On the mechanism of CNT network NH3 sensitivity: modeling and experimental study of the density effect

A carbon nanotubes (CNT) network is a promising gas sensing material for “e-nose” development due to the vast methods of cross-sensitivity modification. However, the dominant sensitivity mechanism remains unclear since both the CNTs and junctions between CNTs can be gas-sensitive. In this paper to estimate the contributions of both mechanisms, we simulated CNT networks with varied densities using an equivalent electrical circuit. Density variation alters the junction’s and CNT’s contribution to the network resistance, and hence the total resistive response. We compared the results with the experimental resistive response of the spray-coated CNT networks toward ammonia (NH₃). A decrease in the network density results in a higher response, which indicates a likely significant role of CNTs junctions in sensitivity of a sparse networks. We also studied the effect of formic acid treatment on CNT networks, which increases both conductivity and sensitivity by removing residual solvent.