Optimizing dye anchoring efficiency: The critical role of esterification catalysts in carboxyl dye-sensitized TiO2 photocatalyst preparation

Dye sensitization, as an effective method to modify the optical properties of TiO₂, has wide applications in photocatalysis and solar cells. Carboxy-functionalized dyes can form stable ester bonds on the TiO₂ surface, which facilitates the transfer of photogenerated electrons. Therefore, the addition of esterification reaction catalysts inevitably influences the sensitization process. This study systematically investigates the catalytic effects of acid catalysts, basic reagents and organocatalysts on carboxy-functionalized dye-sensitized TiO₂ composites, with a focus on their photocatalytic performance and underlying mechanisms. The infrared spectroscopy characterization results confirmed the successful anchoring of the dye on the TiO₂ surface and the formation of ester bonds. Unlike the inhibition of esterification reactions by base reagents, both acid catalysts and organocatalysts led to higher esterification degrees in the dye-TiO₂ system. UV–Vis spectra showed that the dye-TiO₂ systems catalyzed by different catalysts exhibited distinct visible-light absorption compared with pure TiO₂. Notably, dye-TiO₂ (HNO₃) and dye-TiO₂ (EDC-DMAP) demonstrated the optimal visible-light absorption in the acid-catalyzed and organic-catalyzed systems, respectively. EIS confirmed that both acid and organic catalysis resulted in lower interfacial impedance in the dye-TiO₂ system, implying superior charge transfer efficiency and photocatalytic activity. Photocatalytic experiments were also conducted to verify the aforementioned characteristics. Compared with dye-TiO₂, dye-TiO₂ system catalyzed by acid catalysts exhibited the best photocatalytic performance. The photocatalytic efficiency of dye-TiO₂ system catalyzed by organocatalysts had also been improved. In contrast, the dye-TiO₂ system involving basic reagents showed lower photocatalytic performance than the uncatalyzed dye-TiO₂ system.