本研究著重於在低濃度酸下合成中孔分子篩SBA-15的最佳條件並探討矽酸鹽與界面活性劑間的合成界面、合成動力學研究及合成SBA-15的形態學研究。 在低酸濃度下合成SBA-15的最佳條件為在室溫攪拌72 h與90 ℃熱處理24 h,其最佳合成配方比為TEOS:P123:H2O=5 ~ 18:0.6 ~ 3.5: ,當酸濃度界於0.1 ~ 0.005 M之間時,可以合成出高品質的中孔分子篩SBA-15。當酸濃度低於0.005 M時,因矽酸鹽會以≡Si-O-的形式存在,不易界面活性劑上與帶有負電荷的氧吸引而產生氫鍵鍵結,因此當所使用的酸濃度下降至0.005 M以下時無法合成出結構完美的中孔徑分子篩SBA-15。 微胞和矽酸鹽的界面研究方面,我們利用離子分析的方式證明了由Stucky et al. 所提出SBA-15的合成界面[S0H+X-I+]是不正確的,因為實驗數據證明在合成SBA-15的過程中,根本沒有對離子的存在,而是由被酸質子化而帶正電的矽酸鹽聚合物利用氫與三區塊共聚合物上的氧形成氫鍵,利用此一氫鍵作用力形成六角排列結構的中孔洞材料SBA-15,所推測的機構為(S0H+I0)。 合成動力學方面,實驗及理論模型證明了利用較低濃度酸來合成中孔徑分子篩SBA-15時,反應速率與酸濃度的動力學方程式為一級反應且反應速率與酸濃度的動力學方程式為。 合成形態學方面,改變反應速率可合成出具有多種特殊型態的中孔徑分子篩SBA-15,會造成這種變化是高酸濃度時,反應速度較快,區域彎曲能量較大,使柱狀孔洞彎曲需要較高能量,造成用高濃度酸所合成出的產物多成長條狀,在低濃度酸時,反應速率較慢,區域彎曲能量較小,使柱狀孔洞逐漸彎曲形成各種彎曲狀的產物。
Mesoporous sieves SBA-15 could be synthesized at [H+] as low as 0.005 M. SBA-15 can be prepared at room temperature for 3 days and 90 ℃ for 1 day. The recipe of preparing SBA-15 is TEOS:P123:H2O = 5~ 18:0.6 ~ 3.5: at 0.1 to 0.005 M of [HCl] where good quality of SBA-15 can be obtained at the ratio of TEOS / P123 between 2 and 3. Adequate proton concentration is needed to govern the interface between surfactant and silicate to obtain SBA-15 because amorphous would be obtained at pH ≧ 3 [SOH+IO] is the interface interaction of formation in stead of [SOH+X-IO] proposed by Zhou et. al. because no chlorine ion can be observed in the product prepared in the aqueous solution of high and low [HCl]. Here, we proved the kinetics equation of mesoporous formation from the proposed mechanism. It is known, when SBA-15 was synthesized at low acid concentration, the rate constant versus the kinetic equation is allow first order. Morphology of SBA-15 was gradually changed from long rod to curved rope-like disconnected-donut, donut, and ball with lowering acid concentration. The morphology of mesoporous SBA-15 is crucially dependent on the local curvature energy that is present at the interface of the inorganic silica and amphiphilic block copolymer species.
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