Abstarct: In this thesis, the morphological, structural, and optical characteristics of tungsten disulfide (WS2)-baxsed nanocomposite samples, including WS2/rGO and WS2/PANI nanocomposites synthesized by hydrothermal and in situ polymerization methods, were investigated. The synthesized nanocomposite samples were used as a sensor material in fabrication of resistive and capacitive sensors for ammonia gas detection. The photocatalytic properties of WS2/PANI nanocomposites were also investigated for the degradation of industrial methylene blue dye. The XRD spectrum confirmed the successful synthesis of nanocomposites, and Raman spectroscopy showed the formation of both 1T- and 2H-WS2 phases in nanocomposite samples. According to the FESEM images, the WS2/PANI nanocomposites are composed of PANI nanofibers surrounded by WS2 nanosheets and have developed a porous structure, which significantly affects their sensing properties. FESEM images show that the WS2/rGO nanocomposites are made of very thin WS2 nanosheets covering the rGO surface. BET analysis showed that the formation of nanocomposites significantly increases the effective surface area. This increase in surface area is very important for improving catalytic and sensing properties. The sensor fabricated using WS2/rGO nanocomposite at 10 ppm of ammonia improved the gas sensitivity by 85% compared to the pure WS2 sample and also showed a significant reduction in response time at higher concentrations. The response of the WS2/PANI-baxsed sensor showed a greater than 75 times increase in sensitivity compared to the WS2-baxsed sensor exposed to only 2 ppm of the target gas. The results showed that the sensors baxsed on WS2/rGO and WS2/PANI nanocomposites have good detection capability for ammonia gas with high sensitivity and stability and fast response and recovery. The results of investigating the photocatalytic properties of the increase showed more than 15 times dye degradation efficiency for the WS2/PANI composite sample compared to pure WS2. The results of these studies make these nanomaterials a suitable option for industrial, commercial, or research uses in gas sensing and dye degradation applications.