From graphene oxide to pristine graphene: revealing the inner workings of the full structural restoration

Defects boost graphitization for highly conductive graphene films

Fabricating highly crystalline macroscopic films with extraordinary electrical and thermal conductivities from graphene sheets is essential for applications in electronics, telecommunications and thermal management. High-temperature graphitization is the only method known to date for the crystallization of all types of carbon materials, where defects are gradually removed with increasing temperature. However, when using graphene materials as precursors, including graphene oxide, reduced graphene oxide and pristine graphene, even lengthy graphitization at 3000°C can only produce graphene films with small grain sizes and abundant structural disorders, which limit their conductivities. Here, we show that high-temperature defects substantially accelerate the grain growth and ordering of graphene films during graphitization, enabling ideal AB stacking as well as a 100-fold, 64-fold and 28-fold improvement in grain size, electrical conductivity and thermal conductivity, respectively, between 2000°C and 3000°C. This process is realized by nitrogen doping, which retards the lattice restoration of defective graphene, retaining abundant defects such as vacancies, dislocations and grain boundaries in graphene films at a high temperature. With this approach, a highly ordered crystalline graphene film similar to highly oriented pyrolytic graphite is fabricated, with electrical and thermal conductivities (∼2.0 × 10⁴ S cm^-1; ∼1.7 × 10³ W m^-1 K^-1) that are improved by about 6- and 2-fold, respectively, compared to those of the graphene films fabricated by graphene oxide. Such graphene film also exhibits a superhigh electromagnetic interference shielding effectiveness of ∼90 dB at a thickness of 10 μm, outperforming all the synthetic materials of comparable thickness including MXene films. This work not only paves the way for the technological application of highly conductive graphene films but also provides a general strategy to efficiently improve the synthesis and properties of other carbon materials such as graphene fibers, carbon nanotube fibers, carbon fibers, polymer-derived graphite and highly oriented pyrolytic graphite.

A Microwave-Assisted, Solvent-Free Approach for the Versatile Functionalization of Carbon Nanotubes

While the functionalization of carbon nanotubes (CNTs) has attracted extensive interest for a wide range of applications, a facial and versatile strategy remains in demand. Here, we report a microwave-assisted, solvent-free approach to directly functionalize CNTs both in raw form and in arbitrary macroscopic assemblies. Rapid microwave irradiation was applied to generate active sites on the CNTs while not inducing excessive damage to the graphitic network, and a gas-phase deposition afforded controllable grafting for thorough or regioselective functionalization. Using methyl methacrylate (MMA) as a model functional group and a CNT sponge as a model assembly, homogeneous grafting was exhibited by the increased robust hydrophobicity (contact angle increase from 30 to 140°) and improved structural stability (compressive modulus increased by 135%). Therefore, when our MMA-functionalized CNTs served as a solar absorber for saline distillation, high operating stability with a superior water evaporation rate of ∼2.6 kg m^-2 h^-1 was observed. Finally, to highlight the efficacy and versatility of this functionalization approach, we fabricated asymmetrically hydrophobic CNT sponges by regioselective functionalization to serve as a moisture-driven generator, which demonstrated a stable open-circuit voltage of 0.6 mV. This versatile, solvent-free approach can complement conventional solution-based techniques in the design and fabrication of multifunctional nanocarbon-based materials.

Synthesis and Demulsification Properties of Poly (DMDAAC-co-DAMBAC) (9:1) Copolymer

Utilizing the copolymerization modification of dimethyl diallyl ammonium chloride (DMDAAC), the high positive charge density of the copolymer could be maintained, thereby facilitating the deficiency of its monomer in the application. In this paper, poly (DMDAAC-co-DAMBAC) (9:1) was synthesized with an aqueous polymerization method using DMDAAC and methyl benzyl diallyl ammonium chloride (DAMBAC) as monomers and 2,2'-azobis [2-methylpropionamidine] dihydrochloride (V50) as an initiator. Targeted to the product's weight-average relative molecular mass (M_w), the response surface methodology (RSM) was used to optimize the preparation process. The optimal process conditions were obtained as follows: w (M) = 80.0%, m (V50):m (M) = 0.00700%, m (Na₄EDTA):m (M) = 0.00350%, T₁ = 50.0 °C, T₂ = 60.0 °C, and T₃ = 72.5 °C. The intrinsic viscosity ([η]) of the product was 1.780 dL/g, and the corresponding double bond conversion (Conv.) was 90.25 %. Poly (DMDAAC-co-DAMBAC) (9:1) revealed a highest M_w of 5.637 × 10⁵, together with the polydispersity index d (M_w/M_n) as 1.464. For the demulsification performance of simulated crude oil O/W emulsions, the demulsification rate of poly (DMDAAC-co-DAMBAC) (9:1) could reach 97.73%. Our study has illustrated that the copolymerization of DMDAAC and a small amount of DAMBAC with poor reactivity could significantly improve the relative molecular weight of the polymer, enhance its lipophilicity, and thus the application scope of the polymer.

Graphene oxide for photonics, electronics and optoelectronics

Graphene oxide (GO) was initially developed to emulate graphene, but it was soon recognized as a functional material in its own right, addressing an application space that is not accessible to graphene and other carbon materials. Over the past decade, research on GO has made tremendous advances in material synthesis and property tailoring. These, in turn, have led to rapid progress in GO-based photonics, electronics and optoelectronics, paving the way for technological breakthroughs with exceptional performance. In this Review, we provide an overview of the optical, electrical and optoelectronic properties of GO and reduced GO on the basis of their chemical structures and fabrication approaches, together with their applications in key technologies such as solar energy harvesting, energy storage, medical diagnosis, image display and optical communications. We also discuss the challenges of this field, together with exciting opportunities for future technological advances.

Palladium clusters, free and supported on surfaces, and their applications in hydrogen storage

Palladium is a late transition metal element in the 4d row of the periodic table. Palladium nanoparticles show efficient catalytic activity and selectivity in a number of chemical reactions. In this paper, we review the structural and electronic properties of palladium nanoclusters, both isolated and deposited on the surface of different substrates. Careful experiments and extensive calculations have been performed for small Pd clusters which provide ample information on their properties. Work on large Pd clusters is less abundant and more difficult to perform and interpret. Cluster deposition is a method to modify material surfaces for different applications, and we report the known results for the deposition of Pd clusters on the surfaces of a number of interesting substrates: carbonaceous substrates like graphene and some layered novel materials related to graphene, metal oxide substrates, silicon and silicon-related substrates and metallic alloy substrates. Emphasis is placed on revealing how the structural, electronic and magnetic properties change when the clusters are deposited on the substrate surfaces. Some examples of chemical reactions catalyzed by supported Pd clusters and nanoparticles are reported. An issue discussed in detail is the influence of Pd on the storage of hydrogen in porous materials. Experimental work shows that the amount of stored hydrogen increases when the absorbing material is doped with Pd atoms, clusters and nanoparticles, and a spillover mechanism from the metal particle to the substrate is usually accepted as the explanation. To shed light on this issue, a critical analysis based on density functional simulations of the mechanisms of hydrogen spillover in perfect and defective graphene doped with palladium clusters is presented.

Study on the Evolution of Graphene Defects and the Mechanical and Thermal Properties of GNPs/Cu during CVD Repair Process

Graphene has extremely high theoretical strength and electrothermal properties, and its application to Cu-based composites is expected to achieve a breakthrough in the performance of existing composites. As a nano-reinforced body, graphene often needs a long time of ball milling to make it uniformly dispersed, but the ball milling process inevitably brings damage to the graphene, causing the performance of the composite to deviate from expectations. Therefore, this paper uses CH₄ as a carbon source to repair graphene through a CVD process to prepare low-damage graphene/Cu composites. The process of graphene defect generation was studied through the ball milling process. The effects of defect content and temperature on the graphene repair process were studied separately. The study found that the graphene defect repair process, the decomposition process of oxygen-containing functional groups, and the deposition process of active C atoms existed simultaneously in the CVD process. When the repair temperature was low, the C atom deposition process and the oxygen-containing functional group decomposition process dominated. In addition, when the repair temperature is high, the graphene defect repair process dominated. 3 wt% graphene/Cu composites were prepared by pressure infiltration, and it was found that the bending strength was increased by 48%, the plasticity was also slightly increased, and the thermal conductivity was increased by 10-40%. This research will help reduce graphene defects, improve the intrinsic properties of graphene, and provide theoretical guidance for the regulation of C defects in composites.

One-step hydrothermal synthesis of porous Ti3C2Tz MXene/rGO gels for supercapacitor applications

Titanium carbide/reduced graphene oxide (Ti₃C₂T_z/rGO) gels were prepared by a one-step hydrothermal process. The gels show a highly porous structure with a surface area of ∼224 m² g^-1 and average pore diameter of ∼3.6 nm. The content of GO and Ti₃C₂T_z nanosheets in the reaction precursor was varied to yield different microstructures. The supercapacitor performance of Ti₃C₂T_z/rGO gels varied significantly with composition. Specific capacitance initially increased with increasing Ti₃C₂T_z content, but at high Ti₃C₂T_z content gels cannot be formed. Also, the retention of capacitance decreased with increasing Ti₃C₂T_z content. Ti₃C₂T_z/rGO gel electrodes exhibit enhanced supercapacitor properties with high potential window (1.5 V) and large specific capacitance (920 F g^-1) in comparison to pure rGO and Ti₃C₂T_z. The synergistic effect of EDLC from rGO and redox capacitance from Ti₃C₂T_z was the reason for the enhanced supercapacitor performance. A symmetric two-electrode supercapacitor cell was constructed with Ti₃C₂T_z/rGO, which showed very high areal capacitance (158 mF cm^-2), large energy density (∼31.5 μW h cm^-2 corresponding to a power density of ∼370 μW cm^-2), and long stability (∼93% retention) after 10 000 cycles.

Electroanalytical overview: utilising micro- and nano-dimensional sized materials in electrochemical-based biosensing platforms

Research into electrochemical biosensors represents a significant portion of the large interdisciplinary field of biosensing. The drive to develop reliable, sensitive, and selective biosensing platforms for key environmental and medical biomarkers is ever expanding due to the current climate. This push for the detection of vital biomarkers at lower concentrations, with increased reliability, has necessitated the utilisation of micro- and nano-dimensional materials. There is a wide variety of nanomaterials available for exploration, all having unique sets of properties that help to enhance the performance of biosensors. In recent years, a large portion of research has focussed on combining these different materials to utilise the different properties in one sensor platform. This research has allowed biosensors to reach new levels of sensitivity, but we note that there is room for improvement in the reporting of this field. Numerous examples are published that report improvements in the biosensor performance through the mixing of multiple materials, but there is little discussion presented on why each nanomaterial is chosen and whether they synergise well together to warrant the inherent increase in production time and cost. Research into micro-nano materials is vital for the continued development of improved biosensing platforms, and further exploration into understanding their individual and synergistic properties will continue to push the area forward. It will continue to provide solutions for the global sensing requirements through the development of novel materials with beneficial properties, improved incorporation strategies for the materials, the combination of synergetic materials, and the reduction in cost of production of these nanomaterials.

Bispyrene Functionalization Drives Self-Assembly of Graphite Nanoplates into Highly Efficient Heat Spreader Foils

Thermally conductive nanopapers fabricated from graphene and related materials are currently showing great potential in thermal management applications. However, thermal contacts between conductive plates represent the bottleneck for thermal conductivity of nanopapers prepared in the absence of a high temperature step for graphitization. In this work, the problem of ineffective thermal contacts is addressed by the use of bifunctional polyaromatic molecules designed to drive self-assembly of graphite nanoplates (GnP) and establish thermal bridges between them. To preserve the high conductivity associated to a defect-free sp2 structure, non-covalent functionalization with bispyrene compounds, synthesized on purpose with variable tethering chain length, was exploited. Pyrene terminal groups granted for a strong π-π interaction with graphene surface, as demonstrated by UV-Vis, fluorescence, and Raman spectroscopies. Bispyrene molecular junctions between GnP were found to control GnP organization and orientation within the nanopaper, delivering significant enhancement in both in-plane and cross-plane thermal diffusivities. Finally, nanopapers were validated as heat spreader devices for electronic components, evidencing comparable or better thermal dissipation performance than conventional Cu foil, while delivering over 90% weight reduction.

Plasma Assisted Reduction of Graphene Oxide Films

The past decade has seen enormous efforts in the investigation and development of reduced graphene oxide (GO) and its applications. Reduced graphene oxide (rGO) derived from GO is known to have relatively inferior electronic characteristics when compared to pristine graphene. Yet, it has its significance attributed to high-yield production from inexpensive graphite, ease of fabrication with solution processing, and thus a high potential for large-scale applications and commercialization. Amongst several available approaches for GO reduction, the mature use of plasma technologies is noteworthy. Plasma technologies credited with unique merits are well established in the field of nanotechnology and find applications across several fields. The use of plasma techniques for GO development could speed up the pathway to commercialization. In this report, we review the state-of-the-art status of plasma techniques used for the reduction of GO-films. The strength of various techniques is highlighted with a summary of the main findings in the literature. An analysis is included through the prism of chemistry and plasma physics.

The behavior of graphene oxide trapped at the air water interface

Graphene oxide is a derivate of graphene obtained by oxidation of graphite and other carbonaceous materials. The more accepted structure consists in carbonyl and carboxyl groups located at the edge of the graphene network and hydroxyl and epoxy groups attached to the basal plane. The percentage of O-groups depends on the synthesis route and the material used as carbon source. In addition, highly oxidized fragments, called oxidative debris, OD, are produced during the oxidation process. These fragments are adsorbed onto the graphene oxide network and can be removed by alkaline washing. The purified material has lower O/C ratio than graphene oxide and its properties are also quite different. Due to its structure, graphene oxide can be adsorbed at the air-water interface of the aqueous solution by diffusion, Gibbs monolayers, or by spreading on a clean water subphase resulting in a Langmuir film. This review is intended to provide information on the importance of controlling the chemical composition, structure, size, and oxidative debris, on the manufacture of graphene oxide films. To this end the review shows the influence of the synthesis route and the starting material on the structure of graphene oxide and analyzes several examples of the behavior and properties of films prepared with different types of graphene oxides. The great variability of behaviors of graphene oxide films caused by the different structure of this material provides a great opportunity to fine-tune the properties of films according to the needs of different applications.

Nanohybrids of reduced graphene oxide and cobalt hydroxide (Co(OH)2|rGO) for the thermal decomposition of ammonium perchlorate

The catalytic activity of nanoparticles of cobalt hydroxide supported on reduced graphene oxide, Co(OH)₂|rGO, was studied for the decomposition of ammonium perchlorate (AP), the principal ingredient of composite solid propellants. Co(OH)₂|rGO was synthesized by an in situ reduction method, which avoided the application of extremely high temperatures and harsh processes. rGO stabilized the nanoparticles effectively and prevented their agglomeration. The performance of Co(OH)₂|rGO as a catalyst was measured by differential scanning calorimetry. Co(OH)₂|rGO affected the high-temperature decomposition (HTD) of AP positively, decreasing the decomposition temperature of AP to 292 °C, and increasing the energy release to 290 J g^-1. The diminution of the HTD of AP by Co(OH)₂|rGO is in between the best values reported to date, suggesting its potential application as a catalyst for AP decomposition.

Understanding the Role of Oxidative Debris on the Structure of Graphene Oxide Films at the Air-Water Interface: A Neutron Reflectivity Study

We address here the role of oxidation impurities on the structure of graphene oxide films at the air-water interface by specular neutron reflectivity (SNR). We study films of purified graphene oxide (PGO) and nonpurified graphene oxide in the close-packed state. Nonpurified graphene oxide is constituted by graphene oxide (GO) layers with oxidation impurities adsorbed on the basal plane, while in PGO sheets, impurities are eliminated. SNR measurements show that GO films are formed by well-defined bilayers constituted by 2-3 layers of GO stacked in contact with air and a second layer of impurities submerged in the aqueous subphase. In contrast, PGO films are formed by a single layer in contact with air. We show for the first time that impurities constitute a layer submerged in the aqueous subphase, decrease the elasticity, and favor the collapse of graphene oxide films. Our results allow designing the surface properties of GO trapped at fluid interfaces.

Towards Understanding the Raman Spectrum of Graphene Oxide: The Effect of the Chemical Composition

Raman spectroscopy is a technique widely used to detect defects in semiconductors because it provides information of structural or chemical defects produced in its structure. In the case of graphene monolayer, the Raman spectrum presents two bands centered at 1582 cm−1 (G band) and 2700 cm−1 (2D band). However, when the periodic lattice of graphene is broken by different types of defects, new bands appear. This is the situation for the Raman spectrum of graphene oxide. It is well established that the existence of these bands, the position and the intensity or width of peaks can provide information about the origin of defects. However, in the case of the graphene oxide spectrum, we can find in the literature several discrepant results, probably due to differences in chemical composition and the type of defects of the graphene oxide used in these studies. Besides, theoretical calculations proved that the shape of bands, intensity and width, and the position of graphene oxide Raman spectrum depend on the atomic configuration. In the current work, we will summarize our current understanding of the effect of the chemical composition on the Raman spectrum of graphene oxide. Finally, we apply all this information to analyze the evolution of the structure of graphene oxide during the thermal annealing of the heterostructures formed by graphene oxide sandwiches in a hexagonal boron nitride.

Solution-processed graphene oxide electrode for supercapacitors fabricated using low temperature thermal reduction

We present a low temperature and solution-based fabrication process for reduced graphene oxide (rGO) electrodes for electric double layer capacitors (EDLCs). Through the heat treatment at 180 °C between the spin coatings of graphene oxide (GO) solution, an electrode with loosely stacked GO sheets could be obtained, and the GO base coating was partially reduced. The thickness of the electrodes could be freely controlled as these electrodes were prepared without an additive as a spacer. The GO coating layers were then fully reduced to rGO at a relatively low temperature of 300 °C under ambient atmospheric conditions, not in any chemically reducing environment. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) results showed that the changes in oxygen functional groups of GO occurred through the heat treatments at 180 and 300 °C, which clearly confirmed the reduction from GO to rGO in the proposed fabrication process at the low thermal reduction temperatures. The structural changes before and after the thermal reduction of GO to rGO analyzed using Molecular Dynamic (MD) simulation showed the same trends as those characterized using Raman spectroscopy and XPS. An EDLC composed of the low temperature reduced rGO-based electrodes and poly(vinyl alcohol)/phosphoric acid (PVA/H₃PO₄) electrolyte gel was shown to have high specific capacitance of about 240 F g⁻¹ together with excellent energy and power densities of about 33.3 W h kg⁻¹ and 833.3 W kg⁻¹, respectively. Furthermore, a series of multiple rGO-based EDLCs was shown to have fast charging and slow discharging properties that allowed them to light up a white light emitting diode (LED) for 30 min.

We present a low temperature and solution-based fabrication process for reduced graphene oxide (rGO) electrodes for electric double layer capacitors (EDLCs).

Novel in situ synthesis of copper nanoparticles supported on reduced graphene oxide and its application as a new catalyst for the decomposition of composite solid propellants

The catalytic activity of graphene oxide (GO), reduced graphene oxide (rGO), copper nanoparticles (CuNP) and rGO supported copper nanoparticles (rGO|CuNP) was investigated for the thermal decomposition of ammonium perchlorate (AP). GO was synthesized using a methodology based on hydrophilic oxidation, while an environmentally friendly and non-toxic reducing agent, l-ascorbic acid, was applied for the in situ reduction of copper and GO. The supporting rGO reduced the mean size of the copper nanoparticles from approximately 6 to 2 Å due to the presence of stabilizing functional groups on the graphitic structure. Theoretical studies through Density Functional Theory revealed the important role of the epoxy and carbonyl groups of rGO on the stabilization of copper. The thermal decomposition process was studied based on DSC and TGA. GO, and rGO did not show a significant catalytic influence in the decomposition of AP. CuNP reduced the decomposition temperature of AP in greater magnitude than rGO|CuNP however, the synergistic effect of the rGO and CuNP increased the energy release significantly.

The synergistic effect of a copper and reduced graphene oxide nanocomposite increased the energy release in the thermal decomposition of ammonium perchlorate.

Oxygen plasmas: a sharp chisel and handy trowel for nanofabrication

Although extremely chemically reactive, oxygen plasmas feature certain properties that make them attractive not only for material removal via etching and sputtering, but also for driving and sustaining nucleation and growth of various nanostructures in plasma bulk and on plasma-exposed surfaces. In this minireview, a number of representative examples is used to demonstrate key mechanisms and unique capabilities of oxygen plasmas and how these can be used in present-day nano-fabrication. In addition to modification and functionalisation processes typical for oxygen plasmas, their ability to catalyse the growth of complex nanoarchitectures is emphasized. Two types of technologies based on oxygen plasmas, namely surface treatment without a change in the size and shape of surface features, as well as direct growth of oxide structures, are used to better illustrate the capabilities of oxygen plasmas as a powerful process environment. Future applications and possible challenges for the use of oxygen plasmas in nanofabrication are discussed.

Tailoring the Thermal and Mechanical Properties of Graphene Film by Structural Engineering

Due to substantial phonon scattering induced by various structural defects, the in-plane thermal conductivity (K) of graphene films (GFs) is still inferior to the commercial pyrolytic graphite sheet (PGS). Here, the problem is solved by engineering the structures of GFs in the aspects of grain size, film alignment, and thickness, and interlayer binding energy. The maximum K of GFs reaches to 3200 W m-1 K-1 and outperforms PGS by 60%. The superior K of GFs is strongly related to its large and intact grains, which are over four times larger than the best PGS. The large smooth features about 11 µm and good layer alignment of GFs also benefit on reducing phonon scattering induced by wrinkles/defects. In addition, the presence of substantial turbostratic-stacking graphene is found up to 37% in thin GFs. The lacking of order in turbostratic-stacking graphene leads to very weak interlayer binding energy, which can significantly decrease the phonon interfacial scattering. The GFs also demonstrate excellent flexibility and high tensile strength, which is about three times higher than PGS. Therefore, GFs with optimized structures and properties show great potentials in thermal management of form-factor-driven electronics and other high-power-driven systems.

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.

One-step coelectrodeposition-assisted layer-by-layer assembly of gold nanoparticles and reduced graphene oxide and its self-healing three-dimensional nanohybrid for an ultrasensitive DNA sensor

A layer-by-layer (LBL) assembly was employed for preparing multilayer thin films with a controlled architecture and composition. In this study, we report the one-step coelectrodeposition-assisted LBL assembly of both gold nanoparticles (AuNPs) and reduced graphene oxide (rGO) on the surface of a glassy carbon electrode (GCE) for the ultrasensitive electrochemical impedance sensing of DNA hybridization. A self-healable nanohybrid thin film with a three-dimensional (3D) alternate-layered nanoarchitecture was obtained by the one-step simultaneous electro-reduction of both graphene oxide and gold chloride in a high acidic medium of H₂SO₄ using cyclic voltammetry and was confirmed by different characterization techniques. The DNA bioelectrode was prepared by immobilizing the capture DNA onto the surface of the as-obtained self-healable AuNP/rGO/AuNP/GCE with a 3D LBL nanoarchitecture via gold-thiol interactions, which then served as an impedance sensing platform for the label-free ultrasensitive electrochemical detection of DNA hybridization over a wide range from 1.0 × 10^-9 to 1.0 × 10^-13 g ml^-1, a low limit of detection of 3.9 × 10^-14 g ml^-1 (S/N = 3), ultrahigh sensitivity, and excellent selectivity. This study presents a promising electrochemical sensing platform for the label-free ultrasensitive detection of DNA hybridization with potential application in cancer diagnostics and the preparation of a self-healable nanohybrid thin film with a 3D alternate-layered nanoarchitecture via a one-step coelectrodeposition-assisted LBL assembly.

A "Nanopore Lithography" Strategy for Synthesizing Hierarchically Micro/Mesoporous Carbons from ZIF-8/Graphene Oxide Hybrids for Electrochemical Energy Storage

Porous carbons derived from metal-organic frameworks (MOFs) are promising materials for a number of energy- and environment-related applications, but their almost exclusively microporous texture can be an obstacle to their performance in practical uses. Here, we introduce a novel strategy for the generation of very uniform mesoporosity in a prototypical MOF, namely, zeolitic imidazolate framework-8 (ZIF-8). The process, referred to as "nanopore lithography", makes use of graphene oxide (GO) nanosheets enclosing ZIF-8 particles as masks or templates for the transfer of mesoporous texture to the latter. Upon controlled carbonization and activation, nanopores created in the GO envelope serve as selective entry points for localized etching of carbonized ZIF-8, so that such nanopores are replicated in the MOF-derived carbonaceous structure. The resulting porous carbons are dominated by uniform mesopores ∼3-4 nm in width and possess specific surface areas of ∼1300-1400 m² g^-1. Furthermore, we investigate and discuss the specific experimental conditions that afford the mesopore-templating action of the GO nanosheets. Electrochemical characterization revealed an improved capacitance as well as a faster, more reversible charge/discharge kinetics for the ZIF-8-derived porous carbons obtained through nanopore lithography, relative to those for their counterparts with standard activation (no GO templating), thus indicating the potential practical advantage of the present approach in capacitive energy storage applications.

Chemical functionalization and characterization of graphene-based materials

This review offers an overview on the chemical functionalization, characterization and applications of graphene-based materials.

Hydrophilic Graphene Preparation from Gallic Acid Modified Graphene Oxide in Magnesium Self-Propagating High Temperature Synthesis Process

Hydrophilic graphene sheets were synthesized from a mixture of magnesium and gallic acid (GA) modified graphene oxide (GO) in a self-propagating high-temperature synthesis (SHS) process, and hydrophilic graphene sheets displayed the higher C/O ratio (16.36), outstanding conductivity (~88900 S/m) and excellent water-solubility. GO sheets were connected together by GA, and GA was captured to darn GO structure defects through the formation of hydrogen bonds and ester bonds. In SHS process, the most oxygen ions of GO reacted with magnesium to prevent the escape of carbon dioxide and carbon monoxide to from the structure defects associated with vacancies, and GA could take place the high-temperature carbonization, during which a large-area graphene sheets formed with a part of the structure defects being repaired. When only GO was reduced by magnesium in SHS process, and the reduced GO (rGO) exhibited the smaller sheets, the lower C/O ratio (15.26), the weaker conductivity (4200 S/m) and the poor water-solubility because rGO inevitably left behind carbon vacancies and topological defects. Therefore, the larger sheet, less edge defects and free structure defects associated with vacancies play a key role for graphene sheets good dispersion in water.

Biomolecule-assisted exfoliation and dispersion of graphene and other two-dimensional materials: a review of recent progress and applications

Direct liquid-phase exfoliation of layered materials by means of ultrasound, shear forces or electrochemical intercalation holds enormous promise as a convenient, cost-effective approach to the mass production of two-dimensional (2D) materials, particularly in the form of colloidal suspensions of high quality and micrometer- and submicrometer-sized flakes. Of special relevance due to environmental and practical reasons is the production of 2D materials in aqueous medium, which generally requires the use of certain additives (surfactants and other types of dispersants) to assist in the exfoliation and colloidal stabilization processes. In this context, biomolecules have received, in recent years, increasing attention as dispersants for 2D materials, as they provide a number of advantages over more conventional, synthetic surfactants. Here, we review research progress in the use of biomolecules as exfoliating and dispersing agents for the production of 2D materials. Although most efforts in this area have focused on graphene, significant advances have also been reported with transition metal dichalcogenides (MoS2, WS2, etc.) or hexagonal boron nitride. Particular emphasis is placed on the specific merits of different types of biomolecules, including proteins and peptides, nucleotides and nucleic acids (RNA, DNA), polysaccharides, plant extracts and bile salts, on their role as efficient colloidal dispersants of 2D materials, as well as on the potential applications that have been explored for such biomolecule-exfoliated materials. These applications are wide-ranging and encompass the fields of biomedicine (photothermal and photodynamic therapy, bioimaging, biosensing, etc.), energy storage (Li- and Na-ion batteries), catalysis (e.g., catalyst supports for the oxygen reduction reaction or electrocatalysts for the hydrogen evolution reaction), or composite materials. As an incipient area of research, a number of knowledge gaps, unresolved issues and novel future directions remain to be addressed for biomolecule-exfoliated 2D materials, which will be discussed in the last part of this review.

Synergistic Effects of a Multifunctional Graphene Based Interlayer on Electrochemical Behavior and Structural Stability

The ability to rationally design and manipulate the interfacial structure in lithium ion batteries (LIBs) is of utmost technological importance for achieving desired performance requirements as it provides synergistic effects to the electrochemical properties and cycling stability of electrode materials. However, despite considerable efforts and progress made in recent years through the interface engineering based on active electrode materials, relatively little attention has been devoted to address the physical aspects of the interface and interfacial layer between the anode materials layer and the current collector. Here, we propose and successfully grow unique graphene directly on a Cu current collector as an ideal interfacial layer using the modified chemical vapor deposition (CVD). The anode with an engineered graphene interlayer exhibits remarkably improved electrochemical performances, such as large reversible specific capacity (921.4 mAh g(-1) at current density of 200 mA g(-1)), excellent Coulombic efficiency (close to approximately 96%), and superior cycling capacity retention and rate properties compared to the bare Cu. These excellent electrochemical features are discussed in terms of multiple beneficial effects of graphene on interfacial stability and adhesion between the anode and the collector, oxidation or corrosion resistance of the graphene grown Cu current collector, and electrical contact conductance during the charge/discharge process.

Effect of pH on the structure and drug release profiles of layer-by-layer assembled films containing polyelectrolyte, micelles, and graphene oxide

Layer by layer (lbl) assembled multilayer thin films are used in drug delivery systems with attractive advantages such as unlimited selection of building blocks and free modification of the film structure. In this paper, we report the fundamental properties of lbl films constructed from different substances such as PS-b-PAA amphiphilic block copolymer micelles (BCM) as nano-sized drug vehicles, 2D-shaped graphene oxide (GO), and branched polyethylenimine (bPEI). These films were fabricated by successive lbl assembly as a result of electrostatic interactions between the carboxyl group of BCM and amine group of functionalized GO or bPEI under various pH conditions. We also compared the thickness, roughness, morphology and degree of adsorption of the (bPEI/BCM) films to those in the (GO/BCM) films. The results showed significant difference because of the distinct pH dependence of each material. In addition, drug release rates of the GO/BCM film were more rapid those of the (bPEI/BCM) film in pH 7.4 and pH 2 PBS buffer solutions. In (bPEI/BCM/GO/BCM) film, the inserted GO layers into bPEI/BCM multilayer induced rapid drug release. We believe that these materials &pH dependent film properties allow developments in the control of coating techniques for biological and biomedical applications.

Electrolytic exfoliation of graphite in water with multifunctional electrolytes: en route towards high quality, oxide-free graphene flakes

Electrolytic--usually referred to as electrochemical--exfoliation of graphite in water under anodic potential holds enormous promise as a simple, green and high-yield method for the mass production of graphene, but currently suffers from several drawbacks that hinder its widespread adoption, one of the most critical being the oxidation and subsequent structural degradation of the carbon lattice that is usually associated with such a production process. To overcome this and other limitations, we introduce and implement the concept of multifunctional electrolytes. The latter are amphiphilic anions (mostly polyaromatic hydrocarbons appended with sulfonate groups) that play different relevant roles as (1) an intercalating electrolyte to trigger exfoliation of graphite into graphene flakes, (2) a dispersant to afford stable aqueous colloidal suspensions of the flakes suitable for further use, (3) a sacrificial agent to prevent graphene oxidation during exfoliation and (4) a linker to promote nanoparticle anchoring on the graphene flakes, yielding functional hybrids. The implementation of this strategy with some selected amphiphiles even furnishes anodically exfoliated graphenes of a quality similar to that of flakes produced by direct, ultrasound- or shear-induced exfoliation of graphite in the liquid phase (i.e., almost oxide- and defect-free). These high quality materials were used for the preparation of catalytically efficient graphene-Pt nanoparticle hybrids, as demonstrated by model reactions (reduction of nitroarenes). The multifunctional performance of these electrolytes is also discussed and rationalized, and a mechanistic picture of their oxidation-preventing ability is proposed. Overall, the present results open the prospect of anodic exfoliation as a competitive method for the production of very high quality graphene flakes.

Facile fabrication of multilayer films of graphene oxide/copper phthalocyanine with high dielectric properties

Novel multilayer films of graphene oxide/copper phthalocyanine (GO/CuPc) were fabricated by self-assembling in the orientational ordered liquid crystalline state and immobilizing of the ordered structure upon casting and drying.

Controlling the cooperative self-assembly of graphene oxide quantum dots in aqueous solutions

The 3D supramolecular association behavior of the synthesized 2D graphene oxide quantum dots (GOQDs) could be smartly controlled in dilute aqueous solutions to tune their final properties.

Preparation of flexible reduced graphene oxide/poly(vinyl alcohol) film with superior microwave absorption properties

In this study, a large-area reduced graphene oxide (rGO)/poly(vinyl alcohol) (PVA) film with excellent microwave absorption properties in the range of 2–18 GHz has been prepared by a simple solution processing method.