Preparation And Photocatakttic Activity Of Composite Spinel Ferrite Film Materials From Hydrotalcite

Spinel compounds as a kind of new type semiconductor photocatalytic materials, has a narrow forbidden band, high utilization efficiency of visible light, and a wide varieties, which is expected to be more efficient, stable visible light catalysts. In recent years, titanium, gallium, manganese and iron spinel have been applied to decomposes water and degradation organic dyes, showing good visible light catalytic performance. However, the study of iron spinel (ferrite) photocatalytic performance is limited to ZnFe2O4 and ZnFe2O4/ TiO2 composite system, and the reports of research on ferrite thin film is much less. In addition, visible or sunlight as light source can greatly reduce the operation cost of photocatalytic technology, which also is the key for application of photocatalyst. Therefore, developing and perfecting the preparation techniques of ferrite thin film visible light catalyst have far-reaching significance.In the present work, NiZn and Co2+ -doped NiZn spinel ferrite granular films were fabricated successfully using layered double hydroxides (LDHs) as precursors by slurry coating/sintering techniques. The slurries of aqueous NiZnFeⅡFeⅢ-LDHs and CoNiZnFeⅡFeⅢ-LDHs were cast onα-Al2O3 substrates and the resulting LDH precursor films were calcinated at 600～900℃. The materials were characterized by powder X-ray diffraction (XRD), scanning electron microscope (SEM), EDS, vibrating sample magnetometer (VSM)and UV-vis absorption spectroscopy. The results indicated that calcination of the LDH films gave rise to stoichiometricNiZnFe2O4 and Co1-xNi0.2ZnxFe2O4 granular films with surface porous microstructure. Methylene blue (MB) and rhodamine B(RhB) were taken as model pollutants to evaluate the visible light photocatalytic activity of the resulting films. The details are as follows:(1) Ni-Zn-Fe(Ⅱ)-Fe(Ⅲ)-SO42- LDHs have been employed as a single-source precursor in the fabrication of stoichiometric NiZnferritegranular films. The well dispersed and stable suspension precursors of Ni-Zn-Fe(Ⅱ)-Fe(Ⅲ)-SO42- LDHs with initial molar ratio [Ni2+]/[Zn2+]of 4/0, 3/1,2/2,1/3 and 0/4were synthesized by separate nucleation and aging steps. The resulting slurries were cast on a-Al2O3 substrates and the resulting LDH precursor coatings were calcinated at 600～1000℃.The photocatalytic activity of the NiZnferrite films was investigated by degrading methylene blue (MB) dye under ultraviolet-light irradiation.The sample with [Ni2+]/[Zn2+]of 2/2 exihibits good magnetic and photochatlytic properties.(2)Co-Ni-Zn-Fe(Ⅱ)-Fe(Ⅲ)-SO42- LDHs have been employed as a single-source precursor in the fabrication of stoichiometric Co2+ -doped NiZn ferrite granular films. The well dispersed and stable suspension precursors of Co-Ni-Zn-Fe(Ⅱ)-Fe(Ⅲ)-SO42- LDHs with initial molar ratio [Co2+]/[Ni2+]/ [Zn2+]of 0/1/4,1/1/3,2/1/2,3/1/1 and 4/1/0were synthesized by separate nucleation and aging steps.The resulting slurries were cast on a-Al2O3 substrates and the resulting LDH precursor coatings were calcinated at 600～800℃.The photocatalytic activity of the Co2+ -doped NiZnferrite films was investigated by degrading methylene blue (MB) dye under ultraviolet-light irradiation. The results show that the photocatalytic activity of the sample increases with the increase of dopant content and the resulting composite film calcinated at 600℃exhibits good photochatlytic property.