Fabrication of magnetic Fe₃O₄@SiO₂@TiO₂-Au with core-shell structure and its photocatalytic reduction activity

TiO₂-based photocatalysts have been widely used for photoxidation of various organic pollutants and photoreduction of Cr(VI) in aqueous solution. However, less attention has been paid to the photocatalyzed reduction of nitro group to amino group of nitroaromatics. In this study, liquid-phase deposition (LPD) technique was adopted to deposit anatase TiO₂ shell on amorphous SiO₂-coated Fe₃O₄ to form core-shell Fe₃O₄@SiO₂@TiO₂ magnetic photocatalyst. To further promote its photocatalytic activity, uniformly dispersed Au nanoparticles (NPs) were decorated on its surface to obtain Fe₃O₄@SiO₂@TiO₂-Au composite. Both the TiO₂-based magnetic composites were characterized and used as photocatalysts. To evaluate their photocatalytic performance, the photocatalyzed reduction of p-nitroaniline (p-NA) to p-phenylenediamine (p-PDA) was chosen as a model reaction under UV irradiation using HCOONH₄ as a hole scavenger and H source. Although p-NA can be completely reduced to p-PDA by the two photocatalysts, Fe₃O₄@SiO₂@TiO₂-Au exhibits much superior photocatalytic activity to Fe₃O₄@SiO₂@TiO₂. The is because Au NPs decorated on the TiO₂ can efficiently facilitate the photoexcited electron-transfer from the conduction band of TiO₂ to Au, which is favorable for minimizing the recombination rate of electrons and holes and prolong the lifetime of the photoelectrons. In addition, HCOONH₄ plays an indispensable role in improving the photocatalytic reduction of p-NA via capturing photo-generated holes.