Synthesis By Liquid Phase Precipitation And Photocatalytic Property Of FeVO₄ Photocatalyst

Semiconductor-based phtotocatalysis has become increasing promising technology in environmental remediation. Photocatalyst was a key part in photocatalytic process. Of various types of photocatlysis, TiO2 has been identified as the most effective and useful photocatalyst because of its photostable, nontoxic, cheap and active properties in the past decades. However, the study of TiO2 has not larger breakthrough because it has wide energy gap, was only effective under ultra-violet light and difficult to recycle. Therefore, the research and development of new non-TiO2 photocatalytsts has become one of the hot fields, with broad prospects and challenging. Recently, vanadate, as one of the new photocatalyst, is gaining more attention of scholars. However, few vanadate has been developed,most of which being used in water splitting, only a few of which for the photocatalytic degradation of organic pollutants. So, pure iron(III) vanadate (FeVO4) photocatalyst and doped FeVO4 photocatalyst were prepared with simple synthesis methods in the paper. Its structure and photocatalytic properties were explored and researched, broadening the vanadate photocatalysts research field. It may provide a theoretical basis and foundation for further exploring vanadate photocatalyst and doping.In paper, FeVO4 photocatalyst was synthesised with liquid phase precipitation method . As well as Ag, Ba, Cu, Fe and Eu-doped photocatalyst FeVO4 were prepared. The relationships between preparation, sturcure, morphologies and photocatalytic of samples were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area (BET), X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectra (DRS). The photocatalytic activities of the samples were determined by oxidative decomposition of methyl orange in aqueous under UV light and visible light irradiation.Using Iron Nitrate and Vanadium Ammonium as raw materials, series samples were synthesised. The different factors'(n (V) / n (Fe) molar ratio, precipitation pH and calcination temperature) effects on the characterization of FeVO4 were discussed and the optimum preparation conditions of triclinic FeVO4 was concluded. The results showed that the different n (V) / n (Fe) molar ratio and different pH value had impact on the phase formation. The pure FeVO4 was prepared when n (V) / n (Fe) molar ratio was 1 and Fe2O3 or V2O5 phase appeared when n (V) / n (Fe) molar ratio was higher or lower than 1.00 and pH value be higher or lower than 8. Calcining temperature greatly affected the crystallization and the grain size of samples.It was found that the samples prepared with the n (V) / n (Fe) moral ratio be 1,pH=1 and calcinated under 800℃for 4 hours had the best photocatalytic ability. The sample prepared under these conditions was triclinc phase and oxygen-deficient lattice structure due to deviation from oxgen stoichiometric material. The structure was Fe2x2 + Fe3 +1-2 xV5+O4-x, with the particle size be about 74nm. The absorption edge was around 605nm and its band gap was about 2.05eV. But it had small specific surface area: only 2.265m2/g. FeVO4 photocatalyst shows the photocatalytic activity under the visible ligh and it is easy to recovery from the suspension beacause of its good sedimentation ability.The effects of catalyst loading, initial MO concentration, light intensity and pH value on the degree of photo degradation had been investigated.Ag+ doped FeVO4: it was conclued that the method of calcining silver vanadate and iron vanadate mixtures worked best on the basis of comparison of three doping methods. It was found that Ag doping led to distoration and expansion of crystal lattice due to a few of Ag being into the FeVO4 crystal lattice, which increased the degree of oxgen stoichiometric. Ag doping changed crystal surface morphology dramatically, but didn't change the specific surface area. And Ag4V2O7 phase appeared when the doping amount was greater than 10wt%, mainly be on the needle-like material. In the experimental conditions used, the optimal photocatalytic activity for all the prepared samples was reached when the Ag doping was 1 wt% calcined at 800℃for 4h.Ba2+ doped FeVO4 photocatalyst was prepared through calcining silver vanadate and iron vanadate mixtures. It was found that Ba doping had little effect on the grain size of FeVO4, but led to distoration and expansion of crystal lattice due to a few of Ba being into the FeVO4 lattice, which increased the degree of oxgen stoichiometric. BaV2O6 phase appeared when the doping amount was greater than 12wt%, mainly be on the flake-like material. Ba doping changed crystal surface morphology dramatically with almost the same specific surface area .The light absorption ability was intensitied after Ba2+ doping . In the experimental conditions used, the optimal photocatalytic activity for all the prepared samples is reached when the Ag doping was 1 2wt% and the samples calcined at 750℃.Fe2O3/FeVO4 photocatalysts were successfully prepared by liquid phase precipitation. It was found that the samples prepared with the Fe/V moral ratio be 1.01:1 and calcinated under 750℃had the best ability of photodegradation of MO. Doping Fe2O3 maybe inhibit the growth of FeVO4 and increase the surface area which can improve the photo-activity. Also the Fe2O3 can act as electron traps promoting the electron-hole separation and then increase the photo-activity.Cu2+ doped FeVO4 photocatalyst was prepared through calcining cupper vanadate and iron vanadate mixtures. It was found that Cu doping made particle size increased and led to distoration and expansion of crystal lattice, which increased the degree of oxgen stoichiometric. Cu3Fe4(VO4)6 phase appeared when the doping amount was greater than 5wt%. Cu doping changed crystal surface morphology dramatically with almost the same specific surface area. In the experimental conditions used, the optimal photocatalytic activity for all the prepared samples is reached when the Ag doping was 5wt% and the samples calcined at 700℃.Eu/ FeVO4 photocatalysts were prepared by the impregnation method on the basis of comparison of four methods. The results indicated that the Eu/ FeVO4 photocatalysts consist of triclinic phase without signifcant changes of crystalline size. SEM images showed that after loading with Eu,many fine particles were observed on the surface of the FeVO4 particles which maybe greatly increase their specific surface area. The DRS measurements showed that the light absorption of Eu/ FeVO4 novel photocatalyst was greatly increased during 200-500nm.. The photocatalyty activity of Eu/ FeVO4 sample was significantly enhanced when doping content was 0.5wt % and calcined at 250℃.In this paper, pure FeVO4 and the doped FeVO4 have good application prospects because they had photocatalytic activity under visible light irradiation and can be easy to recovery from the suspension and be reused at least 5 times without reducing photocatalytic efficiency. But it was pitful for its small surface area . How to improve the specific surface area is worthy to further study. Using different metal ions doping can effectively enhance its activity. However, there exists an optimum doping amount, higher or lower than this value, the activity should not be very good. In the optimum doping amount, the calcination temperature also affected the activity improved.