预水解时间对多金属氧酸盐/介孔分子筛杂化材料结构的影响

Influence of Prehydrolysis Time on Structure of Polyoxometalate/Mesoporous Molecular Sieve Hybrid Materials

采用嵌段共聚物P123为模板剂,正硅酸乙酯(TEOS)和一缺位Keggin型多金属氧酸盐K8S iW11O39.12H2O(S iW11)为无机前驱体,由溶胶-凝胶法经共缩合途径合成了具有六方介孔结构的杂化分子筛材料S iW11/SBA-15,着重考察了TEOS预水解时间的长短对杂化材料结构的影响.研究结果表明,由于盐析作用,S iW11的引入导致体系中表面活性剂P123的临界胶束浓度降低,有序组装被破坏,因此足够的预水解时间是形成有序介孔的必要条件.而预水解时间的长短则取决于S iW11的用量,S iW11的用量越多,需要的预水解时间越长,所得材料的结构有序度也越低.另外,预水解时间的长短对样品中多金属氧酸盐的分布也有影响,在较长的预水解时间下,键联的多金属氧酸盐主要分布于SBA-15主孔道的孔壁表面.

Hybrid mesoporous molecular sieve materials with hexagonal mesoseopie order and eovalently bound polyoxometalates were synthesized by the co-condensation of tetraethoxysilane （TEOS） with lacunary polyoxometalate, KsSiW11O39 · 12H2O （SiW11 ）, in the presence of triblock copolymer P123 as the structure-directing agent. The influences of prehydrolysis time of TEOS on the structure of hybrid materials were specially investigated. It is found that the introduction of SiWn into the system results in the decreases of critical micelle concentration of surfactant P123 and the consequent loss of ordered assembly due to saltingout effect. Therefore, it is necessary to provide sufficient time for prehydrolysis in order to acquire ordered mesophase. It is also observed that the length of prehydrolysis time depends on the ratio of SiW11 in inorganic precursors. Longer prehydrolysis time is needed and lower structure order is obtained when the ratio of SiW11 increases. In addition, the prehydrolysis time affects the distribution of polyoxometalates in the hybrid materials. The bound polyoxometalates mostly locate on the surface of walls of primary mesopores rather than within the complementary small pores as the prehydrolisis time is increased.