Ammonia Vapor-Induced Pseudomorphic Transformation of Mesoporous TiO2 Sol-Gel Coatings

This study reports the structural rearrangement of TiO2 sol–gel coatings via aqueous ammonia vapor-induced pseudomorphic transformation. The coatings were applied to glass, silica-coated glass, and silica-coated silicon substrates. The transformation was initiated by aging the freshly deposited coatings─still containing the molecular template Pluronic P123─in an aqueous ammonia vapor atmosphere, resulting in significant reorganization of the primarily formed structure. Compared to aqueous vapor treatment for 4 days, the ammonia-based approach was more effective in enhancing optical transmittance, yielding a 1.25% higher average increase after just 4 h. The transformation led to notable changes in material properties: the monolayer coatings exhibited increased open porosity (from 38% to 55%), higher thickness (from 130 to 205 nm), and a reduced specific surface area (from 713 m2/cm3 to 392 m2/cm3). Additionally, a slight increase in pore radius (from 5.6 to 6.6 nm) was observed. While the photocatalytic activity decreased under both UV and visible light due to reduced surface area, the improved optical performance highlights the potential of aqueous ammonia vapor treatment as a powerful tool for tailoring the structure and functionality of mesoporous TiO2 coatings.