Wet Chemical Synthesis And Photocatalytic Activity Of Potassium Niobate K₆Nb_10.8O₃₀ Powders

The textile industry produces large quantities of highly colored effluents, which are toxic and mostly nonbiodegradable and also resistant to destruction by physico-chemical treatment methods. Photocatalytic oxidation technology is an extremely attractive method for water deep treatment, which is of high efficiency, energy saving and non-second contamination and provides a promising strategy for disposing organic dye wastewater. In the past two decades, a variety of niobates had been extensively applied in the field of ferro-electricity and dielectric materials. Recently, people found some niobates have high activity in water splitting. Most of niobates with tungsten bronze (TB) type structure usually were synthesized by solid-state reaction, which needed high temperature. The purity of the compound was not high and the surface area of it was small. In this thesis, we studied the wet chemical synthesis of niobates K₆Nb_10.8O₃₀ and photocatalytic property in photodegrading organic water.The nanometer potassium niobate powders with TB-type structure were synthesized by a wet chemical method and characterized by X-ray diffraction (XRD), scan electron microscopy (SEM), X-ray photoelectron spectrum (XPS), and so on. The result of XRD patterns and SEM confirmed that the compound K₆Nb_10.8O₃₀ which was sintered at 800℃for 24 hours assumed a tetragonal tungsten bronze structure with space group P4/mbm (127) as those given in JCPDS data cards (JCPDS 87-1858) for K₆Nb_10.8O₃₀ crystals. The sample consists of tetragonal columnar particles with an average diameter 150nm and the length of 400-600nm and the size of the particles is more uniform. X-ray photoelectron spectroscopy (XPS) analysis reveals that there are two kinds of valence state of Nb (Nb⁴⁺ and Nb⁵⁺) in K₆Nb_10.8O₃₀, the ratio and binding energy of Nb⁵⁺ were both larger than Nb⁴⁺, and the amount of Nb⁴⁺ in the crystals is more than that of the sample obtained by the solid state reaction method.Acid red G was selected to simulate organic dye wastewater which was treated by photocatalytic oxidation using the K₆Nb_10.8O₃₀ as photocatalyst. The effects of some experimental factors (such as catalyst dosage, initial concentration of acid red G solution, etc) on photocatalytic reactions were studied as well. The Photocatalytic activity of the photocatalyst was compared by the Photocatalytic degradation of 50mg/L acid red G. The experimental results showed that the Photocatalytic activity of K₆Nb_10.8O₃₀ prepared by wet chemical method is better than K₆Nb_10.8O₃₀ by solid-state synthesis and is similar with Degussa P25. After UV-light irradiation for 20min, 67.3% of the acid red G was decoloured, which was nearly higher than 15% of K₆Nb_10.8O₃₀ obtained by solid-state reaction. The results of the UV spectra changes during the Photocatalytic degradation of acid red G show that the structure of azo and condensed nucleus can be destructed by K₆Nb_10.8O₃₀ under UV-light irradiation. Moreover, experiments showed that the degradation rate was influenced by some factors, such as the catalysis synthesis method, reaction temperature and time.The kinetics of photocatalytic oxidation reactions for acid red G by K₆Nb_10.8O₃₀ was studied. The results showed that the reactions belonged to first-order kinetics and followed Langmuir-Hinsheluwood (L-H) equation. The mechanism of acid red G degradation was discussed through infrared analysis (FT-IR) and ultraviolet-visible light analysis (UV-Vis). In conclusion, the degradation of acid red G is not adsorption action, but the Photocatalytic oxidation under the UV irradiation.