Integrated Nano- and Macroscale Investigation of Photoinduced Hydrophilicity in TiO₂ Thin Films

Abstract

The hydrophilicity of titanium dioxide has been investigated for films, deposited on glass by e-beam evaporation, being exposed to UV radiation and subjected to thermal annealing. The wettability alteration has been showed to depend upon both treatments, and insights into how to introduce more stable hydrophilicity into these films have been presented for the sake of boosting their commercial value. Observations from multiple length scales to assess the wetting behavior of as-deposited and high-temperature annealed samples were assessed through macroscopic measurements, i.e., water contact angle measurements, showing that the annealed crystalline samples, treated at 500 °C, are much more hydrophilic (SCA ≈ 20°) than as-deposited TiO films (SCA ≈ 90°), and the nanoscopic experiments performed by amplitude modulation (AM) atomic force microscopy (AFM) indicated that this increased hydrophilicity is related to an enhanced adhesion force and surface energy, resulting in the partial crystallization of TiO and the consequent formation of crystals on its surface rather than being related to morphologic differences. XRD and Raman measurements have highlighted that the crystallinity of the TiO film is crucial in determining its hydrophilicity, in good agreement with the AFM study. The results also indicated that, after irradiation, the samples treated at 500 °C preserve their hydrophilicity for a significant time compared to previous studies.

Photocatalytically active coatings for cement and air lime mortars: Enhancement of the activity by incorporation of superplasticizers

“…The presence of the additive on the surface of the materials can lead to changes in their hydrophilicity (photo-induced superhydrophilicity). As a consequence, materials exhibit self-cleaning performance: the reduction of the water contact angle (WCA) allows the water to easily remove the dirt (oily smog, dust, carbonaceous particles …) [13][14][15].…”

Structural Properties and Wettability of TiO2 Nanorods

“…89‐4921) and infer the formation of a tetragonal system of lattice with space group I 4 1 / amd . The absence of peaks in the as‐deposited TiO 2 and the crystalline peaks in annealed TiO 2 are observed in several reports . The amorphous nature in the as‐deposited films arises due to the inadequate temperature available for the adatoms to nucleate into a crystalline phase of TiO 2 .…”

“…The absence of peaks in the as-deposited TiO 2 and the crystalline peaks in annealed TiO 2 are observed in several reports. [24][25][26][27] The amorphous nature in the as-deposited films arises due to the inadequate temperature available for the adatoms to nucleate into a crystalline phase of TiO 2 . When annealed, with available thermal energy the nucleation of the species takes place which leads to the crystalline phase, i.e., anatase phase of TiO 2 .…”

A facile hydrothermal synthesis and properties of TiO2 nanosheet array films

“…It is usually considered that the wettability of solid surfaces depends on the chemical properties and geometrical shapes [4,22,23]. Moreover, the hydrophilicity of TiO 2 nanosheet array films is affected by the crystal structure, morphology, surface hydroxyl content and specific surface area.…”