Effect of solution concentration on physicochemical and NO2 gas sensing properties of sprayed MoO3 nanobelts

In our previous report, we have reported the work on NO2 gas sensing properties of spray deposited molybdenum trioxide (MoO3) nanobelts at various substrate temperatures ranging from 300 °C to 450 °C with an interval of 50 °C. In the present work, MoO3 nanobelts have been spray deposited at optimized substrate temperature of 400 °C with different solution concentrations ranging from 10 mM to 50 mM at an interval of 10 mM solution concentration. X-ray diffraction study shows that the spray deposited MoO3 films exhibit an orthorhombic crystal structure. The formation of orthorhombic phase of MoO3 is confirmed using Raman spectroscopic study. Field emission-scanning electron microscopy images show the nanobelts-like morphology. Atomic force microscopy micrographs reveals that the root mean square (RMS) surface roughness of nanobelts increases from 12 nm to 17 nm with increase in solution concentration from 10 mM to 40 mM and then decreases to 8 nm for 50 mM solution concentration. Optical properties show that the band gap energy decreases to 3.25 eV for 50 mM solution concentration. For 40 mM solution concentration, 40.3% NO2 gas response at 200 °C is obtained for 100 ppm concentration with response and recovery times of 17 s and 153 s, respectively. Finally, energy band bending model based on chemisorption of O2 and NO2 gas on the surface of MoO3 nanobelts is discussed.