The Study Of Preparation, Characterization And Visible Light Photocatalytic Properties Of ZnFe₂O₄ /MWCNTs Nanocomposites

Zinc ferrite/multi-walled carbon nanotubes (ZnFe2O4/MWCNTs) composites were prepared by a hydrothermal process. XRD, FT-IR, TEM, UV-Vis and BET were used to characterize the products. The results showed that spinel ZnFe2O4 could be prepared at 180℃for 12 h, using MWCNTs as the support could reduce the size of ZnFe2O4. FT-IR spectrum showed that the Zn-O Tetrahedral and Fe-O Octahedral vibration were presenced at the 400 - 600 cm-1. The concentrated H2SO4/HNO3 showed a higher capability to produce a high density of fuctional groups of -OH, -C=O, -COOH, resulting in the dispersion of MWCNTs in aqueous solutions and the capacity for adsorpting cations. The ZnFe2O4/MWCNTs composite with 5 % mass ratio of MWCNTs to ZnFe2O4 showed ZnFe2O4 particles were homogeneously dispersed on the surface of MWCNTs. The visible light response and BET of ZnFe2O4/MWCNTs were improved as compared with pure ZnFe2O4.The photocatalytic properties of ZnFe2O4/MWCNTs were studied by degrading methylene blue (MB) dye under visible-light irradiation. The influences of reaction conditions such as initial concentration of MB, H2O2 concentration, the mass ratio of MWCNTs to ZnFe2O4 and catalyst dosage on the degradation efficiency of MB and their kinetics were also studied. It was found that at the conditions, the MB with its initial concentration of 10 mg/L, the catalyst loading with 1.00 g/L, adding 2.0 % volume of H2O2 to MB, the catalytic activity of ZnFe2O4/MWCNTs composite with 0.8 % mass ratio of MWCNTs to ZnFe2O4 (ZnFe2O4/MWCNTs-0.8) was much higher than that of ZnFe2O4 with 99 % degradation ratio of MB after 6 h visible-light irradiation. The total organic carbon (TOC) in the solution decreased after the photocatalytic reaction, which confirmed that 90 % of MB was mineralized. ZnFe2O4/MWNTs-0.8 photocatalyst could be reused at least three times without photocorruptness, which would be very useful for environmental catalysis.In the present study the possible mechanism of the enhanced photocatalytic activity of ZnFe2O4 in the presence of MWCNTs were studied. The zeta potential showed that the isoelectric point of ZnFe2O4/MWCNTs-0.8 was 6.5 pH unit, which was less than the natural pH = 7.0. So the catalyst was negatively charged and offered a suitable surface for adsorption of MB cation. The photoluminescence (PL) intensity of the ZnFe2O4/MWCNTs-0.8 composite was lower than that of pure ZnFe2O4, which showed that the recombination of photo-generated charge carriers was inhibited greatly. The surface condition of ZnFe2O4/MWCNTs-0.8 was more favorable in the formation of·OH than that of pure ZnFe2O4 or the mixture of ZnFe2O4 and MWCNTs. Therefore, the ZnFe2O4/MWCNTs-0.8 composite exhibits enhanced photocatalytic activity under visible-light irradiation in the presence of H2O2. This is a new kind of photocatalyst and has not been reported before.