氧化鈦奈米粒子的合成與表面改質

TiO2 nanoparticle synthesis and surface modification

黃亮維(Liang-wei Huang)

指導教授 ： 蔣孝澈

國立中央大學/工學院/材料科學與工程研究所/碩士(2007年)

摘要

本研究目的在於如何製作出高折射率的透明有機無機混成塊材，預期折射率要達到1.8左右。其中氧化鈦具有高折射率(~2.5)，因此被選用當作無機成分。有機成分可以是環氧樹酯或壓克力樹酯，其折射率通常在1.5~1.6之間。根據計算，為了使混成塊材折射率達到1.8以上，氧化鈦固含量需要28~35 vol%。從表面積對體積的關係，得知氧化鈦粒子大小約在30 nm才能達到上述固含量的要求。因此研究首要為合成適當大小的氧化鈦奈米粒子。
在氧化鈦奈米粒子的合成方面，我們以氯化鈦在適當pH進行水解縮合得到氫氧化鈦前趨物。透過清洗鹽類後，可以用酸或鹼來解膠，之後得到微藍透光的氧化鈦溶膠，但是結晶尺度僅有5 nm。若以200 oC水熱則可以提升到預期的結晶尺度。
實驗結果顯示，如要水熱長晶，則必須在高鹼性環性下進行，當有添加四級氨的情形下效果會更佳。以200 oC / 4 h的水熱條件下，5 nm的結晶尺度就可以成長到30 nm左右。然而長晶的過程中，粒子聚集的情形也越嚴重(在40~100 nm之間)。另外我們發現氧化鈦濃度與TPAOH比例是影響長晶與粒徑分佈的重要因素。目前在某些條件下結晶可以控制在13 nm，平均粒徑則在40 nm左右。
要將無機粒子與有機樹酯作混合，需要先對粒子表面作改質。這方面我們使用矽烷當作偶合劑。但是奈米氧化鈦粒子的光觸媒活性很強，在接枝矽烷前還必須包覆氧化鋁或氧化矽，用以鈍化光觸媒活性。須注意的是包覆需要完全，否則文獻上有提到反而會提升原本活性，造成有機樹酯黃化更嚴重。
而水熱後的鹼性氧化鈦透過清洗後再度分散到酒精相中，最後再接枝矽烷(GPS 或 MPS)。目前以接枝MPS的氧化鈦能夠穩定分散在MEK中，形成1 wt%的白色懸浮液。

關鍵字

水熱法 ； 溶凝膠法 ； 平均粒徑 ； 結晶尺度 ； 奈米粒子 ； 氧化鈦

並列摘要

The objective of this research is to prepare a transparent and high refractive hybrid material, with a target refractive index of 1.8. We choose TiO2 as the inorganic component, due to its high refractive index (above 2.5). The oganic component may be epoxy or PMMA resin, which has a refractive index of 1.5~1.6. To achieve the desired refractive index, it was calculated that we needs about 28~35 % TiO2 by volume. Based on the surface area to volume ratio, such solid content can only be accomplished if the titania particles were about 30 nm. Therefore, the first step toward the objective is to synthesis uniform titania particles in the appropriate size range.
For the preparation of nano-sized titania, we started from Ti(OH)4 precursors obtained by the hydrolysis and condensation of TiCl4 at designed pH condition. After washing away the salt, the precipitates could be peptized either in acid or alkaline. The peptized sol, although transparent, contains only nuclei of ~ 5 nm in size. Further hydrothermal reaction at ~200 oC was needed to grow the crystals to the desired size.
It turned out that crystal growth only occurred if the hydrothermal was done at high alkalinity, particularly when tertiary amine was used. After 200 oC/ 4h of hydrothermal reaction, the initially 5 nm nuclei grew to about 30 nm as we hope. Unfortunately, the product was an aggregate in most of the cases with particle size about 40~100 nm. We find TiO2 concentration and TPAOH ration were the most important factors on the particle and grain size. Only in one occasion were we able to control the grain size to 13 nm and the particle size about 40 nm.
The blending of inorganic particles into organic resin requires the modification of its surface. This can be done with silane as coupling agent. However, nano-sized TiO2 is known to be photocatalyst. The common practice is to passivate the surface by coating with inert such as Al2O3 or SiO2. The coating has to be complete, for incomplete coating might enhance the photocatalytic effect instead of reducing it.
After obtaining titania from the hydrothermal reaction under TPAOH, they were washed and dispersed in ethanol and grafted with silane (GPS or MPS). Only in the case of MPS grafting were it able to form 1 wt% stable white-colloid in MEK, which is a comparable solvent for future incorporation of polymer.

並列關鍵字

hydrothermal ； sol-gel ； particle size ； grain size ； nanoparticle ； TiO2

參考文獻

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