The worldwide COVID-19 pandemic has resulted in a huge amount of face masks being used up and thrown away, resulting in increased environmental pollution and infection risks. In our work, we have developed a highly efficient process of neutralizing face mask waste into a useful carbon material. Then, the prepared activated carbon was used for CO adsorption studies. A series of activated carbons from face masks used as a precursor were synthesized using KOH and the activation temperature was in the range of 600-800 °C. All materials were characterized by well-developed porosity. The influence of activation temperature on the textural properties of prepared activated carbons and their adsorption abilities were investigated. The highest CO adsorption was received for the M_800 carbon and it was 3.91 mmol/g at the temperature of 0 °C and the pressure of 1 bar. M_800 carbon exhibited also high selectivity of CO over N. Seven equilibrium isotherms were applied to the experimental data to find out the best fit (Langmuir, Freundlich, Sips, Toth, Unilan, Fritz-Schlunder and Radke-Prausnitz isotherms). The presented research provides an environmentally friendly and cost-effective method of recycling waste masks into a valuable product in the form of carbon and its potential use in the absorption of harmful CO influencing the greenhouse effect.