BACTERIAL CADMIUM-SULFIDE SEMICONDUCTOR PARTICLES - AN ASSESSMENT OF THEIR PHOTOACTIVITY BY EPR SPECTROSCOPY

The bacterium Klebsiella aerogenes produces extracellular particles of cadmium sulfide in the presence of cadmium ions, The photoactivity of these particles has been studied using electron paramagnetic resonanc e (EPR) spectroscopy, Bacterial samples containing these semiconductor particles were irradiated with visible light in the presence of a spi n trap, either phenyl-tert-butylnitrone (PBN) or 5,5-dimethyl-1-pyrrol ine-N-oxide (DMPO). The results obtained reveal that a number of radic als, both oxygen and carbon based, are generated. Bacterial samples gr own in the absence of cadmium ions exhibit weak, irradiation-independe nt EPR signals. These bacterially produced radicals are quenched when CdS particles are present. The observation of light-induced radicals p rovides evidence that the bacterial CdS particles are photoactive, beh aving in a similar manner to inorganic CdS particles, and therefore co uld be used to mediate photocatalytic reactions.