| Sizes (nm) | Eg (eV) | Methods | References |
| 2.64 - 8.36 | 3.30 - 3.84 | Co-precipitation method | Zhang et al. [25] |
| 20.00 | 3.22 - 3.26 | Co-precipitation method | Farahmandjou et al. [2] |
| 11.99 - 16.30 | 3.20 - 3.45 | Sol-gel method | Sakthiraj and Karthikeyan [5] |
| 7.90 - 16.40 | 3.56 - 3.71 | Co-precipitation method | Chen and Chang [24] |
| 17.04 - 19.94 | - | Two-emulsion method | Lee et al. [26] |
| 4.43 - 8.51 | 2.51 - 2.80 | Co-precipitation method | Killivalavan et al. [20] |
| 1.26 - 15.40 | 2.68 - 2.82 | Co-precipitation method | Ansari et al. [21] |
| 11.82 - 13.47 | 3.18 - 3.71 | Co-precipitation method | This work |