Coassembly of Graphene Oxide and Nanowires for Large-Area Nanowire Alignment

Chemistry and physics of a single atomic layer: strategies and challenges for functionalization of graphene and graphene-based materials

Graphene has attracted great interest for its superior physical, chemical, mechanical, and electrical properties that enable a wide range of applications from electronics to nanoelectromechanical systems. Functionalization is among the significant vectors that drive graphene towards technological applications. While the physical properties of graphene have been at the center of attention, we still lack the knowledge framework for targeted graphene functionalization. In this critical review, we describe some of the important chemical and physical processes for graphene functionalization. We also identify six major challenges in graphene research and give perspectives and practical strategies for both fundamental studies and applications of graphene (315 references).

Engineering of a novel pluronic F127/graphene nanohybrid for pH responsive drug delivery

Herein, a novel Pluronic F127/graphene nanosheet (PF127/GN) hybrid was prepared via an one-pot process including the simultaneous reduction of graphene oxide and assembly of PF127 and GN. The nanohybrid exhibits high water dispersibility and stability in physiological environment with the hydrophilic chains of PF127 extending to the solution while the hydrophobic segments anchoring at the surface of graphene via hydrophobic interaction. The PF127/GN nanohybrid is found to be capable of effectively encapsulating doxorubicin (DOX) with ultrahigh drug-loading efficiency (DLE; 289%, w/w) and exhibits a pH responsive drug release behavior. The superb DLE of the PF127/GN nanohybrid relies on the introduction of GN which is structurally compatible with DOX. Cellular toxicity assays performed on human breast cancer MCF-7 cells demonstrate that the PF127/GN nanohybrid displays no obvious cytotoxicity, whereas the PF127/GN-loaded DOX (PF127/GN/DOX) shows remarkable cytotoxicity to the MCF-7. Cell internalization study reveals that PF127/GN nanohybrid facilitates the transfer of DOX into MCF-7 cells, evidenced by the image of confocal laser scanning microscopy. The above results indicate the potential application of this novel nanocarrier in biomedicine.

Facile synthesis of two-dimensional graphene/SnO₂ /Pt ternary hybrid nanomaterials and their catalytic properties

In this paper, we reported a simple, aqueous-phase route to the synthesis of two-dimensional graphene/SnO(2) composite nanosheets (GSCN) hybrid nanostructures consisting of 5 nm Pt nanoparticles supported on the both sides of GSCN. Functional two-dimensional GSCN were obtained through the reduction of graphene oxide (GO) using SnCl(2) in the presence of polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA). The main advantages of this preparation are that the reduction of GO, the formation of SnO(2) and the functionalization of GSCN were achieved simultaneously through one-pot reaction. GSCN/Pt ternary hybrid nanomaterials were generated by in situ reduction of negatively charged PtCl(6)(2-) precursors adsorbed on the positively charged surface of GSCN through electrostatic attraction. The as-synthesized GSCN/Pt ternary hybrid nanomaterials exhibited high cycle stabilization during the catalytic reduction of p-nitrophenol into p-aminophenol by NaBH(4). Additionally, our approach is expected to extend to other hybrid nanomaterials. We believe that the obtained GSCN/Pt ternary hybrid nanomaterials have great potential for applications in other field, such as electrochemical energy storage, sensors, and so on.

Influences of graphene oxide support on the electrochemical performances of graphene oxide-MnO2 nanocomposites

MnO2 supported on graphene oxide (GO) made from different graphite materials has been synthesized and further investigated as electrode materials for supercapacitors. The structure and morphology of MnO2-GO nanocomposites are characterized by X-ray diffraction, X-ray photoemission spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and Nitrogen adsorption-desorption. As demonstrated, the GO fabricated from commercial expanded graphite (denoted as GO(1)) possesses more functional groups and larger interplane gap compared to the GO from commercial graphite powder (denoted as GO(2)). The surface area and functionalities of GO have significant effects on the morphology and electrochemical activity of MnO2, which lead to the fact that the loading amount of MnO2 on GO(1) is much higher than that on GO(2). Elemental analysis performed via inductively coupled plasma optical emission spectroscopy confirmed higher amounts of MnO2 loading on GO(1). As the electrode of supercapacitor, MnO2-GO(1) nanocomposites show larger capacitance (307.7 F g-1) and better electrochemical activity than MnO2-GO(2) possibly due to the high loading, good uniformity, and homogeneous distribution of MnO2 on GO(1) support.

An environment-friendly preparation of reduced graphene oxide nanosheets via amino acid

Chemically modified graphene has been studied in many applications due to its excellent electrical, mechanical, and thermal properties. Among the chemically modified graphenes, reduced graphene oxide is the most important for its structure and properties, which are similar to pristine graphene. Here, we introduce an environment-friendly approach for preparation of reduced graphene oxide nanosheets through the reduction of graphene oxide that employs L-cysteine as the reductant under mild reaction conditions. The conductivity of the reduced graphene oxide nanosheets produced in this way increases by about 10(6) times in comparison to that of graphene oxide. This is the first report about using amino acids as a reductant for the preparation of reduced graphene oxide nanosheets, and this procedure offers an alternative route to large-scale production of reduced graphene oxide nanosheets for applications that require such material.

Electrochemical detection of DNA damage induced by acrylamide and its metabolite at the graphene-ionic liquid-Nafion modified pyrolytic graphite electrode

A new electrochemical biosensor for directly detecting DNA damage induced by acrylamide (AA) and its metabolite was presented in this work. The graphene-ionic liquid-Nafion modified pyrolytic graphite electrode (PGE) was prepared, and then horseradish peroxidase (HRP) and natural double-stranded DNA were alternately assembled on the modified electrode by the layer-by-layer method. The PGE/graphene-ionic liquid-Nafion and the construction of the (HRP/DNA)(n) film were characterized by electrochemical impedance spectroscopy. With the guanine signal in DNA as an indicator, the damage of DNA was detected by differential pulse voltammetry after PGE/graphene-ionic liquid-Nafion/(HRP/DNA)(n) was incubated in AA solution or AA+H(2)O(2) solution at 37°C. This method provides a new model to mimic and directly detect DNA damage induced by chemical pollutants and their metabolites in vitro. The results indicated that, in the presence of H(2)O(2), HRP was activated and catalyzed the transformation of AA to glycidamide, which could form DNA adducts and induce more serious damage of DNA than AA. In order to further verify these results, UV-vis spectrophotometry was also used to investigate DNA damage induced by AA and its metabolites in solution and the similar results were obtained.

DNA-directed self-assembly of graphene oxide with applications to ultrasensitive oligonucleotide assay

Controlled graphene or its derivatives' assembly is of growing interest in many areas. However, achieving control over their assembly into precise and predictable architectures has been challenging and is still a bottleneck to their utilization. Herein, we report for the first time the use of DNA hybridization for the controllable assembly of a graphene nanosheet. Moreover, with the help of dynamic light scattering technique, we extended the above studies by exploiting the DNA-graphene dispersed sheets as highly ultrasensitive detection of oligonuleotides for the fabrication of a novel biosensing strategy, which shows high sensitivity and excellent selectivity. This work will show a new general route to graphene-based lamellar composite materials and would bring about advances in the research of graphene-based biofunctional materials for specific applications in biodiagnostics, nanoelectronics, and bionanotechnology.

Vertical arrays of anisotropic particles by gravity-driven self-assembly

Anisotropic particles assemble to spontaneously form columnar arrays. Hybrid nanotube/nanowire particles (silica nanotubes partially filled with metallic cores) deposit with their denser metallic ends towards the surface, orienting them vertically. Up to 84% are observed to be standing over a 0.64 cm(2) area within 15 min. Standing percentage is found to be dependent on particle surface concentration.

Layer-by-layer self-assembly for constructing a graphene/platinum nanoparticle three-dimensional hybrid nanostructure using ionic liquid as a linker

In this report, we succeed in constructing a hybrid three-dimensional (3D) nanocomposite film by alternatively assembling the graphene nanosheets modified by ionic liquid (IL) and Pt nanoparticles (Pt NPs). In this strategy, an imidazolium salt-based ionic liquid (IS-IL)-functionalized graphene was synthesized by covalently binding 1-(3-aminopropyl)-3-methylimidazolium bromide onto graphene nanosheets. The introduction of IS-IL on the surface of graphene nanosheets can obtain dispersed graphene nanosheets with positive charge. Also, the desired functionalization of graphene can form the building blocks for constructing hybrid 3D nanocomposite film. Then, the positively charged IS-IL-functionalized graphene nanosheets are strong enough to drive the formation of the 3D nanomaterials with negatively charged citrate-stabilized Pt NPs through electrostatic interaction. As far as we know, the reports on the layer-by-layer (LBL) self-assembly of G-IS-IL and nanoparticle multilayer films are few at the moment. UV-visible-near-infrared (UV-vis-NIR) absorption spectroscopy, atomic force microscopy (AFM) and cyclic voltammetry (CV) were used to characterize the uniform growth of the multilayer film. The newly prepared 3D nanomaterials containing G-IS-IL and Pt NPs show high electrocatalytic activity toward oxygen reduction. Furthermore, the electrocatalytic activity of the films could be further tailored by simply choosing different cycles in the LBL process. This demonstration offers a new route to assemble graphene/nanoparticle multilayer films and opens up the possibility of building more complex multicomponent nanostructures, which are believed to be useful for electrochemical nanodevices.

Reducing sugar: new functional molecules for the green synthesis of graphene nanosheets

In this paper, we developed a green and facile approach to the synthesis of chemically converted graphene nanosheets (GNS) based on reducing sugars, such as glucose, fructose and sucrose using exfoliated graphite oxide (GO) as precursor. The obtained GNS is characterized with atomic force microscopy, UV-visible absorption spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and so on. The merit of this method is that both the reducing agents themselves and the oxidized products are environmentally friendly. It should be noted that, besides the mild reduction capability to GO, the oxidized products of reducing sugars could also play an important role as a capping reagent in stabilizing as-prepared GNS simultaneously, which exhibited good stability in water. This approach can open up the new possibility for preparing GNS in large-scale production alternatively. Moreover, it is found that GNS-based materials could be of great value for applications in various fields, such as good electrocatalytic activity toward catecholamines (dopamine, epinephrine, and norepinephrine).

Scalable alignment and transfer of nanowires based on oriented polymer nanofibers

We develop a simple and scalable method based on oriented polymer nanofiber films for the parallel assembly and transfer of nanowires at high density. Nanowires dispersed in solution are aligned and selectively deposited at the central space of parallel nanochannels formed by the well-oriented nanofibers as a result of evaporation-induced flow and capillarity. A general contact printing method is used to realize the transfer of the nanowires from the donor nanofiber film to a receiver substrate. The mechanism, which involves ordered alignment of nanowires on oriented polymer nanofiber films, is also explored with an evaporation model of cylindrical droplets. The simplicity of the assembly and transfer, and the facile fabrication of large-area well-oriented nanofiber films, make the present method promising for the application of nanowires, especially for the disordered nanowires synthesized by solution chemistry.

By what means should nanoscaled materials be constructed: molecule, medium, or human?

There is great potential in nanoscale science and technology, and construction of macrosized materials and systems possessing nanoscale structural features is a crucial factor in the everyday application of nanoscience and nanotechnology. Because nanoscale substances are often constructed through self-assembly of unit molecules and nanomaterials, control of the self-assembly process is required. In order to establish general guidelines for the fabrication of materials with nanoscale structural characteristics, i.e., nanoscaled materials, we introduce here examples of recent research in related fields categorised as: (i) self-assembled structures with forms generally determined by intrinsic interactions between molecules and/or unit nanomaterials, (ii) self-assemblies influenced by their surrounding media, especially interfacial environments, (iii) modulation of self-assembly by artificial operation or external stimuli. Examples are not limited to organic molecules, which are often regarded as the archetypal species in self-assembly chemistry, and many examples of inorganic assemblies and hybrid structures are included in this review.

Liquid Crystalline Behavior and Related Properties of Colloidal Systems of Inorganic Oxide Nanosheets

Inorganic layered crystals exemplified by clay minerals can be exfoliated in solvents to form colloidal dispersions of extremely thin inorganic layers that are called nanosheets. The obtained “nanosheet colloids” form lyotropic liquid crystals because of the highly anisotropic shape of the nanosheets. This system is a rare example of liquid crystals consisting of inorganic crystalline mesogens. Nanosheet colloids of photocatalytically active semiconducting oxides can exhibit unusual photoresponses that are not observed for organic liquid crystals. This review summarizes experimental work on the phase behavior of the nanosheet colloids as well as photochemical reactions observed in the clay and semiconducting nanosheets system.

Alignment of tellurium nanorods via a magnetization-alignment-demagnetization ("MAD") process assisted by an external magnetic field

Tellurium (Te) nanorods have been successfully aligned on a solid substrate via a magnetization-alignment-demagnetization ("MAD") process in the presence of an external magnetic field. Te nanorods carrying a poly(tert-butyl methacrylate) shell were first converted into magnetic nanocylinders by assembling magnetite nanoparticles on their surface via a hydrophobic interaction in THF. We demonstrate that, below a critical concentration of the nanoparticles, this assembly process is able to quantitatively tune the magnetite nanoparticles' density on the nanorods in terms of their stoichiometric ratio. Due to the polymer and surfactant on their surface, the formed magnetic nanocylinders are soluble in THF and aligned when dried on a solid substrate in the presence of an external magnetic field. The demagnetization of the prealigned nanocylinders was achieved via an acid-etching process, leaving Te nanorods in an aligned state. This MAD process can be extended as a general procedure for other nonmagnetic 1-D nanostructures. Additionally, the nonetched magnetic nanocylinders can be potentially applied in field of magnetorheology.