Refined surface area determination of graphene oxide using methylene blue as a probe molecule: a comparative approach

In this research, we explored the effectiveness of the methylene blue adsorption method as an alternative approach for determining the specific surface area of graphene oxide. Initially, through a comparative analysis with reference activated carbon, we identified the limitations of utilizing N2 physisorption for specific surface area determination of graphene oxide. Our findings revealed that the standard pretreatment process (heating under vacuum) before N2 physisorption led to damage to the surface oxygen groups on graphene oxide, and the measured surface areas (43 m2/g) do not accurately represent the entire surface area. To optimize methylene blue coverage on graphene oxide, we conducted adsorption equilibrium experiments, focusing on controlling temperature and pH. The pH was significantly important in regulating the coverage of methylene blue. Under the optimized methylene blue adsorption conditions, the specific surface area of graphene oxide was 1,555 m2/g. Our assumptions regarding specific surface area calculations were supported by structural characterization of samples with varying methylene blue uptakes. The results confirmed a uniform coverage of methylene blue on graphene oxide by scanning electron microscopy and energy dispersive X-ray, X-ray diffraction, and atomic force microscopy.