Detection of Acetone Gas using Optical Sensor Coated with ZnO-TiO2 Nanorods

Abstract

Electromagnetic interference in conductometric sensing applications has become a questionable argument in terms of safety and reliability, especially when dealing with a volatile organic compound (VOC) that can be highly flammable and may cause massive damage to the surrounding environment. Semiconductor metal oxide has been used in fabricating the sensor for VOC detection, however, the synthesis process is intricate considering tedious, time-consuming and demanding expensive and high technology equipment. In VOC gas sensing, an optical-based sensor has become an alternative in providing a sensitive sensing response. In this research, an optical sensor is developed by coating a tapered multimode fiber (MMF) with zinc oxide (ZnO) nanorods via a hydrothermal approach for low temperature acetone gas detection. An accessible method of doping titanium dioxide (TiO2) powder is proposed as a catalyst for detecting acetone vapor. To further enhance the sensing ability of the ZnO-TiO2 nanorods sensor, a layer of gold-palladium (Au-Pd) thin film is decorated on the ZnO and ZnO-TiO2 nanorods. A custom-made sealed chamber with a volume of 640 m? is set up for the acetone sensing and operated at a temperature of 87 °C. The spectrometry setup is evaluated by monitoring the light intensity response in relation to its wavelength. The sensor performance is monitored for three different concentrations of acetone gas consisting of 1000 ppm, 5000 ppm and 10,000 ppm. Experimental results present that the light intensity of the sensor decreases linearly with the increasing concentration of acetone vapor at the specified wavelength of 666 nm. For the fiber sensor, the performance has been monitored through the light intensity response when the acetone was injected in for four different fiber samples consist of ZnO nanorods (ZN), ZnO nanorods decorated with Au-Pd thin films (ZNAP), ZnO-15mM TiO2 nanorods (ZTN) and ZnO-15mM TiO2 nanorods decorated with Au-Pd thin films (ZTNAP). Notably, the output intensity responses of ZnO-15mM TiO2 nanorods with Au-Pd decoration fiber sensor are found to have the best sensitivity of 0.0172 a.u./nm, repeatability and standard deviation of 0.0236. respectively, toward the concentration change as compared to the desolated ZnO nanorod fiber sensor.