Synthesis and Characterization of Phosphonic Acid Functionalized Organosilicas with Bimodal Nanostructure

We report on the synthesis of phosphonic acid functionalized mesoporous organosilicas (MES-PA) with bimodal nanostructure by a postsynthesis treatment method. Phosphonate ester functionalized mesoporous organosilicas (MES-P) were first synthesized by one-step cocondensation of 1,2-bis(trimethoxysilyl)ethane (BTME) and diethoxyphosphorylethyltriethoxysilane (PETES) using triblock copolymer Pluronic P123 as the structure-directing agent in acidic medium. MES-PA were prepared by refluxing the as-synthesized MES-P in concentrated HCl. Further condensation of silicon species during the postsynthesis treatment results in material with more ordered mesostructure compared with the untreated one. Bimodal nanostructure is formed by refluxing MES-P (synthesized with PETES/(PETES + BTME) = 30 mol %) in concentrated HCl. The existence of the bimodal mesopore was confirmed by N 2 sorption isotherms and TEM images. The primary pore structure with pore diameter of 6.5 nm is long-range ordered. The secondary pore structure formed by further condensation of the nanostructured aggregates is disordered with pore diameter centered at 65 nm. The generation of phosphonic acid functionalities, the removal of surfactant, and the formation of secondary pore were accomplished at a single step.