Yolk-shell structured Fe3O4@C@F-TiO2 microspheres with surface fluorinated as recyclable visible-light driven photocatalysts

The uniform magnetic Fe3O4@C@fluorinated-TiO2 (Fe3O4@C@F-TiO2) microspheres with multilevel yolk-shell structures were successfully prepared by a simple and improved solvothermal method. The carbon mid-layer containing numerous hydrophilic groups induces TiO2 growth onto its surface and plays a crucial role in protecting Fe3O4 cores from excessive erosion and keeping the integrity of the hollow structure during the solvothermal etching process, meanwhile as an electron acceptor it can reduce electron-hole recombination rate. In the presence of HF, the obtained TiO2 shell possesses an enhanced crystallization resulting from the rapid in situ fluoride-mediated dissolution and recrystallization processes, and plenty of equivalent to Ti-F groups are formed on TiO2 surface through the ligand replacement reaction between F- and hydroxyl group. Furthermore, Fe3O4 cores will be partly etched by HF leading to the yolk-shell structure of an increased surface area of 167.50 m(2)/g while Fe3O4@C@F-TiO2 microspheres still maintain excellent magnetic separability. Due to the efficient molecular transportation and adsorption, and the synergic effect of carbon modification and surface fluorination of TiO2, the Fe3O4@C@F-TiO2 microspheres have been demonstrated to possess superior visible-light driven photocatalytic activity in degradation of Rhodamine-B than commercial P25 TiO2 catalysts. (C) 2014 Elsevier B.V. All rights reserved.