Highly selective and sensitive response of 30.5 % of sprayed molybdenum trioxide (MoO3) nanobelts for nitrogen dioxide (NO2) gas detection

The molybdenum trioxide (MoO3) thin films have been successfully deposited onto the glass substrates using chemical spray pyrolysis (CSP) deposition technique at various substrate temperatures ranging from 300 °C to 450 °C with an interval of 50 °C. The effect of substrate temperature on the structural, morphological, optical and gas sensing properties of MoO3 thin films has been thoroughly investigated. X-ray diffraction analysis reveals that all the films have an orthorhombic crystal structure and are polycrystalline in nature. FE-SEM micrographs depict the formation of nanobelts-like morphology. AFM study reveals that the RMS surface roughness of MoO3 thin films increases from 8.6 nm to 12 nm with increase in substrate temperature from 300 °C to 400 °C and then decreases to 11.5 nm for substrate temperature of 450 °C. Optical results show that the band gap of MoO3 thin films decreases from 3.92 eV to 3.44 eV. The selectivity studies show that the gas response of various gases varies as NH3 < SO2 < CO2 < CO < H2S < NO2. Moreover, typical MoO3 film deposited at substrate temperature of 400 °C is highly selective and sensitive for detection of NO2 gas in comparison with other gases. The maximum response of 30.5 % is obtained towards 100 ppm NO2 gas concentration at an operating temperature of 200 °C with response and recovery times of 20 s and 160 s, respectively. Finally, NO2 gas sensing mechanism model based on the chemisorption process is discussed.

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