In situ real time monitoring of hygroscopic properties of graphene oxide and reduced graphene oxide

Graphene oxide (GO) and reduced graphene oxide (RGO) has gained much attention in the field of gas sensing. However to realize its full potential in this regard, it is important to understand the influence of moisture on GO and RGO. Therefore, in situ and real time monitoring of adsorption and desorption of water molecules on GO and RGO coatings were investigated using quartz crystal microbalance (QCM). Water adsorption were studied under constant relative humidity (RH) levels over a period of time. For both GO and RGO the results show that the adsorption is followed by an equilibrium state. It is shown that for GO the initial rate of water adsorption, the amount of water at the equilibrium and the time to reach the equlibrium vary with RH, where as for RGO no such variations were observed. These observations indicate that at low RH adsorption is primarily throught surface and the edges where as at high RHs water penetrate into the intersitial layers of GO. Thus the latter becoming the rate limiting step for water adsorption at high RH. The results also elucidate on the contribution of surface oxygen functional groups towards the water adsorption rate and the amount adsorbed. The above results provde important information that can be used during GO-based sensor design and calibration.