ZnO Nanocluster-Functionalized Single-Walled Carbon Nanotubes Synthesized by Microwave Irradiation for Highly Sensitive NO₂ Detection at Room Temperature

To improve the NO₂-sensing performance of single-walled carbon nanotube (SWCNT)-based sensors, zinc oxide (ZnO) nanoclusters (NCs) were functionalized by a microwave (MW)-assisted synthesis technique. Gas sensors based on pristine SWCNTs and ZnO NC–SWCNT composites synthesized using different weight ratios (ZnO/SWCNTs = 0.5:1, 1:1, 2:1, and 3:1) were fabricated, and their ability to sense various gases at room temperature (25 °C) was investigated. The results showed that the sensing performance of the ZnO NC–SWCNT composite synthesized with a weight ratio of 1:1 (denoted as Z-SWCNTs) was significantly enhanced with respect to NO₂ response and selectivity. This enhanced sensing performance is thought to be a result of both the modulation of the conduction channel at the ZnO NC–SWCNT heterointerfaces and the generation of defects (or holes) by MW irradiation that act as active sites for the target gases. The results obtained in this work provide not only a facile method of cofunctionalizing oxide NCs and defects but also a new methodology for improving the sensing capabilities of SWCNT-based gas sensors.