Humidity-assisted selective reactivity between NO2 and SO2 gas on carbon nanotubes

Abstract

In spite of the technical importance of detecting environmental SOx and NOx gases, a selective detection has not been realized because of their similar chemical properties. In this report, adsorption and desorption of SO2 and NO2 gas on carbon nanotubes are investigated in terms of different humidity levels at room temperature. A random-network single walled carbon nanotube (SWCNT) resistor is constructed by a dip-pen method using a SWCNT/dichloroethane (DCE) solution. In the case of SO2 gas adsorption, the resistance increases at high humidity level (92%) and shows no obvious change at low humidity levels. On the other hand, in the case of NO2 gas adsorption, the resistance always decreases independent of moisture levels. Our density functional theory (DFT) calculations show that this selective behavior originates from cooperative charge compensation between the SO2–nH2O complex and the p-type CNT resistor. The change of response time and recovery time with different moisture levels is further investigated. This humidity-assisted gas reaction provides a simple route to detect these two gases selectively.