Xusheng Du

Non-covalently modified graphene sheets by imidazolium ionic liquids for multifunctional polymer nanocomposites

Chemical reduction of graphite oxide (GO) to produce graphene nanosheets often results in irreversible agglomeration and precipitation. Herein, stable well-dispersed graphene sheets in solvents were obtained by simultaneous functionalization and reduction of GO under alkaline conditions, in the presence of sodium borohydride and imidazolium ionic liquids (Imi-ILs) containing two vinyl-benzyl groups. In this case, positively charged imidazolium groups of Imi-ILs underwent ion-exchange with negatively charged GO sheets and were linked to their edges, while Imi-ILs were non-covalently attached onto the large surfaces of graphene through π–π and/or cation–π stacking interactions. The vinyl-benzyl reactive sites were then copolymerized in situ with methyl methacrylate to fabricate graphene/poly(methyl methacrylate) (PMMA) composites. Functionalized graphene sheets were uniformly dispersed in the PMMA matrix and contributed to large increases in storage modulus (+58.3%) and glass transition temperature (+19.2 °C) at 2.08 vol.% loading. High electrical conductivity was also achieved at graphene loading levels beyond 1 vol.% (ca. 2.55 Sm−1) with a low percolation threshold (0.25 vol.%) for the composites. Hence, a general methodology which facilitates the development of a multifunctional advanced material has been successfully established. This can be extended to other vinyl polymer-based composites containing graphene.

Ultrafast Synthesis of Multifunctional N-Doped Graphene Foam in an Ethanol Flame

A hard template method to prepare N-doped graphene foams (NGF) with superfast template removal was developed through a pyrolyzing commercial polyurethane (PU) sponge coated with graphene oxide (GO) sheets in an ethanol flame. The removal of the template was fast and facile, and could be completed in less than 60 s in an open environment. The synthesized graphene foams consisted of a unique structure of 3D interconnected hollow struts with highly wrinkled surfaces, and the morphology of the hollow struts could be tuned by controlling the GO dispersion concentration. The foams showed high hydrophobicity and were used as absorbents for a variety of organic solvents and oils. The unique NGF structure afforded a high absorption rate and capacity, and a remarkable 98.7% pore volume of the foam could be utilized for absorption of hexane, exhibiting one of the highest capacity values among existing absorptive counterparts. The N-doping brought higher capacitive performance than conventional graphene foams prepared by chemical vapor deposition on nickel foam templates. The NGFs also displayed high elasticity and could recover completely after 50% compressive strain. Owing to easy availability and reduction environment of the flame, complete thermal decomposition of the PU sponge and highly porous open-cell structure, and flame resistance of the graphene foam, the present flame method was demonstrated to be a simple, effective, and ultrafast approach to fabricate ultra-low-density NGFs with good electromechanical response, excellent organic liquid absorption, and high-energy dissipation capabilities.

Hollow nitrogen-containing core/shell fibrous carbon nanomaterials as support to platinum nanocatalysts and their TEM tomography study.

Core/shell nanostructured carbon materials with carbon nanofiber (CNF) as the core and a nitrogen (N)-doped graphitic layer as the shell were synthesized by pyrolysis of CNF/polyaniline (CNF/PANI) composites prepared by in situ polymerization of aniline on CNFs. High-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared and Raman analyses indicated that the PANI shell was carbonized at 900°C. Platinum (Pt) nanoparticles were reduced by formic acid with catalyst supports. Compared to the untreated CNF/PANI composites, the carbonized composites were proven to be better supporting materials for the Pt nanocatalysts and showed superior performance as catalyst supports for methanol electrochemical oxidation. The current density of methanol oxidation on the catalyst with the core/shell nanostructured carbon materials is approximately seven times of that on the catalyst with CNF/PANI support. TEM tomography revealed that some Pt nanoparticles were embedded in the PANI shells of the CNF/PANI composites, which might decrease the electrocatalyst activity. TEM-energy dispersive spectroscopy mapping confirmed that the Pt nanoparticles in the inner tube of N-doped hollow CNFs could be accessed by the Nafion ionomer electrolyte, contributing to the catalytic oxidation of methanol.

Synthesis of poly(arylene disulfide)-vermiculite nanocomposites via in situ ring-opening reaction of cyclic oligomers

Abstract An exfoliated poly(4,4′-oxybis(benzene)disulfide) (POBDS)/vermiculite (VMT) nanocomposite was prepared by using cyclo(4,4′-oxybis(benzene)disulfide) (COBDS) oligomers and cetyltrimethyl ammonium bromide exchanged VMT. The POBDS/VMT nanocomposites were fabricated in two steps. First, the COBDS oligomers were used to swell and exfoliate organo VMT to afford COBDS–VMT nanocomposite precursor. Subsequently, the exfoliated POBDS–VMT nanocomposite can be made via in situ and instant melt ring-opening polymerization of the COBDS–VMT nanocomposite precursor. High molecular weight POBDS polymer can be formed in a few minutes. The nano scale dispersion of VMT layers within POBDS polymer was confirmed by both the X-ray diffraction patterns and TEM examinations. This methodology provides a potential approach to synthesize high performance polymer nanocomposite.

Improving the electrical conductivity and interface properties of carbon fiber/epoxy composites by low temperature flame growth of carbon nanotubes

Carbon nanotubes (CNTs) were grown in situ on carbon fibers (CFs) at low temperature (∼450 °C) in an ethanol combustion flame to develop multifunctional hierarchical reinforcements for epoxy resin matrices. Because of the low temperature, short duration and reducing atmosphere used in the flame growth process, there was no evident decrease of the tensile strength of the CFs. However, both the electrical conductivity and interfacial properties of the CFs were improved significantly after the CNTs were grown for only 3 minutes, resulting in >170% increase in in-plane electrical conductivity and ∼70% improvement in interfacial shear strength of the carbon fiber/epoxy composites. Electron microscopy studies revealed that both tip and root growth mechanisms were involved during the flame-induced synthesis. A good interfacial bonding strength between the CNTs and CFs was observed and could be attributed to the diffusion of metal catalyst particles into the CF surface and/or the carbon bonding between CNTs and CFs. Substantial improvements in electrical conductivity and interfacial properties without compromising the tensile strength of CFs after the flame growth of CNTs confirmed the efficiency and effectiveness of this method.

Use of facile mechanochemical method to functionalize carbon nanofibers with nanostructured polyaniline and their electrochemical capacitance

A facile approach to functionalize carbon nanofibers [CNFs] with nanostructured polyaniline was developed via in situ mechanochemical polymerization of polyaniline in the presence of chemically treated CNFs. The nanostructured polyaniline grafting on the CNF was mainly in a form of branched nanofibers as well as rough nanolayers. The good dispersibility and processability of the hybrid nanocomposite could be attributed to its overall nanostructure which enhanced its accessibility to the electrolyte. The mechanochemical oxidation polymerization was believed to be related to the strong Lewis acid characteristic of FeCl3 and the Lewis base characteristic of aniline. The growth mechanism of the hierarchical structured nanofibers was also discussed. After functionalization with the nanostructured polyaniline, the hybrid polyaniline/CNF composite showed an enhanced specific capacitance, which might be related to its hierarchical nanostructure and the interaction between the aromatic polyaniline molecules and the CNFs.

Preparation of NBR/Expanded Graphite Nanocomposites by Simple Mixing

Nanocomposites of acrylonitrile-butadiene rubber (NBR) and expanded graphite (EG) were synthesised by melt mixing. Before being mixed with the NBR, the expanded graphite was first sonicated for 10 h, and the powders obtained were then grounding in a ball mill for another 10 h. Scanning electron microscopy (SEM) of the sonicated graphite layers revealed that the expanded graphite was completely torn into nanoscale sheets. Transmission electron microscopy (TEM) of the NBR/EG composites indicated nanoscale dispersion of the EG within the NBR matrix. The mechanical properties of the NBR/EG nanocomposites showed a remarkable improvement in tensile strength. Dynamic mechanical analysis (DMA) showed that the EG imparted a higher storage modulus and lower glass transition temperature to the NBR matrix. The expanded graphite was effective in increasing the electrical conductivity of the composites.

Enhancement of the catalytic performance of a CNT supported Pt nanorod cluster catalyst by controlling their microstructure

A novel Pt/CNT catalyst with a hierarchical structure was prepared. The effect of different morphologies of CNT supports on the catalyst microstructure and catalytic performance was studied. TEM tomography was used to analyse the real microstructure of the catalysts, including both the morphology of flower-like Pt clusters themselves and their distribution on the CNTs. The results revealed that Pt flowers were composed of nanorods, which dispersed in both the inner and outer tube surface of CNTs with larger inner tube diameter (TKCNTs). Comparing with the conventional Pt/CNT catalyst where Pt flowers only dispersed on the outer tube surface, the present Pt/TKCNT catalyst with the novel structure exhibited higher activity (enhanced to be ∼1.5 times higher current density) and better catalytic stability for methanol oxidation. Moreover, it displays ∼2 times higher activity for methanol electro-oxidation than that of CB supported Pt nanorod clusters. The results indicate that the catalytic performance of the Pt nanorods supported on different carbon supports depends on both carbon morphology and the distribution of the metal catalyst on the supports. The improved catalytic performance of the Pt/TKCNT catalyst with the novel hierarchical structure could be attributed to the confinement effect of TKCNTs.