Inactivation of Bacteria by Kaolinite Photocatalysts in Water

Abstract

Photocatalytic inactivation is mainly aimed at bacteria in surface water. Kaolinite is made to become the photocatalyst that has the inactivating capability with Ag⁺, Zn²⁺, and Ti⁴⁺ions. When the kaolinite catalyst is irradiated by a sodium lamp, it produces photocatalytic action to destroy bacteria. The photocatalytic inactivating result shows that kaolinite-Ti catalyst has 100% inactivation efficiency in 150 min, while the inactivation efficiency of kaolinite-Zn catalyst is more than 85% in 200 min. Photocatalytic inactivation of bacteria occurs because when kaolinite catalysts are irradiated by a sodium lamp, catalysts are excited to carry on photocatalytic reaction; irradiation of catalysts with photons of energy equal to or greater than its band-gap results in the promotion of electrons from the valence band to the conduction band of the catalyst particles. This study also compares the inactivation efficiency on bacteria. The result shows that kaolinite-Ti has the best inactivation efficiency, while next comes kaolinite-Ag/Zn catalyst. Coupled kaolinite-Ag/Zn catalyst is formed by combining two kinds of semiconductor catalysts that have different energy gap and energy band sites. It can separate electrons and holes more efficiently and enhance inactivation efficiency. This study also finds that the more the amount of catalysts is added, the easier does the shielding effect take place.