Preparation And Photocatalytic Properties Of Magnetic Graphene Zinc Oxide Nanomaterials

The widespread existence of organic and toxic pollutants has become an urgent issue that needs to be resolved. The present environmental problems call for more environmentally benign technologies. Since the photoelectrochemical splitting of water on semiconductor-based photocatalysts in 1972, the capture and conversion of solar energy by semiconductor-based heterogeneous photocatalysts have received extensive attention because of their great potential for environmental purification and converting photon energy into chemical energy. Among the various semiconductor photocatalysts, ZnO has attracted great attention because of its wide band gap （3.37 eV） and large exaction binding energy （60 meV）. However, there are four serious drawbacks limits the applications of ZnO photocatalysts. Firstly, ZnO suffers from the disadvantage of high recombination rate of photoinduced electron-hole pairs. Secondly, the well known photocorrosion often leads to a decrease in the photostability of ZnO in the recycle process under light irradiation. Thirdly, the smaller ZnO nanoparticles frequently have a large amount of native defects which may result in a large aggregation size in aqueous solution. Lastly, a related issue which to date has been receiving less attention is the separation of the ZnO photocatalysts from the treated wastewater and the studies of photocatalyst ecotoxicity. Therefore, to enhance the photocatalytic efficiency of ZnO, it is of crucial importance to solve the above mentioned problems. Coupling ZnO with magnetic reduced graphene oxide will be an effective and promising strategy to improve the photocatalytic performance, i.e., photocatalytic activity and stability, of ZnO and the composites have the property of magnetic response.Magnetic RGO-Fe₃O₄ and RGO-MFe2O4 （M=Mn2+, Zn2+, Co2+, Ni2+, Mg2+ Ca2+ and Cu+） and ZnO nanoparticles were synthesized separately through solvothermal and sol-gel method, then RGO-Fe₃O₄-ZnO Nanoparticles and RGO-MFe2O4-ZnO Nanoparticles （M=Mn2+, Zn2+, Co2+, Ni2+, Mg2+, Ca2+ and Cu2+） were prepared using a simple solution mixing process through ultrasonication. The FESEM images revealed that the magnetic MFe2O4 nanospheres and ZnO nanoparticles were successfully anchored on the surface of 2D RGO sheets. The morphology of MFe2O4 nanospheres is typically characteristic of the uniform structure with 200～400 nm diameter spheres and the diameter of ZnO nanoparticles were about 20nm. The photocatalytic test of degradation of Rhodamine B shows that the optimal RGO-MgFe2O4-ZnO NPs exhibit nearly the same photocatalytic performance than bare ZnO nanospheres, moreover, the hybrids can be recycled from the treated solution just by applying an external magnetic field.A simple, low-temperature synthesis approach is reported for planting 1D ZnO nanorod arrays on the 2D magnetic reduced graphene oxide to obtain hedgehog-like RGO-Fe₃O₄-ZnO Nanorod arrays and RGO-MFe2O4-ZnO Nanorod arrays （M=Mn2+ Zn2+, Co2+, Ni2+, Mg2+, Ca2+ and Cu2+） ternary hierarchical nanostructure, during which magnetic reduced graphene oxide as a flexible substrate for the formation of ZnO nanorod arrays and ZnO nanoparticles serve as seeds. The photocatalytic test of degradation of Rhodamine B shows that the optimal RGO-ZnFe2O4-ZnO Nanorod arrays exhibit 2-fold enhancement of photoactivity than bare ZnO nanorod arrays, moreover, the hybrids can be recycled from the treated solution just by applying an external magnetic field.