2.2. Preparation of the TiO2 Nano‐photocatalyst

The TiO₂ nano‐photocatalyst was prepared via the sol–gel process (Yang, Huang, Ye, & Chen, ²⁰¹⁰) with tetrabutyl titanate (TBT; C₁₆H₃₆O₄Ti) as the precursor. The detailed preparation procedure is as follows: 10 ml TBT was mixed with 30 ml anhydrous ethanol. Next, a solution mixture comprising 50 ml ethanol, 3 ml water, and 1.5 ml nitric acid was added dropwise into the TBT‐ethanol solution to obtain a light‐yellow gel. The gel was then mixed thoroughly for 12 hr and left to stand at room temperature for 24 hr. Subsequently, the gel sample was heated in a water bath at 80°C to evaporate the solvent. After drying, the gel was ball‐milled for 2 hr to obtain a fine powder, which was calcined in a temperature‐programmed muffle furnace, under inert N₂ atmosphere, at 450°C for 2 hr. Finally, the calcined powder was milled again to produce the TiO₂ nano‐photocatalyst, which was used in the subsequent experiments.