**3. Experimental Details**

*3.1. Synthesis of (TiO2)1*−*<sup>x</sup> (Fe2O3)x Nanoparticles (NPs)*

(TiO2)1−<sup>x</sup> (Fe2O3)x NPs were prepared by the sol-gel process. In brief, 150 mL of ethanol, 3 mL of acetic acid, 5.26 mL of diethanolamine, 10.9 mL of titanium tetrachloride were mixed with vigorously stirring for 15 min, followed by adding 1.8 mL of deionized water. The desired amount of iron (III) acetate hydroxide was gradually added at X = 0.0, 0.1,

0.5, and 1.0 to obtain (TiO2)1−x(Fe2O3)x nanocomposites. The solution was magnetically stirred for 4 h, and the pH value was adjusted at~8. The obtained wet powder was washed three times by water and ethanol, respectively. The wet (TiO2)1−x(Fe2O3)x NPs were dried for 24 h at 100 ◦C, and then it was annealed for 3 h at 450 ◦C. All chemicals applied were purchased from Sigma-Aldrich, Burlington, MA, USA and used without further purification.
