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

Hybrid mesoporous molecular sieve materials with hexagonal mesoscopic order and covalently bound polyoxometalates were synthesized by the co-condensation of tetraethoxysilane (TEOS) with lacunary polyoxometalate, K8SiW11O39 ¤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 SiW11 into the system results in the decreases of critical micelle concentration of surfactant P123 and the consequent loss of ordered assembly due to salting-out 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.a¤