Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

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Graphene-based composites

Graphene based materials: Past, present and future

Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

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Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

Three-dimensional (3D) N-doped graphene aerogel (N-GA)-supported Fe3O4 nanoparticles (Fe3O4/N-GAs) as efficient cathode catalysts for the oxygen reduction reaction (ORR) are reported. The graphene hybrids exhibit an interconnected macroporous framework of graphene sheets with uniform dispersion of Fe3O4 nanoparticles (NPs). In studying the effects of the carbon support on the Fe3O4 NPs for the ORR, we found that Fe3O4/N-GAs show a more positive onset potential, higher cathodic density, lower H2O2 yield, and higher electron transfer number for the ORR in alkaline media than Fe3O4 NPs supported on N-doped carbon black or N-doped graphene sheets, highlighting the importance of the 3D macropores and high specific surface area of the GA support for improving the ORR performance. Furthermore, Fe3O4/N-GAs show better durability than the commercial Pt/C catalyst.

3D Nitrogen-Doped Graphene Aerogel-Supported Fe3O4 Nanoparticles as Efficient Electrocatalysts for the Oxygen Reduction Reaction

Photodynamic therapy (PDT) combining with near infrared (NIR) imaging is attractive. However, the intrinsic hypoxia in tumor and consumption of oxygen during treatment will decrease PDT. Here an artificial red cell was prepared using polypeptides conjugated hemoglobin as an oxygen carrier. A NIR photosensitizer-brominated 4,4-difluoro-4-bora-3a,a-diaza-s-indacene (BODIPY-Br2) possessing both high fluorescence emission and singlet oxygen generation efficiency was synthesized and also conjugated to polypeptides to achieve NIR imaging-guided PDT. In vitro studies performed on HepG2 cancer cells verified the oxygen carrier, cancer tracing and curing abilities of the as-prepared polymeric nanoparticles. Even under hypoxia condition, it also obviously increases the cell killing rate when exposed light at a low energy (25 mW/cm2, 10 min). Meanwhile, the fluorescence of BODIPY in NPs would light up cells for real-time imaging. These results show the potential of the biocompatible and biodegradable P-Hb-B NPs for enhancement of simultaneous tracing and treating of cancer.

Polypeptide-based artificial erythrocytes conjugated with near infrared photosensitizers for imaging-guided photodynamic therapy

Cellulose samples with molecular weights ranging from 8.39 × 104 to 11.00 × 104 g/mol were obtained from wheat straw. The dewaxed wheat straw was pretreated with aqueous hydrochloric acid followed by delignification using an environmentally benign poly (ethyleneglycol)/salt aqueous biphasic system. The yield of cellulose was in the range of 48.9%–55.5% and the cellulose contained 1.2%–3.2% hemicelluloses, and 0.97%–3.47% lignin. All the isolated cellulose samples could be directly dissolved in a 6 wt-% NaOH/4 wt-% urea aqueous solution through a precooling-thawing process to form a homogenous solution. The separation process was investigated and the obtained cellulose and its solution were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray apparatus, and X-ray diffraction. The results revealed that aqueous soluble cellulose can be directly prepared from wheat straw by this method and this study opens a novel pathway to prepare cellulosic materials from agricultural waste.

Isolation of highly purity cellulose from wheat straw using a modified aqueous biphasic system

Furfural is an alternative feedstock and has been used for the production of maleic acid (MA) and fumaric acid (FA) by an oxidation process. Deep eutectic solvents (DESs) were used as the green solvents while sodium chlorate was used as an oxidant and vanadium pentoxide was used as the catalyst at 70–90 ℃ under atmospheric pressure. It was found that several acidic DESs are valid, such as acetic acid/choline chloride (AA/ChCl) and propionic acid/choline chloride (PA/ChCl), and AA/ChCl DES was selected as the solvent for the conversion. The optimal DES is AA/ChCl, and the effect of the amount of oxidant, time, and temperature on the yield of the MA and FA has been systematically studied, and the conversion of furfural can reach 100% while the yield of the MA and FA reached 66.5% under reaction temperature of 80 ℃ for 12 h, which provides a new green route to synthesis valuable monomers from furfural.

Oxidation of Furfural to Maleic Acid and Fumaric Acid in Deep Eutectic Solvent (DES) under Vanadium Pentoxide Catalysis

The aqueous zinc-ion hybrid supercapacitor (ZHSC) is a prospective energy storage device for next-generation wearable electronics due to its high safety, low cost, and high energy density. However, the preparation of gel electrolytes reported in the literature is complex and time-consuming, which limits their application in practice. Herein, we developed a robust and stretchable eutectogel electrolyte through a one-step gelation process in situ without introducing additional initiators and cross-linkers. The eutectogel electrolyte consists of ternary deep eutectic solvent (DES) based on Zn(ClO4)2, AM(acrylamide), and H2O, among which ClO4– triggers the free-radical polymerization of AM monomer and Zn2+ cross-links the polymer chains. The prepared Zn-PAM-1 gel exhibits a high ionic conductivity of 51.7 mS cm–1. Due to the inhibition of the free water activity in DES, the voltage window of the constructed flexible ZHSC was extended to 0–2.2 V. Moreover, the ZHSC in situ formed manifests a maximum energy density of 117.5 W h kg–1 at a power density of 833.8 W kg–1 and shows admirable cycling stability, retaining 87.6% of its capacitance after 4000 cycles. In addition, the supercapacitor possesses remarkable temperature stability within a range of −20 to 70 °C. Furthermore, the assembled flexible device illustrates favorable bendability from 0° to 180° without scarifying capacitance, displaying great promise as flexible wearable electronic devices. In summary, such a feasible approach provides further insight into the exploration of innovative eutectogel electrolyte systems for assembling quasi-solid-state pliable high energy storing devices. 

Ultrahigh Conductive and Stretchable Eutectogel Electrolyte for High-Voltage Flexible Antifreeze Quasi-solid-state Zinc-Ion Hybrid Supercapacitor

A poly(styrene-co-acrylic acid) copolymer was synthesized by surfactant-free polymerization with the assistance of power ultrasound in water. Fourier transform infrared, NMR, and differential scanning calorimetry mea- surements revealed that the copolymer was random. Atomic force microscopy and laser light scattering were used to investigate the self-assembly of the copolymer, and it was found that the copolymer chains formed micelles or other self-assemble structures in solution. Atomic force micros- copy also indicated that the self-assembled structures devel- oped into nanospheres with a poly(acrylic acid)-rich or poly- styrene-rich surface in a film, depending on the solvent used for the preparation of the film. In particular, a wheel-like structure could resulted in a film when the copolymer film was prepared in a moist environment; it resulted from het- erogeneous aggregates of poly(acrylic acid) at the rim of water bubbles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3718 -3726, 2006

Lifeng Yan

Papers

Polypeptide-based artificial erythrocytes conjugated with near infrared photosensitizers for imaging-guided photodynamic therapy

Isolation of highly purity cellulose from wheat straw using a modified aqueous biphasic system

Oxidation of Furfural to Maleic Acid and Fumaric Acid in Deep Eutectic Solvent (DES) under Vanadium Pentoxide Catalysis

Ultrahigh Conductive and Stretchable Eutectogel Electrolyte for High-Voltage Flexible Antifreeze Quasi-solid-state Zinc-Ion Hybrid Supercapacitor

Emulsifier-Free Synthesis and Self-Assembly of an Amphiphilic Poly(styrene-co-acrylic acid) Copolymer