WO_3-x光解水催化剂结构与性能关系研究

【作者】 刘琼莎；

【导师】 尹周澜；

【作者基本信息】 中南大学 ， 冶金物理化学， 2008， 硕士

【摘要】 WO₃是一种性能优良、用途广泛的半导体材料，特别是作为光催化剂在光解水及大气、水等环境有机和无机污染物降解方面有着广阔的应用前景。但由于钨氧化物价态变化大，含氧量难以确定，结构相变多和电学性质复杂等原因，不同晶型WO_3-X的光催化性质一直不能确定。本文以APT和H₂WO₄为原料，通过固相烧结法和水热晶化法合成了WO_3-X光催化剂。通过Raman，XRD，SEM，DRS，TG-DTA和XPS对WO_3-X的结构进行了表征。以Fe³⁺为电子给体，考察了WO_3-X的光分解水析氧活性，探讨了不同原料及不同制备方法合成的WO_3-X结构与光催化分解水析氧性能的关系。所得结论如下：（1）APT经固相烧结法制备的WO_3-X光催化剂，主要由单斜相组成，当处理温度为600℃、处理时间为4h时，出现了六方相WO_3-X，氧指数为2．44，光分解水析氧速率最高，在365nm紫外灯照射下，产氧速率达到145．8μmol／L／h O₂。而APT经水热晶化法制备的WO_3-X为单斜相，光催化分解水性能较差。（2）H₂WO₄经固相烧结法制备的WO_3-X光催化剂均为单斜相，光催化分解水性能随处理温度变化不大。经水热晶化法处理所得WO_3-X中出现了正交相及六方相，氧指数为2．50，光催化分解水性能得到较大提高，其中24h水热晶化产物的光分解水速率最高，在365nm紫外灯照射下，产氧速率达140μmol／L／h O₂。（3）水热晶化法中，随着处理温度的升高，原料经历了由正交WO_3-X·0．33H₂O→六方WO_3-X→单斜WO_3-X的转变过程，直至正交相和六方相完全转变为单斜相。WO_3-X的光催化分解水性能也随着六方相含量的减少而不断降低。因此，介稳态六方WO_3-X的存在有利于提高WO_3-X光催化分解水性能。（4）随着氧指数的逐渐减小，WO_3-X的光催化分解水速率先逐渐升高，达到极限大值后又急剧降低，即WO_3-X的光催化性能存在一最佳氧空位含量；当氧指数小于2．30时，WO_3-X呈现出蓝色；不论原料及制备方法如何，当合成的WO_3-X氧指数值为2．44～2．50时，其光催化分解水析氧性能较高，催化剂的光催化分解水产氧速率均大于108μmol／L／h O₂。更多还原

【Abstract】 WO_3-X is a kind of semiconductor material with excellent performance and has a wide variety of applications in photodecomposition of water, selective catalysis and environmental engineering. However, inconsistent results of photocatalytic activity of different crystal phases of WO_3-X are reported due to its great variation in chemical valence of tungsten, difficulty in determining the atomic ratio between W and O, and complexity in phase transformations and electronic properties.WO_3-X were prepared with APT and H₂WO₄ as raw materials by solid state sintering and hydrothermal methods and were characterized by Raman Spectrum, XRD, SEM, DRS, TG-DTA and XPS. The photodecomposition of water into oxygen with WO_3-X as photocatalyst was investigated using Fe³⁺ as electron donors. The relationship between structure and photocatalytic activity of WO_3-X prepared from different raw materials and by different methods was studied. Conclusions were made as follows:（1） WO_3-X prepared by solid state sintering method with APT as raw material was mainly constituted of monoclinic phase. WO_3-X with oxygen index 2.44 showed the best catalytic activity when APT was heated at 600℃for 4h. Under the ultraviolet radiation at 365nm, the evolution rate of O₂ reached 145.8μmol/L/h. However, WO_3-X prepared by hydrothermal method didn’t exhibit a good catalytic performance.（2）The photocatalytic performance of monoclinic phase WO_3-X synthesized by sintering method with H₂WO₄ as raw material remained almost the same under different sintering temperature. But WO_3-X prepared by hydrothermal crystallization exhibited better phtocatalytic activity because orthogonal phase and hexagonal phase appeared. WO_3-X showed the best catalytic activity after 24 hour’s hydrothermal process. Under the ultraviolet radiation at 365nm, the evolution rate of O₂ reached 140μmol/L/h.（3） In the hydrothermal process, with the increase of temperature, the phase transformation of WO_3-X was in the sequence of orthogonal→ hexagonal→monoclinic until all the orthogonal phase and hexagonal phase were turned into monoclinic phase. The photocatalytic activity of WO_3-X was reduced with the decrease of amount of hexagonal phase. Therefore, the existence of hexagonal phase is significant for the phtocatalytic performance of WO_3-X.（4） With the decrease of oxygen index, the photocatalytic activity of WO_3-X was raised firstly, and then decreased sharply, which indicated that the photocatalytic activity of WO_3-X was determined by the amount of oxygen vacancies. When oxygen index was less than 2.30, the color of WO_3-X was blue. When oxygen index was between 2.44-2.50, WO_3-X exhibited high photocatalytic activity with the evolution rate of O₂ over 108μmol/L/h.更多还原