Inagaki Michio, Nonaka Rie, Tryba Beata, Morawski Antoni W
Faculty of Engineering, Aichi Institute of Technology, Yakusa, Toyota 470-0392, Japan.
Chemosphere. 2006 Jun;64(3):437-45. doi: 10.1016/j.chemosphere.2005.11.052. Epub 2006 Jan 9.
Structural changes in anatase phase in four TiO(2) photocatalysts with annealing at high temperatures were followed by evaluating crystallite size and lattice strain of anatase phase separately and measuring the content of anatase. The rate constant k for the decomposition of methylene blue in its aqueous solution under UV irradiation was determined as a measure of photocatalytic activity. Marked dependences in crystallinity improvement, i.e., the growth of crystallite and the decrease in lattice strain, and in phase transformation from anatase to rutile phases of TiO(2) on annealing temperature was observed above 500 degrees C, depending on starting photocatalysts used. The phase transformation to rutile started after reaching of crystallite size to about 32 nm and of lattice strain to about 0.5 x 10(-3). Rate constant k was found to depend on both crystallite size and lattice strain of anatase; it increased with increasing crystallite size up to about 32 nm and decreasing lattice strain down to about 0.5 x 10(-3). Further increase in crystallite size and decrease in lattice strain induced the decrease in rate constant k, mainly due to the partial transformation of anatase to rutile. The present results showed that the activity of the photocatalysts was possible to be improved by annealing at a high temperature, by selecting an optimal condition of annealing for getting a high crystallinity in anatase phase and no phase transformation to rutile phase.
通过分别评估高温退火后的四种TiO₂光催化剂中锐钛矿相的微晶尺寸和晶格应变，并测量锐钛矿相的含量，跟踪其结构变化。测定了紫外光照射下亚甲基蓝水溶液分解的速率常数k，作为光催化活性的度量。在500℃以上，观察到TiO₂的结晶度改善（即微晶生长和晶格应变降低）以及从锐钛矿相到金红石相的相变对退火温度有明显的依赖性，这取决于所使用的起始光催化剂。当微晶尺寸达到约32nm且晶格应变达到约0.5×10⁻³时，开始向金红石相转变。发现速率常数k取决于锐钛矿相的微晶尺寸和晶格应变；随着微晶尺寸增加到约32nm且晶格应变降低到约0.5×10⁻³，k增大。微晶尺寸的进一步增加和晶格应变的降低导致速率常数k降低，主要是由于锐钛矿相部分转变为金红石相。目前的结果表明，通过高温退火，选择获得锐钛矿相高结晶度且无相转变为金红石相的最佳退火条件，可以提高光催化剂的活性。
