Effects of ammonia/silica molar ratio on the synthesis and structure of bimodal mesopore silica xerogel
Effects of ammonia/silica molar ratio on the synthesis and structure of bimodal mesopore silica xerogel
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DOI：
10.1016/j.micromeso.2004.03.021
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发表时间：
2004-06
影响因子：
5.2
通讯作者：
Xiao-zhong Wang;Wenhuai Li;G. Zhu;S. Qiu;Dongyuan Zhao;B. Zhong
中科院分区：
文献类型：
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作者：
Xiao-zhong Wang;Wenhuai Li;G. Zhu;S. Qiu;Dongyuan Zhao;B. Zhong
在基本条件下，采用合理控制的两相溶胶-凝胶法合成了具有高孔体积、高孔隙度和窄双峰介孔分布的表面活性剂模板化二氧化硅干凝胶（BMS）。利用XRD、29Si MAS NMR、SEM、TEM、TG-DTA和n2吸附等分析技术，研究了BMS二氧化硅介观结构的性质以及氨/二氧化硅摩尔比对所得二氧化硅结构和形貌的影响。研究发现，BMS二氧化硅干凝胶是由胶束包封的纳米二氧化硅颗粒在20 ~ 40 nm范围内组成的，这取决于氨/二氧化硅的摩尔比，并且在12.6 ~ 34.8 nm范围内显示出由表面活性剂去除引起的颗粒内框架介孔和由颗粒间空隙引起的结构介孔，这可以通过改变氨/二氧化硅的摩尔比来调节。所有BMS二氧化硅的结构孔体积均可达到骨架孔体积的两倍或两倍以上，在合成的BMS二氧化硅干凝胶中填充一定量的表面活性剂可能对结构介孔的形成、稳定和有序起着至关重要的作用。快速的水解和缓慢的缩合过程有利于BMS二氧化硅介结构的形成。随着氨/二氧化硅摩尔比的逐渐增加，从而增加缩聚速率，观察到从无序介孔到明确有序的六方介孔MCM-41的双峰介孔产物的介孔结构演变。
A surfactant-templated silica xerogel with high pore volume, high porosity and narrow bimodal mesopore size distribution (designated as BMS) was synthesized by a judiciously controlled two-phase sol–gel processing under basic conditions. The properties of BMS silica mesostructure and the effect of ammonia/silica molar ratio on the resultant silica structure and morphology were assessed using various analytical techniques such as XRD,29Si MAS NMR, SEM, TEM, TG-DTA and N2adsorption measurements. It is found that BMS silica xerogel consists of the packing of the micelle-encapsulated nanometer silica particles in the 20–40 nm range, depending upon the ammonia/silica molar ratio, and shows both an intraparticle framework mesopore resulting from the surfactant removal and a textural mesopore resulting from the interparticle voids, which can be adjusted in the 12.6–34.8 nm range by varying just the ammonia/silica molar ratio. The textural pore volumes for all BMS silica can be two or more times as large as the framework pore volumes, and the fill of a certain amount of surfactant between interparticle voids in as-synthesized BMS silica xerogel may play a crucial role for the formation, stability and ordering of textural mesoporosity. A fast hydrolysis and slow condensation process is beneficial to the formation of BMS silica mesostructure. Following a gradual increase of ammonia/silica molar ratio, thus an increase of condensation rate, the mesostructure evolution of the resultant silica products obtained from a bimodal mesopore via a disordered mesopore to a well-defined ordered hexagonal mesopore MCM-41 was observed.