Boronic Acid Adsorption on Hydrated Rutile TiO₂(110): A DFT + U Study

Boronic acids have emerged as promising anchoring groups for dye-sensitized solar cells (DSSCs). While previous computational studies have examined their adsorption on clean, ideal TiO₂ surfaces, real-world conditions often involve hydrated surfaces. In this work, we investigate the adsorption behavior of boric acid and five functionalized boronic acids on the hydrated rutile TiO₂(110) surface, using density functional theory with the DFT + U Hubbard correction and D3 dispersion corrections. To represent the hydrated surface, five distinct models were constructed, each featuring a different geometry of low-coverage dissociative water adsorption. For each hydrated surface, we examined a variety of molecular and dissociative monodentate and bidentate adsorption configurations. Boric acid was found to preferentially adsorb in a bidentate, doubly dissociative configuration on the hydrated surface, consistent with its optimal binding mode on the clean surface. Hydration weakens the adsorption of boronic acids compared to the clean surface, but preserves the same trends in relative binding strength across functional groupsfunctionalization still enhances binding stability, with fluorophenylboronic acids showing the strongest adsorption. Bader charge analysis reveals that hydration decreases the positive charges on the Ti surface atoms, reducing their Lewis acidity, weakening adsorption, and diminishing the sensitivity of adsorption strength to substitution. This study provides a more realistic benchmark for boronic acid adsorption under ambient conditions and informs the future design of anchoring groups for TiO₂-based applications.