Viscoelastic Engineering and Thermoreversibility of Aqueous TiO 2 Sol–Gels for Efficient Photocatalytic Coatings

Abstract

Water‐based TiO 2 sol–gels are promising for the fabrication of photocatalytic coatings but remain challenging to optimize because of the strong temperature dependence of hydrolysis‐condensation reactions and the resulting variations in sol viscosity and microstructure. This study investigates the relationship between viscoelastic properties and photocatalytic efficiency of sol–gel coatings prepared with titanium isopropoxide (TTIP) and acetic acid under controlled aqueous hydrolysis demonstrating partial thermoreversibility of the observed behavior. Vibro‐viscometry and DLS‐based microrheology were employed to probe microstructural evolution of sols under ambient aging, thermal incubation and cold storage. Ambient aging produced weakly condensed sol with low dynamic viscosity ∼ 1.623 mPa·s, resulting in non‐uniform coatings, low catalyst loading ∼ 0.014 mg/cm 2 , and limited HCHO photodegradation (< 30%). Thermal incubation increased the viscosity to ∼ 8 mPa·s, enabling the formation of uniform, dense, and crack‐free coatings with a catalyst loading of 0.107 mg/cm 2 , controlled thickness (∼ 0.5–0.8 µm), and 100% HCHO degradation. Subsequent cold storage partially reversed these changes, decreasing viscosity, catalyst loading, and photocatalytic efficiency while demonstrating the thermoreversibility of the incubation‐induced colloidal networking. Overall, this study establishes a rheology‐structure‐performance relationship linking sol viscoelasticity to coating formation and photocatalytic activity of water‐based TiO 2 sol–gel systems, offering a rheology‐guided approach for designing high‐performance photocatalytic coatings.