Origin of Physicochemical and Mechanical Stability of Low‐Temperature Prepared TiO ₂ ‐Based Photocatalytic Films: Surface Hydroxyl Density Matching

Low‐temperature prepared Titania (TiO 2 )‐based composite films are promising for photocatalytic applications. However, their practical deployment has been hindered by poor mechanical stability and the uncontrolled release of constituent nanoparticles into the environment. To overcome these limitations, colloidal TiO 2 nanoparticles (TiO 2 ‐NP) and colloidal silica nanoparticles (SiO 2 ‐NP) are used herein to produce nanoscale composite films, which additionally show also 80% higher photocatalytic rate towards toluene removal as compared to P25. Importantly such films exhibit enhanced mechanical robustness, as a consequence of the improved physicochemical stability, attributed to encapsulation of TiO 2 ‐NP and SiO 2 ‐NP within an amorphous SiO 2 matrix. The adhesive and cohesive integrity of the prepared colloidal TiO 2 ‐SiO 2 composite films was evaluated using the ISO 15184:2012 standard for film hardness testing, and the results demonstrate superiority compared with commercial pure TiO 2 (powder or colloidal) and commercial TiO 2 –mesoporous SiO 2 composite films. Characterization reveals that interfacial interactions, particularly between surface hydroxyl groups (Si–OH and Ti–OH), drive this enhanced stability. The presented results indicate a novelty of this research in two directions: 1) proof of superiority in the mechanical stability of the prepared material; 2) explanation of the origin of the superiority in the mechanical stability of the prepared material. The findings offer a viable route to robust, economically efficient, environmentally friendly TiO 2 composite films suitable for scalable deployment in air and water purification systems or self‐cleaning surfaces, addressing key limitations of conventional powder‐based methods.