Insight into enhanced visible light photocatalytic activity of Fe3O4-SiO2-TiO2 core-multishell nanoparticles on the elimination of Escherichia coli

A nano photocatalyst of Fe3O4-SiO2-TiO2 (FST) was produced, which can be used as a magnetic adsorbent in water treatment e.g. elimination of E.coli. Synthesis of shells on the initial Fe3O4 nanocores was carried out via the sol-gel technique. VSM, PSA, XRD, TEM, FE-SEM, EDS, FTIR and ZETA were analyses conducted for characterization. A 10-nm-passive layer of silica was formed between magnetic core and titania shell to inhibit direct contact of core and shell while superparamagnetic property was preserved. For TiO2 synthesis, it was found that the "concentration of water" and "mixing order of water and TBOT (Titanium butoxide)" had significant effect. Moreover, a minimum ratio of water to TBOT was required for TiO2 nucleation on Fe3O4-SiO2 (FS) seeds. Furthermore, an increment of water concentration to 3.8 M has led to 95% TiO2 coverage on FS nanoparticles. Results showed that FST nanoparticles were completely stable at pH = 7 and had acceptable zeta potential approximately -65 mV. Also, TiO2-coated magnetite nanoparticles (FT) were synthesized with the same condition of FST, but without silica midlayer, in order to observe th effect of SiO2 in nanostructure. Treatment of FST nanoparticles with E.coli showed 98% bacteria adsorption after 100 min, as well significant damage to bacteria cell membrane, was observed by SEM images. However, FT nanoparticles represented 82% bacteria removal with no harsh damage to the cells. This work demonstrated effective presence of SiO2 as a passive layer between Fe3O4 and TiO2 for photocatalytic efficiency improvement.