The control incorporation of metals in silica hollow spheres (SHSs) may bring new functions to silica mesoporous structures for applications including catalysis, sensing, molecular delivery, adsorption filtration, and storage. However, the strategies for incorporating metals, whether through pre-loading in the hollow interior or post-encapsulation in the mesoporous shell, still face challenges in achieving quantitative doping of various metals and preventing metal aggregation or channel blockage during usage. In this study, we explored the doping of different metals into silica hollow spheres based on the dissolution-regrowth process of silica. The process may promote the formation of more structural defects and functional silanol groups, which could facilitate the fixation of metals in the silica networks. With this simple and efficient approach, we successfully achieved the integration of ten diverse metal species into silica hollow sphere (SHS). Various single-metal, dual-metal, triple-metal, and quadruple-metal doped SHSs have been prepared, with the doped metals being stable and homogeneously dispersed in the structure. Based on the structural characterizations, we analyzed the influence of metal types on the morphology features of SHSs. The synergistic effects of multi-metals on the catalysis applications were also studied and compared.
Keywords: Metal incorporation; dissolution-regrowth process; hollow sphere; mesoporous silica; multi-metals doping.
Significance of this work: The control incorporation of metals in silica hollow spheres (SHSs) may bring new functions to silica mesoporous structures for applications including catalysis, sensing, molecular delivery, adsorption filtration, and storage. The incorporation of metals within SHSs is always either at the interior core or in the porous shells. The former method mainly utilizes metal nanoparticles as the core and regulates the synthesis of outer porous silica shells. The latter is primarily driven by the capillary force or intermolecular interactions with surface ligands to facilitate the post-loading of metal species in porous silica structures. The main problems associated with metal-doped SHSs include 1) controlled loading of different metals with a homogeneous distribution; 2) fixation of metal species in the structures to prevent aggregation during usage, particularly at high temperatures; 3) pore channel blockage after metal loading, which may hinder the loading of other external molecules. In this work, we developed the dissolution-regrowth of silica strategy for integrating various metals in porous SHSs (M@SHSs) by a one-pot hydrothermal process without using any anchoring molecules. Unlike other sol-gel formations, the growth rate of silica in this process is greatly reduced. It thus may bring more possibilities to introduce external metals within the silica frameworks instead of in the porous channels. By regulating the addition of metal salts in the silica nanoparticles dispersions, we have successfully synthesized stable and highly homogeneous single-metal, dual-metal, triple-metal, and quadruplemetal doped SHSs. Based on the structural characterizations, we analyzed the influence of metal types on the morphology features of SHSs. The synergistic effects of multi-metals on the catalysis applications were also studied and compared. Our results offer a facile and effective strategy for preparing multi-metals as nano-catalysts. Through proper design of the doped metals in SHSs, the structures should find more applications in catalysis, drug delivery, and adsorption with unique and enhanced properties.
© 2024 The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis Group.