Metal-organic frameworks (MOFs), particularly zeolitic imidazolate frameworks (ZIFs), have emerged as promising materials for gas sensing applications due to their high surface area and tunable porosity. In this study, we developed a chemical bath deposition (CBD) process to fabricate ZIF-8 films with precisely controlled thicknesses ranging from 100 nm to 2.5 mm on functionalized gold surfaces. The growth mechanism and film characteristics were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and time-of-flight secondary ion mass spectrometry (ToF-SIMS), combined with in-situ growth monitoring. By integrating these controllable ZIF-8 films with a quartz crystal microbalance (QCM), we developed a gravimetric gas sensor that demonstrated enhanced CO2 adsorption capacity with increasing film thickness and achieved a detection limit of 0.5%. This systematic approach to controlling ZIF-8 film thickness enables precise quantification of gas adsorption, advancing the development of high-precision gas sensors for environmental monitoring applications.