“…However, there are still a lot of unsolved issues in designing and fabricating core-shell nanoparticle structures [19][20][21][22][23]. Studies have shown that TiO2 and ZnO not only are good photocatalytic materials, but also can be coated on Fe3O4 very easily [14,[24][25][26][27][28][29][30][31]. There is significant literature available on graphene, Fe3O4, ZnO and TiO2, as well as the combination of graphene with photocatalytic semiconductor and metal oxides, such as TiO2, ZnO, SnO2, Fe2O3, MnO2 and CdS [1,4,[6][7][8][9][10][11].…”