Surface-Binding Forms of Carboxylic Groups on Nanoparticulate TiO2Surface Studied by the Interface-Sensitive Transient Triplet-State Molecular Probe

Surface binding between the carboxylic group and the TiO 2 nanoparticle is important in the potentially applicable dye-sensitized mesoporous TiO 2 crystalline solar cell. However, the nature of the surface binding is still not clear enough. We propose a new method to study the surface binding between the carboxylic group and the TiO 2 surface atoms by using an interface-sensitive molecular probe. The principle underlying this method is based on the triplet−triplet absorption of the probe molecule all- trans -retinoic acid (ATRA) formed by the photoinduced charge recombination between the TiO 2 nanoparticle and the probe molecule. By characterizing the individual triplet absorption spectra of ATRA in different forms, including the synthesized ester-like linkage model compound tri-butoxyl titanium (IV) all- trans- retinoate (Ti(IV)(OBu) 3 RCOO; RCOO = retinoate), the composition of different surface binding forms of carboxylic groups on TiO 2 nanoparticle surfaces in hexanol has been determined. The result shows that the simple adsorption form (anion, hydrogen bonding) comprises about 3% of the total adsorbed form, the ester-like form accounts for 63%, and chelating together with bridging form accounts for 34%.