Selective functionalization of the outer surface of MCM-48-type mesoporous silica nanoparticles at room temperature

Abstract

In this study, a suitable route for the selective functionalization of the outer surface of MCM-48-type mesoporous silica nanoparticles (MSNs) and its impact on the physicochemical properties were investigated. The synthesis of MCM-48 nanoparticles with intact cubic ordered mesopore structure and functionalized outer particle surface was managed by postsynthetic and co-condensation modification routes with 3-methacryloxypropyltrimethoxy-silane (MPS). The results of FTIR, 29Si and 13C NMR, thermogravimetric, and elemental analysis confirmed the successful silane surface grafting by both methods. The nitrogen sorption analysis showed the selective outer surface functionalization by the postsynthetic route for the synthesized MCM-48 nanoparticles containing the template still inside the pore channels and in the case of the co-condensation route via late addition of the silane precursors into the synthesis batch containing a fully grown silica. The solvent type in the former approach and silane addition time during the particle growth in the later route showed a significant impact on the silane content and site selective binding. The amount of grafted silane was determined by thermogravimetric and elemental analysis. It was found to increase using toluene in the postsynthetic modification route. The average particle size measured from SEM/TEM analysis ranges from 290 to 350 nm. The cubic ordered pore structure of the final silane grafted MSNs was fully preserved in both functionalization routes as corroborated from XRD analysis. In conclusion, MCM-48 nanoparticles selectively functionalized on the outer particle surface are favorable candidates for the subsequent site selective grafting reactions.