Xinlin Yang

pH-Responsive Hollow Polymeric Microspheres and Concentric Hollow Silica Microspheres from Silica−Polymer Core−Shell Microspheres

Nearly monodispersed silica-poly(methacrylic acid) (SiO 2-PMAA) core-shell microspheres were synthesized by distillation-precipitation polymerization from 3-(trimethoxysilyl)propylmethacrylate-silica (SiO 2-MPS) particle templates. SiO 2-PMAA-SiO 2 trilayer hybrid microspheres were subsequently prepared by coating of an outer layer of SiO 2 on the SiO 2-PMAA core-shell microspheres in a sol-gel process. pH-Responsive PMAA hollow microspheres with flexible (deformable) shells were obtained after selective removal of the inorganic SiO 2 core from the SiO 2-PMAA core-shell microspheres by HF etching. The pH-responsive properties of the PMAA hollow microspheres were investigated by dynamic laser scattering (DLS). On the other hand, concentric and rigid hollow silica microspheres were prepared by selective removal of the PMAA interlayer from the SiO 2-PMAA-SiO 2 trilayer hybrid microspheres during calcination. The hybrid composite microspheres, pH-sensitive hollow microspheres, and concentric hollow silica microspheres were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray (EDX) analysis.

Hybrid nanorattles of metal core and stimuli-responsive polymer shell for confined catalytic reactions

Narrowly-dispersed silver@silica@poly(methacrylic acid) (Ag@SiO2@PMAA) core–double shell hybrid nanoparticles (NPs) were first synthesized by distillation–precipitation polymerization, using silver@silica core–shell NPs from the sol–gel reaction as templates. Selective removal of the inorganic silica inner-shell from the Ag@SiO2@PMAA core–double shell hybrid NPs by HF etching produces the Ag@air@PMAA hybrid nanorattles with a Ag nanocore, PMAA shell and free space in between. The Ag nanocores, Ag@SiO2 core–shell NPs, Ag@SiO2@PMAA core–double shell NPs and Ag@air@PMAA hybrid nanorattles were characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectroscopy and energy-dispersive X-ray (EDX) analysis. The as-synthesized Ag@air@PMAA hybrid nanorattles were explored as a nanoreactor system for confined catalytic reaction. The rate of catalytic reaction can be further regulated by controlling molecule diffusion in and out of the stimuli-responsive PMAA shell through the simple variation of environmental stimuli, such as salt (NaCl) concentration of the medium.

Hydrogenation of o-chloronitrobenzene over polymer-stabilized palladium-platinum bimetallic colloidal clusters

Abstract Hydrogenation of o -chloronitrobenzene ( o -CNB) has been studied in methanol at 303 K and atmospheric pressure over polyvinylpyrrolidone-stabilized palladium–platinum (PVP-Pd/Pt) bimetallic colloidal clusters. The catalytic properties for the hydrogenation of o -CNB to o -chloroaniline ( o -CAN) are found to depend on the metal composition of the bimetallic clusters. All the bimetallic clusters are more active than both PVP-Pd and PVP-Pt monometallic clusters. The highest activity (1.81 mol H 2 /mol M s) is obtained when PVP-Pd/Pt (1/2) is used as catalyst. The best selectivity to o -CAN (77.5%) is achieved in PVP-Pd/Pt (1/3) catalytic system, which is much higher than those of PVP-Pt and PVP-Pd monometallic colloidal clusters. The addition of the metal cations to the system can considerably affect the catalytic properties of the bimetallic clusters. The modification behavior of metal cations also depends both on the composition of PVP-Pd/Pt bimetallic clusters and the nature of metal cations. For the PVP-Pd/Pt (1/3) bimetallic clusters, when introducing Cr 3+ and Co 2+ , the high activity (0.96 and 1.03 mol H 2 /mol M s) and the better selectivity (91.5 and 91.4%) compared with those of the neat PVP-Pd/Pt (1/3) catalysts (1.03 mol H 2 /mol M s and 77.5%) are obtained, respectively.

Concentric Hollow Nanospheres of Mesoporous Silica Shell-Titania Core from Combined Inorganic and Polymer Syntheses

Nearly monodispersed concentric hollow nanospheres with a mesoporous silica shell and anatase titania inner core were synthesized by the combination of sol-gel reaction and distillation-precipitation polymerization. The well-defined mesoporous concentric hollow nanospheres, comprising two nanostructured functional inorganics, can be used for confined catalytic reactions. The direct synthesis procedures can be readily extended to preparation of the concentric hollow nanospheres with multiple cores, or other functional concentric hollow nanospheres having different core-shell compositions.

Folic acid-conjugated pH/temperature/redox multi-stimuli responsive polymer microspheres for delivery of anti-cancer drug

The folic acid (FA)-conjugated pH/temperature/redox multi-stimuli responsive poly(methacrylic acid-co-N,N-bis(acryloyl)cystamine/poly(N-isopropylacrylamide-co-glycidyl methacrylate-co-N,N-bis(acryloyl)cystamine) microspheres were prepared by a two-stage distillation-precipitation polymerization with subsequent surface modification with FA. The microspheres were characterized by transmission electron microscopy, dynamical light scattering, Fourier-transform infrared spectra, UV-vis spectra and elemental analysis. The degradation of the functional microspheres could be triggered by a reductive reagent, such as glutathione, due to presence of BAC crosslinker. The drug-loaded microspheres exhibited a pH/temperature/redox multi-stimuli responsive drug release character for doxorubicin hydrochloride as a model anti-cancer drug, which was efficiently loaded into the microspheres with a high loading capacity of 208.0% and an encapsulation efficiency of 85.4%. In vitro drug delivery study indicated that the FA-conjugated microspheres could deliver Dox into MCF-7 cells more efficiently than the microspheres without functionalization of FA. Furthermore, WST-1 assay showed that the microspheres had no obvious toxicity to MCF-7 cells even at a high concentration of 2000 μg mL(-1). The resultant microsphere may be a promising vector for delivery of anti-cancer drugs as it exhibits a low cytotoxicity and degradability, precise molecular targeting property and multi-stimuli responsively controlled drug release.

Zwitterionic microcapsules as water reservoirs and proton carriers within a Nafion membrane to confer high proton conductivity under low humidity.

Zwitterionic microcapsules (ZMCs) based on sulfobetaine with tunable hierarchical structures, superior water retention properties, and high proton conduction capacities are synthesized via precipitation polymerization. The incorporation of ZMCs into a Nafion matrix renders the composite membranes with significantly enhanced proton conductivity especially under low humidity. The composite membrane with 15 wt % ZMC-I displayed the highest proton conductivity of 5.8 × 10(-2) S cm(-1) at 40 °C and 20% relative humidity after 90 min of testing, about 21 times higher than that of the Nafion control membrane. The increased proton conductivity is primarily attributed to the versatile roles of ZMCs as water reservoirs and proton conductors for rendering a stable water environment and an additional proton conduction pathway within the membranes. This study may contribute to the rational design of water-retaining and proton-conducting materials.

Functionalized carbon nanotube via distillation precipitation polymerization and its application in nafion-based composite membranes.

The objective of this study is to develop a novel approach to in situ functionalizing multiwalled carbon nanotubes (MWCNTs) and exploring their application in Nafion-based composite membranes for efficient proton conduction. Covalent grafting of acrylate-modified MWCNTs with poly(methacrylic acid-co-ethylene glycol dimethacrylate), poly(vinylphosphonic acid-co-ethylene glycol dimethacrylate), and sulfonated poly(styrene-co-divinylbenzene) was achieved via surface-initiated distillation precipitation polymerization. The formation of core-shell structure was verified by TEM images, and polymer layers with thickness around 30 nm were uniformly covered on the MWCNTs. The graft yield reached up to 93.3 wt % after 80 min of polymerization. The functionalized CNTs (FCNTs) were incorporated into the Nafion matrix to prepare composite membranes. The influence of various functional groups (-COOH, -PO3H2, and -SO3H) in FCNTs on proton transport of the composite membranes was studied. The incorporation of FCNTs afforded the composite membranes significantly enhanced proton conductivities under reduced relative humidity. The composite membrane containing 5 wt % phosphorylated MWCNTs (PCNTs) showed the highest proton conductivity, which was attributed to the construction of lower-energy-barrier proton transport pathways by PCNTs, and excellent water-retention and proton-conduction properties of the cross-linked polymer in PCNTs. Moreover, the composite membranes exhibited an enhanced mechanical stability.

Double shelled hollow SnO2/polymer microsphere as a high-capacity anode material for superior reversible lithium ion storage

Double shelled hollow tin dioxide/poly(ethyleneglycol dimethacrylate-co-methacrylic acid) (SnO2/P(EGDMA-co-MAA)) microspheres were prepared by selective removal of the silica inner core via etching with hydrofluoric acid from the corresponding SiO2/SnO2/P(EGDMA-co-MAA) tri-layer microspheres. These tri-layer microspheres were synthesized using a combination of the modified Stober method for the silica inner core, a hydrothermal technique for the sandwiched SnO2 layer and distillation precipitation polymerization for the coated P(EGDMA-co-MAA) shell-layer. The double shelled hollow microspheres were utilized as anode materials for lithium ion batteries, which had a significantly enhanced cycling performance compared to when neat SnO2 hollow spheres were used.

Facile synthesis of monodisperse polymer/SiO2/polymer/TiO2 tetra-layer microspheres and the corresponding double-walled hollow SiO2/TiO2 microspheres

Monodisperse tetra-layer poly(ethyleneglycol dimethacrylate-co-methacrylic acid) (P(EGDMA-co-MAA))/SiO(2)/P(EGDMA-co-MAA)/TiO(2) tetra-layer microspheres were facilely synthesized by the combination of the distillation precipitation polymerization for the preparation of P(EGDMA-co-MAA) layers and the controlled sol-gel hydrolysis of inorganic precursors for the formation of silica (SiO(2)) and titania (TiO(2)) layers. The thickness of the outer titania shell-layer was well-controlled via altering the feed of titanium tetrabutoxide (TBOT) during the sol-gel hydrolysis, while the size of polymeric layers were facilely controlled via a multi-step addition of ethyleneglycol dimethacrylate (EGDMA) crosslinker and methacrylic acid (MAA) monomer during the polymerization. The corresponding double-walled hollow inorganic microspheres containing SiO(2) inner shell and TiO(2) outer shell with various thickness were obtained after the selective removal of P(EGDMA-co-MAA) components via the calcination of the tetra-layer polymer/SiO(2)/polymer/TiO(2) microspheres under 550 degrees C for 4 h in air. The structure and morphology of the resultant microspheres were characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD), X-ray photoelectron microscopy (XPS), and thermogravimetric analysis (TGA). Further, the photocatalytic properties of the resultant double-walled hollow SiO(2)/TiO(2) microspheres were studied by photocatalytic degradation of methyl orange (MO) with ultraviolet (UV) irradiation of a 500 W high-pressure mercury lamp.

Modification of metal complex on hydrogenation of o-chloronitrobenzene over polymer-stabilized platinum colloidal clusters

The effect of metal complex on hydrogenation of o-chloronitrobenzene (CNB) over poly-vinylpyrrolidone-stabilized platinum clusters (PVP-Pt) has been studied in methanol at 303 K and atmospheric pressure. The addition of metal complexes to the catalytic system can considerably modulate both the activity and the selectivity of the catalyst. A low activity (0.41 mol H2/mol Pt s) and low selectivity (42.6%) were obtained when the neat PVP-Pt colloidal clusters were used as a catalyst. Upon the addition of the complexes Ni(AcAc)2 and Na[Co(AcAc)3], the better selectivity to o-chloroaniline (o-CAN) were promoted to 76.2% and 76.5%, and the higher activities (0.72 mol H2/mol Pt s and 0.83 mol H2/mol Pt s) were obtained, respectively. On the other hand, when the complex Ni(en)3Cl2 was introduced as a modifier, the highest selectivity to o-CAN (94.0%) was achieved, though the activity was lowered to 0.16 mol H2/mol Pt s.