The Interactions of Chlorophyll a with ZnO Nanoparticles Synthesized by Sol-gel Method

The influence of ZnO nanoparticles on chlorophyll a (Chl-a) was studied by observing their absorption, fluorescence, and Fourier transform infrared spectra (FTIR). Chl-a molecules were absorbed onto the surface of the colloidal nanoparticles due to the electrostatic interactions between Chl-a molecules and particle surfaces which led to a redshift of the absorption peaks of Chl-a upon addition of ZnO nanoparticles to Chl-a benzene solution. The redshift of the fluorescence spectra and the quenching of the fluorescence emission of Chl-a suggested a charge-transfer between Chl-a and ZnO nanoparticles. The difference between the first exci-ted state of Chl-a and the bottom of the conduction band of ZnO may provide the necessary driving force for such a charge-transfer process. An isoemissive point was observed at 654 nm in the fluorescence spectra when excited by 355 nm. No isoemissive point was found when excited by 433 nm, because ZnO nanoparticles have no absorption at this wavelength. Based on the Stern-Volmer relation I0/I=1+K[Q], the quenching mechanism was attributed to static quenching. Besides, changes of Zn—O bond vibration peak in FTIR were also observed after the Chl-a molecules were absorbed onto ZnO nanoparticles. The above studies illustrated a strong interaction between Chl-a and ZnO nanoparticles, and indicated that ZnO nanoparticles may exert negative impact on the photosynthesis process, where Chl-a plays an important role.