Preparation Of K₂Ta₄O₁₁, K₆Ta_10.8O₃₀ And Their Photocatalytic Properties

Photocatalytic oxidation technology is an extremely attractive method for wastewater deep treatment,which is of high efficiency,energy saving and non-second contamination and provides a promising strategy for disposing organic wastewater.Dye wastewater is an important source of environmental contamination,wich are toxic and mostly nonbiodegradable and also resistant to destruction by physico-chemical treatment methods.In the past two decades,many attentions have been paid for finding more efficient photocatalysts besides TiO₂.In this thesis,Tantalates K₂Ta₄0₁1 and K₆Ta_10.8O₃₀were prepared by solid-phase reaction and their photocatalytic properties were studied by the photocatalytic degradation of acid red G.It is the first time to be found that when the compostions of raw materials are the same,the low-temperature phase K₂Ta₄O₁₁and high-temeperature phase K₆Ta_10.8O₃₀in the binary K₂O-Ta₂O₅ can be synthesized respectively.The compound K₂Ta₄O₁₁and K₆Ta_10.8O₃₀are with natrotantite-type and tungsten bronze structurere spectively.The synthesized conditions of the compounds were studied.The results of X-ray diffraction (XRD)confirmed that the pure K₂Ta₄O₁₁can be obtained at 900℃or 1000℃for 4h and the pure K₆Ta_10.8O₃₀can be synthesized at 1100℃for 6h.Thermogravimety analysis(DTA) showed the conversion temperature from K₂Ta₄O₁₁to K₆Ta_10.8O₃₀is about 1076.4℃.The crystal mororphologies of the two compounds were observed by scanning electron micrography(SEM).The results of photocatalytic experiments showed that the photocatalytic acitivity of the compound K₆Ta_10.8O₃₀is higher than that of K₂Ta₄O₁₁.The photocatalytic degradation rate of 30mg/L of acid red G by K₆Ta_10.8O₃₀is 93%and 88%by K₂Ta₄O₁₁under UV irradiation for 120min.The influences of the calcining temperature and time of the catalysts,irradiation intensity,the dosage of the catalysts and the initial concentration of acid red G solution on the photocatalytic degradation rate of acid red G were studied.The K₂Ta₄O₁₁synthesized at at 900℃for 4h and K₆Ta_10.8O₃₀at 1100℃for 6h(2%K excess)both show higher photocatalytic activity.The reaction kinetics of the photocatalytic degradation acid red G solution by the two compounds K₂Ta₄O₁₁and K₆Ta_10.8O₃₀follows first-order reaction.The mechanisms of acid red G degradation in the catalysts were discussed through UV-Vis absorption spectrum and IR analyses as well.