Synthesis and characterization of ordered, very large pore MSU-H silicas assembled from water-soluble silicates
Synthesis and characterization of ordered, very large pore MSU-H silicas assembled from water-soluble silicates
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DOI：
10.1021/jp010773p
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发表时间：
2001-08-16
影响因子：
3.3
通讯作者：
Jaroniec, M
中科院分区：
文献类型：
--
作者：
Kim, SS;Karkamkar, A;Jaroniec, M
以硅酸钠为硅源，以三嵌段共聚物Pluronic P123(EO20PO70EO20)为结构导向剂，通过非离子超分子组装途径组装了具有大均匀介孔(7.6-11.9 nm)的二维六方有序二氧化硅。一步法合成温度从308K提高到333K，使单位晶胞尺寸、孔径、比表面积和孔体积增大，孔壁厚度减小。所得材料在强酸性条件下的吸附性能与通过静电途径组装的SBA-15二氧化硅高度相似，表明MSU-H的骨架结构类似于SBA-15，由孔壁微孔连接的有序大孔组成。当一步合成过程之后，在373K下进行组装后的水热处理，得到的MSU-H二氧化硅的骨架孔扩大了1.7-2.8mN，并显著增加了二次(织构)孔隙率，这是SBA-15所不具备的特征。这些结果表明，使用低成本和方便的试剂合成的二氧化硅在结构裁剪方面具有广泛的可能性。此外，MSU-H二氧化硅的气体吸附数据使我们能够检验最近提出的计算孔径分布的方法的准确性，该方法使用MCM-41二氧化硅进行校准，并在较大孔径上进行外推。结果发现，该方法高估了MSU-H二氧化硅的孔径，这可能与上述外推的不准确有关，也可能与MSU-H的孔形状与长度远大于孔径的均匀圆柱孔的偏差有关。
Two-dimensional, hexagonally ordered silicas with large uniform mesopores (7.6-11.9 nm) have been assembled through a nonionic supramolecular assembly pathway using sodium silicate as a silica source and the triblock copolymer Pluronic P123 (EO20PO70EO20) as a structure-directing agent. An increase in the synthesis temperature from 308 to 333 K in a one-step procedure led to a systematic increase in the unit-cell size, pore diameter, specific surface area, and pore volume, and to a decrease in the pore wall thickness. The resulting materials exhibited adsorption properties highly similar to those of SBA-15 silica assembled through an electrostatic pathway under strongly acidic conditions, indicating that the framework structure of MSU-H is analogous to that of SBA-15 and consists of ordered large pores connected by micropores in the pore walls. When the one-step synthesis procedure was followed by a post-assembly hydrothermal treatment at 373 K, the resultant MSU-H silicas exhibited framework pores enlarged by 1.7-2.8 mn and substantially increased secondary (textural) porosity, a feature that is not characteristic of SBA-15. These results demonstrated a wide range of possibilities in tailoring the structures of silicas synthesized using low-cost and convenient reagents. In addition, gas adsorption data for the MSU-H silicas allowed us to examine the accuracy of a recently proposed procedure for calculation of the pore size distributions, calibrated using MCM-41 silicas and extrapolated over larger pore sizes. It was found that this procedure overestimates pore diameters for MSU-H silicas, which might be related to the inaccuracy of the aforementioned extrapolation, or to deviations of the MSU-H pore shape from uniform cylindrical pores with the length much larger than the pore diameter.