Xiayan Wang

Ruthenium-oxide-coated sodium vanadium fluorophosphate nanowires as high-power cathode materials for sodium-ion batteries.

Sodium-ion batteries are a very promising alternative to lithium-ion batteries because of their reliance on an abundant supply of sodium salts, environmental benignity, and low cost. However, the low rate capability and poor long-term stability still hinder their practical application. A cathode material, formed of RuO2 -coated Na3 V2 O2 (PO4 )2 F nanowires, has a 50 nm diameter with the space group of I4/mmm. When used as a cathode material for Na-ion batteries, a reversible capacity of 120 mAh g(-1) at 1 C and 95 mAh g(-1) at 20 C can be achieved after 1000 charge-discharge cycles. The ultrahigh rate capability and enhanced cycling stability are comparable with high performance lithium cathodes. Combining first principles computational investigation with experimental observations, the excellent performance can be attributed to the uniform and highly conductive RuO2 coating and the preferred growth of the (002) plane in the Na3 V2 O2 (PO4 )2 F nanowires.

Supported sub-5nm Pt–Fe intermetallic compounds for electrocatalytic application

Supported chemically ordered Pt–Fe intermetallic compounds have been prepared through a straightforward two-stage approach. By taking advantage of this straightforward two-stage synthesis, we have for the first time successfully obtained supported Pt3Fe1 and Pt1Fe1 intermetallic nanoparticles with a mean size of less than 5 nm, a narrow size distribution and good dispersion. The nanoparticles of supported intermetallic Pt3Fe1 and Pt1Fe1 compounds showed superior electrocatalytic activities towards the oxygen reduction reaction (ORR). The ORR enhancement in supported electrocatalysts made from Pt–Fe intermetallic compounds may be attributed to their geometric and electronic structure. Accelerated durability tests (ADT) show that Pt3Fe1/C has better durability, the electrochemical surface area (ECSA) values of commercial Pt/C decreased by 49% after 5000 cycles, but Pt1Fe1/C showed a reduction in the ECSA value of 3% after 5000 cycles.

Microfluidic Synthesis Enables Dense and Uniform Loading of Surfactant‐Free PtSn Nanocrystals on Carbon Supports for Enhanced Ethanol Oxidation

Developing new synthetic methods for carbon supported catalysts with improved performance is of fundamental importance in advancing proton exchange membrane fuel cell (PEMFC) technology. Continuous-flow, microfluidic reactions in capillary tube reactors are described, which are capable of synthesizing surfactant-free, ultrafine PtSn alloyed nanoparticles (NPs) on various carbon supports (for example, commercial carbon black particles, carbon nanotubes, and graphene sheets). The PtSn NPs are highly crystalline with sizes smaller than 2 nm, and they are highly dispersed on the carbon supports with high loadings up to 33 wt%. These characteristics make the as-synthesized carbon-supported PtSn NPs more efficient than state of the art commercial Pt/C catalysts applied to the ethanol oxidation reaction (EOR). Significantly enhanced mass catalytic activity (two-times that of Pt/C) and improved stability are obtained.

One-Step, Facile and Ultrafast Synthesis of Phase- and Size-Controlled Pt–Bi Intermetallic Nanocatalysts through Continuous-Flow Microfluidics

Ordered intermetallic nanomaterials are of considerable interest for fuel cell applications because of their unique electronic and structural properties. The synthesis of intermetallic compounds generally requires the use of high temperatures and multiple-step processes. The development of techniques for rapid phase- and size-controlled synthesis remains a formidable challenge. The intermetallic compound Pt1Bi2 is a promising candidate catalyst for direct methanol fuel cells because of its high catalytic activity and excellent methanol tolerance. In this work, we explored a one-step, facile and ultrafast phase- and size-controlled process for synthesizing ordered Pt-Bi intermetallic nanoparticles (NPs) within seconds in microfluidic reactors. Single-phase Pt1Bi1 and Pt1Bi2 intermetallic NPs were prepared by tuning the reaction temperature, and size control was achieved by modifying the solvents and the length of the reaction channel. The as-prepared Pt-Bi intermetallic NPs exhibited excellent methanol tolerance capacity and high electrocatalytic activity. Other intermetallic nanomaterials, such as Pt3Fe intermetallic nanowires with a diameter of 8.6 nm and Pt1Sn1 intermetallic nanowires with a diameter of 6.3 nm, were also successfully synthesized using this method, thus demonstrating its feasibility and generality.

Facile one-step photochemical synthesis of water soluble CdTe(S) nanocrystals with high quantum yields

This paper describes a successful synthesis of water soluble CdTe(S) nanocrystals (NCs) with high quantum yields (QYs) via a mild photochemical route in one step with thioglycolic acid as the stabilizer and sulfur source. The precursor solution of mixed cadmium chloride, freshly prepared sodium hydrogen telluride and thioglycolic acid was subjected directly to UV irradiation using a 500 W high-pressure mercury lamp under the protection of N2. NCs with a small particle size (2.2 nm) and a high photoluminescence quantum yield (up to 80% at room temperature) were formed within 25 min. The NCs were characterized by UV-vis absorption and fluorescence spectroscopy, transmission electron microscopy, powder X-ray diffraction and energy-dispersive X-ray spectroscopy to evaluate their structure, size and composition. The photochemically prepared NCs were compared with CdTe NCs prepared by conventional hydrothermal synthesis and CdTe/CdS core/shell NCs obtained by post-preparative photochemical passivation. The effects of UV irradiation intensity, illumination time, temperature and concentration of Te2− on the optical properties of NCs were studied in detail.

Electrocatalytic Dechlorination of Atrazine Using Binuclear Iron Phthalocyanine as Electrocatalysts

The electrochemical reduction approach has been suggested as a promising method for detoxification of chlorine-containing aromatic hydrocarbons. In this study, the electrocatalytic dechlorination of atrazine was studied by using a non-noble catalyst, binuclear iron phthalocyanine coated onto multi-walled carbon nanotubes (bi-FePc/MWNT). Both experimental and theoretical results indicate that dechlorination of atrazine occurs rapidly on bi-FePc/MWNT electrode. The reaction depends on the adsorption of the chlorinated organic compound on the electrode surface and the reaction rate with hydroxy. By liquid chromatography–tandem mass spectrometer technique, the dechlorination product of atrazine can be assigned to 2-hydroxy-4-ethylamino-6-isopropylamino-1,3,5-triazine, which could be disposed by more convenient and economic biodegradation method.

Highly fluorescent polymeric nanoparticles based on melamine for facile detection of TNT in soil

Analyte oriented selection of the preparation procedure is essential for improving the sensing performance. Herein, we report a one-step approach to synthesize highly fluorescent polymeric nanoparticles through a solvothermal method and their application for sensitive detection of TNT in soil samples by a fluorescence spectrometric method. The polymeric nanoparticles with bright cyan fluorescence were obtained through polycondensation between melamine and terephthalaldehyde at 180 °C for 3 h. The nanoparticles were fully characterized and the effect of synthesis methods was compared based on the fluorescence intensity and quantum yield (QY). The results indicated that trace amounts of TNT could effectively quench the fluorescence of the polymeric nanoparticles. The effect of the possible co-existing substances was systematically investigated and it was proved that nanoparticles could be used for selective and robust detection of TNT. A limit of detection of 1.8 nmol L−1 was achieved. The standard addition recoveries for different soil samples were in the range of 95.3% and 106.4% with relative standard deviations below 5.2%.

Charge Tunable Zwitterionic Polyampholyte Layers Formed in Cyclic Olefin Copolymer Microchannels through Photochemical Graft Polymerization

Zwitterionic layers immobilized on various surfaces exhibit ideal biocompatibility and antifouling capability, but direct immobilization of zwitterionic molecules provides limited choice of surface charges. In this paper, the formation of charge tunable zwitterionic polyampholyte layers onto the surface of microfluidic channels of cyclic olefin copolymer by photochemical graft polymerization of mixed acrylic monomers, [2-(acryloyloxy) ethyl] trimethyl ammonium chloride and 2-acrylamido-2-methyl-1-propanesulfonic, under UV illumination was reported. With this method, surface charge of the resulting modification layers could be tailored through the initial monomer ratio and reaction conditions. The incorporation of both monomers into the grafted layers was confirmed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared (ATR-FTIR). The results indicate that the modified layers are hydrophilic with contact angles of 33.0-44.3°, and the isoelectric points of the modified layers can be tuned from <3 to >9 simply by adjusting the monomer ratios. Elimination of the nonspecific adsorption of proteins on the zwitterionic layers thus formed was proved by fluorescent microscopy and streaming potential measurement. The uniformity of the modified layers was verified through a comparison of electrophoresis inside the modified and native microchannels. A whole blood coagulation time measurement was performed to show its applicability.

The Interactions of Oxygen with Small Gold Clusters on Nitrogen-Doped Graphene

By means of density functional theory, the adsorption properties of O2 molecule on both isolated and N-graphene supported gold clusters have been studied. The N-graphene is modeled by a C65NH22 cluster of finite size. The results indicate that the catalytic activity and the O2 adsorption energies of odd-numbered Au clusters are larger than those of adjacent even-numbered ones. The O2 molecule is in favor of bonding to the bridge sites of odd-numbered Au clusters, whereas for odd-numbered ones, the end-on adsorption mode is favored. The perpendicular adsorption orientation on N-graphene is preferred than the parallel one for Au2, Au3 and Au4 clusters, while for Au5, Au6 and Au7, the parallel ones are favored. When O2 is adsorbed on N-graphene supported Au clusters, the adsorption energies are largely increased compared with those on gas-phase ones. The increased adsorption energies would significantly facilitate the electron transfer from Au d-orbital to π* orbital of O2, which would further weakening the O–O bond and therefore enhancing the catalytic activity. The carbon atoms on N-graphene could anchor the clusters, which could make them more difficult to structural distortion, therefore enhance their stability.

Synthesis and characterization of a novel binuclear iron phthalocyanine/reduced graphene oxide nanocomposite for non-precious electrocatalyst for oxygen reduction

Binuclear iron phthalocyanine/reduced graphene oxide (bi-FePc/RGO) nanocomposite with good electrocatalytic activity for ORR in alkaline medium was prepared in one step. High angle annular dark field image scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectroscopy element mapping results show bi-FePc was uniformly distributed on RGO. An obvious cathodic peak located at about −0.23 V (vs. SCE) in CV and an onset potential of −0.004 V (vs. SCE) in LSV indicate the as-prepared bi-FePc/RGO nanocomposite possesses high activity which is closed to Pt/C for ORR. The ORR on bi-FePc/RGO nanocomposite follows four-electron transfer pathway in alkaline medium. Compared with Pt/C, there is only a slight decrease (about 0.02 V vs. SCE) for bi-FePc/RGO nanocomposite when the methanol exists. The excellent activity and methanol tolerance in alkaline solutions proves that bi-FePc/RGO nanocomposite could be considered as a promising cathode catalyst for alkaline fuel cells.