Identification of functional groups and determination of carboxyl formation temperature in graphene oxide using the XPS O 1s spectrum

Experimental information on the O 1s spectra of GO by X-ray photoelectron spectrometry is limited and this will prove to be a liability when analyzing samples that have high carbon to oxygen ratios. Here, the binding energy (B.E.) information of electrons from the O 1s orbital of oxygen atoms in different functional groups were identified by characterizing GO in an in-situ heating and characterization experiment, performed in a vacuum between 473 and 573 K, and chemically modified GO. The B.E.s of the O 1s electrons in hydroxyls, epoxides, carbonyls and carboxyls on GO were determined and carboxyl formation on GO was found to occur between 543 and 561 K. Here, carboxyl formation is a decrease in the proportion of oxygen atoms bound to GO as hydroxyls and epoxides groups, accompanied by a greater than proportional increase in the proportion of oxygen atoms bound as carboxyls, and this results in the formation of vacancies on the graphene basal plane.