Self-Assembled Three-Dimensional Hierarchical Graphene/Polypyrrole Nanotube Hybrid Aerogel and Its Application for Supercapacitors

A three-dimensional hierarchical graphene/polypyrrole aerogel (GPA) has been fabricated using graphene oxide (GO) and already synthesized one-dimensional hollow polypyrrole nanotubes (PNTs) as the feedstock. The amphiphilic GO is helpful in effectively promoting the dispersion of well-defined PNTs to result in a stable, homogeneous GO/PNT complex solution, while the PNTs not only provide a large accessible surface area for fast transport of hydrate ions but also act as spacers to prevent the restacking of graphene sheets. By a simple one-step reduction self-assembly process, hierarchically structured, low-density, highly compressible GPAs are easily obtained, which favorably combine the advantages of graphene and PNTs. The supercapacitor electrodes based on such materials exhibit excellent electrochemical performance, including a high specific capacitance up to 253 F g^–1, good rate performance, and outstanding cycle stability. Moreover, this method may be feasible to prepare other graphene-based hybrid aerogels with structure-controllable nanostructures in large scale, thereby holding enormous potential in many application fields

Low-Density, Mechanical Compressible, Water-Induced Self-Recoverable Graphene Aerogels for Water Treatment

Graphene aerogels (GAs) have demonstrated great promise in water treatment, acting as separation and sorbent materials, because of their high porosity, large surface area, and high hydrophobicity. In this work, we have fabricated a new series of compressible, lightweight (3.3 mg cm^–3) GAs through simple cross-linking of graphene oxide (GO) and poly­(vinyl alcohol) (PVA) with glutaraldehyde. It is found that the cross-linked GAs (xGAs) show an interesting water-induced self-recovery ability, which can recover to their original volume even under extremely high compression strain or after vacuum-/air drying. Importantly, the amphiphilicity of xGAs can be adjusted facilely by changing the feeding ratio of GO and PVA and it exhibits affinity from polar water to nonpolar organic liquids depended on its amphiphilicity. The hydrophobic xGAs with low feeding ratio of PVA and GO can be used as adsorbent for organic liquid, while the hydrophilic xGAs with high feeding ratio of PVA and GO can be used as the filter material to remove some water-soluble dye in the wastewater. Because of the convenience of our approach in adjusting the amphiphilicity by simply changing the PVA/GO ratio and excellent properties of the resulting xGAs, such as low density, compressive, and water-induced self-recovery, this work suggests a promising technique to prepare GAs-based materials for the water treatment in different environment with high recyclability and long life

Deposition of Three-Dimensional Graphene Aerogel on Nickel Foam as a Binder-Free Supercapacitor Electrode

We reported a new type of graphene aerogel–nickel foam (GA@NF) hybrid material prepared through a facile two-step approach and explored its energy storage application as a binder-free supercapacitor electrode. By simple freeze-drying and the subsequent thermal annealing of graphene oxide hydrogel–NF hybrid precursor, three-dimensional graphene aerogels with high mass, hierarchical porosity, and high conductivity were deposited on a NF framework. The resulting binder-free GA@NF electrode exhibited satisfactory double-layer capacitive behavior with high rate capability, good electrochemical cyclic stability, and a high specific capacitance of 366 F g^–1 at a current density of 2 A g^–1. The versatility of this approach was further verified by the successful preparation of 3D graphene/carbon nanotube hybrid aerogel–NF as a supercapacitor electrode, also with improved electrochemical performance. With advantageous features, such a facile and versatile fabrication technique shows great promise in the preparation of various types of carbon–metal hybrid electrodes

Flow-Induced Enhancement of in Situ Thermal Reduction of Graphene Oxide during the Melt-Processing of Polymer Nanocomposites

In situ thermal reduction (ISTR) of graphene oxide (GO) dispersed in a polymer matrix has attracted broad interest due to its great potential as an environmentally friendly and commercially viable process to prepare polymer/graphene nanocomposites (PGNs). In this work, the ISTR of GO in two dramatically different conditions, quiescent melt and sheared melt, was comparatively studied. Comprehensive characterization of the bulk composites and the extracted graphene-based powders from composites, as well as the results of an independent parallel plate experiment, revealed that the GO in the sheared melt has a higher reduction degree than that in the quiescent melt within identical processing temperatures and times. On the basis of our results, we hypothesize that the more intense reduction of GO in the sheared melts relative to the quiescent melts is associated with the enhanced π–π stacking and the possible radical reaction between polymers and GO sheets