Improving sensing properties of entangled carbon nanotube-based gas sensors by atmospheric plasma surface treatment

Entangled multi-walled carbon nanotubes (MWCNTs) on polyurethane (PUR) after Ar plasma-treatment and He plasma-treatment have been tested as gas sensors for ethanol sensing. It was found that plasma-treated sensors exhibit higher sensitivity compared to the non-treated samples along with different ethanol concentration. Non-treated sensors exhibit similar sensor response with the increase in ethanol concentration, while Ar plasma-treated sensors displays ~5 times improvement and He plasma-treated sensors show ~3 times improvement with an increase in ethanol concentration. The sensitivity of the plasma-treated sensors is also stable for following two-weeks after the preparation compared to the non-treated sensor. Entangled nanotube network exhibits a significant shift in the baseline resistance after both plasma-treatments. The response time of the sensor was increased after the plasma-treatment, while the recovery was rather quick. Surface analyses revealed that plasma-treatment did not make any significant morphological changes. Thus, the improvements in stability and sensitivity after plasma-treatment are attributed to the plasma-enhanced surface modification and formation of functional bonds on the surface of nanotubes, which are sensitive to the ethanol vapour.