Abstract
Introduction
Environmental safety is attracting significant attention due to the increase of dust particles, and toxic gas species (e.g. CO, NOx, etc.) [1]. CO is identified as a major threat for human health. Since CO is a colorless, odorless, and tasteless gas, it can't be detected by human senses. Therefore, sensitive sensor operating in humid air is required for CO gas detection [2]. For metal oxide (MOX) gas sensors, the humidity interferes with the low-level detection of reducing and oxidizing gases. The performances of MOX gas sensors such as SnO2 or CuO can be enhanced, by metal doping, material functionalization or MOX composite [3].
In this work, a comparison between resistive sensors based on CuO and on BaTiO3-CuO bi-layer film will be presented. The sensor responses to three CO gas concentrations in dry air and in 50% of relative humidity (RH) will be discussed.
Method
BaTiO3 nanoparticles (NPs) (<100nm) were dispersed in ethanol by stirring. Copper hydroxide Cu(OH)2 powder (0.2 g) was dissolved in acetic acid (5 ml), water (7 ml) and ethylene glycol (2ml). These two solutions were deposited by drop coating on a silicon oxide substrate provided with interdigitated platinum electrodes (figure 1). CuO films were prepared with one drop of Cu(OH)2 solution. BaTiO3-CuO films were fabricated with one drop of BaTiO3 NPs, an ambient drying for 5 minutes followed by one drop of Cu(OH)2 solution on the top of it. Then, the sensors were annealed at 500°C for 1 h. The sensing properties of these sensors were investigated by CO exposure. NI PXIe-4140 sourcemeter was used to measure the sensor resistance variations for an optimum operating temperature found at 280°C.
Results and Conclusions
Figure 2 shows the x-ray diffractograms of CuO and BaTiO3-CuO materials. The XRD patterns of CuO film indicate the existence of CuO nanoparticles in the monoclinic phase without CuO2 nanoparticles [4]. BaTiO3-CuO bilayer consists of a tetragonal phase of BaTiO3 in addition to monoclinic CuO [5]. Figure 3 presents the responses of CuO and BaTiO3-CuO to CO gas. In dry air, CuO gives a response equals to 1.22, while the response is more important for BaTiO3-CuO (1.41). In 50% RH, the sensor responses with CuO have almost disappeared while the sensors based on BaTiO3-CuO film gave a response equals to 1.32. Therefore, BaTiO3-CuO films have an enhanced response to CO in dry air as well as in the presence of 50% RH. The CO concentration effect on BaTiO3-CuO films was tested for 10, 50, and 100 ppm of CO in dry air and 50% RH (figure 4). Linear responses under CO in dry or wet air make BaTiO3-CuO bilayer films a potential candidate for the CO gas detection application.
We have developed sensors based on BaTiO3-CuO composite for the CO gas detection under dry and wet air. The sensing properties are based on the resistance variation under CO gas. Our results show enhanced responses of BaTiO3-CuO concerning CuO in dry air and 50% RH. Future work will be focused on the proportion of BaTiO3 and CuO investigations to enhance the sensor response under CO.
References
[1] A. Kumar, A. Sanger, A. Kumar, et R. Chandra, « Highly sensitive and selective CO gas sensor based on a hydrophobic SnO2/CuO bilayer », RSC Adv., 6, 52, (2016), 47178–47184. doi: 10.1039/C6RA0653
[2] K. Sircar, J. Clower, M. Kyong Shin, C. Bailey, M. King, et F. Yip, « Carbon monoxide poisoning deaths in the United States, 1999 to 2012 », Am. J. Emerg. Med., 33, (2015), 1140–1145. doi: 10.1016/j.ajem.2015.05.002
[3] M. Hijazi, M. Rieu, V. Stambouli, G. Tournier, J.-P. Viricelle, et C. Pijolat, « Ambient temperature selective ammonia gas sensor based on SnO2 -APTES modifications », Sens. Actuators B Chem., 256, (2018), 440–447. doi: 10.1021/acsomega.9b02185
[4] K. Martin, G. McCarthy, North Dakota State Univ., Fargo, ND, USA., ICDD Grant-in-Aid, 1991.
[5] S. B. Rudraswamy et N. Bhat, « Optimization of RF Sputtered Ag-Doped BaTiO3-CuO Mixed Oxide Thin Film as Carbon Dioxide Sensor for Environmental Pollution Monitoring Application », IEEE Sens. J., 16, (2016), 5145–5151. doi: 10.1109/Jsen.2016.2567220
Figure 1