Hierarchically Ordered Macro-/Mesoporous Silica Monolith: Tuning Macropore Entrance Size for Size-Selective Adsorption of Proteins

In this paper, hierarchically ordered macro-/meso porous silica monoliths with 3D fcc packed macropores and 2D hexagonally arranged mesopores are synthesized by using polymer colloidal crystals as the hard template and block copolymer Pluronic P123 as a soft template. Through the impregnation of the colloidal crystal hard template with an acidic ethanol solution containing silica source and P123, the entrance size of macropores can be tailored by controlling the synthesis conditions. As the acid concentration increases, the resulting mesopore sizes tend to decrease slightly in the range of 4.7−3.6 nm, meanwhile, the macropore entrance size increase gradually from 0 to ca. 200 nm. These highly ordered macro-/mesoporous silica monoliths have a macropore of about 1.0 μm with tunable window size (0−200 nm), high surface area (ca. 330 m²/g) and large pore volume (∼ 0.36 cm³/g). Biomacromolecule adsorption results show that the porous silica monolith with the macropore entrance of about 50 nm has absorption capacity of ∼16.6 mg/g for bovine serum albumin (BSA, ∼10 nm in size), much higher than that (∼3.4 mg/g) of the porous silica materials without macropore entrance, and the porous materials with or without macropore entrances exhibit similar a adsorption capacity for cytochrome c (Cyt.c, dimension: ∼ 3 nm) (∼36.8 mg/g), suggesting that the large guest molecules can be excluded by the porous silica monoliths without the macopore entrances. These results indicate that, through engineering the pore connection and multimodal pore system, porous materials with hierarchically pores and tailorable window sizes can be created for size-selective applications, such as enrichment, nanofiltration, and drug delivery.