Resonant Frequency Tuning Technique for Selective Detection of Alcohols by TiO2 Nanorod-Based Capacitive Device

Selective detection of vapor species, especially belonging to the same group, is a crucial bottleneck for resistive sensor devices. In this paper, methanol, ethanol, and 2-propanol detection by Pd/TiO2 nanorod array/Ti device in capacitive mode was achieved, with improved selectivity, employing a resonant frequency tuning technique. The optimal capacitive response of the device was obtained by identifying the resonant frequency over the frequency range of 0.01-200 kHz. The imaginary part of the impedance (-vertical bar Z vertical bar sin theta as a function of frequency) in air and in alcohols revealed a shift in resonant frequency towards lower frequency regime upon exposure to alcohols. Moreover, the difference in the resonant frequencies (Delta f) from one alcohol to another were found to be almost constant which facilitated the frequency-selective sensing even for varying concentrations of target species (1, 50, and 100 ppm in present case). Such frequency selective nature of the device possibly originated from different degree of polarization of different alcohol molecules at different frequencies which was duly correlated to the corresponding equivalent circuit model. However, for real selective detection, when the target species is unknown, the proposed device does not work properly and an array of devices is necessary.