Synthesis and Characterization of Thin Film Gas Sensors Using Sri Lankan Natural Graphite: Comparative Analysis of Sensitivity to Ammonia, Acetone, and Ethanol Vapors

Gas sensors were synthesized by using Sri Lankan natural graphite as the primary material. Any kind of pure graphite has never been used to identify ammonia, acetone and ethanol vapors. A thin film was coated on Fluorine-doped Tin Oxide (FTO) glass using the doctor blade method, with the graphite mixture prepared using acetone and distilled water and annealed at 100 0C for two hours in air. Surface morphology analysis via Scanning Electron Microscopy (SEM) revealed closely packed irregular shaped particles ranging in size from approximately 4 to 70 μm. The estimated value of the porosity was found to be 8.98%. X-ray Diffraction (XRD) analysis explored calculated crystallite sizes of 60.00782, 73.19767, and 59.28573 nm for the 002, 004, and 006 planes, respectively. X-ray diffraction patterns reveal that single phase of pure graphite is crystallized in thin film form, and there is not any preferred orientation of crystallites. Gas sensitivity, recovery time, and response time were evaluated in 1000 ppm of ammonia (NH3), ethanol, and acetone vapors at room temperature. Among these, acetone vapor exhibited the highest sensitivity at 23.98% for 1000 ppm, compared to 6.37% for NH3 and 7.16% for ethanol. The response and recovery times for acetone vapor were 50 and 22 minutes, respectively. All the samples were measured for three adsorption and desorption cycles to study the repetition of data. The saturated voltage of the sample after adsorbing the gas slightly increases in each cycle with the time for each vapor.