coating on the MWCNTs, the resistance of SnO₂ nanocrystals reduces by 4 orders of magnitude, resulting in easy-matching with external circuit in gas sensors. Fe ion doping transforms SnO₂ nanocrystals from N type semiconductor to P type. This transformation leads to the resistance of Fe doped SnO₂/MWNTs increase when H2/N2 mixture gas in.