Simulating the formation of surfactant-templated mesoporous silica materials: a model with both surfactant self-assembly and silica polymerization.
Simulating the formation of surfactant-templated mesoporous silica materials: a model with both surfactant self-assembly and silica polymerization.
复制标题
模拟表面活性剂模板介孔二氧化硅材料的形成：同时具有表面活性剂自组装和二氧化硅聚合的模型。
DOI：
10.1021/la304475j
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
P. A. Monson
中科院分区：
文献类型：
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作者：
Lin Jin;S. Auerbach;P. A. Monson
我们已经使用Monte Carlo模拟来研究MCM-41介孔二氧化硅材料的形成，与一个新的晶格模型，具有显式表示的两个酸缩合和表面活性剂自组装。受实验合成的启发，我们在模拟过程中采用了以下两步“合成”：（i）高pH值和低温允许具有长程有序的介观结构的初始发生;（ii）较低pH值和较高温度促进不可逆的二氧化硅缩合。在步骤（i）期间，发现前体溶液自发地分离成与富溶剂相平衡的富表面活性剂硅酸盐相。在不同的合成条件下，富含表面活性剂硅酸盐的中间相出现了层状和六边形有序，这与实验观察结果一致。在可以忽略二氧化硅聚合的条件下，我们的模拟被发现通过改变温度在六方相和层状相之间可逆地转变。在步骤（ii）中，二氧化硅聚合在较低的pH值下使用反应系综蒙特卡罗模拟处理二氧化硅去质子化平衡的pH依赖性。Monte Carlo模拟产生了具有孔和无定形二氧化硅壁的六边形阵列的二氧化硅-表面活性剂介观结构，表现出与MCM-41上的（29）Si NMR实验合理一致的Q（n）分布。与体相无定形二氧化硅相比，这些模拟MCM-41材料的壁畴的特征在于更少的顺序，更大比例的3-和4-元环，和更宽的环尺寸分布。
We have used Monte Carlo simulations to study the formation of the MCM-41 mesoporous silica material, with a new lattice model featuring explicit representations of both silicic acid condensation and surfactant self-assembly. Inspired by experimental syntheses, we have adopted the following two-step "synthesis" during our simulations: (i) high pH and low temperature allowing the initial onset of mesostructures with long-range order; (ii) lower pH and higher temperature promoting irreversible silica condensation. During step (i), the precursor solution was found to spontaneously separate into a surfactant-silicate-rich phase in equilibrium with a solvent-rich phase. Lamellar and hexagonal ordering emerged for the surfactant-silicate-rich mesosphases under different synthesis conditions, consistent with experimental observations. Under conditions where silica polymerization can be neglected, our simulations were found to transform reversibly between hexagonal and lamellar phases by changing temperature. During step (ii), silica polymerization was simulated at lower pH using reaction ensemble Monte Carlo to treat the pH dependence of silica deprotonation equilibria. Monte Carlo simulations produced silica-surfactant mesostructures with hexagonal arrays of pores and amorphous silica walls, exhibiting Q(n) distributions in reasonable agreement with (29)Si NMR experiments on MCM-41. Compared with bulk amorphous silica, the wall domains of these simulated MCM-41 materials are characterized by even less order, larger fractions of 3- and 4-membered rings, and wider ring-size distributions.