3.5. Transmission electron microscopy
Furthermore, the destruction process of the morphology of E. coli K-12 for different VL irradiation times with the intensity of 200 mW cm−2 at pH 8 was observed by TEM analysis. Fig. 4a shows the appearance of E. coliK-12 before photocatalytic reaction. Characteristics of the E. coli K-12 were the well-defined cell wall as well as evenly rendered interior of the cell. The morphology of E. coli K-12 irradiated for 8 h greatly changed ( Fig. 4b). Part of the cell wall was decomposed, and an electron translucent region appeared at interior of the cell, indicating that the outer cell membrane was damaged leading to the leakage of the interior component. The further destruction was also observed at 15 and 30 h irradiation ( Figs. 4c and 4d). We found that with a prolonged irradiation, the cell became more and more translucent and the cell wall was greatly ruptured, which indicates that the cell membrane and the cell wall of the bacteria were destroyed by the reactive species.