Cyanobacterial chlorophyll as a sensitizer for colloidal TiO 2

Abstract

Chlorophyll has been extracted from cyanobacteria. The adsorption of chlorophyll on the surface of colloidal TiO 2 through electrostatic interaction was observed. The apparent association constant ( K app) of chlorophyll–TiO 2 obtained from absorption spectra is 3.78 × 10 4 M −1. The K app value of chlorophyll–TiO 2 as determined from fluorescence spectra is 1.81 × 10 4 M −1, which matches well with that determined from the absorption spectra changes. These data indicate that there is an interaction between chlorophyll and colloidal TiO 2 nanoparticle surface. The dynamics of photoinduced electron transfer from chlorophyll to the conduction band of colloidal TiO 2 nanoparticle has been observed and the mechanism of electron transfer has been confirmed by the calculation of free energy change (Δ G et) by applying Rehm–Weller equation as well as energy level diagram. Lifetime measurements gave the rate constant ( k et) for electron injection from the excited state chlorophyll into the conduction band of TiO 2 is 4.2 × 10 8 s −1.