Ordered bimodal mesoporous silica with tunable pore structure and morphology

Abstract

Ordered bimodal mesoporous silica materials with uniform framework large pores of ∼30 nm and small pores of 5–10 nm have been synthesized using triblock copolymer P123 as a template and liquid paraffin as a swelling agent on the water/oil surface following a solution sol–gel pathway. XRD, TEM, SEM and nitrogen sorption were used to characterize the obtained bimodal mesoporous silica samples. Due to the low solubility of liquid paraffin in P123 solution, two types of micelles (P123 micelles and P123-coated liquid paraffin microemulsions) may exist in such water-in-oil system at the same time. Thus, homogeneously interconnected bimodal mesopores were derived from the synchronous assemblies of the two types of micelles with inorganic precursors on the water/oil surface. The bimodal mesoporous materials can be obtained only at a low water/oil volume ratio of ∼2/100. The two scale pores were directly observed in TEM images and indirectly proved by the two step increase in nitrogen sorption isotherms. The small pores were derived from P123 micelles and the pore size can be easily tuned from 5 to 10 nm by varying the aging temperature during the synthesis procedure. The bimodal mesoporous materials display a sheet or a hollow sphere shell morphology, with a thickness of 100–200 nm, which may be influenced by the P123/water ratio in the mixture. Furthermore, a desirable amount of micropores are contained on the pore wall of such bimodal mesoporous materials, which may endow such materials with promising properties in sorption, catalysis, etc.