The interaction between poisonous gases and the surface of a single-walled carbon nanotube (SWCNT) is investigated using density function theory (DFT) in this work. Fluorine (F2), carbon monoxide (CO), and carbon dioxide (CO2) are the toxic gases used in this investigation (CO2). F2 and CO have strong reactivity with the surface of SWCNT, according to adsorption calculations. They are chemical interactions as well. Because of its physical adsorption, the CO2 gas molecule does not interact with the current system. The current nanosystem can detect F2 and CO gas molecules, according to the sensitivity calculation. Only chemical adsorption changed the UV-visible spectrum, and this was visible in F2 and CO interactions. The optical response result describes how to develop and use an optical sensor for CO gas molecule detection in an environmental situation. F2 and CO are acceptors, while CO2 is a donor, according to charge transfer calculations.