Characterization And Photocatalytic Activity Of KSr₂Nb₅O₁₅ With Tungsten Bronze Struture

The dye wastewater from the textile industry is an important source of environmental pollutants because of its toxcity, increasing quantity and variety. However, it is difficult to treat these effluents by conventional methods, such as adsorption, coagulation, electrocoagulation, etc, because the dye molecule in wastewater can not be degradated completely but only be transferred from water to solid using these methods. Heterogeneous photocatalysis has attracted much attention for the purpose of efficiently purifying the dye-containing wastewater.The compound KSr₂Nb₅O₁₅ is a kind of ferroelectric materials with tetragonal tungsten bronze structure (TTB), but its photocatalytic properties for oxidizing organic contaminants in water, has never been reported. In this article, the photocatalytic degradation of acid red G by KSr₂Nb₅O₁₅ was investigated.Using K₂CO₃, SrCO₃ and Nb₂O₅ as starting materials, the compound KSr₂Nb₅O₁₅ was obtained by solid-state reaction method which was then characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). According to JCPDS file 34-0123, the compound KSr₂Nb₅O₁₅ has a tetragonal tungsten bronze structure with space group P4bm. XRD peaks of the sample prepared at 1150℃for 2 hours fit well with the standard XRD peaks, which confirmed that the sample consists of single phase of the compound KSr₂Nb₅O₁₅. As shown in SEM photographs, the KSr₂Nb₅O₁₅ particle sizes ranged from 1 to 2μm with uniform morphology, which indicates a high crystallinity of KSr₂Nb₅O₁₅ calcined at 1150℃for 2 hours. And the band gap absorption edge of the catalyst is determined to be around 385nm by UV-vis diffuse reflectance spectrum of KSr₂Nb₅O₁₅.The effects of photocatalyst dosage and initial concentration of acid red G on the photodegradation processes were studied. The results indicated that the best dosage of catalyst is 2.5g/L, and the degradation rate of 30mg/L acid red G by catalyst synthesized at 1150℃for 2h is more than 85%. The degradation reaction not only destroyed the nitrogen double bond (-N=N-), but also destroyed the benzene and naphthalene rings. The degradation reaction of acid red G belongs to first-order kinetics and follows Langmuir-Hinsheluwood (L-H) equation. And the mechanism of degradation of acid red G was discussed through the analysis of UV-Vis spectrophotometer.