Tannic Acid-Directed Synthesis of Mesoporous Anatase TiO2: Linking Structural, Surface, and Thermodynamic Properties to Photocatalytic Performance

Rational engineering of TiO2 surface architecture offers an effective approach to optimizing its physicochemical and photocatalytic properties in advanced oxidation processes (AOPs). Incorporation of organic structure-directing agents during synthesis provides a versatile strategy for tailoring the structural and surface properties of TiO2, although sustainable, naturally derived alternatives remain relatively unexplored. Tannic acid (TA), a low-cost and renewable polyphenolic compound, is particularly attractive for this purpose. Herein, a sustainable sol–gel approach was developed for the synthesis of mesoporous TiO2 using TA as a bio-derived organic structure-directing agent. Systematic variation of the TA concentration established a concentration-dependent structure–property–activity relationship linking the crystalline structure, morphology, surface characteristics, thermodynamic properties, and optical properties to photocatalytic performance under UV irradiation. The refined lattice parameters closely matched those of standard anatase TiO2, indicating that variations in TA concentration did not substantially alter the anatase crystal structure. Thermodynamic analysis of the oxidation pathways provided quantitative insight into the feasibility of hydroxyl radical formation. Methylene blue degradation followed apparent pseudo-first-order kinetics under the investigated conditions, with the photocatalytic activity reflecting the combined contributions of surface accessibility, light harvesting, and charge-carrier behavior. The results demonstrate that TA can effectively direct the formation of mesoporous TiO2, providing a sustainable route for tailoring photocatalyst properties and promoting pollutant degradation under low-energy UV-LED irradiation.