Abstract
Metal oxides are excellent candidates for the detection of various gases; however, the issues such as the limited operating temperature and selectivity are the most important ones requiring the comprehensive understanding of gas adsorption kinetics on the sensing layer surfaces. To this context, the present study focuses mainly on the fabrication of a Pt/Cr-TiO2/Pt type sensor structure that is highly suitable in reducing the operating temperature (from 400 to 200 °C), extending the lower limit NO2 gas concentration (below 10 ppm) with fast response (37 s) and recovery (24 s) times. This illustrates that the sensor performance is not only solely dependent on the nature of sensing material, but also, it is significantly enhanced by using such a new kind of electrode geometry. Moreover, Cr doping into TiO2 culminates in altering the sensor response from n- to p-type and thus contributes to sensor performance enhancement by detecting low NO2 concentrations selectively at reduced operating temperatures. In addition, the NO2 surface adsorption kinetics are studied by fitting the obtained sensor response curves with Elovich, inter-particle diffusion, and pseudo first-order and pseudo second-order adsorption models. It is found that a pseudo first-order reaction model describes the best NO2 adsorption kinetics toward 7–170 ppm NO2 gas at 200 °C. Finally, the sensing mechanism is discussed on the basis of the obtained results.
Highlights
The detection of oxides of nitrogen (NO and NO2 ) is highly demanding, as the reducing and oxidizing nature of these gases may yield sensor signals in the opposite directions
We demonstrate a highly sensitive Pt/Cr-TiO2 /Pt sensor design suitable for NO2 detection with the reduced operating temperatures (200 ◦ C) and lower limit of the
The XRD, SEM, EDX, and GDOES analyses confirmed that the dominant anatase A (004) crystal structure was preferentially oriented following the crystal orientation of the substrate, which was a morphology of columnar structured
Summary
The detection of oxides of nitrogen (NO and NO2 ) is highly demanding, as the reducing and oxidizing nature of these gases may yield sensor signals in the opposite directions. Some people with bronchitis/asthma are sensitive to NO2 , which causes lung irritations and leads to breathing difficulties [1,2,3,4]. NO2 is a highly perilous gas for the human and environment as well because of its threshold limit value (TLV), which is about 3 and 5 ppm for 8 h and 15 min (this is estimated for the time-weighted average) [5]. Even the inhalation of low concentrations of NO2 by humans can cause severe damage to the respiratory tract, leading to lung cancer. The allowed shorttime exposure of NO2 gas concentration has been reduced to 1 ppm by the Occupational
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