*3.2. Self-Cleaning Coating on PC Substrates*

PC substrates are known to be hydrophobic in nature and so the adhesion is not strong between the coating material and the PC substrate [19]. The hydrophobic nature of PC substrates can be transformed to strongly hydrophilic by UV irradiation due to occurrence of photo-Fries reaction on the surface [20]. At first, PC substrates were gently cleaned by using detergent and water and kept for ultrasonication in double distilled water for 30 min. After drying at room temperature, the PC substrates were illuminated by UV light (365 nm, 2 mW/cm2 ) for 2 h. The PC substrates can photocatalytically degrade, if the TiO2 coating is applied directly on the PC substrates. For this reason, the sol-gel processed silica layer was applied on the PC substrates prior to TiO2 coating. A silica sol was prepared by adding 1.5 mL TEOS in 4 mL ethanol and this mixture was hydrolysed by adding 3 mL of double distilled water with 1 mL of nitric acid. This alcosol was stirred overnight and spin-coated on UV-treated PC substrates at 2000 rpm. This silica coating was annealed at 100 °C for 2 h. The above prepared silica sol was mixed at different vol% (7, 10, 15 and 20 vol%) in commercially available TiO2 nanoparticle solution and spin-coated on SiO2 pre-coated PC substrates with 2000 rpm and annealed in oven at 110 °C for 6 h. No change in PC substrate was observed after annealing at 110 °C, however for annealing above 120 °C, PC substrate start to bend in irregular shape due to softening. The schematic of coating preparation steps are shown in Figure 10.

**Figure 10.** Schematic showing coating preparation steps.
