Graphene oxide as a carbon source for controlled growth of carbon nanowires

Facile preparation of covalently functionalized graphene with 2,4-dinitrophenylhydrazine and investigation of its characteristics

This article reports a fast and easy method for simultaneously in situ reducing and functionalizing graphene oxide. 2,4-Dinitrophenylhydrazine hydrate salt molecules are reduced by graphene oxide by reacting with oxide groups on the surface and removing these groups, and 2,4-dinitrophenylhydrazone groups are replaced with oxide groups. The synthesized materials have been investigated using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and UV absorption. Also, the morphology has been examined with a scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) analysis. The result of the photocurrent response and electrochemical behavior of the samples through cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy (EIS) have been analyzed to investigate the effect of physical and chemical changes compared to graphene.

Facile synthesis of carbon nanobranches towards cobalt ion sensing and high-performance micro-supercapacitors

We present a facile strategy for fabricating a new type of one-dimensional (1D) carbon nanomaterial named carbon nanobranches (CNBs) covered with botryoidal carbon dots (CDs) by direct pyrolysis of a green precursor (starch). The resultant CNBs display both photoluminescence and electrical conductivity and can be assembled into chemical sensors and energy-storage devices. In terms of their bright photoluminescence, CNBs with a fabulous crystalline structure are utilized as fluorescent probes to sensitively and selectively detect Co²⁺ with a very low detection limit of 2.85 nM and a wide linear concentration range from 10 nM to 1 mM. Moreover, an efficient micro-supercapacitor (micro-SC) is constructed based on conductive CNB fibers produced via a customized microfluidic spinning technique. The micro-SCs exhibit a large specific capacitance of 201.4 mF cm^-2, an energy density of 4.5 μW h cm^-2 and high cycling stability, and can successfully power 19 light-emitting diodes (LEDs). The main purpose of this paper is to offer a perspective into simplifying the connecting of research and industry by starting from green carbon-based materials.

Graphene oxide/nanometal composite membranes for nanofiltration: synthesis, mass transport mechanism, and applications

We reviewed the recent developments in graphene-based composite membranes and discussed their challenges in this paper.

S-Doped TiSe2 Nanoplates/Fe3 O4 Nanoparticles Heterostructure

2D Sulfur-doped TiSe₂ /Fe₃ O₄ (named as S-TiSe₂ /Fe₃ O₄ ) heterostructures are synthesized successfully based on a facile oil phase process. The Fe₃ O₄ nanoparticles, with an average size of 8 nm, grow uniformly on the surface of S-doped TiSe₂ (named as S-TiSe₂ ) nanoplates (300 nm in diameter and 15 nm in thickness). These heterostructures combine the advantages of both S-TiSe₂ with good electrical conductivity and Fe₃ O₄ with high theoretical Li storage capacity. As demonstrated potential applications for energy storage, the S-TiSe₂ /Fe₃ O₄ heterostructures possess high reversible capacities (707.4 mAh g^-1 at 0.1 A g^-1 during the 100th cycle), excellent cycling stability (432.3 mAh g^-1 after 200 cycles at 5 A g^-1 ), and good rate capability (e.g., 301.7 mAh g^-1 at 20 A g^-1 ) in lithium-ion batteries. As for sodium-ion batteries, the S-TiSe₂ /Fe₃ O₄ heterostructures also maintain reversible capacities of 402.3 mAh g^-1 at 0.1 A g^-1 after 100 cycles, and a high rate capacity of 203.3 mAh g^-1 at 4 A g^-1 .

Acid-free and oxone oxidant-assisted solvothermal synthesis of graphene quantum dots using various natural carbon materials as resources

To prepare carbon-based fluorescent materials such as graphene quantum dots (GQDs), new and effective methods are needed to convert one-dimensional (1D) or two-dimensional (2D) carbon materials to 0D GQDs. Here, we report a novel acid-free and oxone oxidant-assisted solvothermal synthesis of GQDs using various natural carbon resources including graphite (G), multiwall carbon nanotubes (M), carbon fibers (CF), and charcoal (C). This acid-free method, not requiring the neutralization process of strong acids, exhibits a simple and eco-friendly purification process and also represents a recycling production process, together with mass production and high yield. Newly synthesized GQDs exhibited a strong blue photoluminescence (PL) under 365 nm UV light illumination. The PL emission peaks of all the recycled GQDs did not change.

Dense arrays of highly aligned graphene nanoribbons produced by substrate-controlled metal-assisted etching of graphene

Dense arrays of aligned graphene nanoribbons (GNRs) are fabricated by substrate-controlled etching of large-area single-layer graphene. An adequate choice of etching substrate and catalyst deposition method allows densities up to 25 nanoribbons μm(-1) to be obtained with average widths of 19 nm. The efficacy of the method is evidenced by the high on/off ratios of back-gated transistors made with these GNRs, which can go up to 5000.

Preparation of MoS2-coated three-dimensional graphene networks for high-performance anode material in lithium-ion batteries

A novel composite, MoS2 -coated three-dimensional graphene network (3DGN), referred to as MoS2 /3DGN, is synthesized by a facile CVD method. The 3DGN, composed of interconnected graphene sheets, not only serves as template for the deposition of MoS2 , but also provides good electrical contact between the current collector and deposited MoS2 . As a proof of concept, the MoS2 /3DGN composite, used as an anode material for lithium-ion batteries, shows excellent electrochemical performance, which exhibits reversible capacities of 877 and 665 mAh g(-1) during the 50(th) cycle at current densities of 100 and 500 mA g(-1) , respectively, indicating its good cycling performance. Furthermore, the MoS2 /3DGN composite also shows excellent high-current-density performance, e.g., depicts a 10(th) -cycle capacity of 466 mAh g(-1) at a high current density of 4 A g(-1).

Three-dimensional graphene network composites for detection of hydrogen peroxide

A three-dimensional graphene network (3DGN) prepared by CVD is used as a template to synthesize various composites. These composites are further used as electrodes for electrochemical sensors, which exhibit a low detection limit, quick response time, and wide linear range toward the detection of H2O2 .

Photocatalytic properties of graphdiyne and graphene modified TiO₂: from theory to experiment

The chemical structure and electronic properties of two-dimensional (2D) carbon-supported TiO₂, TiO₂-graphdiyne, and TiO₂-graphene composites have been studied by first-principles density functional theory. Calculation results show that TiO₂(001)-graphdiyne composites possess superior charge separation and oxidation properties, having the longest lifetimes of photoexcited carriers among all of the 2D composites containing TiO₂ of different facets. Our experimental results further proved that TiO₂(001)-graphdiyne composites could be a promising photocatalyst. For photocatalytic degradation of methylene blue, the rate constant of the TiO₂(001)-graphdiyne composite is 1.63 ± 0.15 times that of the pure TiO₂(001) and 1.27 ± 0.12 times that of the TiO₂(001)-graphene composite.

Graphene-based electrodes

Graphene, the thinnest two dimensional carbon material, has become the subject of intensive investigation in various research fields because of its remarkable electronic, mechanical, optical and thermal properties. Graphene-based electrodes, fabricated from mechanically cleaved graphene, chemical vapor deposition (CVD) grown graphene, or massively produced graphene derivatives from bulk graphite, have been applied in a broad range of applications, such as in light emitting diodes, touch screens, field-effect transistors, solar cells, supercapacitors, batteries, and sensors. In this Review, after a short introduction to the properties and synthetic methods of graphene and its derivatives, we will discuss the importance of graphene-based electrodes, their fabrication techniques, and application areas.

Factors governing the growth mode of carbon nanotubes on carbon-based substrates

The formation of carbon nanotubes (CNTs) through precipitated carbons emerging from supersaturated metal catalysts is an established mechanism for their growth during the CVD process. Here, the CNT growth mode is determined by the interaction between the substrate and the catalyst nanoparticle, e.g., the tip-growth mode for the weak adhesion between them and the base-growth mode for the strong adhesion case. With microscopic evidence, this study reports another factor that governs the growth mode of CNTs on carbon-based substrates. Catalyst nanoparticles after only sputtering and annealing processes before the chemical vapor deposition (CVD) process are fully or partially wrapped with some graphitic layers, which are formed by carbons escaping from the carbon substrate. The formation of the wrapping graphitic layers is initiated by catalyst atoms diffusing into the carbon substrate during the catalyst sputtering process. The diffused catalyst atoms later coalesce into the nanoparticles, during which carbon atoms escape from the carbon substrate, forming the graphitic layers which wrap around the catalyst nanoparticles for energy minimization. Then, the carbon atoms generated from the catalytic reactions during the CVD process interact with the carbons in the graphitic layers wrapped around the catalyst nanoparticles, bringing about clear tip-growth of CNTs on carbon-based substrates and a stable interface (carbon-carbon bonding) between CNTs and carbon-based substrates.

Controlled synthesis of carbon-coated cobalt sulfide nanostructures in oil phase with enhanced li storage performances

A novel solvothermal process was developed for the synthesis of carbon-coated Co9S8 nanodandelions using 1-dodecanethiol as the sulfur source and the soft template. Replacing 1-dodecanethiol with sulfur powder as the sulfur source leads to the formation of 20 nm Co9S8 nanoparticles without carbon coating. When tested as LIB anode, the C@Co9S8 dandelion delivers a specific capacity of 520 mA h g(-1) at a current density of 1 A g(-1) (1.8 C) during the 50th cycle, which is much higher than that of Co9S8 nanoparticles (e.g. 338 mA h g(-1)). Furthermore, the C@Co9S8 dandelion also exhibits excellent high C-rate performance, e.g., depicts a 10th-cycle capacity of 373 mA h g(-1) at a current density of 6 A g(-1) (10.9 C), which is better than that of many reported anode materials. Such synthesis approach is attractive for the preparation of sulfide anode materials with high Li storage properties.

Fabrication of nanoelectrode ensembles by electrodepositon of Au nanoparticles on single-layer graphene oxide sheets

Nanoelectrode ensembles (NEEs) have been fabricated by the electrodeposition of Au nanoparticles (AuNPs) on single-layer graphene oxide (GO) sheets coated on a glassy carbon electrode (GCE). The fabricated NEEs show a typical sigmoidal shaped voltammetric profile, arising from the low coverage density of AuNPs on GCE and large distance among them, which can be easily controlled by varying the electrodeposition time. As a proof of concept, after the probe HS-DNA is immobilized on the NEEs through the Au-S bonding, the target DNA is detected with the methylene blue intercalator. Our results show that the target DNA can be detected as low as 100 fM, i.e. 0.5 amol DNA in 5 μL solution.

Chemical approaches toward graphene-based nanomaterials and their applications in energy-related areas

A 'gold rush' has been triggered all over the world for exploiting the possible applications of graphene-based nanomaterials. For this purpose, two important problems have to be solved; one is the preparation of graphene-based nanomaterials with well-defined structures, and the other is the controllable fabrication of these materials into functional devices. This review gives a brief overview of the recent research concerning chemical and thermal approaches toward the production of well-defined graphene-based nanomaterials and their applications in energy-related areas, including solar cells, lithium ion secondary batteries, supercapacitors, and catalysis.

Comparative studies on single-layer reduced graphene oxide films obtained by electrochemical reduction and hydrazine vapor reduction

The comparison between two kinds of single-layer reduced graphene oxide (rGO) sheets, obtained by reduction of graphene oxide (GO) with the electrochemical method and hydrazine vapor reduction, referred to as E-rGO and C-rGO, respectively, is systematically studied. Although there is no morphology difference between the E-rGO and C-rGO films adsorbed on solid substrates observed by AFM, the reduction process to obtain the E-rGO and C-rGO films is quite different. In the hydrazine vapor reduction, the nitrogen element is incorporated into the obtained C-rGO film, while no additional element is introduced to the E-rGO film during the electrochemical reduction. Moreover, Raman spectra show that the electrochemical method is more effective than the hydrazine vapor reduction method to reduce the GO films. In addition, E-rGO shows better electrocatalysis towards dopamine than does C-rGO. This study is helpful for researchers to understand these two different reduction methods and choose a suitable one to reduce GO based on their experimental requirements.

Catalytic conversion of graphene into carbon nanotubes via gold nanoclusters at low temperatures

Here, we present the catalytic conversion of graphene layers into carbon nanotubes (CNTs), in the presence of Au nanoparticles (AuNPs) without the need for an additional carbon source. We have demonstrated that this catalytic process takes place at temperatures as low as 500 °C. No other oxide supports decorated with AuNPs were found to grow CNTs at this temperature. These findings highlight the high activity of graphene when used as a support for catalytic reactions.

Real-time DNA detection using Pt nanoparticle-decorated reduced graphene oxide field-effect transistors

A large-area, continuous, few-layer reduced graphene oxide (rGO) thin film has been fabricated on a Si/SiO(2) wafer using the Langmuir-Blodgett (LB) method followed by thermal reduction. After photochemical reduction of Pt nanoparticles (PtNPs) on rGO, the obtained PtNPs/rGO composite is employed as the conductive channel in a solution-gated field effect transistor (FET), which is then used for real-time detection of hybridization of single-stranded DNA (ssDNA) with high sensitivity (2.4 nM). Such a simple, but effective method for fabrication of rGO-based transistors shows great potential for mass-production of graphene-based electronic biosensors.

Synthesis of Au nanoparticles decorated graphene oxide nanosheets: noncovalent functionalization by TWEEN 20 in situ reduction of aqueous chloroaurate ions for hydrazine detection and catalytic reduction of 4-nitrophenol

In this paper, we develop a cost-effective and simple route for the synthesis of Au nanoparticles (AuNPs) decorated graphene oxide (GO) nanosheets using polyoxyethylene sorbitol anhydride monolaurate (TWEEN 20) as a stabilizing agent for GO as well as a reducing and immobilizing agent for AuNPs. The AuNPs assemble on the surface of TWEEN-functionalized GO by the in situ reduction of HAuCl(4) aqueous solution. The morphologies of these composites were characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is found that the resultant AuNPs decorated GO nanosheets (AuNPs/TWEEN/GO) exhibit remarkable catalytic performance for hydrazine oxidation. This hydrazine sensor has a fast amperometric response time of less than 3s. The linear range is estimated to be from 5 μM to 3 mM (r=0.999), and the detection limit is estimated to be 78 nM at a signal-to-noise ratio of 3. The AuNPs/TWEEN/GO composites also exhibit good catalytic activity toward 4-nitrophenol (4-NP) reduction and the GO supports also enhance the catalytic activity via a synergistic effect.

Photothermally enhanced photodynamic therapy delivered by nano-graphene oxide

Graphene with unique physical and chemical properties has shown various potential applications in biomedicine. In this work, a photosensitizer molecule, Chlorin e6 (Ce6), is loaded on polyethylene glycol (PEG)-functionalized graphene oxide (GO) via supramolecular π-π stacking. The obtained GO-PEG-Ce6 complex shows excellent water solubility and is able to generate cytotoxic singlet oxygen under light excitation for photodynamic therapy (PDT). Owing to the significantly enhanced intracellular trafficking of photosensitizers, our GO-PEG-Ce6 complex offers a remarkably improved cancer cell photodynamic destruction effect compared to free Ce6. More importantly, we show that the photothermal effect of graphene can be utilized to promote the delivery of Ce6 molecules by mild local heating when exposed to a near-infrared laser at a low power density, further enhancing the PDT efficacy against cancer cells. Our work highlights the promise of using graphene for potential multifunctional cancer therapies.

Adsorption of double-stranded DNA to graphene oxide preventing enzymatic digestion

Investigation into the interactions between graphene oxide (GO) and biomolecules is very important for broad applications of GO in bioassay and bioanalysis. In this work, we describe the interactions between double-stranded DNA (dsDNA) and GO. We demonstrated that dsDNA can bind to GO forming complexes (dsDNA/GO) in the presence of certain salts, which protects dsDNA from being enzymatically digested. On the other hand, we found that a nonionic surfactant, such as triton X-100, can block the formation of dsDNA/GO complexes, so that the enzymatic digestion of dsDNA is restored. These results lead us to believe that the reason for GO protecting dsDNA from enzymatic digestion is the formation of dsDNA/GO complexes hindering the access of DNA enzymes to dsDNA, rather than direct inactivation of the DNA enzymes.

Crystallographically aligned carbon nanotubes grown on few-layer graphene films

Carbon nanotubes are grown on few-layer graphene films using chemical vapor deposition without a carbon feedstock gas. We find that the nanotubes show a striking alignment to specific crystal orientations of the few-layer graphene films. The nanotubes are oriented predominantly at 60 degree intervals and are offset 30 degrees from crystallographically oriented etch tracks, indicating alignment to the armchair axes of the few-layer graphene films. Nanotubes grown on various thicknesses of few-layer graphene under identical process conditions show that the thinnest films, in the sub-6 atomic layer regime, demonstrate significantly improved crystallographic alignment. Intricate crystallographic patterns are also observed having sharp kinks with bending radii less than the ∼10 nm lateral resolution of the electron and atomic force microscopy used to image them. Some of these kinks occur independently without interactions between nanotubes while others result when two nanotubes intersect. These intersections can trap nanotubes between two parallel nanotubes resulting in crystallographic back and forth zigzag geometries. These interactions suggest a tip-growth mechanism such that the catalyst particles remain within several nanometers of the few-layer graphene surface as they move leaving a nanotube in their wake.

Chemically functionalized surface patterning

Patterning substrates with versatile chemical functionalities from micro- to nanometer scale is a long-standing and interesting topic. This review provides an overview of a range of techniques commonly used for surface patterning. The first section briefly introduces conventional micropatterning tools, such as photolithography and microcontact printing. The second section focuses on the currently used nanolithographic techniques, for example, scanning probe lithography (SPL), and their applications in surface patterning. Their advantages and disadvantages are also demonstrated. In the last section, dip-pen nanolithography (DPN) is emphatically illustrated, with a particular stress on the patterning and applications of biomolecules.

In situ self-assembly of mild chemical reduction graphene for three-dimensional architectures

Three-dimensional (3D) architectures of graphene are of interest in applications in electronics, catalysis devices, and sensors. However, it is still a challenge to fabricate macroscopic all-graphene 3D architectures under mild conditions. Here, a simple method for the preparation of 3D architectures of graphene is developed via the in situ self-assembly of graphene prepared by mild chemical reduction at 95 °C under atmospheric pressure without stirring. No chemical or physical cross-linkers or high pressures are required. The reducing agents include NaHSO(3), Na(2)S, Vitamin C, HI, and hydroquinone. Both graphene hydrogels and aerogels can be prepared by this method, and the shapes of the 3D architectures can be controlled by changing the type of reactor. The 3D architectures of graphene have low densities, high mechanical properties, thermal stability, high electrical conductivity, and high specific capacitance, which make them candidates for potential applications in supercapacitors, hydrogen storage and as supports for catalysts.

Graphene-based composites

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).

Graphene-based materials: synthesis, characterization, properties, and applications

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.

Transparent, flexible, all-reduced graphene oxide thin film transistors

Owing to their unique thickness-dependent electronic properties, together with perfect flexibility and transparency, graphene and its relatives make fantastic material for use in both active channel and electrodes in various electronic devices. On the other hand, the electronic sensors based on graphene show high potential in detection of both chemical and biological species with high sensitivity. In this contribution, we report the fabrication of all-reduced graphene oxide (rGO) thin film transistors by a combination of solution-processed rGO electrodes with a micropatterned rGO channel, and then study their applications in biosensing. Our all-rGO devices are cost-effective, highly reproducible, and reliable. The fabricated electronic sensor is perfectly flexible with high transparency, showing good sensitivity in detecting proteins in the physiological buffer. As a proof of concept, fibronectin as low as 0.5 nM was successfully detected, which is comparable with the previously reported protein sensors based on single-layer pristine graphene obtained from mechanical cleavage. The specific detection of avidin by using biotinylated all-rGO sensor is also successfully demonstrated.