Structural Feature, Modification Of Layered HNbWO₆and Its Photocatalytic Application

HNbW06can be modified by many organic and inorganic compounds through ion-exchange, and then producing diverse characteristics and functional layered composites due to its unique layered structure and regulation performance of interlayer H+. In addition, the as-prepared nanosheets after exfoliation as a new basic unit can be used to synthetize new composite material. So we can prepare efficient photocatalyst through exfoliation-restacking of the HNbWO6nanosheets and semiconductor nanoparticle such as TiO2、Fe2O3and ZnO.HNbWO6was prepared through proton-exchange of the precursor a-LiNbW06, which was synthesized by a solid state reaction method. The HNbW06/MOx (M=Ti, Fe and Zn) composite materials were prepared by exfoliation-restacking reaction. The catalysts were characterized by means of XRD, SEM, TEM, TG-DTA, FT-IR, BET, UV-vis DRS and Raman spectroscopy. The structure thermal stability of HNbWO6was emphasized to be investigated. The photocatalytic performance of the composite materials was estimated by degradation for methylene blue.The research results revealed that both the as-prepared a-LiNbWO6and HNbWO6·1.5H2O had layered structure obviously. And HNbWO6·1.5H2O had an significant increase in the interlayer spacing for a large number of water molecules in the interlayer after proton-exchange reaction. Moreover, the HNbWO6nanosheets still maintained the original skeletal structure with the accrescent interlayer spacing and a big increase in the specific surface area nearly30-fold comparing to HNbWO6. The study on thermal stability of the basic material demonstrated that the interlayer H+ions of HNbWO6·1.5H2O existed in two hydrated forms of H3O+and H5O2+in the range of40-180℃. Further, as the increase of heat treatment temperature, the X-ray diffraction peaks, skeletal vibration and acidic characteristics of the samples changed regularly with the removal of the neutral water molecules and crystal water in the interlayer.HNbWO6/MOx (M=Ti, Fe, and Zn) composite materials were prepared by exfoliation-restacking and all its heat treatment temperature were chosen at300℃according to the thermal gravimetric analysis. The optical response characteristic showed that the band-gap energy of the samples in the order:HNbWO6/ZnO-300℃> HNbWO6/ZnO> HNbWO6/TiO2> HNbWO6/TiO2-300℃> HNbWO6nanosheets> HNbWO6> HNbWO6/Fe2O3-300℃> HNbWO6/Fe2O3. At the same time, the band-gap energy of HNbWO6nanosheets almost unchanged, but the HNbW06changed significantly after proton-exchange. Those indicated that the type of interlayer cations had some influence in the electron transfer of the laminate and it had closely related with the band gap energy and the state of interlayer cations.The HNbW06/MOx (M=Ti, Fe, and Zn) composites exsited a synergistic effect between its host and guest. And the samples after calcining at300℃had a significant more interaction between the host laminate and interlayer oxide. Due to this synergistic effect of the HNbWO6/MOx composites, the host-guest crosslinking had an effect on electronic coupling and the transfer of photo-generated electron in the photocatalytic process. The activity of the photocatalyst under ultraviolet irradiation as follows: HNbWO6/TiO2-300℃> HNbWO6/TiO2> HNbWO6/ZnO-300℃> HNbWO6/ZnO> HNbWO6> HNbWO6nanosheets> HNbWO6/Fe2O3-300℃> HNbWO6/FeO3>> methylene blue self-degradation, indicated that all the catalysts had good photocatalytic activity of degradation for methylene blue.