Silanized hierarchical TiO2/g-C3N4 heterojunctions for multifunctional acrylic coatings: Enhanced photocatalytic activity, mechanical reinforcement, and self-cleaning performance

This study presents the development of multifunctional acrylic-based photocatalytic coatings through the incorporation of titanium dioxide (TiO 2 ) nanoparticles and graphitic carbon nitride (g-C 3 N 4 ) nanosheets, both synthesized via modified routes to enhance structural and interfacial properties. TiO 2 nanoparticles were prepared by a controlled hydrolysis–condensation process using titanium tetra butoxide (TBOT) as precursor, while g-C 3 N 4 was synthesized through thermal polymerization of melamine with a pre-saturation step to improve its crystallinity and surface reactivity. The resulting g-C 3 N 4 nanosheets were then decorated with TiO₂ nanoparticles to form a hierarchical heterojunction, followed by surface functionalization with 3-aminopropyltriethoxysilane (APTES) via a silanization treatment. This strategy enabled excellent nanofiller dispersion, strong filler–matrix interaction, and scalable integration into an acrylic resin matrix. UV–Vis diffuse reflectance spectroscopy and Tauc plot analysis revealed a bandgap narrowing to 2.55 eV in the functionalized heterostructure, facilitating visible-light activation. The hybrid exhibited significantly suppressed photoluminescence intensity and a threefold increase in transient photocurrent density, indicating improved charge separation. Electrochemical impedance spectroscopy confirmed reduced interfacial resistance, enhancing charge transport across the coating interface. Colorimetric analysis showed superior methylene blue (MB) dye degradation under UV (Δb* = 40) and visible light (Δb* = 42), compared to neat acrylic resin (Δb*˂ 3.5). ESR and scavenger studies identified photogenerated holes as dominant species, assisted by ·OH and ·O₂ − radicals. Enhanced reinforcement index (3.2), toughness (15 mj/mm 2 ), and stiffness (9 N/mm) were achieved, alongside high thermal and mechanical stability. Furthermore, over 95 % photocatalytic efficiency was retained after five cycles, confirming the system's recyclability. These findings highlight the promise of APTES-functionalized TiO₂/g-C₃N₄ nano-heterojunctions as robust, self-cleaning, and sustainable materials for smart coating applications. • TiO₂/g-C₃N₄ heterojunction was formed with APTES to enhance photocatalytic performance. • The composite achieved 97 % MB degradation under UV and 80 % under visible light. • The bandgap was reduced from 3.2 eV to 2.55 eV, boosting visible-light activity. • The mechanical properties of the films were improved, including increased stiffness, toughness, and thermal stability.