*2.2. Membrane Surface Modification*

In order to synthesize titanium oxide nanoparticles (Figure 1), ethanol, 2,4-pentanedione, perchloric acid 70%, titanium tetraisopropoxide, and Milli-Q water were mixed, at room temperature to form a stable sol of the nanoparticles. The sol was stirred for an hour. The molar ratios of each component in the resulting sol were TTIP: Pluronic F127: 2,4-pentanedione: HClO4:H2O: Ethanol = 1:0.004:0.5:0.5:0.45:4.76. PEG (1000 g/mol) is also substituted with the Pluronic F127 to see the effect of hydrophilic templating agent on the coating films [32].

**Figure 1.** The synthesis of TiO<sup>2</sup> nanoparticles using the sol-gel method: (**a**) mixing ethanol and 2,4-pentanedione; (**b**) adding perchloric acid 70%; (**c**) stirring the solution and adding titanium tetraisopropoxide; (**d**) adding Milli-Q water dropwise; (**e**) stirring the solution for an hour at room temperature; (**f**) the TiO<sup>2</sup> sol gel solution.

The operation was carried out by the dip-coating process. The stages of this process are explained below (Figure 2). The dip coater was used to coat TiO<sup>2</sup> nanoparticles on the membrane by dipping the membrane in the sol-gel solution at a speed of 50 mm/s and holding it in the solution for 8 s. Then, the membrane was removed at the same speed. Afterward, the sample was dried in an oven at 120 ◦C for one hour. Some nanoparticles do not create a strong chemical bond during the coating process or merely create a weak physical bond with the surface. The hydrothermal process is performed to increase the energy of these particles to make a strong bond with the surface after coating the nanoparticles on the membrane surface. The membrane coated with a sol-gel solution was placed in a sealed container overflowed with Milli-Q water and was placed in an autoclave at 90 ◦C for 2 h. After coating and heat treatment, the sample was radiated with ultraviolet light (UV) for 6 h. The residual organic sediments were decomposed by this radiation. Finally, the membrane was called 'TiO2-PVDF'.

**Figure 2.** Coating TiO<sup>2</sup> nanoparticles on the PVDF membrane: (**a**) dip-coating the membrane in the TiO<sup>2</sup> sol-gel solution (coating speed: 50 mm/s; holding time: 8 s); (**b**) drying the membrane at 120 ◦<sup>C</sup> for an hour; (**c**) treating the membrane using the hydrothermal method at a low temperature (90 ◦C) for two hours; (**d**) the separation of the weakly bonded nanoparticles after heat treatment; (**e**) exposing the membrane to UV light for six hours; (**f**) the TiO2–PVDF membrane.
