Close-celled aromatic polyimide (PI)/graphene foams with low density and improved flexibility were fabricated by thermal foaming of poly(amic ester)/graphene oxide (PAE/GO) precursor powders. The PAE/GO precursor powders were prepared by grafting GO nanosheets with PAE chains, which led to efficient dispersion of the GO nanosheets in PAE matrix. Incorporation of GO resulted in an enhanced foaming capability of the precursor, i.e. enlarged cell size and decreased foam density.Notably, a decrease of 50% in the foam density was obtained by addition of only 2 wt% GO in the precursor. In the foaming process, the GO nanosheets functioned as a versatile agent that not only provided heterogeneous nucleation sites but also produced gaseous molecules. By analyzing the foaming mechanism, the excellent features of GO in heat transfer, gas barrier, and strength reinforcement also facilitated to obtain large and uniform cells in the foams. In addition, the PI/graphene foams exhibited a prominent flexibility and enhanced flexural strength, as an elastic-to-nonelastic conversion of the initial stage of the compressive stress-strain curves was observed by increasing the content of graphene in the PI matrix and an increase of 22.5% in flexural strength was obtained by
Surface functionalization of graphene oxide (GO) sheets using polymers has emerged as a subject of enormous scientific interest due to the wide applications of GO in polymer composites and functional graphene-based materials. In this study, we grafted GO sheets with polystyrene (PS) and poly(styrene−isoprene) (PSI) using GO itself as a cationic initiator for homopolymerization of styrene and copolymerization of styrene and isoprene. The resultant GOg-PS and GO-g-PSI composites displayed enhanced dispersibility in common organic solvents. With increasing the loading of isoprene in the copolymerization reaction, the glass transition temperature of the obtained products gradually decreased, combining the increased roughness of the GO-g-PSI sheets compared with the GO-g-PS sheets, which indicated the increased phase separation between the PS and PI segments in the PSI layer. Therefore, the packing of the GO-g-PS sheets, as well as the GO-g-PSI sheets, was not as compact as that of the GO sheets, leaving gradually increased quantity of pores in the films prepared with GO-g-PS and GO-g-PSI. Capitalizing on these tunable characters, hybridized membranes prepared by depositing GO sheets, GO-g-PS sheets, and the GO-g-PSI sheets obtained with gradually increased loading of isoprene in the copolymerization on the surfaces of commercially available polytetrafluoroethylene membranes displayed gradually increased gas permeability.
The morphologies of transition metal oxides have decisive impact on the performance of their applications. Here, we report a new and facile strategy for in situ preparation of anatase TiO2 nanospindles in three-dimensional reduced graphene oxide (RGO) structure (3D TiO2@RGO) using cellulose as both an intermediate agent eliminating the negative effect of graphene oxide (GO) on the growth of TiO2 crystals and as a structure-directing agent for the shape-controlled synthesis of TiO2 crystals. High-resolution transmission electron microscopy and X-ray diffractometer analysis indicated that the spindle shape of TiO2 crystals was formed through the restriction of the growth of high energy {010} facets due to preferential adsorption of cellulose on these facets. Because of the 3D structure of the composite, the large aspect ratio of the TiO2 nanospindles, and the exposed high-energy {010} facets of the TiO2 crystals, the 3D TiO2@RGO(Ce 1.7) exhibited excellent capacitive performance as an electrode material for supercapacitors, with a high specific capacitance (ca. 397 F g(-1)), a high energy density (55.7 Wh kg(-1)), and a high power density (1327 W kg(-1)) on the basis of the masses of RGO and TiO2. These levels of capacitive performance far exceed those of previously reported TiO2-based composites.
Fabrication of hybridized structures is an effective strategy to promote the performances of graphene-based composites for energy storage/conversion applications. In this work, macroporous structured graphene thin films (MGTFs) are fabricated on various substrates including flexible graphene papers (GPs) through an ice-crystal-induced phase separation process. The MGTFs prepared on GPs (MGTF@GPs) are recognized with remarkable features such as interconnected macroporous configuration, sufficient exfoliation of the conductive RGO sheets, and good mechanical flexibility. As such, the flexible MGTF@GPs are demonstrated as a versatile conductive platform for depositing conducting polymers (CPs), e.g., polyaniline (PAn), polypyrrole, and polythiophene, through in situ electropolymerization. The contents of the CPs in the composite films are readily controlled by varying the electropolymerization time. Notably, electrodeposition of PAn leads to the formation of nanostructures of PAn nanofibers on the walls of the macroporous structured RGO framework (PAn@MGTF@GPs): thereafter, the PAn@MGTF@GPs display a unique structural feature that combine the nanostructures of PAn nanofibers and the macroporous structures of RGO sheets. Being used as binder-free electrodes for flexible supercapacitors, the PAn@MGTF@GPs exhibit excellent electrochemical performance, in particular a high areal specific capacity (538 mF cm(-2)), high cycling stability, and remarkable capacitive stability to deformation, due to the unique electrode structures.
4334 wileyonlinelibrary.com strength, [ 2 ] and prominent optical and electrochemical properties. [ 3 ] However, the macroscopic properties of graphene materials are determined by the assembled structures of graphene sheets. So far, various types of graphene-assembled structures have been developed, including graphene fi bers, [ 4 ] 2D compact constructs including graphene papers and fi lms, [ 5 ] and 3D porous graphene scaffolds such as monoliths [ 6 ] and beads. [ 7 ] 2D compact graphene thin fi lms (CGTFs) can be prepared by chemical vapor deposition (CVD), [ 8 ] vacuum fi ltration, [ 5a,b ] Langmuir-Blodgett method, [ 5c ] spin coating, [ 9 ] and layer-by-layer assembly, [ 10 ] and they have been demonstrated potential applications in photo response and chemical/biological sensors, [ 10,11 ] as well as transparent electrodes for fl exible electronic and optoelectronic devices. [ 5b , 12 ] 3D porous graph ene structures can be prepared by hard template-assisted CVD, [ 6a ] hydrothermal approach, [ 13 ] freeze-drying method, [ 6b ] and functional polymer-assisted assembly. [ 7,14 ] And such 3D graphene structures have been widely used in electromagnetic interference shielding, catalyst carriers, and energy storage and conversion. [13][14][15] As a new assembly structure of graphene, transparent macroporous graphene thin fi lms (MGTFs) that combine the features of the 2D graphene fi lms (being micrometers thick and transparent) and the 3D porous monoliths (having macroporous structure and large specifi c surface area) are destined to be promising as porous electrode materials for applications such as optoelectronics, photo/photoelectrochemical catalysis, energy storage/conversion devices, and chemical/biological sensing, where the specifi c surface area and/or the transparency play important roles in determining the performance of electrodes. [ 16 ] However, preparation of such transparent MGTFs is challengeable due to both scientifi c and technical limitations: the π-π stacking and van der Waals force interactions between the basal planes of graphene sheets result in irreversible aggregation and restacking of the graphene sheets during processing. Recently, strategies, including nucleate boiling, [ 17 ] breath fi gure, [ 18 ] and electrochemical deposition of graphene oxide (GO), [ 15e ] were proposed to assemble graphene sheets into macroporous thin fi lms. However, the walls in the macroporous structures prepared by these methods were thick due to the restacking of GO Controllable Fabrication of Transparent Macroporous Graphene Thin Films and Versatile Applications as a Conducting PlatformJinhua Sun , Mushtaque A. Memon , Wei Bai , Linhong Xiao , Bin Zhang , Yongdong Jin , Yong Huang , and Jianxin Geng * Graphene sheets have been demonstrated to be the building blocks for various assembly structures, which eventually determine the macroscopic properties of graphene materials. As a new assembly structure, transparent macroporous graphene thin fi lms (MGTFs) are not readily prepared due to the...
The melt recrystallization of vacuum carbon evaporated melt-drawn iPP thin films at varying melting temperature, melting time and recrystallization temperature was studied by means of transmission electron microscopy combined with electron diffraction.
A macroporous graphene thin films coated on ITO substrates (MGTFs@ITO) have been developed as electrodes for the electrochemical detection of heavy metal ions. The MGTF@ITO electrodes were characterized by scanning electron microscopy, Raman spectroscopy and contact angle measurements. The results demonstrated that the MGTF@ITO has a high specific area with robust macroporous framework and a hydrophilic surface. The cyclic voltammetry and electrochemical impedance spectroscopy using MGTFs@ITO as electrochemical electrodes indicated enhanced currents at the redox peaks, enlarged electrochemical surface area and a decreased charge transfer resistance. Based on these outstanding properties, the MGTF@ITO electrodes exhibited excellent stripping performace for the analysis of Ag(I) with a detection limit of 0.005 μg L-1. The high sensitivity of the MGTF@ITO electrodes can be ascribed to the well defined macroporous framework, high electrical conductivity, high specific area and good wettability. The MGTF@ITO electrodes were further demonstrated applicable to the simultaneous determination of Zn(II), Cd(II), Pb(II), Cu(II) and Ag(I) ions with outstanding sensing performance.
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