A method for capturing CO2 from a gas stream using a metal organic framework (MOF) based physisorbent CO2 concentrator is provided. In the method, MOF material is pretreated, a gas stream is then introduced into the CO2 concentrator which comprises the pretreated MOF material. CO2 from the gas stream is captured with the CO2 concentrator to generate a CO2-free stream, which is discharged the from the CO2 concentrator into the atmosphere. Introduction of the gas stream into the CO2 concentrator is stopped when the pretreated MOF material becomes saturated with CO2. The CO2 concentrator with the saturated MOF material is then regenerated by introducing hot air, hot nitrogen, vacuum, or a combination thereof into the CO2 concentrator thereby generating a CO2-rich stream. The CO2-rich stream is diverted for purification and the regenerated CO2 concentrator is recycled for future capture of CO2.