Browsing by Author "Kong, LX"

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    Reinforcement and deformation behaviors of polyvinyl alcohol/graphene/montmorillonite clay composites
    (Elsevier, 2015-10-30) Li, CP; Li, YZ; She, XD; Vongsvivut, JP; Li, JH; She, FH; Gao, WM; Kong, LX
    We report the synergistic reinforcement and deformation of polyvinyl alcohol (PVA)/graphene/montmorillonite clay (MMT) composites with the tensile properties being improved greatly. Particularly, the tensile strength and modulus of PVA composite with 0.9 wt% graphene and 0.3 wt% of MMT were improved by more than 58% and 43% when compared to the neat PVA, respectively, and were at least 10% higher than the enhanced sum of dual PVA composites with 0.9 wt% graphene and 0.3 wt% MMT. This reinforcement was resulted from the good dispersion and effective interfacial interactions as confirmed from morphology investigation, increased glass transition temperature and the shift of O–H stretching. When there were no fillers i.e. in situ reduced graphene (IRG) or MMT or their loading was low, high alignment of PVA could be observed, with increased crystallinity, melting point, lamellae thickness but narrowed crystallite size distribution. The synergistic reinforcement of PVA achieved from combined incorporation of IRG and MMT will pave the way for the development of stronger PVA composites in various applications. © 2015 Elsevier Ltd.
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    Silver nanoparticles prepared by gamma irradiation across metal organic framework templates
    (Royal Society of Chemistry, 2015-01-07) He, L; Dumée, LF; Liu, D; Velleman, L; She, FH; Banos, C; Davies, JB; Kong, LX
    In this study, we demonstrate for the first time the successful fabrication of well-dispersed ultrafine silver nanoparticles inside metal–organic frameworks through a single step gamma irradiation at room temperature. HKUST-1 crystals are soaked in silver nitrate aqueous solution and irradiated with a Cobalt 60 source across a range of irradiation doses to synthesize highly uniformly distributed silver nano-particles. The average size of the silver nanoparticles across the Ag@HKUST-1 materials is found to vary between 1.4 and 3 nm for dose exposures between 1 and 200 kGy, respectively. The Ag@HKUST-1 hybrid crystals exhibit strong surface plasmon resonance and are highly durable and efficient catalytic materials for the reduction of 4-nitrophenol to 4-aminophenol (up to 14.46 × 10−3 s−1 for 1 kGy Ag@HKUST-1). The crystals can be easily recycled for at least five successive cycles of reaction with a conversion efficiency higher than 99.9%. The gamma irradiation is demonstrated to be an effective and environmental friendly process for the synthesis of nano-particles across confined metal–organic frameworks at room temperature with potential applications in environmental science. © 2015 The Royal Society of Chemistry
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    Simultaneous crystallization and decomposition of PVA/MMT composites during non-isothermal process
    (Elsevier, 2015-10-20) Li, CP; Hou, TT; Vongsvivut, JP; Li, YZ; She, XD; She, FH; Gao, WM; Kong, LX
    Decomposition of poly(vinyl alcohol)/montmorillonite clay (PVA/MMT) composites during melting-crystallization was experimentally confirmed by morphology and molecular structure changes. In particular, FTIR spectra show the shift of O-H stretching band as well as enhanced intensities of C-O stretching and CH2 rocking vibrational modes. Furthermore, Raman deconvolution indicates that C-H wagging, CH2-CH wagging, CH-CO bending and CH2 wagging modes in amorphous domains were all decreased greatly. Moreover, this decomposition leads to decreased melting enthalpy, melting point, crystallization enthalpy and crystallization temperature. Crystallization analysis shows that the MMT incorporated slows down the crystallization process in the PVA matrix regardless of the nucleation capability of MMT. Despite the severe decomposition, the crystallization kinetics still corroborated well with common classical models. As a result, molecular structure changes and crystallization retardation observed in this study clearly indicate the strong effects of the thermal degradation on the non-isothermal crystallization of PVA/MMT composites. © 2015 Elsevier B.V.
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    Single step preparation of meso-porous and reduced graphene oxide by gamma-ray irradiation in gaseous phase
    (Elsevier B.V., 2014-04-01) Dumée, LF; Feng, CF; He, L; Yi, ZF; She, FS; Peng, Z; Gao, WM; Banos, C; Davies, JB; Huynh, C; Hawkins, S; Duke, MC; Gray, S; Hodgson, PD; Kong, LX
    A facile and highly efficient route to produce simultaneously porous and reduced graphene oxide by gamma ray irradiation in hydrogen is here demonstrated. Narrowly distributed nano-scale pores (average size of ∼3 nm and surface density >44,900 pore μm−2) were generated across 10 μm thick graphene oxide bucky-papers at a total irradiation dose of 500 kGy. The graphene oxide sheet reduction was confirmed to occur homogeneously across the structures by Fourier transform infrared spectroscopy and Raman analysis. This one-step, catalyst-free, high penetration and through-put technique, offers great promises potential for the mass production of reduced graphene oxide from cheap graphene oxide. © 2014 Elsevier B.V.
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    Tuning the grade of graphene: gamma ray irradiation of free-standing graphene oxide films in gaseous phase
    (Elsevier V.V., 2014-12-15) Dumée, LF; Feng, CF; He, L; Allioux, FM; Yi, ZF; Gao, WM; Banos, C; Davies, JB; Kong, LX
    A direct approach to functionalize and reduce pre-shaped graphene oxide 3D architectures is demonstrated by gamma ray irradiation in gaseous phase under analytical grade air, N2 or H2. The formation of radicals upon gamma ray irradiation is shown to lead to surface functionalization of the graphene oxide sheets. The reduction degree of graphene oxide, which can be controlled through varying the γ-ray total dose irradiation, leads to the synthesis of highly crystalline and near defect-free graphene based materials. The crystalline structure of the graphene oxide and γ-ray reduced graphene oxide was investigated by x-ray diffraction and Raman spectroscopy. The results reveal no noticeable changes in the size of sp2 graphitic structures for the range of tested gases and total exposure doses suggesting that the irradiation in gaseous phase does not damage the graphene crystalline domains. As confirmed by X-ray photoemission spectroscopy, the C/O ratio of γ-ray reduced graphene oxide is increasing from 2.37 for graphene oxide to 6.25 upon irradiation in hydrogen gas. The removal of oxygen atoms with this reduction process in hydrogen results in a sharp 400 times increase of the electrical conductivity of γ-ray reduced graphene oxide from 0.05 S cm−1 to as high as 23 S cm−1. A significant increase of the contact angle of the γ-ray reduced graphene oxide bucky-papers and weakened oxygen rich groups characteristic peaks across the Fourier transform infrared spectra further illustrate the efficacy of the γ-ray reduction process. A mechanism correlating the interaction between hydrogen radicals formed upon γ-ray irradiation of hydrogen gas and the oxygen rich groups on the surface of the graphene oxide bucky-papers is proposed, in order to contribute to the synthesis of reduced graphene materials through solution-free chemistry routes. © 2014 Elsevier B.V.