Table 2.

Surface composition of γ-Fe₂O₃, γ-Fe₂O₃/CeO_x, and γ-Fe₂O₃/CeO_x@PEG_2,000 nanoparticles determined by XPS analysis.

Electronic state of element	γ-Fe2O3(wt.%)	γ-Fe2O3/CeOx(wt.%)	γ-Fe2O3/CeOx@PEG2, 000(wt.%)
P 2p	–a	–	1.8 ± 0.1
C 1s	7.5 ± 1.9	8.8 ± 1.2	34.0 ± 0.5 26.1 ± 0.1b
N 1s	–	–	0.9 ± 0.1
O 1s	28.0 ± 0.4	26.2 ± 0.8	36.2 ± 0.2
Fe 2p	64.5 ± 2.2	38.7 ± 1.4	13.9 ± 0.2
Ce 3d	–	26.3 ± 0.7	13.2 ± 0.4
Ce4+/Ce3+	–	7.8 ± 0.1	7.7 ± 0.2

^aBelow the detection limit of XPS measurement;

^bcontent of PEG according to C-O-C bond.