Wee Shong Chin

α-Fe2O3 nanotubes-reduced graphene oxide composites as synergistic electrochemical capacitor materials

We present a facile approach for the fabrication of a nanocomposite comprising α-Fe(2)O(3) nanotubes (NTs) anchored on reduced graphene oxide (rGO) for electrochemical capacitors (ECs). The hollow tubular structure of the α-Fe(2)O(3) NTs presents a high surface area for reaction, while the incorporation of rGO provides an efficient two-dimensional conductive pathway to allow fast, reversible redox reaction. As a result, the nanocomposite materials exhibit a specific capacitance which is remarkably higher (~7 times) than α-Fe(2)O(3) NTs alone. In addition, the nanocomposites show excellent cycling life and large negative potential window. These findings suggest that such nanocomposites are a promising candidate as negative electrodes in asymmetrical capacitors with neutral electrolytes.

Cobalt-based compounds and composites as electrode materials for high-performance electrochemical capacitors

Transition metal compounds (oxides, hydroxides, etc.) are emerging electrode materials for electrochemical capacitors (ECs) due to their rich redox properties involving multiple oxidation states and different ions. Pseudocapacitance derived from the reversible faradaic reactions can be ten times higher than those of the state-of-the-art carbon-based electric double layer capacitors (EDLCs). As one of the most well-known electroactive inorganic materials, extensive studies of cobalt-based compounds (Co3O4, Co(OH)2, CoOOH, CoS, etc.) for ECs have mushroomed, and the relevant literature has grown exponentially in the past ten years. This review consolidates and evaluates the recent progress, achievements, weaknesses and challenges in the research of cobalt-based compounds and nanocomposites for ECs. The triangular relationship between synthesis strategies, tailored material properties and the electrochemical performances is thoroughly assessed, unveiling the advanced electrode material design and development.

CoOOH nanosheet electrodes: Simple fabrication for sensitive electrochemical sensing of hydrogen peroxide and hydrazine

Cobalt oxyhydroxide, CoOOH, nanosheets were prepared via a surface alkaline treatment of cobalt foil at room temperature without using templates and catalysts. The morphology, chemical composition and structures of the nanosheets were characterized by XRD, FTIR and Raman spectroscopy, FESEM and TEM. These oriented and nanostructured arrays can be used directly as electrodes, thus simplifying the electrode fabrication process, as well as offering advantages such as enhanced electrode-electrolyte contact area, minimum diffusion resistance and direct active material-current collector connection for fast electron transport. The electrode was used as an electrochemical sensor towards non-enzymatic detection of hydrogen peroxide and hydrazine in alkaline solution. The amperometric detection of H(2)O(2) and N(2)H(4) was carried out at low potential (0V and 0.1V). At 0.1V, the amperometric signals are linearly proportional to H(2)O(2) concentration up to 1.6mM (R(2)=0.995), showing a detection limit (S/N=3) of 40μM and a high sensitivity of 99μA mM(-1)cm(-2). For N(2)H(4), the amperometric signals are linearly proportional to concentration up to 1.2mM (R(2)=0.99), showing a detection limit (S/N=3) of 20μM and a high sensitivity of 155μA mM(-1)cm(-2) at 0.1V.

Synthesis and characterization of Eu:Y2O3 nanoparticles

The red-emitting nanophosphor Eu:Y2O3 was synthesized using the the microemulsions method. The microemulsion system was composed of petroleum ether (60-80??C), nonionic surfactants NP5/NP9, aqueous yttrium nitrate/europium nitrate and ammonium hydroxide solution. The nanoparticles were studied by thermal analysis, x-ray diffraction, transmission electronic microscopy, scanning electron microscopy and photoluminescence. The size of the nanoparticles was in the range 10-100?nm, and showed a narrow size distribution, high crystallinity and special luminescent properties. Compared with the phosphors prepared by the conventional method, the quenching concentration of Eu was raised remarkably. For this type of nanophosphor, quenching starts at a Eu concentration of 10% (mol%), while a value of 6-8% was obtained for the conventional one (Tao?Y 1996 Mater. Lett. 28 137-40). Based on this study, we have successfully prepared some promising nanophosphors.

Excitonic nonlinear absorption in CdS nanocrystals studied using Z-scan technique

Irradiance dependence of excitonic nonlinear absorption in cadmium sulfide (CdS) nanocrystals has been studied by using Z-scan method with nanosecond laser pulses. The wavelength dependence of nonlinear absorption has also been measured near the excitonic transition of 1S(e)–1S3/2(h). We observe the saturable absorption, which can be described by a third-order and a fifth-order nonlinear process for both 3.0-nm-sized and 2.3-nm-sized CdS nanocrystals. The experimental results show that the excitonic nonlinear absorption of CdS nanocrystals is greatly enhanced with decreasing particle size. A two-level model is utilized to explain both irradiance and wavelength dependence of the excitonic nonlinearity.

Anthracene-fused BODIPYs as near-infrared dyes with high photostability.

An anthracene unit was successfully fused to the zigzag edge of a boron dipyrromethene (BODIPY) core by an FeCl(3)-mediated oxidative cyclodehydrogenation reaction. Meanwhile, a dimer was also formed by both intramolecular cyclization and intermolecular coupling. The anthracene-fused BODIPY monomer 7a and dimer 7b showed small energy gaps (∼1.4 eV) and near-infrared absorption/emission. Moreover, they exhibited high photostability.

Synthesis and Characterization of Multifunctional FePt/ZnO Core/Shell Nanoparticles

Multicomponent hybrid nanostructures containing two or more nanosized components that are arranged in a controlled way are of fundamental and practical significance for many different disciplines, including physics, chemistry, materials science, and medicine. Due to the synergistic properties induced by the intimate contact and the interaction between different components, hybrid nanostructures can achieve enhanced properties and provide novel functions not available in the single-phase nanostructures. Furthermore, hybrid nanostructures are usually multifunctional. These advantages make hybrid nanostructures one of the most promising candidates for the exploration of new applications. Hybrid semiconducting and magnetic nanostructures are currently a research focus owing to their potential in optoelectronic, spintronic, nanoelectronic, and biomedicine applications. FePt alloys are an important class of magnetic materials with high anisotropy of 7 10 erg cm 3 and high chemical stability. Monodispersed FePt nanoparticles with a tunable size of 3–10 nm and controllable compositions can be synthesized by various techniques. ZnO is a transparent oxide semiconductor that possesses piezoelectric properties, which has been widely used for solar cells, nanolasers, optoelectronic devices, and electromechanical coupled sensors and transducers. Moreover, ZnO is biocompatible and can be directly used for biomedical applications. It is expected that the hybrid nanostructure of ZnO and FePt, arranged in a well-controlled way, would be multifunctional and offers unique applications. However, it is well known to be difficult to grow the two materials together in a controlled manner due to lattice mismatch and a large difference in their surface free energies. Here, we report a successful synthesis of multifunctional FePt/ZnO core/shell nanoparticles by seed-mediated growth. High-resolution transmission electron microscopy (HRTEM) showed a quasiepitaxial growth between the FePt core and the ZnO shell. The ZnO shell was found to be highly deformed and a spontaneous polarization of about 0.08 8Cm 2 could be induced. Two additional green PL peaks appeared for the core/shell nanoparticles, which were not found for the pure ZnO nanoparticles. The core/shell nanoparticles were superparamagnetic at room temperature but ferromagnetic at 5 K. The successful synthesis of FePt/ZnO core/shell nanoparticles with functions of semiconducting, magnetic, and piezoelectric properties offers a way to finely tune the material response to magnetic, electrical, optical, and mechanical stimuli, which has potential in data storage, optoelectronic, magneto-electromechanical, and biomedicine applications. Scheme 1 shows the overall process employed to fabricate FePt/ZnO core/shell nanoparticles. First, Fe56Pt44 nanoparticles were synthesized and used as the hetero-nucleation seeds for the preparation of FePt/ZnO core/shell nanoparticles. The FePt/ZnO core/shell nanoparticles were fabricated by thermolysis of a zinc metal source to form a ZnO shell directly onto the preformed FePt nanoparticles. Experiemental details regarding the synthesis procedure are given in the Experimental section. In the formation of FePt/ZnO core/shell nanostructures, oleylamine played dual roles. On one hand, it could coordinate with zinc acetate to form a zinc–oleylamine complex, which is soluble in octylether (zinc acetate could not dissolve in octyl ether without oleylamine) and can chemically absorbs onto the preformed FePt nanoparticles. On the other hand, it could decompose the zinc complex into zinc oxides, which then coat onto the surface of FePt nanoparticles to form core/shell structures. Slow heating of the colloidal solution containing both FePt particles and zinc complex was essential for the formation of core/shell structures. The alternative procedure of injecting zinc–oleylamine complex into the crude FePt solution at elevated temperature (260 8C) will lead to the co-existence of separate FePt and ZnO nanoparticles, together with some FePt/ZnO core/shell nanoparticles. Recent reports have shown that the work of formation of an embryo on a seed particle is always much smaller than that of a Kelvin-size embryo in homogeneous nucleation. At a low heating rate, the concentration of ZnO monomers/clusters formed by decomposition would be below the homogeneous nucleation threshold. Due to the much lower nucleation energy required, the formed ZnO monomers/clusters would nucleate heterogeneously on the surface of FePt seeds rather than nucleate homogeneously to form new ZnO particles. Figure 1a presents a 2D assembly of the as-synthesized FePt nanoparticles. The FePt nanoparticles are monodispersed with diameter of 3.3 0.2 nm. The inset in Figure 1a shows an

Nano-hybrid luminescent dot: synthesis, characterization and optical properties

A series of nano-hybrid light emitting dots with diameter range from 2 nm to 4 nm were synthesized through grafting organic conjugated chains directly onto an inorganic rigid cage polyhedral oligomeric silsesquioxanes (POSS). The effect of chain length, side groups, polarity of solvents on the property of light emitting dots were studied using FTIR, XRD, DSC, UV, PL, AFM and SEM. The unique structure of these nano-hybrid dots renders them with excellent PL properties which are much different from bulk organic molecules or conjugated polymers. The incorporation of conjugated molecules onto POSS transforms the oligo-conjugated arms from crystalline state to non-crystalline solid which can be solution processed. The PLQE (PL quantum efficiency) of the oligo-conjugated arms in condensed state increases significantly after grafting onto POSS. The light emitting dots are very sensitive to the polarity of organic solvents due to their nano-scaled size. PL spectrum of the nano-hybrid dots in solid film was blue shift from that in most of organic solvents.

A comparative ab initio and DFT study of neutral aniline oligomers

Comparative ab initio restricted Hartree–Fock (RHF) and density functional theory (DFT) calculations were performed to investigate the geometric and electronic structures of various neutral aniline oligomers. These oligomers were selected to model polyaniline (PANI) in different intrinsic oxidation states, with an aim to study the applicability and extendibility of the theoretical methods to conjugated polymers. In general, we found that DFT calculations produce results that are in good agreement with observations from x-ray diffraction, ultraviolet-visible absorption, ultraviolet photoelectron and x-ray photoelectron spectroscopy. The DFT method has reproduced well the ∼4.0 eV π–π* transition of leucoemeraldine base and the ∼2.0 eV Peierls gap transition of pernigraniline base. The valence band structure and the ∼1.2 eV energy separation of nitrogen core levels of emeraldine base are also correctly predicted. On the other hand, large discrepancies with experimental measurements are predicted by the RHF m...

The alternative thermal decomposition mode of 2-oxetanone and 2-azetidinone: a DFT and PES study

Abstract We have found that, while 2-oxetanone undergoes thermal decarboxylation at 350°C to give CO 2 and ethene, 2-azetidinone proceeds in two different modes at 550°C, giving isocyanic acid, ethene, ketene, hydrogen cyanide and carbon monoxide among the pyrolysis products. B3LYP/6-31G ** calculations were performed to investigate the two alternative cycloreversion pathways for the two compounds. Theoretical thermodynamic data predicted that decarboxylation of 2-oxetanone has among the lowest activation barrier (159 kJ mol −1 ) and free energy (Δ G =−183 kJ mol −1 ). While the cycloreversion to ethene can be classified as a concerted asynchronous process, natural bond orbital (NBO) analysis suggested that the cycloreversion to ketene is more asynchronous for 2-azetidinone than for 2-oxetanone.