Design of Novel Functionalized Hollow Microspheres and Composites for Versatile Purposes

Author:Xu Ze Hai

Supervisor:zhang guo liang gao cong


Degree Year:2017





As one of the most important class of functional materials,hollow microspheres with unique structural features and attractive physicochemical properties have attracted tremendous research interests in wide applications,including catalysis,adsorption,separation,biological medicine,energy storage and chemical sensors.However,the configuration of most synthesized hollow microspheres is relative simple.Despite the progress achieved in preparation of materials and strcucture design,rational synthesis and functionalization of hollow microspheres with high complexity still remains a big challenge.Although hollow microspheres with complex structure have been developed by template methods and Ostwald ripening strategies,there still exist many limitations of these approaches.Therefore,further improvement of the template and template-free strategies for complex hollow microspheres is of paramount importance.Moreover,the synthesis of hollow microspheres with high complexity is often time-consuming and high cost compared with simple hollow spheres.The development of facile methods to fabricate complex hollow microspheres is highly desirable.In this work,we focused on designing series of novel hollow microspheres with complex chemical compositions,morphologies,lattice structures and physicochemical properties.On the basis of hollow microspheres with mesoporous structure,we explore the catalytic applications for these microspheres.Meanwhile,the modification and functionalization of hybrid shells has been achieved to obtain hollow microcapsules and antimicrobial membranes blended with hollow microspheres.The main research contents and results are listed as follows:(1)We synthesized a series of cobalt-based spinel multishelled hollow microspheres with a solvothermal method which provided a generation of metal-glycerin phase with ion redistribution and subsequent a disequilibrium calcining process which induced the crystallization of spinel phase and formation of hollow frameworks.The strategy described here can be used as a universal method for the controllable fabrication of various bimetallic spinel hollow microspheres.On the basis of our synthetic route,other cobalt-based spinel multishelled hollow microspheres such as cobalt iron and cobalt zinc spinels have been successfully synthesized.By simply changing the content of starting materials,the crystal phase transformed from tetragonal to cubic phase.The formed nanoparticles stacked together to produce wrinkles on the surface so as to form mesoporous frameworks.The mesoporous shell layer afforded a short diffusion pathway for reactant gases and the sites for anchoring active species.Physical models obtained by HRTEM and XPS calculations demonstrate that O vacancies at the exposed {110} facet possess superiority in cubic spinel phase,the reactivity of adsorbed oxygen species and lattice oxygen migration can be easily promoted,resulting in the enhancement of catalytic activity during oxidation process.(2)We report the synthesis of hybrid Fe2O3/rGO microspheres assembled on the surface of atomized droplets via a simple and effective spray-drying process.L-ascorbic acid with mildly reductive ability was used to reduce GO and improve velocity of electrons transfer.Owing to the existence of L-ascorbic acid and rapid spray-drying approach,the in situ Fe2O3 nanoparticles with a mean size of 5-10 nm were uniformly dispersed on graphene nanosheets.With the enhancement of Brownian motion,graphene sheets moved to the surface of droplet to form a spherical shell.The well dispersed nanoparticles not only generated more active sites and bigger contact interfaces which were beneficial to enhance the stability of catalysts,but also acted as pillars between the graphene layers to form mesoporous structure.Moreover,the strong interactions between graphene and Fe2O3 nanoparticles induced the formation of Fe-O-C bond which can promote the enhancement of the stability for hybrid microspheres.(3)Self-assembly of novel graphene oxide microcapsules derived from atomized droplets was realized by a simple spray-drying strategy with no need for removing templates and extra surfactants.In general,molecules with several hundred daltons can not pass through the compact stacked GO nanosheets.In order to promote the permeability of GO microcapsules,the improvement of mass transfer channels is highly desirable.Nanochannels in the microcapsule wall can be adjusted after the introduction of nontoxic water-soluble macromolecules,such as PVP.The results demonstrated that the as-prepared PVP/GO microcapsules had better performance than pure GO samples in release procedures.Furthermore,The strategy described here can be used to encapsulate metal organic frameworks to produce novel MOF@GO superstructures.The prepared CuTPA/GO superstructure possessed good dispersion in water which attributed to the increase of hydrophilicity caused by GO shells.(4)On the basis of double-shelled ZnO microspheres prepared by template method,composite zinc oxide microspheres with elaborate hollow structures of multi-shell and L-dopa coating surface were sucessfully constructed.Different polysulfone(PSF)membranes with competitive antimicrobial properties toward Staphylococcus aureus and Escherichia coli were synthesized by applying ZnO nanoparticles,single-shell ZnO microspheres,double-shelled ZnO microspheres and dopa-ZnO hybrid microspheres via phase inversion for comparison.Since the rate of zinc ions diffusion can be limited due to the barriers created by the multi shells of hollow microspheres and adhesion layer with catechol and indole functional groups,the prepared porous membranes can keep good balance between structure and antimicrobial feature.In the filtration process,the hybrid membranes exhibited fascinating pure water flux(179.8 L m-2 h-1),at least three times higher than that of pure PSF membrane,and the rejection rate for BSA reached 91.2%.Moreover,as multi layer structure can obviously improve the mechanical strength of colloids,the prepared membranes exhibited attractive pressure resistant ability which will be beneficial to future application.