Carboxylic Anchoring Dye p-Ethyl Red Does Not Adsorb Directly onto TiO2 Particles in Protic Solvents (original) (raw)

Adsorption of the carboxylic anchoring dye, pethyl red (p-ER), onto TiO 2 nanoparticles in protic vs aprotic solvents was studied in situ using the surface-specific technique, second harmonic light scattering (SHS). Two different adsorption schemes were proposed to account for pER interactions with TiO 2 under different solvent environments. In aprotic solvents, pER adsorbs directly onto TiO 2. Conversely, in protic solvents, in which solvent molecules bind stronger than pER with TiO 2 , the dye molecules adsorb onto the solvent shell around the particle but not directly to the TiO 2 surface. In addition, a portion of the pER molecules form hydrogen bonds with the protic solvent molecules. The two different adsorption models reproduce the measured adsorption isotherms detected by SHS. Specifically, the pER molecules adsorb with a smaller free energy change and a larger density in protic solvents than in aprotic solvents. Our results indicate that protic solvents are undesirable for administering adsorption of carboxylic dyes in dye-sensitized solar cell applications as the dye molecules do not directly adsorb onto the TiO 2 particle.