CO2 absorption mechanism in sheets of graphene layers prepared by thermal exfoliation of graphene oxide was investigated using surface acoustic waves. In this experiment, LiNbO3 SAW delay-line device was spray coated with graphene flakes. The transmission at SAW frequencies was attenuated by more than 12.7 dB due to deposition of graphene. A maximum phase change ∼34 degrees was observed as the CO2 pressure inside the chamber increased from 0.01 Torr to 700 Torr, which is at least 10 times than the phase shift observed on free surface of LiNbO3 under similar conditions. Transient measurements on the graphene-coated sample indicate a phase change of 4 degree because of 0.43 mg/cm3 of CO2 absorption and subsequent full recovery after 20 min of CO2 purging.
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