Cyanobacterial chlorophyll as a sensitizer for colloidal TiO2

Chlorophyll has been extracted from cyanobacteria. The adsorption of chlorophyll on the surface of colloidal TiO2 through electrostatic interaction was observed. The apparent association constant (Kapp) of chlorophyll–TiO2 obtained from absorption spectra is 3.78 × 104 M−1. The Kapp value of chlorophyll–TiO2 as determined from fluorescence spectra is 1.81 × 104 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 TiO2 nanoparticle surface. The dynamics of photoinduced electron transfer from chlorophyll to the conduction band of colloidal TiO2 nanoparticle has been observed and the mechanism of electron transfer has been confirmed by the calculation of free energy change (ΔGet) by applying Rehm–Weller equation as well as energy level diagram. Lifetime measurements gave the rate constant (ket) for electron injection from the excited state chlorophyll into the conduction band of TiO2 is 4.2 × 108 s−1.