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In this study, MoO3 thin films were coated using a simple chemical precipitation technique at room temperature, without using an autoclave or other complex equipment. Films were deposited on precoated MoO3 seed layers prepared by spray pyrolysis on glass substrates. The effects of the seed layer growth conditions and pH value of the precipitation method’s solution on the characteristics of MoO3 films were investigated. The Raman and X-ray diffraction techniques showed that MoO3 films have grown in mixed hexagonal (h) and orthorhombic (α) crystal structures and the scanning electron microscope verified that the samples’ surface was covered of both hexagonal micro rods and lamellar micro belts. The XRD patterns indicated that the crystallinity was significantly improved using a seed layer sprayed under lower carrier gas pressure, and lower pH value of the precipitation method’s solution. The UV–Visible spectra showed that using seed layers prepared at higher carrier gas pressure decreases the bandgap of the films prepared by precipitation, due to the incorporation of more oxygen vacancies. The photoluminescence studies showed that the film deposited at a higher solution’s pH value has higher PL intensity, which indicates that this sample is a suitable candidate for optoelectronic applications.

Successful fabrication and optimization of molybdenum disulfide (MoS2)/polyaniline (PANI) nanocomposite-based room temperature ammonia sensors have been reported in this work. The hydrothermal technique was used to synthesize nanocomposites of MoS2 and PANI at different amounts of PANI. For this, the precursor values were changed by choosing three different values of 0.65 (MP1), 1.1 (MP2), and 2.2 (MP3) for the ammonium heptamolybdate/PANI weight ratio. Successful fabrication of nanocomposites was confirmed by Raman analysis and X-ray diffraction. According to FESEM images, MoS2/PANI nanocomposites have been composed of 1D-PANI nanofibers covered by 2D-MoS2 nanosheets and created a porous morphology that influenced their sensing characteristics significantly. The samples’ ability to detect ammonia at room temperature was examined by fabricating sensor devices using the synthesized MoS2, PANI, and nanocomposites. The fabricated sensor using MP2 showed much better gas-sensing properties than other samples. This sensor showed about 4.6 and 1.6 times higher response than pristine PANI and MoS2 sensors for 10 ppm of ammonia, respectively, with better selectivity toward ammonia than other gas species. This research shows that compositing PANI with MoS2 significantly improves the gas detection performance of MoS2.