Controllable Synthesis Of Dendritic Mesoporous Silica Nanoparticles-metal Organic Framework Composites

Nanoporous materials have received great attention of researchers due to their unique properties,such as large specific surface area,adjustable pore sizes,controllable compositions and structures,and the ease of post-modification.Metal organic frameworks（MOFs）are a kind of hybrid nanoporous material composed of metal nodes and organic ligands,which have been widely applied adsorption,separation,catalysis,energy storage and other fields.However,most MOFs（e.g.,ZIF-8 and ZIF-90）possess small pore sizes（usually<2 nm）,which limits their applications such as loading large biomolecules inside the pores.As another class of nanoporous materials,mesoporous materials with pore sizes ranging from 2 to 50 nm are more favourable for carrying large biomolecules.Among mesoporous materials,mesoporous silica materials（MSMs）,especially mesoporous silica nanoparticles（MSNs）,have been widely studied due to their good chemical stability,excellent biocompatibility and tunable particle/pore sizes.Nevertheless,the plain chemistry of silica may limit their functions and applications.Therefore,combining MOFs with MSMs/MSNs to form a novel composite material could integrate the advantages both MOFs and MSMs/MSNs to the overall improve preformance and broaden the range of applications.To date,various strategies have been developed to combine MOF with MSM/MSN,including in situ direct synthesis,functional group pre-modification and metal oxide conversion.However,limitations lie in these strategies.Thus,developing new strategies for the synthesis of MSM-MOF composite materials is in great demand.In this thesis,we used dendritic mesoporous silica nanoparticles（DMSNs）and dendritic mesoporous organosilicon nanoparticles（DMONs）as silica support and synthesized the following MSM-MOF composite materials:（1）Development of metal oxide conversion strategy-based methods for synthesis of DMSN-ZIF composite materials.We utilized metal oxide conversion strategy and synthesized DMSN-ZIF-8 composites with high MOF contents（the moler ratio of Zn:Si was 0.4:1 to 0.8:1）.When the molar ratio of Zn:Si was 0.4:1,the composite material could preserve both mesopores and micropores.We further investigated the necessity of using DMSN as silica support and the conversion of zinc nitrate into zinc oxide during the synthesis process.In addition,we demonstrated the ratio of ZIF-8 to Zn O in the composite material could be regulated by controlling the reaction time.This strategy could also be used for the synthesis of DMSN-ZIF-90 composites.（2）The metal oxide conversion strategies reported are not suitable for thermally unstabled organosilicon nanoparticles.To overcome the problem of the synthesis of mesoporous organosilicon-MOFs composite materials,we developed a gas phase-controlled precursor conversion strategy and successfully synthesized DMON-ZIF-90composites.Zinc salts were first physically adsorbed onto DMONs and converted into insoluble zinc compounds by controlled gas phase conversion.Then,DMON-ZIF-90composite were further synthesized by heterogeneous nucleation in solution.We demonstrated that selecting an appropriate precursor is the key to DMON-ZIF-90preparation.Using sodium bicarbonate solution to generate carbon dioxide and ammonia that converted the zinc nitrate adsorbed onto DMONs into insoluble zinc compounds as precursor,could lead to successful synthesis of DMON-ZIF-90.While using thioacetamide to generated H₂S that convert zinc nitrate into zinc sulfide precursor with smaller K_sp was difficult to form DMON-ZIF-90.In addition,DMON-ZIF-67 composites were also successfully synthesized by using this gas phase-controlled precursor conversion strategy.（3）The performance of DMON-ZIF-90 in cellular drug delivery were preliminarily investigated.The cellular and non-cellular glutathione-degrading capacities of DMON-ZIF-90 and DMON-ZIF-8 were investigated,also their cytotoxicity in murine breast cancer cell line（4T1）.We demonstrated that DMON-ZIF-90 had high glutathione-degrading capacity and the cytotoxicity of DMON-ZIF-90 was significantly higher than DMON and DMON-ZIF-8.In addition,we used doxorubicin（DOX）as a model drug model and investigated the drug loading capacity and drug release profile of DMON-ZIF-90.These results indicated that DMON-ZIF-90 has the potential to apply as a drug delivery system.