Li Wan

Hubei University, Wu-han-shih, Hubei, China

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Publications (26)50.64 Total impact

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    ABSTRACT: Water-soluble polyaniline/graphene nanocomposites have been prepared via a simple in-situ polymerization of aniline in graphene dispersion. TEM measurement confirmed that polyaniline was homogeneously coated on the graphene sheets. The nanocomposites solution can be used for film fabrication by common technology, such as drop coating. When these different polyaniline/graphene nanocomposites were applied as the counter electrode materials for dye-sensitized solar cells, the short-circuit current density and power-conversion efficiency of the devices were measured to be 12.19 mA cm-2 and 4.46%, respectively, which was comparable to 5.71% for the cell with a Pt counter electrode under the same experimental conditions.
    Reactive and Functional Polymers 06/2014; · 2.51 Impact Factor
  • Carbon - Science and Technology 10/2013; 62:157-164.
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    ABSTRACT: The TiO2 film electrodes sensitized with CdS quantum dots (QDs) via chemical bath deposition method were successfully prepared as the photoanode of dye-sensitized solar cells (DSSCs). Microstructural characterizations by XRD, SEM, TEM and EDX show that the CdS nanocrystals with the cubic structure have intimate contact to the TiO2 films. The amount of CdS QDs can be controlled by varying the dipping time. The experiment results demonstrate that the CdS QDs-sensitized solar cells show a wider absorption in the solar spectrum and an enhanced surface photovoltage response. The maximal photoelectric conversion efficiency of 5.57% was achieved by the DSSC based on CdS QDs-sensitized TiO2 film with 4 min. The performance improvement is ascribed to the enhancement of electron transport, the reduction of electron recombination and the long electron lifetime.
    Materials Research Bulletin. 07/2013; 48(7):2566–2570.
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    ABSTRACT: Functionalized reduced graphene oxide (RGO) was obtained by reaction of graphene oxide with dodecyl (12C), octyl (8C) and propyl (3C) trimethoxysilane and subsequent reduction using hydrazine hydrate. The results showed the successful grafting of the alkyl groups onto the surface of RGO, and that the longer alkylated chains made graphene more lipophilic. Furthermore, the RGO-12C was incorporated into polypropylene matrix as a reinforcing component by solution mixing. The resulting nanocomposites displayed a significant improvement in thermal stability, crystallinity and mechanical properties. This work suggests a new route to improve the solubility and dispersion of graphene in polymer matrix.
    Chemical Physics Letters 05/2013; 570:125–131. · 2.15 Impact Factor
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    ABSTRACT: A facile means to generate carbon dots/ionic liquids (ILs) blend using ionic liquid-assisted electrochemical exfoliation was demonstrated. Two kinds of ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), were used in this work. Transmission electron microscopy and UV–vis spectrum were employed to characterize the formed carbon dots/ILs. The carbon dots/ILs were used for fabricating quasi-solid-state dye-sensitized solar cells (DSSCs), where 1-butyl-3-methylimidazolium iodide and LiI/I2 were added to enhance the performance of DSSCs. Effects of the varied contents of components in the complex on the performance of DCCSs have been studied in detail at ambient temperature. The electrochemical impedance spectroscopy showed that the introduction of carbon dots into ionic liquids can enhance the electrical properties by facilitating charge transfer processes of the electrolytes. The overall energy-conversion efficiency (η) was 2.71% and 2.41% for carbon dots/[bmim][PF6] and carbon dots/[bmim][BF4] based blend electrolytes, respectively. A 82% enhancement in η was obtained by introduction of carbon dots into [bmim][PF6] comparing with pure [bmim][PF6] (η = 1.49%). In addition, the cells exhibited good stability under continuous illumination in room temperature without any further sealing.
    Electrochimica Acta 01/2013; 88:100–106. · 4.09 Impact Factor
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    ABSTRACT: Bi2O3 nanostructures with high surface-to-volume ratio are attracting particular interest in catalysis, gas sensors, solar-energy conversion, and so on. In this paper, we present the impact of annealing on morphology, structure, and optical properties of Bi2O3 nanotube-based urchin-like microarchitectures, which is very important to determine before their applications in many potential fields. Our results showed that below 400 °C, the microarchitectures possessed good thermal stability. While annealing at 500 °C, jointed nanoparticles with an average size of 350 nm were formed. On further increasing the annealing temperature to 600 °C, the microarchitectures were transformed into stable α-Bi2O3 microcrystal film with a larger particle size of about 800 nm. The optical bandgaps of the annealed products were also changed according to their changes of morphology and structure.
    physica status solidi (a) 11/2012; 209(11):2157-2160. · 1.21 Impact Factor
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    ABSTRACT: A controllable preparation of novel graphene-based inorganic semi-conducting composites has aroused great attention in the optoelectronic device and powerful electronic anode materials. In this article, we demonstrate a simple two-step strategy for the synthesis of cadmium sulfide/reduced graphene oxide (CdS/RGO) nanocomposites, of which the preparing process includes modification of the exfoliated graphene oxide acylated with thionyl chloride, immobilization of the CdS nanoparticles on the graphene oxide (GO) surface by an amide reaction between the amino groups located on the CdS particles and the acyl chloride bound to the GO surface, and reduction by hydrazine and ammonia. Our results showed that the CdS nanoparticles with an average size of 20 nm were homogeneously dispersed on the surface of RGO sheets. The CdS/RGO nanocomposites can form a homogeneous and stable solution in dimethylformamide, and CV analysis indicated a remarkable increase for the CdS/RGO modified electrode in the electrochemical current relative to that at a glass carbon electrode.
    Materials Chemistry and Physics 08/2012; 135(s 2–3):687–693. · 2.07 Impact Factor
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    ABSTRACT: This work reports a facile and rapid method assisted by microwave irradiation for the synthesis of hemin functionalized reduced graphene oxide (hemin–RGO) materials. Our investigation confirmed that the hemin molecules were covalently grafted to the surface of graphene by the amidation reaction of the NH2 groups on the edges of ethylenediamine functionalized graphene oxide with the COOH groups of hemin. Hemin–RGO exhibits a homogeneous dispersion in water, dimethylformamide, and acetone after more than one month, indicating that hemin can effectively improve the dispersion and solubility of RGO in the solvent. Hemin–RGO was used as a counter electrode in dye-sensitized solar cells and exhibited preferable electrocatalytic activity for I3− to I− reduction compared with RGO.
    Materials Chemistry and Physics. 02/2012; 132(2–3):858-864.
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    ABSTRACT: Graphene nanosheets–gold (GNS-Au) nanocomposites have been successfully prepared by microwave radiation in aqueous media via a rapid one-step method. The as-obtained nanocomposites were characterized by Fourier transform infrared spectra, X-ray power diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry, Raman spectrum and UV-visible absorption spectra. The results show that Au nanoparticles with a mean diameter of 9.3 nm are densely coated on the surface of graphene nanosheets, which disturbs the van der Waals interactions and prevents graphene nanosheets from approaching each other. Cyclic voltammetry measurements reveal that GNS–Au modified glassy carbon electrode (GNS–Au/GCE) has a greatly enhanced electrochemical response compared with bare GCE and the GNS modified glassy carbon electrode (GNS/GCE), suggesting that the GNS–Au nanocomposites may be a promising nanomaterial for highly sensitive electrochemical sensors.
    Fullerenes Nanotubes and Carbon Nanostructures - FULLER NANOTUB CARBON NANOSTR. 01/2012; 20(1):31-40.
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    ABSTRACT: A novel TiO(2) double-layer (DL) film consisting of TiO(2) hollow spheres (HSs) as overlayer and single-crystalline TiO(2) nanorod arrays (RAs) as underlayer was designed as the photoanode of dye-sensitized solar cells (DSSCs). This new-typed TiO(2) HS/RA DL film could significantly improve the efficiency of DSSCs owing to its synergic effects, i.e. the relatively large specific surface area of TiO(2) HSs for effective dye adsorption, enhanced light harvesting capability originated from TiO(2) RA film, and rapid interfacial electron transport in one-dimensional TiO(2) nanorod arrays. The overall energy-conversion efficiency of 4.57% was achieved by the formation of TiO(2) DL film, which is 16% higher than that formed by TiO(2) HS film and far larger than that formed by TiO(2) RA film (η=0.99%). The light absorption and interfacial electron transport, which play important roles in the efficiency of DSSCs, were investigated by UV-vis absorption spectra and electrochemical impedance spectra.
    Journal of Colloid and Interface Science 09/2011; 365(1):46-52. · 3.55 Impact Factor
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    ABSTRACT: Hydroxypropyl-β-cyclodextrin (HP-β-CD) modified graphenenanosheets were successfully prepared using a facile and rapid method assisted by microwave irradiation in water medium, which involves the reaction between the carboxyl groups of graphene oxide (GO) and the hydroxylgroups of HP-β-CD followed by the reduction of GO into reduced GO (RGO) utilizing hydrazine hydrate. The as-prepared HP-β-CD-RGO nanocomposites were characterized by Fourier transform infrared spectra, Raman spectra, X-ray photoelectron spectroscopy, thermogravimetric analyses, contact angle measurement, transmission electron microscopy, atomic force microscopy and electrochemical impedance spectroscopy. The new nanocomposites possess unique properties of high surface area and host–guest recognition, thus can be used to enrich and detect inorganic, organic and biological molecules. Cyclic voltammetry measurement (CV) revealed that the HP-β-CD-RGO modified glassy carbon electrode exhibited outstanding supramolecular recognition and high electrochemical response to several phenolic organic pollutants, and the oxidative peak current decreased linearly with the concentration of Nitrophenol down to a detection limit of 1 × 10−8 M.
    Journal of Materials Chemistry 07/2011; 21(28):10463-10471. · 6.63 Impact Factor
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    ABSTRACT: Graphene films with controllable thicknesses, electrical and optical properties are fabricated on variable substrates at room temperature by a simple, efficient and low-cost solution-based method. This process is completely compatible with flexible substrates (polyethylene terephthalate, PET), fluorine-doped tin oxide (FTO) conductive glasses, and even glassy carbon electrodes. The graphene films show excellent conductivity and electrochemical activity. The films prepared on FTO conductive glasses, as an alternative to ubiquitously employed platinum-based counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), are demonstrated. The results suggest a new start in the direction of graphene CEs for the development of next generation of optoelectronics.
    Solid State Sciences. 01/2011; 13(2):468-475.
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    ABSTRACT: Spectroscopic ellipsometry was used to characterize the optical response of few layer reduced graphene oxide and graphene oxide in visible range. Lorentz oscillator model is added to analyze the ellipsometric parameters. The experiment shows the optical response of few layer reduced graphene oxide and monolayer exfoliated graphene in visible range is quite similar with slight difference due to the structure defects. The Lorentz oscillator model gives experimental support to investigate the band-gap tuning through the reduction process in details.
    Applied Physics Letters 01/2011; 99. · 3.52 Impact Factor
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    ABSTRACT: Precise interface control and dispersal of graphene nanosheets in polymer hosts are challenging to develop high performance graphene-based nanocomposites due to their strong interlayer cohesive energy and surface inertia. Here, we firstly report an efficient and novel method to functionalize graphene nanosheets with vinyl triethoxysilane (VTES) and successfully blend them with low density polyethylene (LDPE) to prepare nanocomposites. Fourier transforms infrared spectra (FTIR), Raman spectra, and thermogravimetric analysis (TGA) proved that the graphene sheets were covalently bonded with VTES. The resulting nanocomposites obtained the increases of up to 27.0 and 92.8% in the tensile strength and Young’s modulus, respectively, compared to neat LDPE. The VTES–graphene not only remarkably improved the tensile strength of the composites, but also enhanced its toughness by 17.7%. Oil permeability measurements showed that the absorption ratio of toluene by the LDPE/graphene composites decreased from 56 to 39%, and its barrier properties have obviously been improved. This study opens a new route to optimize interface structures and improve the comprehensive performances of graphene–polymer nanocomposites. KeywordsGraphene–Nanocomposites–Covalent functionalization–Barrier property–Mechanical property
    Journal of Nanoparticle Research 01/2011; 13(2):869-878. · 2.18 Impact Factor
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    ABSTRACT: We report an effective method for bulk obtaining exfoliated graphene oxide (GO) solids from their aqueous solutions, which were prepared from nature graphite by an oxidation method. Tyndall effect proved that GO solution has a colloidal nature. Different flocculants were used to coagulate GO colloidal, and it was found that NaOH had the most obvious coagulation effect to GO. Transmission electron microscopy, X-ray diffraction and atomic force microscopy analysis demonstrated that there were a large number of complete few-layer GO sheets with thickness of about 0.8 nm, and the surfaces were very smooth, almost free of impurities. Liquid state 13C NMR and Fourier transformation infrared spectra showed the presence of abundant benzene carboxylic, hydroxyl and epoxide groups in the basal planes of GO. The graphene materials reduced from GO solids had good electrical conductivity. Our work explored a simple and effective route to extract GO from their solution, which is the most important to GO and graphene researches and applications.
    Chinese Journal of Chemistry 10/2010; 28(10). · 0.92 Impact Factor
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    ABSTRACT: β-Cyclodextrin (β-CD) functionalized graphene materials were synthesized by nucleophilic addition reaction between hydroxypropyl-β-Cyclodextrin (HPCD) and thionyl chloride modified graphene oxides (GO). The photoinduced electron-transfer between tetra-phenyl-porphyrin (TPP) and HPCD modified graphene materials were studied through fluorescence absorption spectroscopy, and obvious quenching was observed after adding HPCD-graphene to the DMF solution of TPP. However, the fluorescence intensity of TPP in the DMF solution was hardly changed in the presence of HPCD-GO. Cyclic voltammetry measurement (CV) was used to investigate the electrochemical interactions between hemoglobin (Hb) and TPP. The HPCD-GO/TPP modified electrode showed 5.0 × 10−9 M of the detection limit to Hb, indicating high bio-recognition capability.Graphical abstractβ-Cyclodextrin (β-CD) functionalized graphene materials were synthesized by nucleophilic addition reaction between hydroxypropyl-β-Cyclodextrin (HPCD) and thionyl chloride modified graphene oxides (GO). The physically blended sample of HPCD-GO with tetra-phenyl-porphyrin (TPP) exhibits excellent photoinduced electron-transfer properties and high bio-recognition capability.View high quality image (135K)Research highlights► β-Cyclodextrinfunctionalized graphene materials synthesized by nucleophilic addition reaction. ► Good electrochemical activities. ► High bio-recognition capability.
    Chemical Physics Letters 01/2010; 498:162-167. · 2.15 Impact Factor
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    ABSTRACT: Graphene nanosheets–polystyrene nanocomposites were prepared by in situ emulsion polymerization and reduction of graphene oxide using hydrazine hydrate. PS microspheres covalently linked to the edges of graphene nanosheets. The polystyrene-absorbed graphene has been dispersed well in the solvents of toluene and chloroform. The nanocomposites display high electrical conductivity, and a considerable increase in glass-transition temperature and good thermal stability of PS are also achieved. The facile and environmental-friendly technique presented here is an effective and promising method of functionalization of graphene sheets by polymers or other compounds.
    Chemical Physics Letters 01/2010; 484(4):247-253. · 2.15 Impact Factor
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    ABSTRACT: The carbon nanotubes (CNTs) periodically decorated by high-density polyethylene (HDPE) composites with nanohybrid shish kebabs (NHSK) structures were prepared by CNTs-initiated solution crystallization. The disc-shaped HDPE crystalline lamellae were periodically located on the surface of CNTs in the direction perpendicular to the nanotube axis. Observations from scanning electron microscopy and transmission electron microscopy showed that with the increasing of crystallization temperature, the lateral dimension of the lamellae was decreased and the distance between two neighboring lamellae was increased. However, the thickness of the lamellae did not vary with the crystallization temperature. The formation mechanism of the NHSK structures was also explained. The one-dimensional structure and the ultra-high curved surface of CNTs lead to strong geometry confinement, which plays a main role in the formation of the NHSKs.
    Science in China Series B Chemistry 07/2009; 52(7):905-910. · 1.20 Impact Factor
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    ABSTRACT: Poly(methyl methacrylate) (PMMA) nanobeads-decorated multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) nanocomposites were prepared using two processing steps. Initially, spherical PMMA nanoparticles were synthesized using an emulsion polymerization method. Afterward, the PMMA nanobeads were decorated to MWNTs and SWNTs using benzoyl peroxide as an initiator in water during a high temperature refluxing process. The results confirmed the linkage of the nanotubes to the surrounding PMMA nanobeads via a covalent bond. The resultant nanocomposites showed high solubility in chloroform without flocculation after 24h. In addition, the nanotubes/PMMA nanocomposites were characterized by electrical resistance measurements to analyze their electrical conductivity and examined as electrorheological (ER) materials when dispersed in silicone oil.
    Composites Part A Applied Science and Manufacturing 04/2009; 40(4):413-417. · 2.74 Impact Factor
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    ABSTRACT: Microwave-assisted chemical functionalization of single-walled carbon nanotubes, with undecyl groups decomposed from lauroyl peroxides was reported. This rapid efficient procedure reduced the reaction time to 10 min, and obtained the products with higher functionalized degree than that by the conventional refluxing method. The influence of different reaction time and microwave power on the functionalized degree has been explored by using FT-IR, TGA and Raman analyses. The results show that longer treatment time will lead to partial defunctionalization, and higher microwave power (higher than 900 W) can reduce the functionalized degree by removing some initially-attached functional groups. Dispersion stability images and HRTEM images show that the resulting SWNT has enhanced dispersivity in organic solvents compared to the pristine nanotubes.
    Chinese Journal of Chemistry 03/2009; 27(2):359 - 364. · 0.92 Impact Factor