Low-temperature thermal reduction of graphene oxide films in ambient atmosphere: Infra-red spectroscopic studies and gas sensing applications

Low-temperature (<= 300 degrees C) thermal treatment of graphene oxide (GO) films in ambient air is examined. In particular, the role of low to moderate heating temperatures, to the evolution of the original functional groups anchored on the GO skeleton, is closely investigated by Fourier transform infra red (FT-IR) spectroscopy. The study shows that, contrary to vacuum or inert ambient heating, heating under ambient atmosphere triggers concomitant reduction and oxidation reactions. Hydroxyl and epoxy groups are progressively eliminated, but at the same time newly formed carbonyls appear due to oxidation. Electrical measurements indicate that despite the presence of oxygen containing groups in the restored graphene sp(2) network, the conductivity enhances. The process, therefore, lends itself to the production of conductive reduced GO with increased functionalities suitable for application in gas sensor fabrication. The concept is evaluated with a humidity sensor where thermally reduced GO is prepared at different reduction temperatures. The evaluation unveils that a critical reduction temperature exists where sensor sensitivity is optimized. (C) 2016 Elsevier B.V. All rights reserved.