Self-assembly of graphene oxide at interfaces

Atomistic and Coarse-Grained Modeling of the Adsorption of Graphene Nanoflakes at the Oil-Water Interface

The high interfacial tension between two immiscible liquids can provide the necessary driving force for the self-assembly of nanoparticles at the interface. Particularly, the interface between water and oily liquids (hydrocarbon chains) has been exploited to prepare networks of highly interconnected graphene sheets of only a few layers thickness, which are well suited for industrial applications. Studying such complex systems through particle-based simulations could greatly enhance the understanding of the various driving forces in action and could possibly give more control over the self-assembly process. However, the interaction potentials used in particle-based simulations are typically derived by reproducing bulk properties and are therefore not suitable for describing systems dominated by interfaces. To address this issue, we introduce a methodology to derive solid-liquid interaction potentials that yield an accurate representation of the balance between interfacial interactions at atomistic and coarse-grained resolutions. Our approach is validated through its ability to lead to the adsorption of graphene nanoflakes at the interface between water and n-hexane. The development of accurate coarse-grained potentials that our approach enables will allow us to perform large-scale simulations to study the assembly of graphene nanoparticles at the interface between immiscible liquids. Our methodology is illustrated through a simulation of many graphene nanoflakes adsorbing at the interface.

A review on suppression and utilization of the coffee-ring effect

Evaporation of sessile droplets containing non-volatile solutes dispersed in a volatile solvent leaves behind ring-like solid stains. As the volatile species evaporates, pinning of the contact line gives rise to capillary flows that transport non-volatile solutes to the contact line. This phenomenon, called the coffee-ring effect, compromises the overall performance of industrially relevant manufacturing processes involving evaporation such as printing, biochemical analysis, manufacturing of nano-structured materials through colloidal and macromolecular patterning. Various approaches have been developed to suppress this phenomenon, which is otherwise difficult to avoid. The coffee-ring effect has also been leveraged to prepare new materials through convection induced assembly. This review underlines not only the strategies developed to suppress the coffee-ring effect but also sheds light on approaches to arrive at novel processes and materials. Working principles and applicability of these strategies are discussed together with a critical comparison.

Highly Conductive and Transparent Reduced Graphene Oxide Nanoscale Films via Thermal Conversion of Polymer-Encapsulated Graphene Oxide Sheets

Despite noteworthy progress in the fabrication of large-area graphene sheetlike nanomaterials, the vapor-based processing still requires sophisticated equipment and a multistage handling of the material. An alternative approach to manufacturing functional graphene-based films includes the employment of graphene oxide (GO) micrometer-scale sheets as precursors. However, search for a scalable manufacturing technique for the production of high-quality GO nanoscale films with high uniformity and high electrical conductivity is still continuing. Here we show that conventional dip-coating technique can offer fabrication of high quality mono- and bilayered films made of GO sheets. The method is based on our recent discovery that encapsulating individual GO sheets in a nanometer thick molecular brush copolymer layer allows for the nearly perfect formation of the GO layers via dip coating from water. By thermal reduction the bilayers (cemented by a carbon-forming polymer linker) are converted into highly conductive and transparent reduced GO films with a high conductivity up to 10⁴ S/cm and optical transparency on the level of 90%. The value is the highest electrical conductivity reported for thermally reduced nanoscale GO films and is close to the conductivity of indium tin oxide currently in use for transparent electronic devices, thus making these layers intriguing candidates for replacement of ITO films.

Thermally and Electrically Conductive Nanopapers from Reduced Graphene Oxide: Effect of Nanoflakes Thermal Annealing on the Film Structure and Properties

In this study, we report a novel strategy to prepare graphene nanopapers from direct vacuum filtration. Instead of the conventional method, i.e., thermal annealing nanopapers at extremely high temperatures prepared from graphene oxide (GO) or partially reduced GO, we fabricate our graphene nanopapers directly from suspensions of fully reduced graphene oxide (RGO), obtained after RGO and thermal annealing at 1700 °C in vacuum. By using this approach, we studied the effect of thermal annealing on the physical properties of the macroscopic graphene-based papers. Indeed, we demonstrated that the enhancement of the thermal and electrical properties of graphene nanopapers prepared from annealed RGO is strongly influenced by the absence of oxygen functionalities and the morphology of the nanoflakes. Hence, our methodology can be considered as a valid alternative to the classical approach.

High-Performance Nanocomposites Inspired by Nature

Natural materials, including nacre, bone, and the lobster cuticle, exhibit excellent mechanical properties, combining high strength and toughness. Such materials have the added benefit of being light in weight. These advantageous features are due to such natural materials' orderly hierarchical architectures and abundant interface interactions. How to utilize these design principles created by nature to fabricate high-performance bioinspired nanocomposites remains a great research challenge. A logical roadmap for developing these nanocomposites can be described as "discovery, invention, and creation." Here, the discovery of the relationship between natural materials' design principles and such materials' extraordinary mechanical properties is discussed. Then, the invention of bioinspired strategies for mimicking natural materials is considered and representative strategies addressed. Next, the creation of multifunctional nanocomposites is discussed and bioinspired nanocomposites, including fiber nanocomposites, 2D film nanocomposites, and 3D bulk nanocomposites reviewed. Finally, a perspective and outlook for future directions in making bioinspired nanocomposites is provided to offer inspiration to the community and a clear vision for future research.

A Charge-Density-Tunable Three/Two-Dimensional Polymer/Graphene Oxide Heterogeneous Nanoporous Membrane for Ion Transport

The design and fabrication of a robust nanoporous membrane in large scale is still a challenge and is of fundamental importance for practical applications. Here, a robust three/two-dimensional polymer/graphene oxide heterogeneous nanoporous membrane is constructed in large scale via the self-assembly approach by chemically designing a robust charge-density-tunable nanoporous ionomer with uniform pore size. To obtain a nanoporous polymer that maintains high mechanical strength and promotes multifunctionality, we designed a series of amphiphilic copolymers by introducing a positively charged pyridine moiety into the engineered polymer polyphenylsulfone. The multiphysical-chemical properties of the membrane enable it to work as a nanogate switch with synergy between wettability and surface charge change in response to pH. Then we systematically studied the transmembrane ionic transport properties of this two-/three-dimensional porous system. By adjusting the charge density of the copolymer via chemical copolymerization through a controlled design route, the rectifying ratio of this asymmetric membrane could be amplified 4 times. Furthermore, we equipped a concentration-gradient-driven energy harvesting device with this charge-density-tunable nanoporous membrane, and a maximum power of ≈0.76 W m^-2 was obtained. We expect this methodology for construction of a charge-density-tunable heterogeneous membrane by chemical design will shed light on the material design, and this membrane may further be used in energy devices, biosensors, and smart gating nanofluidic devices.

Pickering emulsions stabilized by a metal-organic framework (MOF) and graphene oxide (GO) for producing MOF/GO composites

Herein we demonstrate the formation of a novel kind of Pickering emulsion that is stabilized by a Zr-based metal-organic framework (Zr-MOF) and graphene oxide (GO). It was found that the Zr-BDC-NO₂ and GO solids assembling at the oil/water interface can effectively stabilize the oil droplets that are dispersed in the water phase. Such a Pickering emulsion offers a facile route for fabricating Zr-MOF/GO composite materials. After removing water and oil by freeze drying from Pickering emulsions, the Zr-MOF/GO composites were obtained and their morphologies, structures and interaction properties were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectrometry, respectively. The influences of the concentration of GO and Zr-MOF on the emulsion microstructures and the properties of the MOF/GO composites were studied. Based on experimental results, the mechanisms for the emulsion formation by Zr-MOF and GO and the as-synthesized superstructures of the Zr-MOF/GO composite were proposed. It is expected that this facile and tunable route can be applied to the synthesis of different kinds of MOF-based or GO-based composite materials.

Carboxylated Fullerene at the Oil/Water Interface

The self-assembly of carboxylated fullerene with poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) with different molecular weights, poly-2-vinylpyridine, and amine-terminated polystyrene, at the interface between toluene and water was investigated. For all values of the pH, the functionalized fullerene interacted with the polymers at the water/toluene interface, forming a nanoparticle network, reducing the interfacial tension. At pH values of 4.84 and 7.8, robust, elastic films were formed at the interface, such that hollow tubules could be formed in situ when an aqueous solution of the functionalized fullerene was jetted into a toluene solution of PS-b-P2VP at a pH of 4.84. With variation of the pH, the mechanical properties of the fullerene/polymer assemblies can be varied by tuning the strength of the interactions between the functionalized fullerenes and the PS-b-P2VP.

Controlled Gelation of Graphene Towards Unprecedented Superstructures

Graphene exhibits a range of exceptional physical properties and holds great promise for development of novel bulk materials for widespread applications. Properly engineering of assembled structures of graphene at multiple length scales is essential to realize its full potential in bulk forms. In this Concept article, we highlight the unique colloidal and gelation behavior of a commonly used precursor for graphene, graphene oxide (GO), and discuss how the colloidal chemistry of GO and reduced GO can enable new scalable and cost-effective approaches to construct graphene-based soft superstructures with excellent properties.

Graphene oxide-stabilized perfluorocarbon emulsions for controlled oxygen delivery

Perfluorocarbon (PFC) emulsions are capable of absorbing large quantities of oxygen. They are widely used as blood alternates for quick oxygenation of tissues. However, they are unsuitable for applications where sustained oxygen supply is desired over an extended period of time. Here, we have designed a new PFC oxygen delivery system that combines perfluorodecalin with graphene oxide (GO), where GO acts both as an emulsifier and a stabilizing agent. The resulting emulsions (PFC@GO) release oxygen at least one order of magnitude slower than emulsions prepared with other common surfactants. The release rate can be controlled by varying the thickness of the GO layer. Controlled release of oxygen make these emulsions excellent oxygen carriers for applications where sustained oxygen delivery is required e.g. in tissue regeneration and vascular wound healing.

Self-Assembled Carbon Dot Nanosphere: A Robust, Near-Infrared Light-Responsive, and Vein Injectable Photosensitizer

Self-assembly "activated" carbon dot photosensitizer: a robust, NIR-light responsive, and vein injectable carbon dot nanosphere (CDNS) photosensitizer with ¹ O₂ quantum yield of 0.45 under 671 nm laser irradiation has been developed through self-assembly using individual CD as building units. This study develops the biomedical applications of CD, highlights the self-assembly for designing well-defined CD-based photosensitizers, and promotes future explorations of this CDNS photosensitizer in nanomedical and clinical applications.

Understanding the colloidal dispersion stability of 1D and 2D materials: Perspectives from molecular simulations and theoretical modeling

The colloidal dispersion stability of 1D and 2D materials in the liquid phase is critical for scalable nano-manufacturing, chemical modification, composites production, and deployment as conductive inks or nanofluids. Here, we review recent computational and theoretical studies carried out by our group to model the dispersion stability of 1D and 2D materials, including single-walled carbon nanotubes, graphene, and graphene oxide in aqueous surfactant solutions or organic solvents. All-atomistic (AA) molecular dynamics (MD) simulations can probe the molecular level details of the adsorption morphology of surfactants and solvents around these materials, as well as quantify the interaction energy between the nanomaterials mediated by surfactants or solvents. Utilizing concepts from reaction kinetics and diffusion, one can directly predict the rate constants for the aggregation kinetics and dispersion life times using MD outputs. Furthermore, the use of coarse-grained (CG) MD simulations allows quantitative prediction of surfactant adsorption isotherms. Combined with the Poisson-Boltzmann equation, the Langmuir isotherm, and the DLVO theory, one can directly use CGMD outputs to: (i) predict electrostatic potentials around the nanomaterial, (ii) correlate surfactant surface coverages with surfactant concentrations in the bulk dispersion medium, and (iii) determine energy barriers against coagulation. Finally, we discuss challenges associated with studying emerging 2D materials, such as, hexagonal boron nitride (h-BN), phosphorene, and transition metal dichalcogenides (TMDCs), including molybdenum disulfide (MoS₂). An outlook is provided to address these challenges with plans to develop force-field parameters for MD simulations to enable predictive modeling of emerging 2D materials in the liquid phase.

Solution-assisted ultrafast transfer of graphene-based thin films for solar cells and humidity sensors

Vacuum filtration enables the fabrication of large-area graphene-based membranes (GBMs), possessing a smoother surface than that by spray, spin coating or drop casting. However, due to the strong interaction with substrates, the separation of thin GBMs from the filter is problematic. Conventional stamping separation/transfer of graphene oxide (GO) thin films requires another substrate and pressing for >10 h, which may damage the delicate structure of the transfer substrates. Other methods require GO to be reduced on filters before separation, thus limiting the reduction methods. Inspired by a coagulation bath that enables rapid formation of ultrastrong GO fibers, we present an ultrafast (<1 min) and solution-assisted strategy to fabricate smooth and freestanding GO films. The diverse interfacial energy of hydrogen bonds also demonstrates another reason for the successful separation. The film thickness ranges from 45 nm to several micrometers. When used as a composite of counter electrodes in dye sensitized solar cells, it showed higher (8.58%) power conversion efficiency than its spin-(7.71%) and spray-coated (8.07%) counterparts. It also showed promising performance in capacitive humidity sensors. The capacitance varied by three orders of magnitude in the range of the relative humidity of 15%-95%. Therefore the strategy realizes an ultrafast and high-quality film production which is suitable for various applications.

Progress in 3D Printing of Carbon Materials for Energy-Related Applications

The additive-manufacturing (AM) technique, known as three-dimensional (3D) printing, has attracted much attention in industry and academia in recent years. 3D printing has been developed for a variety of applications. Printable inks are the most important component for 3D printing, and are related to the materials, the printing method, and the structures of the final 3D-printed products. Carbon materials, due to their good chemical stability and versatile nanostructure, have been widely used in 3D printing for different applications. Good inks are mainly based on volatile solutions having carbon materials as fillers such as graphene oxide (GO), carbon nanotubes (CNT), carbon blacks, and solvent, as well as polymers and other additives. Studies of carbon materials in 3D printing, especially GO-based materials, have been extensively reported for energy-related applications. In these circumstances, understanding the very recent developments of 3D-printed carbon materials and their extended applications to address energy-related challenges and bring new concepts for material designs are becoming urgent and important. Here, recent developments in 3D printing of emerging devices for energy-related applications are reviewed, including energy-storage applications, electronic circuits, and thermal-energy applications at high temperature. To close, a conclusion and outlook are provided, pointing out future designs and developments of 3D-printing technology based on carbon materials for energy-related applications and beyond.

Improvement of performance of a ductile/brittle polymer system by graphite nanoplatelets: effect of component coupling

The upgrade of a PA/PS system based on the combination of reactive compatibilization of polymer components and their coupling with carbon nanoplatelets.

Cisplatin-induced self-assembly of graphene oxide sheets into spherical nanoparticles for damaging sub-cellular DNA

Cisplatin induced self-assembly of 2D-graphene oxide sheets into 3D-spherical nanoparticles for sub-cellular DNA damage.

High Volumetric Energy Density Asymmetric Supercapacitors Based on Well-Balanced Graphene and Graphene-MnO2 Electrodes with Densely Stacked Architectures

The well-matched electrochemical parameters of positive and negative electrodes, such as specific capacitance, rate performance, and cycling stability, are important for obtaining high-performance asymmetric supercapacitors. Herein, a facile and cost-effective strategy is demonstrated for the fabrication of 3D densely stacked graphene (DSG) and graphene-MnO₂ (G-MnO₂ ) architectures as the electrode materials for asymmetric supercapacitors (ASCs) by using MnO₂ -intercalated graphite oxide (GO-MnO₂ ) as the precursor. DSG has a stacked graphene structure with continuous ion transport network in-between the sheets, resulting in a high volumetric capacitance of 366 F cm^-3 , almost 2.5 times than that of reduced graphene oxide, as well as long cycle life (93% capacitance retention after 10 000 cycles). More importantly, almost similar electrochemical properties, such as specific capacitance, rate performance, and cycling stability, are obtained for DSG as the negative electrode and G-MnO₂ as the positive electrode. As a result, the assembled ASC delivers both ultrahigh gravimetric and volumetric energy densities of 62.4 Wh kg^-1 and 54.4 Wh L^-1 (based on total volume of two electrodes) in 1 m Na₂ SO₄ aqueous electrolyte, respectively, much higher than most of previously reported ASCs in aqueous electrolytes.

Biosensors based on graphene oxide and its biomedical application

Graphene oxide (GO) is one of the most attributed materials for opening new possibilities in the development of next generation biosensors. Due to the coexistence of hydrophobic domain from pristine graphite structure and hydrophilic oxygen containing functional groups, GO exhibits good water dispersibility, biocompatibility, and high affinity for specific biomolecules as well as properties of graphene itself partly depending on preparation methods. These properties of GO provided a lot of opportunities for the development of novel biological sensing platforms, including biosensors based on fluorescence resonance energy transfer (FRET), laser desorption/ionization mass spectrometry (LDI-MS), surface-enhanced Raman spectroscopy (SERS), and electrochemical detection. In this review, we classify GO-based biological sensors developed so far by their signal generation strategy and provide the comprehensive overview of them. In addition, we offer insights into how the GO attributed in each sensor system and how they improved the sensing performance.

Simple Synthesis of Molybdenum Disulfide/Reduced Graphene Oxide Composite Hollow Microspheres as Supercapacitor Electrode Material

MoS₂/RGO composite hollow microspheres were hydrothermally synthesized by using SiO₂/GO microspheres as a template, which were obtained via the sonication-assisted interfacial self-assembly of tiny GO sheets on positively charged SiO₂ microspheres. The structure, morphology, phase, and chemical composition of MoS₂/RGO hollow microspheres were systematically investigated by a series of techniques such as FE-SEM, TEM, XRD, TGA, BET, and Raman characterizations, meanwhile, their electrochemical properties were carefully evaluated by CV, GCD, and EIS measurements. It was found that MoS₂/RGO hollow microspheres possessed unique porous hollow architecture with high-level hierarchy and large specific surface area up to 63.7 m²·g⁻¹. When used as supercapacitor electrode material, MoS₂/RGO hollow microspheres delivered a maximum specific capacitance of 218.1 F·g⁻¹ at the current density of 1 A·g⁻¹, which was much higher than that of contrastive bare MoS₂ microspheres developed in the present work and most of other reported MoS₂-based materials. The enhancement of supercapacitive behaviors of MoS₂/RGO hollow microspheres was likely due to the improved conductivity together with their distinct structure and morphology, which not only promoted the charge transport but also facilitated the electrolyte diffusion. Moreover, MoS₂/RGO hollow microsphere electrode displayed satisfactory long-term stability with 91.8% retention of the initial capacitance after 1000 charge/discharge cycles at the current density of 3 A·g⁻¹, showing excellent application potential.

Bioinspired Graphene-Based Nanocomposites and Their Application in Flexible Energy Devices

Graphene is the strongest and stiffest material ever identified and the best electrical conductor known to date, making it an ideal candidate for constructing nanocomposites used in flexible energy devices. However, it remains a great challenge to assemble graphene nanosheets into macro-sized high-performance nanocomposites in practical applications of flexible energy devices using traditional approaches. Nacre, the gold standard for biomimicry, provides an excellent example and guideline for assembling two-dimensional nanosheets into high-performance nanocomposites. This review summarizes recent research on the bioinspired graphene-based nanocomposites (BGBNs), and discusses different bioinspired assembly strategies for constructing integrated high-strength and -toughness graphene-based nanocomposites through various synergistic effects. Fundamental properties of graphene-based nanocomposites, such as strength, toughness, and electrical conductivities, are highlighted. Applications of the BGBNs in flexible energy devices, as well as potential challenges, are addressed. Inspired from the past work done by the community a roadmap for the future of the BGBNs in flexible energy device applications is depicted.

The dispersion and aggregation of graphene oxide in aqueous media

Graphene oxide (GO), as a typical two-dimensional material, possesses a range of oxygen-containing groups and shows surfactant and/or polyelectrolyte-like characteristics. Herein, GO sheets with narrow size distribution were prepared by an ultracentrifugation-based process and the aggregation behaviour of GO in pure water and an electrolyte aqueous solution were studied using laser light scattering (LLS). When adding common electrolytes, such as NaCl and MgCl2, into the GO dispersions, aggregation occurs and irreversible coagulation eventually occurs too. However, the GO dispersion can still remain stable when adding excess AlCl3. The zeta potential of the GO dispersion changes from negative to positive after the addition of access AlCl3, indicating that electrostatic repulsion is still responsible for the dispersion of GO, which is in good agreement with the LLS results. This finding on the dispersion of GO may be applied in the solution processing of GO. It also expands the scope of the design and preparation of new GO-based hybrid materials with different functions.

From Solution to Biointerface: Graphene Self-Assemblies of Varying Lateral Sizes and Surface Properties for Biofilm Control and Osteodifferentiation

Bringing multifunctional graphene out of solution through facile self-assembly to form 2D surface nanostructures, with control over the lateral size and surface properties, would be an intriguing accomplishment, especially in biomedical fields where biointerfaces with functional diversity are in high demand. Guided by this goal, in this work, we built such graphene-based self-assemblies on orthopedic titanium, attempting to selectively regulate bacterial activities and osteoblastic functions, which are both crucial in bone regeneration. Briefly, large-area graphene oxide (GO) sheets and functionalized reduced GO (rGO) micro-/nanosheets were self-assembled spontaneously and controllably onto solid Ti, through an evaporation-assisted electrostatic assembly process and a mussel-inspired one-pot assembly process, respectively. The resultant layers were characterized in terms of topological structure, chemical composition, hydrophilicity, and protein adsorption properties. The antibacterial efficacies of the assemblies were examined by challenging them with pathogenic Staphylococcus aureus (S. aureus) bacteria that produce biofilms, whereby around 50% antiadhesion effects and considerable antibiofilm activities were observed for both layer types but through dissimilar modes of action. Their cytocompatibility and osteogenic potential were also investigated. Interfaced with MC3T3-E1 cells, the functionalized rGO sheets evoked better cell adhesion and growth than GO sheets, whereas the latter elicited higher osteodifferentiation activity throughout a 28-day in vitro culture. In this work, we showed that it is technically possible to construct graphene interface layers of varying lateral dimensions and surface properties and confirmed the concept of using the obtained assemblies to address the two major challenges facing orthopedic clinics. In addition, we determined fundamental implications for understanding the surface-biology relationship of graphene biomaterials, in efforts to better design and more safely use them for future biomedicine.

A Highly Efficient Metal-Free Oxygen Reduction Electrocatalyst Assembled from Carbon Nanotubes and Graphene

A novel carbon-nanotube-graphene hybrid nanostructure is developed using an aerosol-assisted assembly approach. After doping with nitrogen and phosphorus, the prepared hybrid nanomaterials exhibit excellent electrocatalytic performance for oxygen reduction in both alkaline and acidic media. This research presents a continuous and low-cost route to prepare high-performance metal-free electrocatalysts while replacing Pt-based materials.

Graphene functionalized with poly(vinyl alcohol) as a Pickering stabilizer for suspension polymerization of poly(methyl methacrylate)

Two types of thermally reduced graphenes (TRGs) having different lateral sizes were non-covalently modified with poly(vinyl alcohol) to endow water-dispersibility. The modified TRGs were examined as Pickering stabilizers for the suspension polymerization of methyl methacrylate (MMA). They were effective graphene-based Pickering stabilizers for the system with almost all of the polymerized composite microparticles having a regular spherical shape. The particle size of the composite microparticles was tunable by the size or the amount of modified TRG used as stabilizer. The almost perfect core-shell structure of the composite microparticles effectively enhanced the thermal stability of the core PMMA. In addition, when the core-shell microparticles were compression molded into a monolith, the obtained composite exhibited an ultra-low percolation threshold of electrical conductivity of around 0.04vol%.

Graphene Emerges as a Versatile Template for Materials Preparation

Graphene and its derivatives are emerging as a class of novel but versatile templates for the controlled preparation and functionalization of materials. In this paper a conceptual review on graphene-based templates is given, highlighting their versatile roles in materials preparation. Graphene is capable of acting as a low-dimensional hard template, where its two-dimensional morphology directs the formation of novel nanostructures. Graphene oxide and other functionalized graphenes are amphiphilic and may be seen as soft templates for formatting the growth or inducing the controlled assembly of nanostructures. In addition, nanospaces in restacked graphene can be used for confining the growth of sheet-like nanostructures, and assemblies of interlinked graphenes can behave either as skeletons for the formation of composite materials or as sacrificial templates for novel materials with a controlled network structure. In summary, flexible graphene and its derivatives together with an increasing number of assembled structures show great potentials as templates for materials production. Many challenges remain, for example precise structural control of such novel templates and the removal of the non-functional remaining templates.

Evaporative Self-Assembly of Gold Nanorods into Macroscopic 3D Plasmonic Superlattice Arrays

Millimeter-scale 3D superlattice arrays composed of dense, regular, and vertically aligned gold nanorods are fabricated by evaporative self-assembly. The regular organization of the gold nanorods into a macroscopic superlattice enables the production of a plasmonic substrate with excellent sensitivity and reproducibility, as well as reliability in surface-enhanced Raman scattering. The work bridges the gap between nanoscale materials and macroscopic applications.

Supramolecular self-assembly of graphene oxide and metal nanoparticles into stacked multilayers by means of a multitasking protein ring

Graphene oxide (GO) is rapidly emerging worldwide as a breakthrough precursor material for next-generation devices. However, this requires the transition of its two-dimensional layered structure into more accessible three-dimensional (3D) arrays. Peroxiredoxins (Prx) are a family of multitasking redox enzymes, self-assembling into ring-like architectures. Taking advantage of both their symmetric structure and function, 3D reduced GO-based composites are hereby built up. Results reveal that the "double-faced" Prx rings can adhere flat on single GO layers and partially reduce them by their sulfur-containing amino acids, driving their stacking into 3D multi-layer reduced GO-Prx composites. This process occurs in aqueous solution at a very low GO concentration, i.e. 0.2 mg ml(-1). Further, protein engineering allows the Prx ring to be enriched with metal binding sites inside its lumen. This feature is exploited to both capture presynthesized gold nanoparticles and grow in situ palladium nanoparticles paving the way to straightforward and "green" routes to 3D reduced GO-metal composite materials.

Fabrication, Characterization, and Biocompatibility of Polymer Cored Reduced Graphene Oxide Nanofibers

Graphene nanofibers have shown a promising potential across a wide spectrum of areas, including biology, energy, and the environment. However, fabrication of graphene nanofibers remains a challenging issue due to the broad size distribution and extremely poor solubility of graphene. Herein, we report a facile yet efficient approach for fabricating a novel class of polymer core-reduced graphene oxide shell nanofiber mat (RGO-CSNFM) by direct heat-driven self-assembly of graphene oxide sheets onto the surface of electrospun polymeric nanofibers without any requirement of surface treatment. Thus-prepared RGO-CSNFM demonstrated excellent mechanical, electrical, and biocompatible properties. RGO-CSNFM also promoted a higher cell anchorage and proliferation of human bone marrow mesenchymal stem cells (hMSCs) compared to the free-standing RGO film without the nanoscale fibrous structure. Further, cell viability of hMSCs was comparable to that on the tissue culture plates (TCPs) with a distinctive healthy morphology, indicating that the nanoscale fibrous architecture plays a critically constructive role in supporting cellular activities. In addition, the RGO-CSNFM exhibited excellent electrical conductivity, making them an ideal candidate for conductive cell culture, biosensing, and tissue engineering applications. These findings could provide a new benchmark for preparing well-defined graphene-based nanomaterial configurations and interfaces for biomedical applications.

Free-Standing Graphene Oxide-Palygorskite Nanohybrid Membrane for Oil/Water Separation

Graphene oxide (GO) is an emerging kind of building block for advanced membranes with tunable passageway for water molecules. To synergistically manipulate the channel and surface structures/properties of GO-based membranes, the different building blocks are combined and the specific interfacial interactions are designed in this study. With vacuum-assisted filtration self-assembly, palygorskite nanorods are intercalated into adjacent GO nanosheets, and GO nanosheets are assembled into laminate structures through π-π stacking and cation cross-linking. The palygorskite nanorods in the free-standing GOP nanohybrid membranes take a 3-fold role, rendering enlarged mass transfer channels, elevating hydration capacity, and creating hierarchical nanostructures of membrane surfaces. Accordingly, the permeate fluxes from 267 L/(m(2) h) for GO membrane to 1867 L/(m(2) h) for GOP membrane. The hydration capacity and hierarchical nanostructures synergistically endow GOP membranes with underwater superoleophobic and low oil-adhesive water/membrane interfaces. Moreover, by rationally imparting chemical and physical joint defense mechanisms, the GOP membranes exhibit outstanding separation performance and antifouling properties for various oil-in-water emulsion systems (with different concentration, pH, or oil species). The high water permeability, high separation efficiency, as well as superior anti-oil-fouling properties of GOP membranes enlighten the great prospects of graphene-based nanostructured materials in water purification and wastewater treatment.

A timesaving, low-cost, high-yield method for the synthesis of ultrasmall uniform graphene oxide nanosheets and their application in surfactants

Graphene oxide nanosheets (GONSs) with a lateral size less than 100 nm have attracted more and more attention for their wide range of potential applications, from bionanotechnology and nanobiomedicine to surfactants. However, at present GONSs are commonly prepared from graphite nanofibers or graphite nanopowders which are both expensive. Here, a timesaving, low-cost, high-yield method is proposed for preparing ultrasmall uniform GONSs with an average lateral size of ∼30 nm, utilizing common graphite powder as the raw material in the absence of a strong acid. The obtained GONSs are able to disperse single-walled carbon nanotubes (SWCNTs) effectively, and the dispersion could withstand high-speed centrifugation. Consequently, GONSs could indeed serve as a superior surfactant for the dispersion of SWCNTs, and the dispersion could be further applied in electronics, as the GONSs may be further reduced to reduced GONSs or graphene nanosheets.

Biocompatible, Free-Standing Film Composed of Bacterial Cellulose Nanofibers-Graphene Composite

In recent years, graphene films have been used in a series of wide applications in the biomedical area, because of several advantageous characteristics. Currently, these films are derived from graphene oxide (GO) via chemical or physical reduction methods, which results in a significant decrease in surface hydrophilicity, although the electrical property could be greatly improved, because of the reduction process. Hence, the comprehensive performance of the graphene films showed practical limitations in the biomedical field, because of incompatibility of highly hydrophobic surfaces to support cell adhesion and growth. In this work, we present a novel fabrication of bacterial cellulose nanofibers/reduced graphene oxide (BC-RGO) film, using a bacterial reduction method. Thus-prepared BC-RGO films maintained excellent hydrophilicity, while electrical properties were improved by bacterial reduction of GO films in culture. Human marrow mesenchymal stem cells (hMSCs) cultured on these surfaces showed improved cellular response with higher cell proliferation on the BC-RGO film, compared to free-standing reduced graphene oxide film without the nanoscale fibrous structure. Furthermore, the cellular adhesion and proliferation were even comparable to that on the tissue culture plate, indicating that the bacterial cellulose nanofibers play a critically contructive role in supporting cellular activities. The novel fabrication method greatly enhanced the biochemical activity of the cells on the surface, which could aid in realizing several potential applications of graphene film in biomedical area, such as tissue engineering, bacterial devices, etc.

Insight into the Nanoscale Mechanism of Rapid H2O Transport within a Graphene Oxide Membrane: Impact of Oxygen Functional Group Clustering

Realistic models of graphene oxide membranes were developed and validated to interpret the exceptional water permeation in association with X-ray photoelectron spectroscopy, thermogravimetric and differential scanning calorimetry analysis, and dynamic vapor sorption measurements. With respect to the GO oxidization level, surface distributions of functionalized domains were analyzed in line with TEM observations, and 3 types of interlayer domains in slit pores of GO membranes were identified. The hydrophilicity degrees of as-defined domains strongly influence their H2O uptake capacities. Calculated sorption enthalpies and isotherms are in good agreement with experimental data, and the results indicate the dominant role of dipole interactions. GO expansion shows a transition from the interstratification of an H2O monolayer to the accumulation of H2O multilayers at an interlayer distance of 0.8 nm. The evolution of both hydrogen bonds and H2O diffusivities suggests the existence of three types of H2O species with different binding states and molecular mobilities. The computed H2O permeability on the basis of sorption-diffusion theory supports the exceptional H2O transport capacity in GO membranes.

Preparation of rGO–mesoporous silica nanosheets as Pickering interfacial catalysts

A series of reduced graphene oxide–mesoporous silica nanoflakes (rGO–MSN) with adjustable surface wettability were developed and employed as Pickering interfacial catalyst for acetal reaction.

Graphene oxide as a sacrificial material for fabricating molecularly imprinted polymers via Pickering emulsion polymerization

Graphene oxide (GO) was introduced as a sacrificial material, for the first time, to fabricate a hollow molecularly imprinted polymer (HMIP) via Pickering emulsion polymerization.

Rapid self-assembly of ultrathin graphene oxide film and application to silver nanowire flexible transparent electrodes

A self-assembled ultrathin graphene oxide film was rapidly prepared within only 3 minutes to improve silver nanowire electrode performance.

Synthesis and applications of large-area single-layer graphene

The progresses in syntheses of large-area single-layer graphene and applications in membrane separation are summarized in this review.

Selective mono-facial modification of graphene oxide nanosheets in suspension

Graphene oxide (GO) is selectively functionalized on one face to prepare Janus platelets which are characterized by various spectroscopic and microscopic techniques.

Two-Dimensional Porous Carbon: Synthesis and Ion-Transport Properties

Their chemical stability, high specific surface area, and electric conductivity enable porous carbon materials to be the most commonly used electrode materials for electrochemical capacitors (also known as supercapacitors). To further increase the energy and power density, engineering of the pore structures with a higher electrochemical accessible surface area, faster ion-transport path and a more-robust interface with the electrolyte is widely investigated. Compared with traditional porous carbons, two-dimensional (2D) porous carbon sheets with an interlinked hierarchical porous structure are a good candidate for supercapacitors due to their advantages in high aspect ratio for electrode packing and electron transport, hierarchical pore structures for ion transport, and short ion-transport length. Recent progress on the synthesis of 2D porous carbons is reported here, along with the improved electrochemical behavior due to enhanced ion transport. Challenges for the controlled preparation of 2D porous carbons with desired properties are also discussed; these require precise tuning of the hierarchical structure and a clarification of the formation mechanisms.