Composition and Electronic Structure of La(2)O(3)/CNFs@C Core-Shell Nanoparticles with Variable Oxygen Content

La(2)O(3) nanoparticles stabilized on carbon nanoflake (CNF) matrix were synthesized and graphitized to produce core-shell structures La(2)O(3)/CNFs@C. Further oxidation of these structures by nitric acid vapors for 1, 3 or 6 h was performed, and surface-oxidized particles La(2)O(3)/CNFs@C_x (x = 1, 3, 6) were produced. Bulk and surface compositions of La(2)O(3)/CNFs@C and La(2)O(3)/CNFs@C_x were investigated by thermogravimetric analysis and X-ray photoelectron spectroscopy. With increasing the duration of oxidation, the oxygen and La(2)O(3) content in the La(2)O(3)/CNFs@C_x samples increased. The electronic structures of samples were assessed by electron paramagnetic resonance. Two paramagnetic centers were associated with unpaired localized and mobile electrons and were registered in all samples. The correlation between bulk and surface compositions of the samples and their electronic structures was investigated for the first time. The impact of the ratio between sp(2)- and sp(3)-hybridized C atoms, the number and nature of oxygen-containing groups on the surface and the presence and proportion of coordinated La atoms on the EPR spectra was demonstrated.