Sungkyunkwan University, Republic of Korea
Srijita Nundy completed her BSc and MSc degree in Physics at the age of 25 years from Calcutta University and Shoolini University, India respectively in 2015. Since January 2015, she researched on ferromagnetic material synthesis and application from Chung Yuan University, Taiwan and worked as a physic researcher in Onnuritech, Seoul, Republic of Korea till 2017. Currently, she is pursuing her PhD studies on nanomaterial synthesis and device fabrication for application in various fields of biosensors and metal oxide based gas sensors at Advanced Material Science Engineering (AMSE) department of Sungkyunkwan University, Suwon, Republic of Korea.
Nitrogen oxides (NOX) is considered as toxic molecule giving harmful influences not only on human body, but also on environment . A highly selective and sensitive NOX gas sensor operating at room temperature (25°C) based on flower-like ZnO (FZO) microstructures were successfully fabricated by a CTAB-assisted hydrothermal process at 90°C. We report hydrothermal synthesis of ZnO microstructures with gradual increase of CTAB concentration forming nanorods (0M) , nanorods assembled structure (0.001M) to flower-like (0.005M) (figure 1) and studied morphology dependent gas sensing behavior to NOx gas at low temperature (25°C). The characterizations of the as-prepared samples were done in details by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, photoluminescence (PL) spectroscopy and Brunauer-Emmett-Teller (BET). The gas sensing performance of sensors fabricated with as-prepared ZnO structures to various concentrations of NOX, ammonia, toluene , carbon-monoxide, acetone and ethanol, at various operation temperatures (25 to 150°C) were noted . A clear trend showing effects of the morphology on the sensing behavior with temperature was demonstrated (figure 2b). The flower-like ZnO exhibited stability (up to 140 days) and excellent sensitivity with a high gas response of 29 which drops sharply with increase of temperature and is highly selective towards 0.74 ppm of NOX at 25°C without additional use of UV irradiation or doping materials such as Pt or Pd. The ZnO sample with 0.001M of CTAB shows a similar trend but with much lower sensitivities at low temperatures. For the sample without CTAB , the temperature behavior switches to a volcano-type one, in which the sensitivity is low at a low temperature and increases gradually with the temperature increasing. Thus, we proposed possible reason for the evolution of overall characteristics by suggesting changing reactions between ZnO and reacting gases in various operating temperatures.