Solar photocatalysis : Inactivation of bacteria by smectite catalysts

Engineering Consultant, Kelee Environmental Consultant Corporation, 6F.-2, No. 288-8, Sinya Road,

Kaohsiung City 806, Taiwan

E-mail : singsuey@ms28.hinet.net

Department of Civil and Ecological Engineering, I-Shou University, No. 1, Sec. 1, Syecheng Rd.,

Daishu District, Kaohsiung City 840, Taiwan

E-mail : edmywu@isu.edu.tw

Manuscript received online 20 January 2014, accepted 04 June 2014

This study uses smectite clays as the catalyst carriers and exchange Ag⁺ and Zn²⁺ onto the carriers by the method of ion exchange. Meanwhile, with photocatalytic activities under the irradiation of a sodium lamp, the cell structures of bacteria in the water can be totally destroyed to finally achieve inactivation of bacteria.

The modified smectite catalysts undergo the functional-group analysis through the Fourier Transform Infrared Spectroscopy (FTIR). The results show that high-temperature sintering does not damage the mineral structures of smectite catalysts. As for the effect on inactivation of bacteria, owing to the semiconductor properties of the modified smectite catalysts, when a sodium lamp emits light on the catalyst particles, catalyst particles can be excited to cause photocatalysis and generate •OH radicals, which would then damage the internal structures and compositions of bacterial cells, causing oxidative splitting of cell walls and membranes and overall decomposition of cells to achieve the purpose of bacterial inactivation. Meanwhile, among the different types of smectite catalysts and catalysts with different weight percentages, smectite-Ag catalyst with a 0.06 weight percent and smectite-Zn catalyst with a 0.04 weight percent can achieve highest efficiencies of bacterial inacitivation. This study shows that the possibility of shadowing effects gets higher with higher weight percentages. In other words, excessive catalysts will take over the light locations, reduce the amount of sodium light activities over the surface of bacteria, and therefore lower the efficiency of bacterial inactivation.