Interaction of sulfonated graphene oxide with U(VI) studied by spectroscopic analysis and theoretical calculations

The interaction mechanism of high effective enrichment of U(VI) on sulfonated graphene oxide (GO) at ultralow pH still remains unclear. The batch characteristic results showed that sulfonated GO presented a variety of functional groups such as hydroxyl ([sbnd]OH), carboxyl ([sbnd]COOH) and sulfonyl ([sbnd]OSO₃H) groups. The macroscopic results indicated that the sorption of U(VI) on sulfonated GO was independent of ionic strength, and the maximum sorption capacity calculated from Langmuir model was 45.05 mg/g at pH 2.0. The change of relative intensities for S 2p spectra was significantly higher than that of O 1s spectra by XPS analysis. According to EXAFS analysis, the significant splitting of equatorial oxygen (U-O_eq) shell at pH 2.0 was attributed to the electron scattering of the elemental sulfur. The energy of uranyl-sulfonyl (−3198.511 hartree/particle) at pH 2.0 calculated based on theoretical calculations was lower than that of uranyl-carboxyl (−3198.498 hartree/particle), indicating that uranyl-sulfonyl was more stable at ultralow pH. These observations indicated that the sulfonyl of GO was responsible for high effective removal of U(VI) at ultralow pH, which is vital to the application of functionalized GO in the preconcentration of U(VI) in nuclear waste management and the removal of U(VI) from wastewater at low pH values.