Comparison of the UV-vis data of O²⁻(2p) → Co³⁺(e_g) and O²⁻(2p) → Co³⁺(t_2g) peak maxima obtained from Co₃O₄ NPs of different sizes with literature data.

Size [nm]	O2−(2p) → Co3+(eg) [nm]	O2−(2p) → Co3+(t2g) [nm]	Morphology	Source
31.3	∼500	∼775	Irregular	Makhlouf et al.58
22	441	756	Thin film	Jiang et al.55
15.8	∼425	∼725	Irregular	Makhlouf et al.58
10.9	390	677	Cuboid NPs	This work
4.7	376	669	Spherical NPs	This work
2.8	369	664	Spherical NPs	This work