Table 1.

Details of the ceria nanomaterials UV-Vis absorption analyses.

References	Preparation Procedure	Sample	Band Gap a(eV)
			Ed	Ei
e[2]	Polyol	Polycrystalline CeO2	3.19	N.A.
		CeO2 nanospheres (80–100 nm),	3.46
		Microrods (d WD several100 nm; d L 15 to 20 μm, d AR 25 to 33),	3.62
		Spindle-like (d WD several 100 nm, d L 2 to 4 μm, d AR 4-8)	3.36
[49]	Hydrothermal	Spindle like (d WD 800 nm and d L 5 μm)	3.55	N.A.
[50]	Hydrothermal	CeO2 prism-like mesocrystal Bulk CeO2	3.02 3.19	N.A.
[51]	Spray pyrolysis	CeO2 films (cerium chloride) (cerium nitrate)	3.6 3.53	N.A.
[52]	Electron beam evaporation; Ion beam assisted deposition	Nanostructured CeO2−x	3.48	3.18
e[11]	Ultrasonication	CeO2 nanorods (d AR 10 to 15:1, d L 50–150 nm)	2.9	2.67
[53]	Microemulsion	Ceria ultrafine nanostructure	3.44 2.6	2.87 2.73
[54]	Pulsed electron beam	CeO2 nanocrystalline films	N.A.	2.58
[56–58]	Physical vapor-deposited	CeO2 films	N.A.	3.15–3.5
[59]	Spray deposition	CeO2 films	N.A.	3.06–3.08
[60]	Sol-gel method	CeO2 films	N.A.	3.03–3.07

Notes:

^aAccording to the solid band theory for a semiconductor (hν)ⁿ = constant(hν – E_g), where hυ is the photo energy, α is the absorption coefficient, constant is relative to the material, E_g is the band gap;

^bE_d: Band gap energy for direct transitions in where n = 2; E_i: Band gap energy for indirect transitions in where n = 1/2;

^dAR = aspect ratio; L = length; N.A. = not available; WD = width;

^eSurfactant method.