<p>Graphitic carbon nitride (g-C₃N₄) is a metal free organic semiconductor which can be synthesized in two dimensional layered structure. We have synthesized g-C₃N₄ powders using three different precursors: melamine, thiourea and a mixture of melamine and thiourea. The morphologies, structures and optical properties of the above three g-C₃N₄ samples were investigated by field emission scanning electron microscopy (FESEM), X-rays diffraction (XRD) and diffuse reflectance spectrometry (DRS), respectively. The g-C₃N₄ powder synthesized from the mixed precursor (melamine + thiourea) contained two dimensional (2D) lamellar structures. The chemical state identification and the compositional analysis were performed by X-rays photoelectron spectroscopy (XPS). The XPS analyses reveal that the atomic ratios of the carbon and the nitrogen (C/N ratio) in our g-C₃N₄ are more than 0.75 that indicate nitrogen deficiencies. The band gap energy determined from the Tauc’s plot was 2.73 eV for all three g-C₃N₄ powders. The g-C₃N₄ emitted intense, visible light in the blue green region under ultraviolet laser excitation. The luminescence intensity decreased with an increase in the C/N ratio which evidenced the occurrence of N vacancy defects in the g-C₃N₄. Acetic acid gas sensing properties of g-C₃N₄ were investigated at room temperature. The g-C₃N₄ synthesized from the mixed precursor (melamine + thiourea) showed a response of 33.5 towards 78 ppm acetic acid gas at room temperature (30 °C) in a relative humidity (RH (%)) of 55%. The above response corresponded to a sensitivity of 0.43 ppm⁻¹. The response and recovery times for the above sensor were 52 s and 34 s, respectively. Our g-C₃N₄ based sensors exhibited a very good selectivity towards acetic acid gas at room temperature.</p>