Mercaptopropyl-functionalized helical mesoporous silica nanoparticles with c2mm symmetry: Cocondensation synthesis and structural transformation in the dilute solution of mixed cationic and nonionic surfactants

Mercaptopropyl-functionalized mesoporous silica nanoparticles with c2mm symmetry and short-pitch helical channels were prepared by the cocondensation synthesis in the dilute solution of cetyltrimethylammonium bromide and tetraethylene glycol dodecyl ether (C12EO4) under alkaline conditions. The amount and distribution of the covalently coupled organic groups within the nanoparticles were investigated. Interestingly, the mesostructure transformed toward p6mm phase when the amount of mercaptopropyltrimethoxysilane was increased, and a reverse p6mm-to-c2mm transformation took place as the mole percentage of C12EO4 was further increased. The presence of C12EO4 was also found crucial for helical arrangement of the channels. In situ small-angle X-ray scattering measurements showed that the addition of the functional silane slightly accelerated both the growth and structural deformation of the materials. The results were discussed based on the kinetics of the cooperative assembly of silicate species and the micelles of mixed surfactants and the interplay between the hydrolyzed silanes and surfactant molecules.

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► Thiol-functionalized helical mesoporous silica nanoparticles are prepared.
► They are synthesized in dilute solution of mixed cationic/nonionic surfactants.
► They have tunable 2D-rectangular lattice.
► The nonionic surfactant is crucial for forming short-pitch helical channels.