Preparation And Performances Investigation Of Spinel Ferrites Based Composite Photocatalysts

Photocatalytic technology has attracted more and more attention because of its wide application in the fields of energy and environment concerns in recent years. Especially, the photocatalysts play the key important roles in photocatalysis. As a traditional semiconductor material, TiO₂ has been widely used in recent decades due to its low price, nontoxicity and high photocatalytic activities. However, TiO₂ is limited by low quantum efficiency caused by rapid recombination of photogenerated electron-hole pairs. On the other hand, TiO₂ is only sensitive to UV light due to its broad band gap（about 3.0 eV）. The two disadvantages have greatly limited the application of TiO₂,Spinel ferrites are considered as a promising semiconductor material due to their narrow band gap（about 2.0 eV） and high resistance to photo-corrosion. Furthermore, spinel ferrites are a kind of magnetic material and can be easily separated by external magnetic field from the reaction mixture. Unfortunately, ferrites are also limited by low photocatalytic efficiency. So a photocatalyst with high effectiveness and broad light absorption range is very desirable. Generally, methods of doping and composition are adopted to tune the structure and improve the catalytic activities of the photocatalysts.In this work, many efforts have been put to develop high efficiency and magnetically recyclable photocatalysts based on ferrites and following main results were obtained.（1） Magnetic ferrite CoxNi1-xFe₂O₄ nano-crystalline complex oxides were prepared by sol–gel auto-combustion method and well characterized by FT-IR,XRD, SEM, TEM and UV–vis DRs methods. The catalytic performances of the as-prepared samples were evaluated in photocatalytic oxidation of benzyl alcohol using molecular oxygen as oxidant under visible-light irradiation. The results have shown that the samples exhibited a remarkably high activity for the photocatalytic oxidation of benzyl alcohol. Especially, the benzyl alcohol conversion of 18.9 % and selectivity to benzaldehyde of 90.1 % was obtained using Co0.3Ni0.7Fe₂O₄ under optimum conditions.（2） Composite photocatalysts MFe₂O₄/C₃N₄（M=Mg, Ca, Sr and Ba） were synthesized using a simple method and characterized by FT-IR, XRD, TEM and UV-vis DRs methods. Photodegradation of Rhodamine B（RhB） was selected as probe reaction to investigate the photocatalytic activities of the as-prepared catalysts. The results have shown that the composite photocatalysts exhibit higher photocatalytic activities than each of the two moieties. Especially, the composite SrFe₂O₄/C₃N₄（w/w=1:1） exhibits the best photocatalytic activity for Photodegradation of RhB. The effects of pH of RhB aqueous as well as the kinetic analysis were investigated. The catalyst can be magnetically separated easily and exhibits excellent reusability.（3） CaFe₂O₄/Bi₂WO₆ composite photo-catalysts with different mass ratios were synthesized using a grinding-calcined method and characterized with FT-IR, XRD, TEM and UV-vis DRs methods. Photodegradation of methylene blue（MB） was selected as probe reaction to investigate the photocatalytic activities of the as-prepared catalysts. The results have shown that the composite photocatalysts exhibit higher photocatalytic activities than each of the two moieties in the photodegradation of MB. Especially, the composite CaFe₂O₄/Bi₂WO₆（w/w=1:3） exhibits the best photocatalytic activity for photodegradation of MB. The effects of calcination temperature, pH and addition of H₂O₂ on photocatalytic activity were also investigated. Moreover, the catalyst can be magnetically separated easily and exhibits excellent reusability.