Enhancing photocatalytic efficiency and interfacial bonding on cement-based surfaces by constructing CaO-TiO2 hybrid catalysts

The application of titanium dioxide (TiO₂) coating in cement-based materials faces challenges regarding its durability. This study presented the concept of ‘induced bonding’ for enhancing coating adhesion. By modifying TiO₂ with CaO, nucleation sites were constructed on its surface, inducing the growth of hydration products and connecting the catalytic materials to the substrate. As a result, a novel dual-effect CaO-TiO₂ hybrid catalytic material with enhanced photocatalytic efficiency and interfacial bonding was successfully developed using a mechanochemical-thermochemical method. The CaO-TiO₂ catalyst was coated onto cement surfaces, and the mechanisms of interface enhancement were revealed by micro-scratch and microstructural tests. The results indicated that the synthetic catalytic materials exhibited excellent NO photocatalytic degradation performance, particularly at an activation temperature of 300 °C; the optimized NO degradation efficiency hit around 40 % with a NO_x comprehensive removal amount approximately twice that of conventional TiO₂. Moreover, the minimal generation of NO₂ demonstrated a strong photocatalytic selectivity. This exceptional photocatalytic performance can be attributed to the interaction between TiO₂ and CaO, along with its derivatives such as CaTiO₃ and CaCO₃, which promoted the formation of active species (•OH, •O²⁻, h⁺), and increased the absorption efficiency in the visible light region. Furthermore, the wear resistance and interface critical load of CaO-TiO₂ coatings were more robust than reference coatings. The CaO-TiO₂ catalyst promoted hydration to form widely distributed and interlocked fibrous C-S-H gel, bridging the catalyst particles and enhancing the adhesion of the coating with the cement substrate, thereby improving its interfacial bonding performance.