Chitosan wrapped multiwalled carbon nanotubes as quartz crystal microbalance sensing material for humidity detection

In this work, the chitosan wrapped multiwalled carbon nanotubes (MWCNTs-CS) composited material was prepared by surface deposition and crosslinking method. This mild process can maintain the unique properties of the original carbon nanotubes intact. The morphological character of MWCNTs-CS was examined via Fourier transform infrared spectroscopy and field emission scanning electron microscopy. MWCNTs-CS was used as sensing film to fabricate quartz crystal microbalance (QCM) humidity sensors. The optimized sensor possesses high response sensitivity (46.7 Hz/% RH), negligible humidity hysteresis (around 1.1% RH), quick response and recovery time (75 s/34 s), and remarkable reversibility, repeatability, long-term stability and selectivity. Langmuir adsorption isotherm model was used to study the adsorption process of water molecules on MWCNTs-CS film, and the Gibbs free adsorption energy was calculated as -21.85 kJ/mol. By combining the good mechanic properties of MWCNTs and the high hydrophilia of chitosan, the MWCNTs-CS composites are promising for humidity sensing application.