Template Preparation And Properties Of Core-shell Fibrous Silica Nanomaterials

Fibrous mesoporous silica nanoparticles have attracted widely attentions in recent years because of its dendritic continuous canyon-like pore structures which are different from traditional two-dimensional hexagonal pores.The increased active sites and improved accessibility allow more loading of functional substance?such as metal,metal oxides,organic molecules,etc.?onto the silica surface without blocking the pores.However,due to the limited synthesis methods and template selections,the morphologies of the synthesized fibrous silica nanoparticles are mostly spherical while the synthesis of non-spherical fibrous silica have been rarely reported,which makes the fabrication of non-spherical fibrous silica on the high-curvature surface become a difficult problem in this field.Besides,silica is also widely used as a confinement hard template and used to derive new materials.Therefore,the synthesis of silica materials with new morphologies and structures are particularly important.Due to their well-defined good metal-organic framework structure and predictable chemical behavior,Prussian blue analogs have become effective precursors of many nitrogen-containing carbon materials and metal materials,but their poor alkali resistance limits the application under alkaline conditions.In this research,we conducted three studies on above problems:First,two kinds of Prussian blue analogues with proper chemical structure and novel morphologies nanoframes?NFs?and nanocuboids-assembled frame-like superstructures?NAFSs?were adopted as hard template,and fibrous silica was successfully coated on the surface of Prussian blue analogs in oil-water bicontinuous microemulsion system.Using KOH as alkali source to adjust the appropriate pH?¹1?,the low-temperature cosolvent-free method can fabricate a uniform fibrous silica shell with the shell thickness of 25-35 nm on the surface of Prussian blue analogs.The synthesized core-shell materials have obvious concave defect structures or even pore structures on the face center.The size distributions of nanoparticles are250-380 nm.Second,the influences of different experimental conditions on products are researched such as temperature,different alkali,oil phase,surfactant,different silica source,cosolvent and reaction time.The results show that the shell thickness of synthesized core-shell materials could be adjusted?8-35 nm?by controlling the reaction time.Fiber thickness and distances between fibers could be controlled by changing oil phase and cosolvent.The appropriate hydrolysis and condensation rate of TEOS have significant influences on the morphology of the products during synthesis process.Finally,the Prussian blue analogs core nanoparticles were removed by calcination and acid etching process to obtain two different derived hollow cubic silica nanoframes with fibrous morphology.XRD results showed that the main components of the Co-Fe oxides formed after calcination were CoFeO4,Co3O4,KCoO3.After acid etching,the peaks of the oxides disappeared,left with silica peaks only.Energy dispersive spectrometer line scan results showed that all of them have fine frame-like structures,which are consistent with the results of electron microscopes.N₂ adsorption and desorption data indicate that the specific surface area and pore volume of core and shell materials are 144.4 m²/g and 1.05 cm³/g,and the corresponding parameters of hollow silica nanoframes are 357.5 m²/g and 20.60 cm³/g,respectively.The reaction process and synthesis mechanism were also discussed.It is found that stable intermediates which consist of Prussian blue analogs and surrounded bicontinious microemulsion droplets play important roles in the synthesis of core-shell materials with good morphology.The adsorption results show hollow cubic silica nanoframes have good adsorption abilities to methylene blue.