【作者】 贺方升；

【导师】 张高科；

【作者基本信息】 武汉理工大学 ， 环境工程， 2006， 硕士

【摘要】 近年来,层状铌酸盐化合物,如Ni-K₄Nb₆0₁₇、Bi₂InNbO₇等,在光催化分解水制氢方面表现出了优异的催化性能,引起了人们对层状铌酸盐光催化性能的注意。KNb₃O₈、K₄Nb₆O₁₇都是具有层状类钙钛矿结构的铌酸盐化合物。其中,KNb₃O₈的研究报道相对较少,K₄Yb₆O₁₇是一种被广泛研究的铌酸盐,其光催化活性的研究集中在光解水方面,对其在光催化降解有机物方面的研究则很少报道。 本文通过水热方法合成了两种铌酸盐催化剂KNb₃O₈和K₄Yb₆O₁₇;研究了合成的铌酸盐光催化降解酸性红G的性能,初步探讨了其催化机理,具体包括: （一）本文采用Nb₂O₅与KOH直接水热反应合成了K₄Nb₆O₁₇,合成条件较为宽松,在较宽的反应温度、反应时间和碱浓度范围内均可合成。XRD分析表明,水热合成的K₄Nb₆O₁₇为斜方相,衍射峰有明显的宽化现象,据此计算的平均粒径为13.9nm,SEM和TEM结果表明其为片状结构,片厚度在100nm以下,热重差热分析表明其结构中含有层间水。采用“水热溶解—pH值调节—水热晶化”三步合成路线,合成了KNb₃O₈。其中,调节pH值是关键,只有将pH调节在5-6才能生成纯KNb₃O₈。XRD分析表明,水热合成的KNb₃O₈为斜方相,SEM图像表明其具有叶状纳米网络结构形貌,片厚约为100nm,与XRD分析的平均粒径76.4nm基本相符,比表面积为7.22m²/g,带隙能为3.47eV。 （二）以100mg/L的酸性红G为降解对象的光催化降解实验表明,水热法合成的K₄Nb₆O₁₇的光催化降解活性优于固相法合成的样品以及Degussa P25。光催化降解20min后,水热法合成的K₄Nb₆O₁₇的脱色率已达60%,而高温固相法的K₄Nb₆O₁₇和Degussa P25的脱色率都仅为20%。水热法合成的KNb₂O₈的光催化脱色效果也优于Degussa P25（ViO₂）,KNb₃O₈在60min时脱色率达到了78%,而P25的脱色率为66%。对降解液进行紫外可见光谱分析,结果表明,K₄Nb₆O₁₇和KNb₃O₈可以将酸性红G的偶氮结构、稠环结构破坏分解。同时实验还表明,催化剂合成方法、合成温度及时间等因素对催化降解效率都有影响。 最后,结合红外光谱和紫外可见光谱分析结果,探讨了层状铌酸盐光催化降解酸性红G的机理。酸性红G溶液的脱色不是因催化剂的吸附作用,而是铌酸盐催化剂在紫光灯照射下的催化降解作用。更多还原

【Abstract】 In recent years, the layered niobate compounds, such as Ni-K₄Nb₆O₁7 Bi₂InNbO₇ etc, show outstanding catalytic property in the field of water splitting to H₂ and O₂, which has been paid more attention by many researchers. KNb₃O₈ and K₄Nb₆O₁7 are typical layered niobate compounds. The Photocatalytic activity of was studied less, the research on K₄Nb₆O₁7 was mainly focused on the Photocatalytic water-splitting property.In this thesis, K₄Nb₆O₁7 and KNb₃O₈ were synthesized by hydrothermal method. The Photocatalytic activity of photocatalysts for Photocatalytic degradation of acid red G was studied, and the mechanics of Photocatalytic degradation of acid red G by catalysts was discussed as well, which are as follow:a) The K₄Nb₆O₁7 can be obtained directly by the reaction of Nb₂O₅ and KOH within a wide range of reaction conditions, such as hydrothermal temperature, reaction time and concentration of KOH. SEM and XRD were used to characterize the morphologies and structure of the photocatalyst. The as-prepared K₄Nb₆O₁7 is assumed to orthorhombic structure and with the average size 13.9nm. SEM pattern showed the sheet morphology of K₄Nb₆O₁7 with the sheet-width less than 100nm. TG-DTA showed H₂O moleculars exist in the layers space of K₄Nb₆O₁7. The pure triniobate （KNb₃O₈） was obtained via tri-steps synthesis route: "hydrothermal dissolution - pH adjustment - hydrothermal crystallization". It was known that controlling the alkalinity of the reaction system is the crucial step during the hydrothermal synthesis process of KNb₃O₈. The pure KNb₃O₈ can be synthesized only under the appropriate pH （pH=5-6）. The as-obtained KNb₃O₈ is assumed to orthorhombic structure and with nanometer leaf-like network morphologies. SEM confirmed the leaf-thickness is around 100nm which is about 70nm through calculating from the XRD results. The band gap and the Specific Surface Area （BET） of KNb₃O₈ crystals is estimated to be about 3.47 eV and 7.22 m²/g respectively.b) The Photocatalytic activity of the photocatalyst was evaluated by the Photocatalytic degradation of 100mg/l acid red G. The experimental results showed that the Photocatalytic activity of K₄Nb₆O₁7 prepared by hydrothermal method is better than K₄Nb₆O₁7 by solid-state synthesis and Degussa P25. After UV-light irradiation for 20min, 60% of the acid red G was decoloured, which was higher than 20% of the Degussa P25 and K₄Nb₆O₁7 obtained by solid-state reaction. KNb₃O₈ photocatalyst obtained by hydrothermal method also showed higher Photocatalytic activity than Degussa P25. After UV-light irradiation for 60min, the degradation rate of KNb₃O₈ could reach 78%, which was higher than 66% of P25. The results of the UV spectra changes during the Photocatalytic degradation of acid red G show that the structure of azo, condensed nucleus can be destructed by K₄Nb₆O₁7 and KNb₃O₈ 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.Finally, the mechanics of Photocatalytic degradation of acid red G by catalysts was analyzed by infrared analysis （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.更多还原