Preparation Of Thermosensitive Magnetic Yolk - Shell Microspheres And Its Temperature Control Catalytic Performance

Hollow microspheres with movable cores, also known as yolk/shell particles or rattle-type particles, are the hybrid of core-shell and hollow structures with a distinctive core/void/shell configuration, and therefore the core is movable in the hollow shell, thus can doing many kinds of morphologies control and respectively functional to the inner cores and outer shells, they have various applications in catalysis, artificial cells, drug and gene delivery, and biomedical fields. The aim of this study is to prepare thermosensitive magnetic yolk-shell microspheres, and as an inverse catalyst to test the catalytic activity under different temperature.1) Based on two solvothermal reactions (Deng et al., Angew. Chem. Int. Ed. 2005,44,2782 and Liu et al, Angew. Chem. Int. Ed.2009,48,5875), to fabricate monodisperse, strong magnetic responsiveness and highly water-dispersible magnetic nanoparticles (MNPs), and as magneitc beads to load the catalytic unit (Au NPs) following two ways. The first, MNPs were surface amino modification with 3-aminopropyl triethylsilane (APTES) in the system of ethanol and isopropanol, then magnetic Fe3O4/Au NPs were prepared by depositing Au NPs under ultrasound; the second one is to utilize synchronous hydrolysis of double silane coupling agents tetraethyl orthosilicate (TEOS) and APTES in the system of ethanol and water, using sol-gel method to prepare Fe3O4/Au nanostructure with controllable thickness of transitional silica layer and density of terminal amino groups. The results showed that Fe3O4 MNPs were synthesized using biocompatible Na3Cit as an electrostatic stabilizer, which possessing more advantages in operational simplicity and uniformity of the coating, thus favoring the follow-up operation.2) Nonionic surfactant polyvinylpyrrolidone (PVP), an amphiphilic polymer, can enhance the affinity of Au NPs and silica layer, so it can be used as coupling agent to modify the surface of FesO4/Au nanostructure into vitreophilicity, making to evently coat transitional silica layer easily.3-(methacryloyloxy)propyl trimethoxysilane (MPS), a polymerizable silane coupling agent, was used to functionalize the magnetic composites with terminal double bonds (C=C) simultaneously, so N-isopropylacrylamide (NIPAM) can polymerize with N,N’-methylenebisacrylamide (MBA) in the presence of MPS modified silica-coated magnetic composites as seeds to form a robust polymer coating, after etching transition silica by diluted HF solution, Fe3O4/Au/void/PNIPAM yolk-shell microspheres were obtained. The results of thermoregulated catalysis indicated that when the circumstance temperature increased, all reaction rates slowened because of the thermoresponsive PNIPAM. Moreover, at a lower cross-linking degree (10%) and temperature (T<LCST), the mass transfer of 4-NP and catalytic activity of the yolk-shell microspheres were dominated by the hydrophilicity of PNIPAM shells, while those of yolk-shell microspheres were dominated by the rigidity of PNIPAM shells at a higher cross-linking degree (20%) and temperature (T>LCST).