*2.2. Sol-Gel Dip-Coating*

A homemade dip-coating apparatus was used to prepare the TiO2 thin films on glass substrates (F-SnO2, 1.5 cm × 6 cm, Pilkington-NSG, St Helens, UK). The substrates were dip-coated into the sol with a controlled removal speed of 2.8 cm/min. The number of dips was varied to include samples with one to three layers by repeating the number of dips. Before each additional layer was added, the substrates were left under a fume hood for 30 min to allow the solvent to evaporate. After dip-coating, the samples were left overnight under a fume hood to evaporate any remaining solvent. Samples were annealed using a Carbolite Type 301 programmable furnace (Carbolite, Hope, UK) at 500 °C for 15 min with a ramp rate of 288.15 K·min<sup>í</sup><sup>1</sup> .


**Table 1.** Sol gel names with surfactants used and relevant concentrations with number of layer and annealing temperature and times.
