Spray coating of TiO2 nanoparticles obtained by continuous hydrothermal flow for photocatalytic applications

Titanium dioxide (TiO₂) thin films are extensively studied for photocatalytic applications due to their chemical stability, low cost, and environmental relevance. This work focuses on optimizing the spray coating of TiO₂ films using nanoparticles synthesized by continuous hydrothermal flow. The powders were supplied externally and produced using standard methods with recycled inputs to support a more sustainable material approach. The study investigated how spray-coating parameters — including deposition temperature, number of layers, and flow rate — influence film quality. To address challenges in adhesion and uniformity, polyvinyl alcohol (PVA) was introduced as a binder. Additional strategies such as surface pretreatments (e.g., plasma cleaning, TEOS underlayers), post-deposition annealing, and dip coating were also explored. Standard laboratory-grade TiO₂ was used later for comparison in photocatalytic performance and selected characterizations. The deposited films were characterized to understand their morphology, structure, and functionality. Scanning electron microscopy (SEM) was used to assess surface coverage and film quality. Profilometry confirmed film thicknesses in the thin-film range (200–400 nm) and highlighted surface roughness differences between formulations. X-ray diffraction (XRD) was used to analyze the crystalline phase evolution before and after annealing. Photocatalytic activity was evaluated through Fourier-transform infrared (FTIR) spectroscopy by tracking the UV-induced degradation of stearic acid. The findings show that both deposition conditions and post-treatments significantly affect film structure and function. While PVA improved initial adhesion, it compromised thermal stability, and binder-free films responded better to annealing. These results offer practical insights for tailoring scalable TiO₂ thin films in photocatalytic applications.