Effect of light on the wettability properties of films made by the assembly of SiO₂ and α − Fe₂O₃ nanoparticles

We report an experimental study of the effect of visible and UV light irradiation on the wettability of films made by the assembly of SiO2 and α − Fe2O3 particles in the nanometer range. To optimize the conditions for the film formation (adhesion of nanoparticles on glass substrates) using a dip-coating technique, we have analyzed the colloidal stability through Zeta-potential measurements of the nanoparticles by varying the pH of the solution. Additionally, X-ray diffraction (XRD), Raman, and Fourier transform infrared (FTIR) spectroscopy were used to study the structural and optical properties of the samples. The wettability behavior was performed by contact angle (CA) measurements using a sessile drop method. The atomic force microscope (AFM) results showed similar roughness parameters for both systems; however, we have obtained different wettability characteristics: superhydrophilic for SiO2 and hydrophilic for α − Fe2O3. This difference is due to its physicochemical nature rather than the morphological structure of their surfaces, as predicted by the Wenzel equation. The CA of α − Fe2O3 surface changed upon irradiation by visible (2.7 eV) and UV (4.2 eV) light, i.e. from 38° (hydrophilic) to 15° (highly hydrophilic), respectively, while the SiO2 case was kept constant (around 7°). These changes in CA can be attributed to the amount and mechanism of electron-hole pair photogenerated that breakdown organic molecules or dissociate water from moisture, lead to increasing hydroxyl species on the surface. The present study could provide new insights to control the wettability on hydrophilic surfaces with complex structures when it is irradiated with light at different wavelengths.