Wet-Chemical Assembly of 2D Nanomaterials into Lightweight, Microtube-Shaped, and Macroscopic 3D Networks

Despite tremendous efforts toward fabrication of three-dimensional macrostructures of two-dimensional (2D) materials, the existing approaches still lack sufficient control over microscopic (morphology, porosity, pore size) and macroscopic (shape, size) properties of the resulting structures. In this work, a facile fabrication method for the wet-chemical assembly of carbon 2D nanomaterials into macroscopic networks of interconnected, hollow microtubes is introduced. As demonstrated for electrochemically exfoliated graphene, graphene oxide, and reduced graphene oxide, the approach allows for the preparation of highly porous (> 99.9%) and lightweight (<2 mg cm^-3) aeromaterials with tailored porosity and pore size as well as tailorable shape and size. The unique tubelike morphology with high aspect ratio enables ultralow-percolation-threshold graphene composites (0.03 S m^-1, 0.05 vol%) which even outperform most of the carbon nanotube-based composites, as well as highly conductive aeronetworks (8 S m^-1, 4 mg cm^-3). On top of that, long-term compression cycling of the aeronetworks demonstrates remarkable mechanical stability over 10 000 cycles, even though no chemical cross-linking is employed. The developed strategy could pave the way for fabrication of various macrostructures of 2D nanomaterials with defined shape, size, as well as micro- and nanostructure, crucial for numerous applications such as batteries, supercapacitors, and filters.

Recent advances in three-dimensional graphene based materials for catalysis applications

This review presents recent theoretical and experimental progress in the construction, properties, and catalytic applications of 3D graphene-based materials.

A three-dimensional graphene aerogel containing solvent-free polyaniline fluid for high performance supercapacitors

Conducting polymer based supercapacitors usually suffer from the difficulty of achieving high specific capacitance and good long-term stability simultaneously. In this communication, a long-chain protonic acid doped solvent-free self-suspended polyaniline (S-PANI) fluid and reduced graphene oxide (RGO) were used to fabricate a three-dimensional RGO/S-PANI aerogel via a simple self-assembled hydrothermal method, which was then applied as a supercapacitor electrode. This 3D RGO/S-PANI composite exhibited a high specific capacitance of up to 480 F g^-1 at a current density of 1 A g^-1 and 334 F g^-1 even at a high discharge rate of 40 A g^-1. An outstanding cycling performance, with 96.14% of the initial capacitance remaining after 10 000 charging/discharging cycles at a rate of 10 A g^-1, was also achieved. Compared with the conventional conducting polymer materials, the 3D RGO/S-PANI composite presented more reliable rate capability and cycling stability. Moreover, S-PANI possesses excellent processability, thereby revealing its enormous potential in large scale production. We anticipate that the solvent-free fluid technique is also applicable to the preparation of other 3D graphene/polymer materials for energy storage.

Facile synthesis of uniformly dispersed ZnO nanoparticles on a polystyrene/rGO matrix and its superior electrical conductivity and photocurrent generation

Herein, a ZnO/PS/rGO composite was prepared via a simple reflex method and its microstructural and physical properties were characterized using XRD, SEM, HRTEM, TGA, FTIR, UV-visible, PL spectroscopy, PCTR and OCVD measurements.

Functional Three-Dimensional Graphene/Polymer Composites

Integration of graphene with polymers to construct three-dimensional porous graphene/polymer composites (3DGPCs) has attracted considerable attention in the past few years for both fundamental studies and diverse technological applications. With the broad diversity in molecular structures of graphene and polymers via rich chemical routes, a number of 3DGPCs have been developed with unique structural, electrical, and mechanical properties, chemical tenability, and attractive functions, which greatly expands the research horizon of graphene-based composites. In particular, the properties and functions of the 3DGPCs can be readily tuned by precisely controlling the hierarchical porosity in the 3D graphene architecture as well as the intricate synergistic interactions between graphene and polymers. In this paper, we review the recent progress in 3DGPCs, including their synthetic strategies and potential applications in environmental protection, energy storage, sensors, and conducting composites. Lastly, we will conclude with a brief perspective on the challenges and future opportunities.

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.

Three-dimensional macro-structures of two-dimensional nanomaterials

This review summarizes the recent progress and efforts in the synthesis, structure, properties, and applications of three-dimensional macro-structures of two-dimensional nanomaterials.

A novel & effective visible light-driven TiO2/magnetic porous graphene oxide nanocomposite for the degradation of dye pollutants

A novel & effective visible light-driven TiO₂/magnetic porous graphene oxide nanocomposite synthesized and the nanocatalyst was applied for degrading dye pollutant.

Three-dimensional graphene-based composites for energy applications

Three-dimensional (3D) graphene-based composites have drawn increasing attention for energy applications due to their unique structures and properties. By combining the merits of 3D graphene (3DG), e.g., a porous and interconnected network, a high electrical conductivity, a large accessible surface area, and excellent mechanical strength and thermal stability, with the high chemical/electrochemical activities of active materials, 3DG-based composites show great promise as high-performance electrode materials in various energy devices. This article reviews recent progress in 3DG-based composites and their applications in energy storage/conversion devices, i.e., supercapacitors, lithium-ion batteries, dye-sensitized solar cells, and fuel cells.

The preparation and catalytic performance of graphene-reinforced ion-exchange resins

The structural and thermal stability of graphene-based polymer nanocomposites were improved with chemical bonded interaction of graphene within the polymer networks.

Porous graphene materials for advanced electrochemical energy storage and conversion devices

Combining the advantages from both porous materials and graphene, porous graphene materials have attracted vast interests due to their large surface areas, unique porous structures, diversified compositions and excellent electronic conductivity. These unordinary features enable porous graphene materials to serve as key components in high-performance electrochemical energy storage and conversion devices such as lithium ion batteries, supercapacitors, and fuel cells. This progress report summarizes the typical fabrication methods for porous graphene materials with micro-, meso-, and macro-porous structures. The structure-property relationships of these materials and their application in advanced electrochemical devices are also discussed.

Electrochemically fabricated flower-like graphene as a highly efficient Pt electrocatalyst support for methanol oxidation

Flower-like graphene (f-RGO) with a porous structure was firstly fabricated by an electrochemical method, showing high catalytic activity toward methanol oxidation.

Significantly reduced thermal diffusivity of free-standing two-layer graphene in graphene foam

We report on a thermal diffusivity study of suspended graphene foam (GF) using the transient electro-thermal technique. Our Raman study confirms the GF is composed of two-layer graphene. By measuring GF of different lengths, we are able to exclude the radiation effect. Using Schuetz's model, the intrinsic thermal diffusivity of the free-standing two-layer graphene is determined with a high accuracy without using knowledge of the porosity of the GF. The intrinsic thermal diffusivity of the two-layer graphene is determined at 1.16-2.22 × 10(-4) m(2) s(-1). The corresponding intrinsic thermal conductivity is 182-349 W m(-1) K(-1), about one order of magnitude lower than those reported for single-layer graphene. Extensive surface impurity defects, wrinkles and rough edges are observed under a scanning electron microscope for the studied GF. These structural defects induce substantial phonon scattering and explain the observed significant thermal conductivity reduction. Our thermal diffusivity characterization of GF provides an advanced way to look into the thermal transport capacity of free-standing graphene with high accuracy and ease of experimental implementation.

Macroporous graphene oxide-polymer composite prepared through pickering high internal phase emulsions

Macroporous polymer-graphene oxide (GO) composites were successfully prepared using Pickering high internal phase emulsion (HIPE) templates. GO flakes were modified by the cationic surfactant cetyltrimethylammonium bromide (CTAB) and used as the stabilizer of water-in-oil (W/O) Pickering emulsions. CTAB-modified GO is effective at stabilizing W/O Pickering HIPEs, and the lowest GO content is only about 0.2 mg mL(-1) (relative to the volume of the oil phase). The close-cell morphology of the resulting poly-Pickering HIPEs is observed, and the void size of the porous polymers is tuned by varying the concentration of GO. Three-dimensional macroporous chemically modified graphene (CMG) monoliths with a high specific surface area of about 490 m(2) g(-1) were obtained after removing the cellular polymer substrates through calcination. The micropores were also found in CMGs, which may be caused by the decomposition of CTAB adsorbed on the surface of GO.

Excellent catalytic effects of highly crumpled graphene nanosheets on hydrogenation/dehydrogenation of magnesium hydride

Highly crumpled graphene nanosheets (GNS) with a BET surface area as high as 1159 m(2) g(-1) was fabricated by a thermal exfoliation method. A systematic investigation was performed on the hydrogen sorption properties of MgH(2)-5 wt% GNS nanocomposites acquired by ball-milling. It was found that the as-synthesized GNS exhibited a superior catalytic effect on hydrogenation/dehydrogenation of MgH(2). Differential Scanning Calorimetry (DSC) and isothermal hydrogenation/dehydrogenation measurements indicated that both hydrogen sorption capacity and dehydrogenation/hydrogenation kinetics of the composites improved with increasing milling time. The composites MgH(2)-GNS milled for 20 h can absorb 6.6 wt% H(2) within 1 min at 300 °C and 6.3 wt% within 40 min at 200 °C, even at 150 °C, it can also absorb 6.0 wt% H(2) within 180 min. It was also demonstrated that MgH(2)-GNS-20 h could release 6.1 wt% H(2) at 300 °C within 40 min. In addition, microstructure measurements based on XRD, SEM, TEM as well as Raman spectra revealed that the grain size of thus-prepared MgH(2)-GNS nanocomposites decreased with increasing milling time, moreover, the graphene layers were broken into smaller graphene nanosheets in a disordered and irregular manner during milling. It was confirmed that these smaller graphene nanosheets on the composite surface, providing more edge sites and hydrogen diffusion channels, prevented the nanograins from sintering and agglomerating, thus, leading to promotion of the hydrogenation/dehydrogenation kinetics of MgH(2).

Functional nanoporous graphene foams with controlled pore sizes

A simple hydrophobic-affinity-derived assembly approach to pack graphene sheets into a nanoporous foam structure has been developed. Nanoporous graphene foams with the highest pore volume and large surface area are obtained. The pore diameter of the graphene foams can be finely adjusted from the mesopore to the macropore range by employing spherical templates with different sizes.