Tuning Anatase Surface Reactivity toward Carboxylic Acid Anchor Groups.

The effect of different post-treatments on TiO ₂ anatase surface reactivity was investigated in order to obtain the best techniques for enhancing anatase performance in diverse applications, e.g., in photocatalysis and especially as photoelectrodes for dye-sensitized solar cells (DSSCs). Different post-treatments of compact anodic anatase TiO ₂ were compared, including O ₂ plasma, UV irradiation, immersion in H ₂ O ₂ , vapor thermal treatment, and post-anodization, evaluating the increase of the amount of OH reactive groups on the surface and removal of surface contamination. In XPS spectra, the increase of OH groups is evident by the O 1s peak at higher binding energy. ToF-SIMS principal component analysis demonstrated that treatments performed in aqueous media led to a cleaner surface, with substantial removal of electrolyte residues. Stearic acid and the organic dye N719 were adsorbed to the differently post-treated anatase, and adsorption was evaluated by contact angle and dye desorption measurements. A higher loading with molecules containing carboxylic acid functionalities was confirmed by both techniques on the treated samples. The post-treatments that presented the highest amounts of dye were used to prepare photoelectrodes, and these were tested in DSSCs where the efficiency values doubled in comparison with the non-post-treated electrode.