Adsorption, desorption, and sensitization of low-index anatase and rutile surfaces by the ruthenium complex dye N3

Single-crystal anatase(101), (001) and rutile(100), (001) surfaces with atomically flat terraces were prepared and their structure verified with atomic force microscopy. A ruthenium complex dye, cis-di(thiocyanato)-bis (2, 2′ -bipyridyl- 4, 4′ -dicarboxylate) ruthenium(II) (usually known as N3) was used to sensitize these surfaces. The N3 coverage dependence of the incident photon to current efficiencies (IPCE) was measured for all four surfaces. IPCE values were much higher on anatase(101) and rutile(100) than on the other two surfaces. The kinetics of N3 adsorption was also studied on the four surfaces. The adsorption kinetics for a slow adsorption step could be fit with a Langmuir kinetic model. The differences in the adsorption of N3 and the IPCE values are discussed based on the structure of the N3 and the geometry and reactivity of the binding sites on the four surfaces.