Cage-like hierarchically mesoporous hollow silica microspheres templated by mesomorphous polyelectrolyte-surfactant complexes for noble metal nanoparticles immobilization

In this paper, well-defined CHMSs were synthesized through co-hydrolysis of tetraethylsiloxane (TEOS) and 3-aminopropyltriethoxysilane (APTS) template by mesomorphous complexes of hexadecylpyridinium chloride (CPC) and poly(acrylic acid) (PAA). It was demonstrated that the adding amount of APTS in the reaction system played a key role in the formation of the hollow cage-like structure and a possible formation mechanism of CHMSs was proposed. The synthesized CHMSs presented as uniform microsphers with average diameter of 600 nm and possessed tri-model pore structure that were the ordered mesopores ((similar to)3 nm) originated from CPC micelle, the secondary nanopores ((similar to)55 nm) templated by phase separated PAA chain in the silica shell as well as the hollow cavity (several hundred nanometer). At the same time, the co-hydrolysis of APTS resulted in amino groups functionalized silica framework of the CHMSs. Ascribed to the unique structure and the inherent amino groups, the CHMSs were utilized as scaffold for preparation of heterogeneous noble metal nanoparticle catalysts. By choosing the palladium (Pd) as a typical example, 1-Pd@CHSMs catalysts containing 1.0 wt% Pd and uniform distributed small size Pd nanoparticles ((similar to)2.9 nm) were obtained. The catalytic reduction of 4-nitrophenol demonstrated that the heterogeneous 1-Pd@CHSMs catalyst was efficient and reusable.