Extremely defect
graphene oxide (dGO) is proposed as an advanced
sorbent for treatment of radioactive waste and contaminated natural
waters. dGO prepared using a modified Hummers oxidation procedure,
starting from reduced graphene oxide (rGO) as a precursor, shows significantly
higher sorption of U(VI), Am(III), and Eu(III) than standard graphene
oxides (GOs). Earlier studies revealed the mechanism of radionuclide
sorption related to defects in GO sheets. Therefore, explosive thermal
exfoliation of graphite oxide was used to prepare rGO with a large
number of defects and holes. Defects and holes are additionally introduced
by Hummers oxidation of rGO, thus providing an extremely defect-rich
material. Analysis of characterization by XPS, TGA, and FTIR shows
that dGO oxygen functionalization is predominantly related to defects,
such as flake edges and edge atoms of holes, whereas standard GO exhibits
oxygen functional groups mostly on the planar surface. The high abundance
of defects in dGO results in a 15-fold increase in sorption capacity
of U(VI) compared to that in standard Hummers GO. The improved sorption
capacity of dGO is related to abundant carboxylic group attached hole
edge atoms of GO flakes as revealed by synchrotron-based extended
X-ray absorption fine structure (EXAFS) and high-energy resolution
fluorescence detected X-ray absorption near edge structure (HERFD-XANES)
spectroscopy.
This is the accepted version of a paper published in Carbon. This paper has been peerreviewed but does not include the final publisher proof-corrections or journal pagination.
Extended X-ray absorption fine structure (EXAFS) is a comprehensive and usable method for characterizing the structures of various materials, including radioactive and nuclear materials. Unceasing discussions about the interpretation of EXAFS results for actinide nanoparticles (NPs) or colloids were still present during the last decade. In this study, new experimental data for PuO2 and CeO2 NPs with different average sizes were compared with published data on AnO2 NPs that highlight the best fit and interpretation of the structural data. In terms of the structure, PuO2, CeO2, ThO2, and UO2 NPs exhibit similar behaviors. Only ThO2 NPs have a more disordered and even partly amorphous structure, which results in EXAFS characteristics. The proposed new core-shell model for NPs with calculated effective coordination number perfectly fits the results of the variations in a metal–metal shell with a decrease in NP size.
The combination of advanced spectroscopic and microscopic methods used in this work enables molecular and atomic levels understanding of the Pu(iv) nanoparticles formation under acidic conditions (pH 1–4).
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