Yiqun Yang

Glucose sensors based on electrodeposition of molecularly imprinted polymeric micelles: A novel strategy for MIP sensors

A voltammetric glucose sensor was prepared from novel molecularly imprinted polymeric micelles (MIPMs) through direct electrodeposition. The MIPMs, which were photo-crosslinkable and nano-scaled with high specific surface area, were prepared via macromolecule self-assembly of an amphiphilic photo-crosslinkable copolymer, combined with a molecular imprinting technique using glucose as the template molecule. A MIP film was formed in situ on the electrode surface by electrodeposition of the MIPMs, while photo-crosslinking led to a robust film which showed good solvent resistant to dissolution. With these features, the resulting sensor showed good response and selectivity towards glucose. In particular, the linear response of this glucose sensor ranged from 0.2 mM to 8 mM and its comparatively higher detection limit, about 10 mM, indicated numerous effective recognition sites among the polymer matrix due to the large specific surface area of MIPM. In addition, this MIP sensor also showed good stability and reversibility. The contribution of this work lies in not only the invention of a new type of glucose MIP sensor with good performance, but also the creation of a novel strategy to develop advanced MIP sensors for a wide range of templates in viewing of the versatility of the amphiphilic copolymers and the ease of control and applicability of the electrodeposition process.

Pickering emulsions stabilized by self-assembled colloidal particles of copolymers of P(St-alt-MAn)-co-P(VM-alt-MAn)

A new type of copolymer containing two alternating segments, poly-(styrene-alt-maleic anhydride)-co-poly (7-(4-vinylbenzyloxyl)-4-methylcoumarin-alt-maleic anhydride) P(St-alt-MAn)-co-P(VM-alt-MAn)(PSMVM), was prepared. The copolymer self-assembled into nanoparticles with internal microphase structures in water because the hydrophilicity of segment P(VM-alt-MAn) is higher than that of P(St-alt-MAn). The particle size, morphology, ζ potential and surface properties and their dependence on the pH and slat concentrations were studied with a combination of techniques. The nanoparticles of PSMVM showed surface activity and pH sensitivity for producing Pickering oil-in-water emulsions. The emulsion volume increased and the size of oil/water droplet decreased with increasing salt concentration. Furthermore, cross-linked nanoparticles (CLPs) were obtained by photo-dimerization of the pendent coumarin groups in PSMVM under UV irradiation. The emulsions produced by using the CLPs as emulsifiers showed even better stability upon standing. Solid oil-phase droplets were obtained by preparation of CLPs-stabilized Pickering emulsions with an oil phase of styrene containing the initiator AIBN followed by the polymerization of styrene. Thus, the enrichment and aggregation of the CLPs on the emulsion droplets was visible because the solid droplets remained unchanged during the SEM sample preparation.

Tin dioxide@carbon core-shell nanoarchitectures anchored on wrinkled graphene for ultrafast and stable lithium storage.

The SnO2@C@GS composites as a new type of 3D nanoarchitecture have been successfully synthesized by a facile hydrothermal process followed by a sintering strategy. Such a 3D nanoarchitecture is made up of SnO2@C core-shell nanospheres and nanochains anchored on wrinkled graphene sheets (GSs). Transmission electron microscopy shows that these core-shell nanoparticles consist of 3-9 nm diameter secondary SnO2 nanoparticles embedded in about 50 nm diameter primary carbon nanospheres. Large quantities of core-shell nanoparticles are uniformly attached to the surface of wrinkled graphene nanosheets, with a portion of them further connected into nanochains. This new 3D nanoarchitecture consists of two different kinds of carbon-buffering matrixes, i.e., the carbon layer produced by glucose carbonization and the added GS template, leading to enhanced lithium storage properties. The lithium-cycling properties of the SnO2@C@GS composite have been evaluated by galvanostatic discharge-charge cycling and electrochemical impedance spectroscopy. Results show that the SnO2@C@GS composite has discharge capacities of 883.5, 845.7, and 830.5 mA h g(-1) in the 20th, 50th and 100th cycles, respectively, at a current density of 200 mA g(-1) and delivers a desirable discharge capacity of 645.2 mA h g(-1) at a rate of 1680 mA g(-1). This new 3D nanoarchitecture exhibits a high capability and excellent cycling and rate performance, holding great potential as a high-rate and stable anode material for lithium storage.

Mesoporous Hybrids of Reduced Graphene Oxide and Vanadium Pentoxide for Enhanced Performance in Lithium-Ion Batteries and Electrochemical Capacitors

Mesoporous hybrids of V2O5 nanoparticles anchored on reduced graphene oxide (rGO) have been synthesized by slow hydrolysis of vanadium oxytriisopropoxide using a two-step solvothermal method followed by vacuum annealing. The hybrid material possesses a hierarchical structure with 20-30 nm V2O5 nanoparticles uniformly grown on rGO nanosheets, leading to a high surface area with mesoscale porosity. Such hybrid materials present significantly improved electronic conductivity and fast electrolyte ion diffusion, which synergistically enhance the electrical energy storage performance. Symmetrical electrochemical capacitors with two rGO-V2O5 hybrid electrodes show excellent cycling stability, good rate capability, and a high specific capacitance up to ∼466 F g(-1) (regarding the total mass of V2O5) in a neutral aqueous electrolyte (1.0 M Na2SO4). When used as the cathode in lithium-ion batteries, the rGO-V2O5 hybrid demonstrates excellent cycling stability and power capability, able to deliver a specific capacity of 295, 220, and 132 mAh g(-1) (regarding the mass of V2O5) at a rate of C/9, 1C, and 10C, respectively. The value at C/9 rate matches the full theoretical capacity of V2O5 for reversible 2 Li(+) insertion/extraction between 4.0 and 2.0 V (vs Li/Li(+)). It retains ∼83% of the discharge capacity after 150 cycles at 1C rate, with only 0.12% decrease per cycle. The enhanced performance in electrical energy storage reveals the effectiveness of rGO as the structure template and more conductive electron pathway in the hybrid material to overcome the intrinsic limits of single-phase V2O5 materials.

Preparation and Characterization of TiO2 Barrier Layers for Dye-Sensitized Solar Cells

A TiO2 barrier layer is critical in enhancing the performance of dye-sensitized solar cells (DSSCs). Two methods to prepare the TiO2 barrier layer on fluorine-doped tin dioxide (FTO) surface were systematically studied in order to minimize electron-hole recombination and electron backflow during photovoltaic processes of DSSCs. The film structure and materials properties were correlated with the photovoltaic characteristics and electrochemical properties. In the first approach, a porous TiO2 layer was deposited by wet chemical treatment of the sample with TiCl4 solution for time periods varying from 0 to 60 min. The N719 dye molecules were found to be able to insert into the porous barrier layers. The 20 min treatment formed a nonuniform but intact TiO2 layer of ∼100-300 nm in thickness, which gave the highest open-circuit voltage VOC, short-circuit photocurrent density JSC, and energy conversion efficiency. But thicker TiO2 barrier layers by this method caused a decrease in JSC, possibly limited by lower electrical conductance. In the second approach, a compact TiO2 barrier layer was created by sputter-coating 0-15 nm Ti metal films on FTO/glass and then oxidizing them into TiO2 with thermal treatment at 500 °C in the air for 30 min. The dye molecules were found to only attach at the outer surface of the barrier layer and slightly increased with the layer thickness. These two kinds of barrier layer showed different characteristics and may be tailored for different DSSC studies.

Research on Amphiphilic Copolymer MIP Micelles Electrochemical Sensor

Novel molecularly imprinted polymeric (MIP) micelles were prepared via macromolecule self-assembly of a photo-crosslinkable copolymer, combined with molecular imprinting technique using 4-acetaminophenol as the template molecule. First, an acrylic copolymer poly(DMA-co-HEA-co-EHA-co-St) was synthesized via free radical polymerization using (dimethylamino)ethylmethacrylate (DMA), 2-hydroxy ethylacrylate (HEA), 2-ethylhexyl acrylate (EHA) and styrene (St). Further post functionalization introduced a cross-linkable acrylate side groups into the polymer to form the photo-crosslinkable copolymer using isophorone diisocyanate (IPDI) as bridges. The photo-crosslinkable copolymer and 4-acetaminophenol were dissolved to give copolymer mixed solution. Water as a non-solvent, was added to the mixed solu- tion to induce the self-assembly micellization of the photo-crosslinkable copolymer, during which the template molecules (4-acetaminophenol) was entrapped in the micelles through the interactions between 4-acetaminophenol and the copolymer chain. The properties and morphology of MIP micelles were characterized by dynamic light scattering (DLS), zeta potential and transmission electron microscope (TEM). DLS results showed that the average hydrodynamic diameter was about 70 nm, which was supported by the result from the TEM measurements. The MIP micelle solution prepared was used as a bath solu- tion for electrodeposition. A MIP film was formed in situ on the electrode surface by electrodeposition of the MIP micelles and then crosslinked by UV radiation to lock the structure and improve the stability of the film. Finally the template mole- cules were removed from the film by extraction, leading to 4-acetaminophenol imprinted electrode. The electrochemical per- formance of the MIP electrode was evaluated by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV). The resulting MIP sensor showed good response and selectivity towards 4-acetaminophenol. In addition, this MIP sensor showed excellent selectivity to 4-acetaminophenol, and the interferences from structurely similar analogues were ef- fectively avoided. The linear range was from 1×10