- 學位論文
共沉層狀雙氫氧化合物之特性研究
The preparation characteristics of Mg–Al layered double hydroxides
摘要
鎂鋁層狀雙氫氧化合物中金屬氫氧化合物層是以水鎂石的結構為基礎，以鋁離子同構取代鎂離子使得此結構帶正電荷；層與層之間存在水分子及用以維持電中性的陰離子，因此被視為陰離子黏土。本研究以共沉法合成鎂鋁層狀雙氫氧化合物，控制變因為添加硝酸鎂與硝酸鋁的莫耳比例、沉降時水溶液的酸鹼值及沉澱物乾燥方法。 由示差熱分析的結果得知，脫去水分子所需的鍵能會隨著鋁離子在陽離子中的比例愈大而愈高。合成層狀雙氫氧化合物的鎂鋁莫爾比為2:1時，在煆燒溫度為300℃及500℃時結晶性最強。然而當煆燒溫度為850℃時其結晶性大幅降低。鎂鋁莫爾比為3:1的層狀雙氫氧化合物相較於其他比例，其結晶性穩定且好。溶液中酸鹼值為10的條件下合成的鎂鋁層狀雙氫氧化合物，在X光繞射圖譜中(003)面之半寬高較小且結晶性也較高。
並列摘要
The structure of layered double hydroxides (LDH) consists three elements: the lamellar structure, the anions and the water molecules. The lamellar structures are brucite–like structures with positive charge, which are attributed to the isomorphic substitution. The anions in the interlayer spaces are used to compensate LDH for its neutral. The water molecules are also in the interlayer spaces, and LDH is regarded as anionic clays. In the study, the Mg–Al LDHs is synthesized by the coprecipitation route through three control variables: the molar ratio of Mg(NO3)2·6H2O and Al(NO3)3·9H2O, the pH value in the solution, and the dried processes. The DTA results suggest that water molecules are bonded much more strongly when the Al3+ occupied more in the interlayer region. The sample prepared at Mg2+/ Al3+ molar ratio of 2:1 has the strongest crystallinity under the calcination at 300℃ and 500℃, but it is more stable at 3:1. And about the pH value, the sample prepared at pH 10 has more crystallinity than pH 7 under the situation of 3:1.