Functional Design, Structural Control, And Fundamental Application Of Magnetic Nanoclusters/Polymer Composite Microspheres

Magnetic colloidal nanocrystal clusters (MCNCs)/polymer composite microspheres combine the high saturation magnetization, excellent conductivity and various structural properties (porosity...) of the MCNCs component, together with the designable capability of thermosenstivity, pH sensitivity and fluorescence of the polymer component, thus receiving immense attention in nanocomposites research field. This thesis mainly focus on the structural control and functionalization of such composite materials, starting from the polymer-directed structure formation of MCNCs, to the introduction of surface functional groups based on emulsion polymerization, and the introduction of antitumor efficacy and electrochemical activity via coordination polymerization, aiming to the realization of function into the nanocomposite. Afterwards, functionalized composites are applied as drug delivery vehicles, chiral catalysis substrates and supercapacitors. Chief outcomes are listed as follows:(1) Biopolymer directed fabrication of high-specific-surface-area porous MCNCs as drug delivery vehicles based on solvothermal reaction. Under solvothermal condition, casein, soybean protein or poly(y-glutamic acid) could be used as self-sacrificial template for one-step formation of high-specific-surface-area porous MCNCs. Brunauer-Emmett-Teller(BET)surface area of the product is shown to be as high as 207 m2/g, with pore volume reaching 0.34 cm3/g and Barrett-Joyner-Halenda (BJH) average pore diameter of 6.3 nm。Moreover, the surface capped biopolymer chains endow the porous MCNCs with excellent biocompatibility and colloidal dispersity and stability. Taking the one with high surface area (102 m2/g), pore volume (0.28 cm3/g) and high magnetization (57 emu/g) as drug carries, the loading capacity of anticancer drug Docetaxel (DOC) could reach as high as 24 wt.%. In vitro cell viability test demonstrates that DOC-loaded MCNCs exhibits remarkable inhibition effect towards the growth of bladder cancerous T24 cells. Furthermore, simultaneously loading DOC and Cermide within porous MCNCs reveals enhanced inhibition effect towards prostate cancerous PC-3 cells, much better than using DOC/CER or single drug loaded MCNCs as treatments.(2) Casein mediated fabrication of hollow porous MCNCs via highly efficient microwave irradiation and exploration as drug delivery vehicles. Microwave irradiation could facilitate the formation of 72 emu/g solid MCNCs at 150℃ within 10 min. Moreover, the addition of casein could serve as a kind of self-sacrificial template towards the hollow structure formation, meanwhile providing excellent biocompatibility and colloidal stability to the resulting hollow MCNCs. With increased casein dosage, the inner cavity size could be effectively tuned from 30nm to 100nm. Under suitable amount of casein, the BET surface area of hollow MCNCs could reach 60 m2/g, with pore volume of 0.23 cm3/g, BJH average pore diameter 4.0 run and magnetization 54emu/g. After nanoprecipitation method, the hollow porous MCNCs have high doxorubicin (DOX) loading content of 37 wt.% and the in-vitro drug release has a pH-dependent manner. Cell viability assay from MTS reveals that DOX-loaded hollow MCNCs is non-toxic towards normal HEK 293 cells, whereas obviously inhibited the growth of cancerous KB cells, with antitumor efficacy approaching that of DOX.(3) Investigation on the structure-controllable fabrication of novel core-shell MCNCs/polymer composite microspheres. Using the vinyl-capped MCNCs as seeds and potassium sulfate as initiator, core-shell structured MCNCs/polystyrene composite microspheres are prepared via surfactant-free emulsion polymerization. Increase the ratio of monomer/seed could realize the morphology transition of product from raspberry-like structures, flower-like structures to eccentric structures. And increase of crosslinking agent divinyl benzene (DVB) results concentric core-shell structures. The combined effect of interfacial tension between hydrophilic MCNCs and hydrophobic polymer, and viscosity of polymer shell play key role during the morphology transition. Through copolymerization of styrene with acrylate acid,2-hydroxyethyl methacrylate, or glycidyl methacrylate could introduce carboxyl, hydroxyl, or epoxy functionality into the composites. FT-IR demonstrates the successful introduction of functionalities. The saturation magnetization of functionalized composites could remain within the range of 28 emu/g～47 emu/g, beneficial for further separation and application.(4) Fabrication investigation towards platinum nanoparticles loaded MCNCs/ hyper-crosslinked porous polymer composites microspheres structures. Based on the previously prepared MCNCs/polystyrene composites, second step of emulsion polymerization is done to prepared DVB crosslinked poly(4-vinyl benzyl chloride, 4-VBC) shell. Further treatment in 1,2-dichloroethane leads to the generation of mesoporosity, and hyper-crosslinking reaction catalyzed by FeCl3 results in microporosity in the polymer shell structures. By changing the DVB/VBC molar ratio could control the porosity. When DVB/VBC is fixed at 40/60, the BET specific surface area reaches 477 m2/g, with pore volume of 0.72 cm3/g. Such porous composite microspheres is used to the in-situ immobilization of Pt NPs by reduction of NaBH4 with 10 wt.% of H2PtCl6. Under 20bar of H2 pressure, Pt-loaded composites are used to catalyze the enantioselective hydrogenations of ethyl pyruvate, with conversion reaching 99.8% and e.e.% up to 80.7%, better than the well-known commerialized Pt/meso-Al2O3 catalysis (e.e.%,75.8%). The excellent catalytic property of the composite probably results from the enrichment of reactant from microspores and immobilization of Pt NPs within mesoporous channels. Besides, the catalysis system exhibits excellent recyclability with conversion>98% and e.e.% of 78% after 5 cycles.(5) Designed fabrication of MCNCs/Salphen-In(Ⅲ) composite microspheres and investigation on the antitumor activity. Through the coordination bonding between fluorescence salphen ligand and In(Ⅲ),MCNCs/Salphen-In(III) core-shell structures could be prepared as a form of prodrug. Tuning the ratio of salphen to In(III) could effectively control the shell thickness from 5-50nm. And the salphen moiety within the structure could reach 29 wt.% with saturation magnetization remaining 36 emu/g. At pH 7.4 condition the composite could keep the structure intact. Howerer, at slight acidic environment (pH 5.0), Salphen-In(Ⅲ) shell will undergo bonding cleavage to give rise to salphen ligand with fluorescence, meanwhile, the porous MCNCs structure will also collapse to form iron ion, which could coordinate with salphen to form Fe-salphen complex with antitumor activity. This realizes the pH-dependent release of drug with fluorescence quenching because of the electron transfer. In-vitro cell viability test shows the prodrug is non-toxic toward normal 16HBE cells, whereas undergoing structural collapse after endocytosis into relatively acidic environment of lysosomes, resulting in the formation of Fe-salphen antitumor agent causing cell apoptosis.(6) Fabrication of MCNCs/polyoxometalates (POM) composite microspheres and application investigation as supercapacitor. Through the coordination bonding between amino-modified functional POM ligand and Zn(II), MCNCs/POM-Zn(II) core-shell structures could result. EDX, elemental mapping and FT-IR results demonstrate the existence of POM-Zn(Ⅱ) moiety within the structures. The POM-Zn(Ⅱ) shell thickness could vary from 10nm to 40nm depending on the POM dosage and Zn(Ⅱ):POM ratio. The highest POM coverage on the structures could reach 40 wt.%. The film electrode based on such composites reveals stability after 500 times of charging-discharging behaviors. Under the current density of 0.01 mA/cm2, the areal capacitance is as high as 2.9 mA/cm2, which is as much as 15 folds and 28 folds of POM-Zn(Ⅱ) film electrode and MCNCs film electrode, respectively, approaching those well-known metal oxide array film electrode, such as TiO2 (0.54-0.91 mF/cm2), NiO-TiO2 (2.3-2.6 mF/cm2), Fe3O4-SnO2 (2.3-7.0 mF/cm2). The solution resistance (Rs) is 0.73Ω and charge-transfer resistance (Rct) is as low as 1.3 Ω, revealing the fast electron transfer and electronic conductivity from POM and MCNCs component.