Fabrication And Application Of Porous Materials Based On Fibrous Mesoporous Silica Microspheres

The intrinsic high specific surface area and tunable pore size endows mesoporous materials to be widely used and become an influential member of porous materials.To date,the application of mesoporous materials was continually enlarged,including adsorption,hydrogen storage and electrochemistry,sensor,thermal insulation and biotechnology.Nowadays,the development of mesoporous materials was mainly focus on materials with ordered pore structure and uniform pore size,such as SBA-15 and MCM-41.But,these mesoporous materials are limited to certain application fields for their disadvantages.Fibrous mesoporous silica?F-SiO₂?microspheres not only possess high surface area and large pore volume,but also has wide mesopore size distribution and large mesopore size.Meanwhile,the special fibrous morphology act as macropores,ensuring the transport of molecules inside F-SiO₂ microspheres.Therefore,researchers devote much attention to this mesoporous silica microspheres with special morphology.The formation mechanism of F-SiO₂ microspheres was systematacially investigated in this thesis.Based on the emulsion system and F-SiO₂ microspheres,different hierarchical porous materials were degined to meet the demands in different application fields.This thesis was mainly divided into four contents:explore the effect of each component of the emulsion and reaction condition on the morphology of F-SiO₂ microspheres and design new emulsion system to uncover the formation mechanism of the special morphology;amidoxime-functionalized F-SiO₂ microspheres made by in situ synthesis and post-modification applied in heavy metal ions adsorption;fibrous N-doped carbon microspheres fabricated by F-SiO₂ template microspheres was used as sorbent to remove rhodamine B in aqueous solution;composite microspheres was synthesized in nanoparticles stabilized Pickering emulsion and the exploration of its peroxide-like activity.The main contents and the according results are as follows:1.Based on the typical emulsion system used to synthesis F-SiO₂ microspheres,the effect of surfactant,co-solvent,oil phase,and reaction condition on the morphology of silica micro spheres were explored detailly.The results illustrated that cetyltrimethylammonium bromde?CTAB?and oil phase play a decisive role on the formation of fibrous morphology and the oil-water interface has deep relationship with morphology formation.Based on these results,oil-in-water miniemulsion systems was designed and F-SiO₂ microspheres was successfully fabricated by adjusting ethyl silicate?TEOS?to cyclohexane ratio in weight.High content of cyclohexane is more beneficial to fabricate F-SiO₂ microspheres.Then,we propose a formation mechanism of F-SiO₂ that fibrous morphology of silica microsphere is being prepared on oil-in-water emulsion system through droplet nucleation with an outside-in process.The formation of lamellar structure is the result of the microphase separation of cyclohexane in the oil phase and the condensation of the silica oligomer at the oil-water interface.The content of cyclohexane in oil phase determines the morphology of the synthesized silica.2.Submicron fibrous cyano-modified mesoporous SiO₂ microspheres have been successfully fabricated by in-situ synthesis and post-modification method respectively in the presence of?2-cyanoethyl?triethoxysilane?CETEOS?.The N₂ adsorption-desorption isotherms analysis indicates that the prepared fibrous SiO₂ microspheres possess both mesopores?10?20 nm?and macropores?50?100 nm?and have a similar pore size distribution.The SiO₂ microspheres prepared by post-modification method?2-SiO₂-CN400?have a relatively higher specific surface area and total pore volume than those prepared by in-situ synthesis?1-SiO₂-CN₃?,although the specific surface area and total pore volume of these two samples are lower than those of fibrous SiO₂ formed by pure TEOS?F-SiO₂?.The immobilized cyano groups were furtherly transformed to amidoxime groups,and 2-SiO₂-CN400 show higher amidoximation efficiency than 1-SiO₂-CN₃.The adsorption behavior of AD-1-SiO₂-CN₃ and AD-2-SiO₂-CN400 for Fe³⁺,Cu²⁺ and Pb²⁺ was investigated,and the results show that the fibrous amidoxime-functionalized mesoporous SiO₂ microspheres can selectively adsorb Pb²⁺.The adsorption capacity of AD-2-SiO₂-CN400 for Pb²⁺ reaches as high as 97.4 mg·g-1 at an initial ion concentration of 50 mg·L-1,better than that of AD-1-SiO₂-CN₃.3.Fibrous N-doped porous carbon?FNC?microspheres could be successfully fabricated by in situ polymerization of AN on F-SiO₂ microspheres induced by ?-ray radiation,followed by a carbonization and an etching?in HF solution?process in order.FNC microspheres have a hierarchical structure,i.e.micro-macroporous structure,and possess high specific surface area?554.5 m2·g-1?.The X-ray photoelectron spectroscopy?XPS?analysis demonstrated that the molar ratio of C/N is 5.2.FNC microspheres have a good water dispersibility and show an excellent adsorption ability to RhB dissolved in water.The calculated equilibrium adsorption capacity of FNC microspheres to RhB is as high as 95.4 mg.g-1 at the concentration of RhB is 47.8 mg.L-1,1.6 times higher than that of the primary F-SiO₂ microspheres.The adsorption kinetics and thermodynamics of FNC microspheres are in line with pseudo-second-order equation and Freundlich model,respectively.This work demonstrates that doping with N element and the special micro-macroporous structure can significantly improve the adsorption capacity of carbon based microspheres and provides a new approach to fabricate carbon based adsorbents with excellent adsorption performance.4.Oleic acid modified ferroferric oxide?O-Fe₃O₄?nanoparticles was first prepared and used as seed to prepare core-shell O-Fe₃O₄@SiO₂ microspheres.These O-Fe₃O₄@SiO₂ microspheres was identified to have hollow structure and the isolated fan-shaped F-SiO₂ was decorated on the surface of shell assembled by O-Fe₃O₄ nanoparticles.The density of isolated fan-shaped F-SiO₂ can be adjusted by the content of O-Fe₃O₄ nanoparticles.The formation mechanism of these special core-shell microspheres was furtherly identified,that is,the oil droplet was stabilized by O-Fe₃O₄ to form a Pickering emulsion,and the selectively growth of fan-shaped F-SiO₂ shell is mainly due to naked parts of O-Fe₃O₄ nanoparticles without oleic acid coatings.After calcined under N₂ atmosphere,these core-shell microspheres show an excellent peroxide-like activity and sensitive to trace H₂O₂.