Effect of functional groups on dielectric, optical gas sensing properties of graphene oxide and reduced graphene oxide at room temperature†
Graphene oxide (GO) was synthesized from graphite through a chemical oxidation process and heat treated at 110 and 220 °C in a vacuum atmosphere. The partial reduction and sp3 to sp2 phase transition of GO was characterized by powder X-ray diffraction, Fourier-transform infrared, micro Raman, ultraviolet-visible-near infrared spectroscopy techniques. Dielectric properties of pristine GO and heat-treated GO were studied in the frequency range 102 to 106 Hz at 27 °C. Hydroxyl, carboxyl functional groups removed GO after 220 °C heat treatment, expressed higher electrical conductivity, dielectric constant and dielectric loss in the order of 10−2 S m−1, 103 and 105 respectively than the pristine GO (10−6 S m−1, 101 and 101). Pristine and heat-treated GO were coated on the partially cladding removed poly-methyl methacrylate optical fiber and used as fiber optic gas sensors. GO and heat treated GO coated fibers were responsive to detect ammonia, ethanol and methanol vapors from 0 to 500 ppm at 27 °C. Sensitivities of GO coated fiber optic sensor were calculated as −0.32, −0.26 and −0.20 counts per ppm for ammonia, ethanol and methanol vapors respectively. The effect of functional groups on dielectric and gas sensing properties of GO was investigated and reported.