On the adsorption kinetics and mechanism of enhanced photocatalytic activity of Fe3 O4 -SiO2 -TiO2 core-multishell nanoparticles against E. coli.

Abstract

In the present study, a Fe3 O4 -TiO2 (FT) core-shell and a core-multishell structure of Fe3 O4 -SiO2 -TiO2 (FST) were synthesized, and their bactericidal capability was investigated on Escherichia coli (E. coli). Scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV-vis), X-ray diffraction, Brunauer-Emmett-Teller, zeta potential, and fluorimetry were carried out to characterize properties of synthesized nanoparticles. An efficiency of 98% adsorption and harsh bacterial damage was observed when E. coli was put in contact with FST. Weaker adsorption of bacteria in contact with FT demonstrated that heterojunction has destructive effects on nanostructure. Further investigation proved that more OH were produced on the surface of FST, which is a sign of its longer lifetime. Moreover, results revealed that the presence of SiO2 in the structure caused enhanced coverage, surface area, and porosity in TiO2 outer layer, all of which have positive effects on adsorption. However, UV-vis showed smaller band gap for FT. It suggests that although photoactivity of FST is less influenced by light absorption, it possesses more e/h lifetime for generation of reactive oxygen species. Results point to the importance of SiO2 as an obstacle of heterojunction on both adsorption and photoactivity. It was also proposed that increasing band gap in FST can be attributed to the porosity of SiO2 that causes suppression of TiO2 nanocrystallite growth.