Study On Gas Sensing Characteristics Of Doping Multi-wall Carbon Nanotubes

Carbon nanotube has porous microstructure with high surface area and energy, which makes it a promising gas sensing material. In this dissertation, the preparation and characteristic of gas sensor based on doping multi-wall carbon nanotubes (MWNTs) for formaldehyde and xylene detection were discussed.Carbon nanotube was thought to be p-type semiconductor at room temperature. After adsorption of reducing gas, the density of the hole carrier will decrease, leading to a weakening conductibility of the sensing membrane. With a constant voltage, change of the conductance could be calculated by the change of current. The electrical conductivity of the dried carbon nanotubes film decreased when the electrode was exposed to formaldehyde and xylene. And there was a good linear correlation between the decreasing amplitude and the gas concentration.MWNT showed highly sensitivity and selectivity during gas detection at room temperature. Cation-doped MWNTs, Pd modified MWNTs, electric plating MWNTs and lauryl amine modified MWNTs were all prepared and detected. The size and uniformity of the doped metal grain were found important to the doping effects. Notable lifting was found to the sensitivity of Pd loaded MWNTs, which also shows intensifying selectivity to xylene.Multiple doping processing to MWNTs was performed to lift the selectivity of the gas sensor. MWCNTs loaded with palladium by reduction method were then electric plated before used as sensing material. And lauryl amine modified MWNTs were used as doping agent to the highly-ordered carbon nanotubes arrays. Sensing membrane was then fabricated by the complexes of MWNTs and highly-ordered carbon nanotubes arrays. Sensors based on Multiple doping MWNTs show better selectivity, which suggests that Multiple doping processing could be a promising treating method to lift the selectivity of gas sensors.Doping with different metal particles, charge transmission between the MWNTs and gas could be impacted by their catalysis function. Pd nano-particles loaded by reduction method generated dramatic sensing response to xylene by strengthening the charge delivery between xylene and MWNTs. Lauryl amine modified MWNTs exhibit outstanding sensitivity and selectivity to formaldehyde with long hydrocarbon chain which could obstruct the adsorption of xylene. Preliminary theoretical analysis and calculation were carried out in the dissertation to study the sensing characteristic of the doping MWNTs.