Correlation Between Ammonia Selectivity and Temperature Dependent Functional Group Tuning of GO

Starting from room temperature (27 °C), graphene oxide (GO) was annealed stepwise at 100 °C, 200 °C and 300 °C and detailed structural characterizations like FTIR (Fourier transform infrared spectroscopy), XPS (X-ray photoelectron spectroscopy), XRD (X-ray powder diffraction) and Raman spectroscopy revealed that with increase in temperature, transformation from GO to rGO (reduced graphene oxide) took place and complete conversion was achieved at 300 °C. With increase in temperature, the functional groups like epoxy, ether, carbonyl and carboxyl were gradually reduced and at 300 °C, only the hydroxyl group became dominant. The gas sensing study was carried out using NH3 and alcohols in the concentration range of 125 ppb-700 ppm. It was observed that for lower ppm (5-50 ppm) the GO based sensors offered better selectivity towards NH3, while rGO exhibited better NH3 selectivity at higher concentrations (200-700 ppm). Possibly, presence of hydroxyl group is favorable for NH3 adsorption and therefore NH3 selectivity is better in rGO particularly at high concentrations. On the other hand, at low NH3 concentrations, presence of various types of functional groups in GO gives a resultant selectivity which is better compared to that of rGO.