*4.1.3. Effect of pH*

It is reported that the inactivation of bacteria was not influenced by changing the pH of the solution. The rate constant also remains constant for all pH range [64]. The zero point of charge (ZPC) for TiO2 -AgNP and *E. coli* can be estimated as ZPC (TiO2 -AgNP) = 4.0 and ZPC (*E. coli*) = 2.5, respectively. At all the pH values studied, both *E. coli* and the catalyst had a negative surface charge. Therefore, the electrostatic repulsion between bacterial cells and catalyst particles could result in the similar inactivation effect.
