Quasi Similar Routes of NO2 and NO Sensing by Nanocrystalline WO3: Evidence by In Situ DRIFT Spectroscopy.

Lili Yang,Marina Rumyantseva,Elizaveta Konstantinova,Nikolay Khmelevsky,Artem Marikutsa,Alexander Gaskov

doi:10.3390/s19153405

Abstract

Tungsten oxide is a renowned material for resistive type gas sensors with high sensitivity to nitrogen oxides. Most studies have been focused on sensing applications of WO3 for the detection of NO2 and a sensing mechanism has been established. However, less is known about NO sensing routes. There is disagreement on whether NO is detected as an oxidizing or reducing gas, due to the ambivalent redox behavior of nitric oxide. In this work, nanocrystalline WO3 with different particle size was synthesized by aqueous deposition of tungstic acid and heat treatment. A high sensitivity to NO2 and NO and low cross-sensitivities to interfering gases were established by DC-resistance measurements of WO3 sensors. Both nitrogen oxides were detected as the oxidizing gases. Sensor signals increased with the decrease of WO3 particle size and had similar dependence on temperature and humidity. By means of in situ infrared (DRIFT) spectroscopy similar interaction routes of NO2 and NO with the surface of tungsten oxide were unveiled. Analysis of the effect of reaction conditions on sensor signals and infrared spectra led to the conclusion that the interaction of WO3 surface with NO was independent of gas-phase oxidation to NO2.

Highlights

Nitrogen oxides (NOx ) are toxic atmospheric pollutants produced by fuel combustion in industry and diesel engines
We focused on a comparative study of NO2 and nitric oxide (NO) sensing pathways using tungsten oxide
The size of the nanoparticles was 5–10 nm for the sample annealed at 300 ◦ C, and 15–25 nm for the sample annealed at 450 ◦ C, in agreement with the estimations by X−ray powder diffraction (XRD) (7–9 nm and 19–22 nm, respectively)

Summary

Introduction

Nitrogen oxides (NOx ) are toxic atmospheric pollutants produced by fuel combustion in industry and diesel engines. Since nitrogen oxides have prominent redox activity, resistive-type sensors based on semiconductor metal oxides (SMOx) are suitable for sensing NOx. A wide range of sensor materials was elaborated with advantageous sensing behavior to NO2 , including tin dioxide, indium oxide, and composites with noble metals and organic-inorganic perovskites [8,9]. Tungsten oxide has been established as one of the most sensitive materials for NO2 sensors [1,2,10,11]. Numerous works demonstrate the advantageous sensitivity and selectivity of WO3 -based sensors to NO [2,6,12,13,14]. An intrinsic oxygen deficiency of tungsten oxide that can be Sensors 2019, 19, 3405; doi:10.3390/s19153405 www.mdpi.com/journal/sensors

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