- 學位論文
FT-IR觀測甲基碘在奈米級二氧化鈦及二氧化矽改質二氧化鈦粉體
FT-IR Study of Photooxidation of CH3I on Hydrothermal-prepared TiO2 and TiO2-SiO2
摘要
本實驗的第一部分為使用自製奈米級二氧化鈦與碘甲烷(CH3I)進行光氧化分解反應，反應中以FT-IR觀測以了解其催化效率及反應過程。所採用二氧化鈦有兩種: (一)利用溶膠-水熱法(sol-hydrothermal)合成奈米級的二氧化鈦，及(二)經二氧化矽干擾結晶狀態，製備所得多孔隙二氧化矽(porous TiO2)。CH3I大部分的分解在前4小時進行最快，而後速率遞減。光氧化反應的主要最終產物包含有CH3OH、CO2(g)、HCOOH(a)、CH3OCH3(g)、CH2O(g)等，其中未經光氧化前熱處理動作的反應，發現反應主要的最終產物不包含HCOOH，而經光氧化前熱處理動作的水熱5小時二氧化鈦，顯示出其是唯一主要最終產物不包含CH3OCH3的反應，且產物具有相對量較高的HCOOH，以及相對含量較低的CH2O。與未經熱處理動作的水熱5小時二氧化鈦比較，在經過熱處理步驟後，其光氧化活性較高，CH3I分解速率較快，並於第20小時將CH3I分解完，而未經熱處理步驟的二氧化鈦則須約30小時才將CH3I分解完。不論有無經過熱處理的動作，CH3I的分解速率皆與二氧化鈦的比表面積成比例，顯示出本實驗的主要控制因素是比表面積的大小。 第二部分的實驗，以摻混二氧化矽的二氧化鈦(SiO2-TiO2)進行與CH3I的光氧化反應，相同地利用FT-IR觀測反應的進行，反應的主要最終產物與純二氧化鈦相同，包含有CH3OH、CO2(g)、HCOOH(a)、CH3OCH3(g)、CH2O(g)等。從含不同比例二氧化矽樣品發現加入微量的二氧化矽，可以提高觸媒分解CH3I的速率，然而過多的二氧化矽反而使得混合觸媒的活性下降，甚至無法將CHI3I完全分解。可能的反應機構將於本論文中詳加探討。
並列摘要
The purpose of this thesis is the study of photooxidation of methyl iodie (CH3I) on TiO2 (part I) and SiO2-TiO2 (part II) using Fourier-transformed infrared (FT-IR) spectroscopy. By in-situ monitoring the decrease of CH3I signal and the increase of reaction products, the decomposition efficiency and reaction mechanisms on TiO2-based photocatalysts can be obtained. The nano TiO2 particles employed in part I are prepared by sol-hydrothermal technique with (porous TiO2) and without the interference of SiO2. Most of the CH3I decomposed in the first 4 hours and then its decomposition rates decreased gradually. The product is dependent on the pretreatment of TiO2 sample. With heat treatment, the major products are CH3OH、CO2(g)、HCOOH(a)、CH3OCH3(g) and CH2O(g). Without heat treatment, however, no HCOOH can be observed. The reaction of HT5 TiO2 though heat treatment before photooxdation presented its major products were not inclusive of CH3OCH3, and had relatively high quantity of HCOOH and relatively low quantity of CH2O. Compared with the reaction without heat treatment, its photocatalytic activity is better to decompose CH3I. The time of entire decomposition of CH3I of HT5 TiO2 processing heat treatment was about 20 hours, and the one without heat traetment decomposed CH3I completely using around 30 hours. It is concluded that the decomposion rates of CH3I were solely dependent on the specific surface area of TiO2. For the reaction on SiO2-TiO2 samples (part II), similar major products (CH3OH、CO2(g)、HCOOH(a)、CH3OCH3(g) and CH2O(g)) were found. The photooxidation efficiency can be enhanced by low quantity of mixed SiO2. However, excessive SiO2 decreases the photocatalytic activity in the decomposition of methyl iodide. Possible reaction mechanism is proposed and discussed in the thesis.