Study On Preparation And Properties Of Modified Layer Niobate

In recent years, the layered niobate compounds show outstanding catalytic property in the field of splitting water to H₂ and O₂, which has been paid more attention by many researchers. K₄Nb₆O₁₇ are typical layered niobate compounds, which have ion-exchange capacity and photocatalytic properties. The research on K₄Nb₆O₁₇ was mainly focused on the Photocatalytic water-splitting property, but the study of photocatalytic degradation organic sulfide has been reported rarely.In this thesis, K₄Nb₆O₁₇ was synthesized by hydrothermal method; the different reaction time what affect synthesized objectives were researched. The photocatalysts were prepared by modifying Potassium Niobate (K₄Nb₆O₁₇), which was prepared by hydrothermal method, through Ni2+ and Fe3+ ion-exchange respectively. Used Pechini method to prepare the film photocatalyst of K₄Nb₆O₁₇.X - ray diffraction (XRD), UV - visible diffuse reflectance spectroscopy (UV-vis-DRS), SEM, etc,were used to characterize the morphology and structure of the photocatalyst. The adsorption feature and photocatalytic oxidation activity for different organic sulfide gas in the different experimental atmosphere were evaluated through infrared spectroscopy technique.â‘´Different reaction time is one of the most important factors what influence of crystalling phase and purity. The crystallinity of the K₄Nb₆O₁₇ synthetic samples will continuously improve over time and grain keep getting bigger. XRD patterns shows, reaction after 24 hours, relatively pure orthorhombic crystalling phase K₄Nb₆O₁₇ was prepared which has a typical layer structure. Calculated by bragg equation,λ=2dsinθ, the distances of (020) planes of (020) planes of K₄Nb₆O₁₇ is 2.0122 nm.⑵Two kinds of modified niobate catalyst, Ni₂Nb₆O₁₇ and Fe_0.75Nb₆O₁₇, were prepared by using 24-hour-crystalized K₄Nb₆O₁₇ as precursor and the method of ion exchange. XRD patterns show that the modified niobate catalyst are of typical layered structure and their diffraction angles of (020) and (040) planes are shifted to the higher 2θvalues, which indicates the layer spacing decreasing. Calculated by bragg equation,λ=2dsinθ, the distances of (020) planes of Ni₂Nb₆O₁₇ and Fe_0.75Nb₆O₁₇ are 1.7802 and 1.6474 nm respectively. UV-visible reflection spectrum shows the absorption band of modified niobate catalysts was shifted from ultraviolet light to visible light region and the absorption performance increases. Besides, the red shift of the border of K₄Nb₆O₁₇ absorption band occurs after Ni2+ ion exchange and a weak absorption band appears in visible light region. However, two absorption bands of K₄Nb₆O₁₇ come into being after Fe³⁺ ion exchange. One absorption band is in the ultraviolet light region and the other in the visible light region. The border of absorption band appears near the wavelength of 545 nm.⑶The film of K₄Nb₆O₁₇ was prepared by Pechine method, amount of citric acid has great effect to the stability of coordination with metal cations. The experiment shows that the optimum proportion of citric acid and metal ions was 6:1, the stable Nb- citric acid solution can be obtained. The result of the UV-vis indicates the film of K₄Nb₆O₁₇ responded to the UV-vis changed when the variation of layers. With the increase of layers, the absorption band of the film catalysts was shifted to visible light region. When layers reached to 5 layers, Absorb threshold of 5 layers made great different from 1 layer ,however,Absorb threshold was almost invariant when the layer further increase .â‘·The research investigated the adsorption efficiency and catalytic ability of the niobate catalyst for different organic sulfur in different experimental environment. The result is showed that methyl mercaptan as an objective degradation products, and can be oxidated to sulfinic acid ester through natural light or UV-light irradiation and the catalytic of Ni₂Nb₆O₁₇. Methyl mercaptan C-S bond decomposed into sulfurous acid ester under the catalytic of Fe_0.75Nb₆O₁₇. Modified niobate catalyst have adsorption to dimethyl sulfide when dimethyl sulfide as an objective degradation products. After iron ion exchanging, the modified niobate catalyst adsorption efficiency of Fe_0.75Nb₆O₁₇ have stronger than Ni₂Nb₆O₁₇ for organic sulphides .