Fabrication and characterization of a transparent, hydrophilic, and self-cleaning polyurethane coating on glass with a silica buffer layer and Ag₃PO₄/TiO₂ nanocomposite

Abstract

Self-cleaning coatings have attracted considerable interest in recent decades due to their potential to reduce maintenance costs and enhance surface durability. Among the various strategies, hydrophilic coatings incorporating metal oxides utilize the photocatalytic effects to remove organic contaminants via solar-assisted chemical degradation and water sheeting mechanisms. In this study, a polyurethane (PU)-based self-cleaning coating was fabricated by integrating Ag₃PO₄/TiO₂ (APT) nanocomposites into the PU matrix. Ag₃PO₄ was selected for its high photocatalytic activity under visible light, while TiO₂ was added to improve photostability and suppress electron-hole recombination. To enhance optical clarity and mechanical adhesion, a SiO₂ interlayer was first deposited onto glass substrates using the sol-gel method followed by dip-coating. Subsequently, the PU@APT top layer was applied via dip-coating, maintaining an immersion and withdrawal rate of 200 mm/min at a 90° dipping angle. APT nanocomposites with varying TiO₂ content—10 wt%, 30 wt%, and 50 wt%—were synthesized, yielding three formulations: APT10, APT30, and APT50. Comprehensive characterization was conducted using X-ray diffraction (XRD), Attenuated total Reflectance-Fourier transform infrared (ATR-FTIR), field emission scanning electron microscopy (FESEM), photoluminescence (PL) spectroscopy, Electrochemical impedance spectroscopy (EIS) and UV–Vis diffuse reflectance (DRS). Hydrophilicity was assessed via water contact angle (WCA) measurements, while surface roughness was evaluated using Atomic Force Microscopy (AFM). Photocatalytic performance was quantified through methylene blue (MB) dye degradation under visible light irradiation. Among the developed coatings, the SiO₂-PU@APT30 exhibited optimal performance, achieving 58 % MB degradation within 3 h, significantly outperforming the SiO₂-PU@TiO₂ and Si-PU@Ag₃PO₄, which showed only 16 % and 31 % degradation, respectively. The observed enhancement is attributed to the synergistic interaction between Ag₃PO₄ and TiO₂, facilitating improved charge separation and photocatalytic efficiency. The SiO₂-PU@APT30 coated glass achieved an impressive transmittance of 86 %. By facilitating the formation of a uniform water film instead of droplets, it effectively prevents fog accumulation, providing a significant advantage over uncoated glass. Additionally, the final coating exhibited excellent hydrophilicity, with the water contact angle (WCA) significantly reduced from approximately 63° to 27° and after 30 min of visible light exposure, completely prevents condensation and droplet formation, demonstrating superior antifogging performance compared to bare glass. This, combined with its outstanding anti-fogging performance and superior photocatalytic activity, highlights its potential as an efficient and effective self-cleaning surface treatment.