Facile synthetic route to exfoliate high quality and super-large lateral size graphene-based sheets and their applications in SERS and CO2 gas sensing.

A combination of low-cost synthetic route and simplified exfoliation technique to develop high-quality graphene-based sheets with very large lateral dimensions, which are viable to scale up, remains a challenging problem. Herein, super-large graphene oxide (GO) sheets with lateral size up to 104 µm with a surface area of 6831 µm2 have been developed based on a simple approach using mild heating conditions, and subsequent deoxygenation yields reduced graphene oxide (rGO) sheets. With the decrease in number of layers (<10, <5, bi-layer and mono-layer) in GO, the Raman intensity ratio, I D/I G value increases systematically from 0.73 to 0.97. The efficacy of reducing oxygen-containing functional groups from GO to rGO is confirmed from Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-visible absorption spectroscopy, photoluminescence, and thermogravimetric analysis. Current-voltage measurements revealed substantial improvement of current by three orders of magnitude upon reduction of GO to rGO, which is consistent with the significant decrease in charge transfer resistance in rGO, as revealed from the electrochemical impedance spectra. The large-area GO and rGO sheets when applied in surface-enhanced Raman scattering (SERS) exhibited a large enhancement factor of 104 and high detection capability down to a concentration of 10 nM for Rhodamine B. Furthermore, the rGO incorporated hybrid rGO-SnO2 demonstrated ∼50% improvement in sensitivity for CO2 gas sensing as compared to the commercial SnO2 based gas sensor. The higher sensitivity in the rGO case is ascribed to its high surface area, as revealed from the BET analysis. Therefore, the present simplified and economical approach of large-area graphene oxide could potentially open up a new strategy for industrial-scale production in the future.