SYNERGETIC EFFECT OF CARBOXYLIC-ACID FUNCTIONAL-GROUPS AND FRACTAL SURFACE CHARACTERISTICS FOR EFFICIENT DYE SENSITIZATION OF TITANIUM-OXIDE

FTIR spectroscopy has been used to investigate the surface interaction of TiO2 powder particles sensitized with two of the most efficient se nsitizers, the mono-nuclear complex [RuL2(SCN)(2) and the tri-nuclear complex RuL2[mu-(CN)Ru(CN)L-2'](2) {L = 4,4'-dicarboxylic acid-2,2'-bi pyridine and L' = 2,2'-bipyridine}, both having ligands substituted wi th carboxylic acid (-COOH) functional groups. C=O band peak frequency shifts of about 20 cm(-1) higher than that of bulk complexes and disap pearance of the CN- and SCN- band vibrations were observed on derivati ve samples. The C=O shift was attributed to chemical adsorption of the dyes onto the oxide particles via ester-like binding between the carb oxylic acid groups and the OH moieties on TiO2. Incident light-electri city conversion efficiencies approaching unity with the above two ruth enium-bpy complexes attached on transparent nanocrystalline TiO2 films were reported. The morphology and the surface characteristics of the films studied by AFM showed the presence of a fractal network of inter connected grains whose diameter were between 15 and 25 nm. The height distribution of surface features has a maximum around 60 nm. On such l arge surface area electrodes efficient adsorption of the Ru-bpy comple xes via ester linkages leads to extremely high photoconversion yields. (C) 1998 Elsevier Science B.V. All rights reserved.