In the present study, we designed the pristine C₃N and Ti-doped C₃N nanosheets to investigate the geometrical, electrical, and optical properties using density functional theory calculation. The negative value of the cohesive energy of both nanosheets indicates the structures are energetically stable. Ti-doping in C₃N results in a conductor-to-semiconductor transition with a band gap of 0.15 eV. We studied the adsorption of COCl₂, O₃, and HCN gas molecules on the designed structures. The adsorption energy for COCl₂, O₃, and HCN gases significantly increased to -8.63, -9.80, and -5.98 eV respectively after Ti-doping. A significant variation in the band gap of Ti-doped C₃N is observed due to gas adsorption. The complex structures show a high absorption coefficient of over 10⁴ cm^-1 in the visible range with a significant red/blue shifting of absorption peaks. The study proves the Ti-doped C₃N to be a potential candidate for sensing COCl₂, O₃, and HCN gases.