Large mesopore FDU‑ 12 silica for papain encapsulation

Abstract

The usual synthesis of face-centered cubic FDU- 12 mesoporous silica reported in the literature does not mention the role of some experimental conditions that govern its structural and textural properties. In particular, the order of introducing the silica source into the reaction medium, the closing of the recipient setup, the concentration of the swelling agent, as well as the more researched influence of heat treatment on the material characteristics. In this study, the results indicated that the homogenization of F127 and TMB is essential before the introduction of TEOS into the reaction chamber to obtain a more ordered porous structure. This, together with maintaining the nominal concentrations of all chemical compounds by properly isolating the reaction chamber from the outside atmosphere, was crucial. The evaluation of TMB concentration revealed that the increase of TMB resulted in increased surface area, pore volume, and size, leading to entrance pores of different sizes, related to different amounts of TMB inside the F127 micelles. The best structural/textural results were achieved by a hydrothermal treatment (HT) of 100 °C, while higher HT increased pores sizes, but it raised disorder. Finally, the papain incorporation in the silica matrix preserved its catalytic properties and induced better catalytic activity, with around 42% higher efficiency than the isolated enzyme. The evaluation of papain delivery showed rapid release within one hour, followed by a slow, continuous release over time, finishing in 1 h.