Morphological and Structural Evolution of Mesoporous Silicas in a Mild Buffer Solution and Lysozyme Adsorption

Abstract

Mesoporous silicas with various morphologies and structures were synthesized with the aid of 2,2,4-trimethylpentane (TMP) in the presence of nonionic surfactant P123 [(EO)₂₀(PO)₇₀(EO)₂₀] as a structure-directing agent under mild reaction conditions (HAc−NaAc buffer solution, pH 4.4). The ropelike particles formed by end-to-end interconnected nanorods were obtained at a TMP/P123 weight ratio of 0.5. It is noteworthy to mention that the mesoporous nanorods have channels running parallel to the short axis. The silica hollow spheres can be obtained at a higher TMP/P123 weight ratio because of the fusion of the primary nanorods around the interface of the O/W emulsion. Initial synthesis temperatures of 15, 25, and 40 °C can lead to mesoporous silicas with highly ordered 2D hexagonal mesostructure, vesicular mesostructure, and mesostructured cellular foams (MCF), respectively. The mesoporous silicas exhibit high adsorption capacity (up to 536 mg g^-1) and very rapid (<5 min to reach equilibrium) lysozyme immobilization. More importantly, it is revealed that mesoporous silica hollow spheres with rugged surfaces can greatly accelerate the adsorption rate of the enzyme during the adsorption process.