Large-scale Production Of Graphene Research Articles

Upscaling Brønsted acid intercalation and exfoliation of graphite into graphene by polyoxometalate clusters for sodium-ion battery application

Non-oxidative intercalation of graphite avoids damage to graphene lattices and is a suitable method to produce high-quality graphene. However, the yield of exfoliated graphene is low in this process due to the poor delamination efficiency of guest species. In this study, a Brønsted acid intercalation protocol is developed involving polyoxometalate (POM) clusters (H6P2W18O62) as guests and intercalation of graphite is realized at the sub-nanometer scale. Theoretical simulation based on DFT elucidates the stepwise intercalation mechanism of Brønsted acid molecules and clusters. Unlike common molecules/ionic guests, intercalation of POM clusters induces large expansion and extensive donor–acceptor interactions among graphite interlayers. This significantly weakens the van der Waals forces and promotes exfoliation efficiency of graphene layers. The exfoliated graphene possesses outstanding features of large lateral size, thin thickness, and high purity, and shows excellent performance as the anode for high power sodium-ion batteries. This work proffers a new pathway toward non-oxidative intercalation of graphite for large-scale production of graphene.

Analysis of large-scale high-quality graphene production and applications

Graphene, a single-atom-thick layer of carbon atoms arranged in a hexagonal lattice, is the thinnest and strongest material known to mankind. It has excellent electrical, thermal, and mechanical properties, making it a promising material for a wide range of applications in electronics, optoelectronics, energy storage, and more. With the increasing demand for graphene in various applications, large-scale and high-quality graphene production has become a significant challenge. While early methods of graphene production involved mechanical exfoliation, this method is limited in terms of scalability and yield. To meet the increasing demand for large-scale production of graphene, various methods have been developed in recent years, including chemical vapor precipitation, epitaxial crystal growth, graphene oxide reduction and solvent exfoliation and so on. This study aims to introduce several existing methods for the mass production of graphene with high quality and analyzes the advantages and disadvantage involve thereof. The findings in this paper may provide a valuable reference for the industrial-scale production of graphene.

Large-Area Fabrication of Porous Graphene Networks on Carbon Fabric via Millisecond Photothermal Processing of Polyaniline for Supercapacitors.

Supercapacitors demonstrate promising potential for flexible, multi-functional energy storage devices; however, their widespread adoption is confronted by fabrication challenges. To access a combination of desirable device qualities such as flexibility, lightweight, structural stability, and enhanced electrochemical performance, carbon fiber (CF) can be utilized as a current collector, alongside graphene as an electrochemically active material. Yet achieving a cost-effective, large-scale graphene production, particularly on CF, remains challenging. Here, a rapid (<1min) photothermal approach is developed for the large-scale production of graphene directly onto CF, utilizing polyaniline (PANI) as a polymer precursor. The in situ electropolymerization of PANI on CF facilitates its rapid synthesis on large areas, followed by conversion into graphene networks, enabling the binder-free fabrication of supercapacitor devices. These devices exhibit an areal capacitance of 180mFcm-2 (at 2mAcm-2 in 1mH2SO4), an order of magnitude higher than other fabric-based devices. Moreover, the devised photothermal strategy allows for one-step preparation of supercapacitor devices on areas exceeding 100cm-2, yielding an absolute areal capacitance of 4.5F. The proportional increase in capacitance with device area facilitates scaling and indicates the commercial viability of this approach for low-cost, energy-efficient, and high-throughput production of lightweight, high-performance graphene-based multi-functional supercapacitor devices.

Nanobubble-assisted liquid phase exfoliation of graphene in deionized water

In this study, we propose a novel method utilizing nanobubbles (NBs) to assist in liquid phase exfoliation. The size, thickness, and number of layers of the resulting graphene solution were characterized and quantified. A highly concentrated graphene solution was achieved through ultrasonic processing in deionized (DI) water, without the need for any surfactant. The observed increase in yield can be attributed to the heightened cavitation within the NBs solution. This study presents a sustainable and cost-effective approach for the large-scale production of graphene, aligning with green and eco-friendly principles.

Large-scale production of graphene encapsulated silicon nanospheres as flexible anodes for lithium ion batteries

Silicon (Si) is regarded as the most promising anode candidate for the next high energy density lithium ion batteries (LIBs) owing to its highest theoretical specific capacity and low lithiation potential. However, the practical application of Si-based materials is severely limited due to their enormous volume expansion, which leads to the breakdown of the electrode structure and shortens the cycle life. Herein, we successfully fabricated a free-standing graphene encapsulated silicon nanospheres (Si/rGO) film through homogenizing nano-Si in the lyotropic liquid crystallinity of graphene oxide (GO), followed by coating on the PET substrate and hot pressing technology. For the first time during the preparation process, the dispersion of nano-Si in deionized water was quantitatively characterized through real-time measurements of zeta potential and average particle size. Benefiting from the highly ordered layer-to-layer stacking and dense framework, the as-prepared Si/rGO film shows a high initial discharge capacity of 1727.2 mAh/g at 200 mA/g and superior cycling stability (1024.2 mAh/g over 200 cycles). This straightforward and easy-to-implement method can be used for industrial-scale production through continuous feeding.

Electrochemical Exfoliation and Thermal Deoxygenation of Pristine Graphene for Various Industrial Applications

The transition of graphene from the lab to consumer goods is still a challenging job that necessitates efficient and cost-effective large-scale graphene production. This study combines electrochemical exfoliation in an aqueous solution of sulfuric acid (1M H2SO[Formula: see text] and hydrogen peroxide (3% H2O[Formula: see text] followed by thermal deoxygenation at a temperature of 800[Formula: see text]C within the ambient environment. This method allows the inexpensive synthesis of pristine graphene for various industrial applications. X-Ray diffraction (XRD) results for pristine graphene showed a distinct peak at 2[Formula: see text] with a corresponding interplanar distance ([Formula: see text] of 3.3754 Å and a crystallite size of 18 nm. XRD statistics indicated that the crystal structure of the original graphene was preserved. The crystalline structure was recovered and the interplaner distance was decreased following the high temperature thermal reduction. According to Raman spectroscopy, the impurity degree (I[Formula: see text]/I[Formula: see text] region fraction of pristine graphene was 0.211. This indicates that the original graph produced by the current method has little distortion. Raman analysis shows that there is a linear red shift in peaks D-band (D), G-band (G), and second order of the D-band (2D) due to the increase in phonon–phonon nonlinear interactions with increasing temperature, so that peaks (D), (G) and (2D) shifts are shown. The majority of the functional groups were discovered to be eliminated after high temperature thermal treatment. The three-dimensional graphene sheet is highly defined and intricately coupled in the microstructure analysis, resulting in a laxer and porous structure. When treated at a temperature below 800[Formula: see text]C, there was only minor damage to the reduced graphene oxide (RGO) microstructure. The results of the Atom Force Microscope (AFM) demonstrated that the flaws spread over time from the layer boundaries and pores to the edges and eventually resulted in a separate RGO archipelago. According to TGA analysis, at temperatures up to 800[Formula: see text]C, the RGO sheet loses up to 45% of its weight.

Molecular-scale grinding of uniform small-size graphene flakes for use as lubricating oil additives

A variety of industrial preparation methods to obtain graphene from graphite have been developed, the most prominent of which are the chemical reduction of graphene oxide and intercalation-exfoliation methods. However, the low-cost, thin-layer, large-scale production of graphene with a radial dimension smaller than 1 μm (SG) remains a great challenge, which has limited the industrial development and application of small-scale graphene in areas such as textile fibers, engine oil additives, and graphene-polymer composites. We have developed a novel way to solve this problem by improved ball milling methods which form molecular-scale grinding aids between the graphite layers. This method can produce uniform, small-size (less than 1 μm) and thin-layer graphene nanosheets at a low cost, while ensuring minimal damage to the internal graphene structure. We also show that using this SG as an additive in lubricating oil not only solves the current dispersion stability of graphene, but also reduces the friction coefficient by more than 27% and wear by more than 38.8%. The SG preparation method reported is simple, low-cost, and has a significant effect in lubricating applications, which is of great commercial value.

(Invited) Rapid, Large Area Preparation of Few-Layer Graphene Films Using Xenon Flash Lamp Pyrolysis for High-Performance Structural Micro-Supercapacitors

Graphene offers excellent electrical conductivity and very high surface area, which holds great promise for energy storage applications including supercapacitors. Current preparation methods for graphene require relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involve multi-step reactions that present challenges for high throughput fabrication of graphene-based energy storage devices. We report a novel photothermal route to large-scale production of graphene within milliseconds using a commercially available polymers (polybenzoxazine, polyacrylonitrile and polyaniline) and a high intensity xenon flash lamp on various substrates, including carbon fibers, at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into few layer graphene upon millisecond exposures. The precursor material is heated to extremely high temperatures in a fraction of a second – a duration that is much shorter than the timescale for thermal equilibrium. This enabled the conversion of the polymeric material into few layer graphene in air and at room temperature, and without thermally damaging the substrate. Conversion to few-layer graphene was strongly dependent on pulse energy and the local temperature which was controlled via pulse power modulation. The obtained graphene composites at optimized conditions exhibited excellent conductivity (0.1 ohm-cm) with ID/IG ratio of 0.3 (Figure 1a). Particularly, graphene derived from polyaniline resulted in the formation of macroporous network (Figure 1b) with good adhesion to the carbon fiber, all of which facilitate the transport of ions through the material. The fabricated supercapacitor devices exhibited a very high areal capacitance of 200 mF/cm2 at 10 mV/s with retention of more than 70% of their capacitance, even at scan rates up to 100 mV/s. Moreover, mechanically, and structurally stable graphene derived from polyaniline on carbon fiber was utilized for the preparation of structural energy storage devices. We assembled symmetric structural supercapacitor comprised of carbonaceous material (carbon fiber and few-layer graphene) and polymer gel electrolyte. This resulted in the preparation of large area device (40 cm2) as shown in the Figure 1c with the capacitance exceeding 2000 mF and almost complete retention of capacitance after 5000 cycles.The preparation of high-quality graphene via photothermal pyrolysis of polymer is amenable to high throughput processing, enabling large-scale production of high performance structural electrochemical energy storage devices. Figure 1

Rapid Fabrication of Porous Graphene Network Derived Using Photothermal Flash Lamp Processing for High Performance Electrochemical Energy Storage Devices

Graphene offers superior electrical conductivity and remarkable surface area, which holds great promise for electrochemical energy storage applications including supercapacitors and lithium-ion batteries. Current preparation methods for graphene-like materials require relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involve multi-step reactions that present challenges for high throughput fabrication of graphene-based devices. Moreover, supercapacitor devices fabricated using graphene typically exhibit low areal capacitance, which limits use of the devices. We report a photothermal route to large-scale production of graphene within milliseconds from polymers using high intensity xenon flash lamp on carbon fiber at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into graphene upon millisecond exposures. This photothermally heating of polymeric material led to the formation of macroporous few layer graphene-containing network with excellent conductivity, and good adhesion to the carbon fiber all of which facilitate the transport of ions through the material. The fabricated supercapacitor devices exhibited a very high areal capacitance of 200 mF/cm2 at 10 mV/s with retention of more than 70% of its capacitance even after increasing the scan rate to 100 mV/s. Anodes for lithium-ion batteries derived from porous graphene networks on carbon fiber resulted in the device with the performance of 170 mAh/g with mass loading as high as 12 mg/cm2 (including the mass of bare CF). The preparation of high-quality graphene via photothermal pyrolysis of polyaniline is amenable to high throughput processing, enabling large-scale production of electrochemical energy storage devices.

Scalable production of electrochemically exfoliated graphene by an extensible electrochemical reactor with encapsulated anode and dual cathodes

Graphene is a carbon material with excellent physical and chemical properties, and the wide-range applications of graphene rely on the realization of its large-scale production. Electrochemical exfoliation is a green and low-cost technology ideal for large-scale graphene production. However, the falling of large particles and disconnection of large chunks of the substrate ascribing to the uncontrolled and uneven exfoliation of graphite during the process leads to low yield. Here, an efficient encapsulate electrode for the electrochemical exfoliation approach is developed, in which graphite particles can be accessed to potential connect during the overall exfoliation. Using flexible encapsulated graphite with filter cloth as both anode and cathode for the electrolyzer can approach deep exfoliation and achieve a high yield of graphene. With this new design, the yield of graphene is increased from 31 % to 57 %, while the graphene’s oxygen content (O% ∼20 %) has no distinct increase compared to the bare one (O% ∼17 %). Moreover, the exfoliation rate of the larger extensible electrochemical reactor can approach 70 g h-1, and the graphene sheets are 3 ∼ 6 layers. This simple and practical electrode with efficient exfoliation will boost the development of large-scale production of graphene and access to its application.

Enhanced room-temperature reduction of graphene oxide using Al as a supplement in the liquid phase HI

Chemical reduction of graphene oxide has emerged as one of the most suitable processes for low-cost and large-scale production of graphene for potential applications. Here we report a simple, efficient, scalable, room-temperature method for enhanced reduction of graphene oxide (GO). Nowadays, hydroiodic acid (HI) is being widely used as a reducing agent for synthesizing highly conductive reduced graphene oxide. Herein, aluminum (Al) powder was used in the second step to improve the extent of reduction using HI. Al3+, which is a strong lewis acid, helps further in the reduction and enhances the one-step reduction by HI. Field Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD), Raman and X-Ray Photoelectron Spectroscopy (XPS) confirmed the formation of GO and assisted in understanding the potential of HI and Al–HI as reducing agents. The comparative analysis demonstrates the enhancement in the reduction properties of the novel Al supplemented reduced GO. Additionally, an electrically conductive dip-coated film with a sheet resistance of 4.56 × 104 Ω/sq was successfully fabricated using this Al-supplemented reduction technique.

Effect of free radicals and electric field on preparation of coal pitch-derived graphene using flash Joule heating

Most of the traditional graphene production processes were not only solvent-intensive but also time-and-energy-consuming. Flash Joule heating (FJH) is an efficient approach to green and scalable large-scale production of graphene. However, its reaction mechanism is not clear during the process of electric field and free radical on graphene generation. In this work, synthesis of coal pitch-based graphene by FJH under the coupling effect of temperature and electric field, and Raman spectroscopy and electron transient magnetic resonance were studied at different input energies. The results show that the input energy is positively correlated with the generated radicals and is beneficial for the quality improvement of graphene. In addition, the mechanism is explained using ReaxFF molecular dynamics and DFT calculations: Joule heat provides energy for the kinetics and thermodynamics of the reaction. High temperature (3000 K) can dissociate branch chains in coal tar molecules to generate highly reactive alkane and alkene radicals. Different cooling rates affect the quality of graphene generation. When the cooling rate is slow, the graphite microplates will grow in layers, and a multi-layer phenomenon will appear; when the cooling rate is fast, the generated graphene will be in a turbostratic order. At the same time, the DFT calculation shows that the coal tar molecules are ionized under the action of the electric field and are oriented and arranged to reduce the reaction potential barrier.

Rapid Fabrication of Graphene Derived Micro-Supercapacitors on Flexible Substrates Using Millisecond Photothermal Flash Lamp Carbonization

Graphene offers excellent electrical conductivity and very high surface area, which holds great promise for energy storage applications including supercapacitors. Current preparation methods for graphene require relatively long processing times, extremely high temperatures within controlled atmospheres, and/or involve multi-step reactions that present challenges for high throughput fabrication of graphene-based devices. We report a novel photothermal route to large-scale production of graphene within milliseconds using a commercially available benzoxazine polymer and a high intensity xenon flash lamp on various substrates including carbon fiber, Kapton and stainless steel at ambient conditions. The xenon flash lamp provides large-area illumination and a wide emission band (300 nm –1100 nm) that was used to convert the polymeric material directly into graphene upon millisecond exposures. The absorption spectrum of the precursor overlaps well with the maxima of the xenon flash lamp emission spectrum. The precursor material is heated to extremely high temperatures in a fraction of a second – a duration that is much shorter than the timescale for thermal equilibrium. This enables the conversion of the polymeric material to graphene in air and at room temperature, and without thermally damaging the substrate. Characterization of these graphene composites revealed high porosity, excellent conductivity, and good adhesion. Using carbon fiber as the substrate, we prepared micro-supercapacitors exhibiting a very high areal capacitance of 3.2 mF/cm2. Furthermore, we utilized the mechanically and chemically stable graphene/carbon fiber composite as a substrate for the electrochemical deposition of MnO2 which boosted the energy storage capability of the device. The obtained pseudocapacitor has an exceptional capacitance of 300 mF/cm2 at 1mA/cm2. The device retained more than 88% of its capacitance after charging/discharging for 2000 cycles. The preparation of high-quality graphene via photothermal pyrolysis of appropriate precursors is amenable to roll-to-roll processing, and thus large-scale production of electrochemical energy storage devices can be enabled by this approach. Figure 1

INVESTIGATION THE EFFECT OF pH VALUE IN GRAPHENE OXIDE PRODUCTION

In recent years, the use of graphene oxide (GO) in advanced application areas has attracted great interest. GO consists of a carbon basal plane containing various functional groups. Thanks to its properties, GO can improve the properties of the materials to which it is added. Therefore, GO is used in various photocatalytic, sensor and battery applications. Moreover, large-scale production of graphene, which has outstanding propertiessuch as high electrical conductivity, thermal conductivity, and high surface area, is possible by reduction of GO. Therefore, quality and controllable GO production is required. GO is generally produced with the Hummer's Method, which is a suitable chemical method for industrial production. In Hummer's Method, graphite oxide is obtained by oxidizing of graphite with the help of oxidizing agents. Afterwards, GO is obtained by exfoliating of the graphite oxide. However, the original Hummer Method has many disadvantages due to the emission of harmful, dangerous gases and its low efficiency. Many Hummer's methods have been derived by researchers from past to present. As a result of various modifications, the Modified Hummer's Method, which includes efficient, non-toxic and harmless production method steps, was preferred in GO production. Each stage of production process affects the properties and structures of the obtained GO. Understanding the effect of GO production parameters on GO structure, is important for its use in electronics, optics, biological, and graphene production applications. In Hummer's Method, after the oxidation of graphite, washing with HCl followed by distilled water is applied to remove impurities. The final step, which is the washing process, is an important step for the final structure properties of GO. In this study, the effect of pH value on the obtained GO structure was investigated by using the Modified Hummer's Method that we developed. Structural characterization studies of GO samples from solutions at different pH levels were performed using X-Ray Diffractometry (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet - Visible Spectrophotometer (UV-Vis). According to the obtained results, it was determined that the difference in pH level of solution changed the structure of GO and affected the degree of exfoliation. Keywords: Graphene oxide, pH, Purification, Modified Hummer’s, XRD, FTIR.

Ultrafine Li4Ti5O12 nanocrystals as building blocks for ultrahigh-power lithium-ion battery anodes

Exploiting fast-kinetics anode materials for lithium-ion batteries shows significant importance for promoting their power density. Herein, we exhibit a rational synthesis strategy of ultrafine spinel Li4Ti5O12 nanocrystals and 3D hierarchical architectured composite by an aerosol process in which homogenous suspension of Li4Ti5O12, carbon black, and graphene oxide are atomized and assembled into spherical LTO/CB-G superstructure. The unique 3D architecture is well characterized, and its formation mechanism is discussed in detail. When applied in battery electrode, LTO/CB-G delivers superior rate performance and long cycling durability. Considering the potential large-scale production of graphene and the scalable aerosol-assisted process, 3D Li4Ti5O12-based nanocomposites hold great promise for high-power anodes in real applications of electric transportations.

Electric-Field-Triggered Graphene Production: From Fundamental Energy Applications to Perspectives

ConspectusTwo-dimensional sp2-hybridized graphene has been seriously considered and applied in various fields, such as materials science, energy storage/conversion, catalysis, and biomedicine, on account of its unique long-range-ordered and π-conjugated structure as well as excellent thermal and electric conductivity. At present, the adopted methods for graphene synthesis cover micromechanical exfoliation, epitaxial growth, chemical reduction of graphite oxide, chemical vapor deposition, and liquid-phase exfoliation. Nonetheless, a number of issues and challenges still existed in these employed methods in terms of sustainable and green energy chemistry and environmental friendliness. Electrochemical exfoliation is one of the most promising methods for the large-scale production of graphene by virtue of simple/eco-friendly operation and high-efficiency production. Depending on different exfoliation methods (anodic, cathodic, and dual-electrode) and electrochemical exfoliation conditions such as the reaction device, raw material, electrolyte, and power-supply mode, the exfoliated graphene features various and versatile characteristics. The relatively perfect graphene with intrinsic long-range π-conjugated character is accompanied by the fast capability of electron transfer. The defective graphene features the adjustable size and defect density and tunable amphipathicity. As a result, the corresponding graphene has been employed in energy storage/conversion, biology, and medicine fields. In this Account, we summarize the recent progress in the fundamentals of electrochemical exfoliation to produce the graphene and the derivative exfoliation method and their applications in energy-related fields, and the corresponding perspectives are also highlighted. First, we describe the fundamentals for different exfoliation methods and electric-field-induced effects that can help to guide us to prepare and produce graphene with various properties, covering the size, defect density, and surface chemistry. Subsequently, three electric-field-triggered methods (anodic, cathodic, and dual-electrode exfoliation) are discussed in detail. In particular, the effects of various electrolytes and power-supply modes on electrochemically exfoliated graphene (EEG) are systematically underlined in terms of the exfoliation principles and process, which are the significant factors affecting the structure and properties of EEG and the efficiency of intercalation and exfoliation. In addition, the recent progress in multilevel applications of EEG in energy storage/conversion fields such as supercapacitors, secondary batteries, the oxygen evolution reaction, the hydrogen evolution reaction, the carbon dioxide reduction reaction, and so forth is also summarized. Finally, the expectations and future research directions for the EEG in terms of controllably technological parameters and conditions, precise monitoring and in-depth comprehension of the exfoliation processes, multiscale and diverse products (carbon quantum dots, graphene quantum dots, and single-atom catalysts), and large-scale preparation and application are discussed, which hope to provide significant guidance for future research.

Large-scale Graphene Production and Transfer for Industrial Applications

Compared to chemically derived graphene (Gr), chemical deposition (CVD) grown Gr has better crystal quality and hence superior electrical properties, which render it applicable for next-generation electronic and applications including solar cells, , , sensors, etc. Though the excellent performance of CVD grown Gr based devices has been demonstrated on the lab scale, Industrial scale production of these devices is limited by reliable large-scale production and transfer of CVD grown Gr. In this review, we will summarize the latest developments on large scale CVD production of Gr and industrially applicable transfer methods.

Influence of temperature variations on the dielectric parameters of thermally reduced graphene oxide

Large-scale production of graphene remains a great challenge in which the oxidation of graphite is a promising approach for it. Graphene has unique thermal, electrical, and mechanical properties, but it is in the most common solvents insoluble. Graphene oxide can be considered as an insulator or semiconductor material. As compared to the properties of graphene and graphene oxide (GO), the reduced graphene oxide (rGO) behaves as an intermediate state between graphene and GO. Graphene oxide has been successfully synthesized from graphite powder via Hummer’s method and followed by thermal treated at 800 °C for the reduction GO in order to obtain rGO. This work elucidates the preparation method of GO and rGO step-by-step in detail. Structural characterization by X-ray diffraction of the synthesized rGO explains that the preparation and reduction of GO were effective. The morphology and structure of GO and rGO were analyzed using Scanning Electron Microscopy (SEM). Fourier Transform Infrared (FTIR) analysis displayed the disappearing of some oxygen functional groups in rGO in comparison to GO, as well as some peaks of rGO were flattened due to the removal of the carbonyl group. The aim of this paper is to analyze the dielectric properties of rGO as a function of temperature. The pellet of rGO was prepared to study the dielectric properties with respect to temperature in the range of 25 °C–300 °C for selected frequencies using LCR meter. The relative dielectric constant (ε′), dielectric loss factor (ε′′), dielectric loss tangent (tanδ), and the impedance of rGO were found to depend highly on the extent of temperature.

(Invited) Microwave Plasmas Applied for a Large-Scale Production of Graphene & Derivatives

As graphene&derivatives penetrate the industry, it becomes crucial to develop the means to mass produce high quality across all related product segments. Research efforts meet formidable challenges in the marketplace because of the lack of discernible protocols to fabricate customized products at increasingly higher yields while maintaining its quality. Notably, a recent study on the commercial graphene purchased from 60 companies worldwide has found that the majority of companies are selling a product containing less than 10% graphene content and that none of them supplied samples containing more than 50% graphene [1]. To find pathways to broad commercialization of graphene&derivatives the constant efforts must be focused on disruptively improved material synthesis.In the present report we provide substantial evidence that microwave plasma based technologies can be used as a competitive and disruptive alternative to existing chemical methods in the production of free-standing flakes of graphene and N-graphene at a large scale. Prioritizing operational flexibility, microwave plasma induced by surface waves (SW) at atmospheric pressure conditions has been employed [2]. The surface wave sustained plasma produced by the field of a traveling wave has an extended active zone outside the wave launcher because the plasma is sustained by a wave that simultaneously propagates and creates its own propagation structure. In this way, large microwave power densities can be injected into processing area and high population densities of active species of interest can be achieved. The reactor can be virtually separated in two different zones. The first one is the "hot" plasma zone. Here, the wave power is absorbed primarily by plasma electrons, which transfer the power to heavy particles via elastic and inelastic collisions resulting in gas temperatures up to 4000 K. The gas temperature gradually decreases moving away from the SW launcher and drops to about 500 K in the "mild" plasma zone. The carbon precursor mixed with background argon gas is injected in the "hot" high energy density zone where decomposition processes of the injected carbonaceous molecules take place as a result of particles collisions and intensified chemistry. The created radicals become precursors of chain reactions leading to creation of the main building blocks, i.e. carbon atoms and C2 radicals. The transport of plasma generated carbon atoms/molecules into colder zones of the reactor results in formation of solid carbon nuclei that are gradually withdrawn in the outlet plasma stream where kinetic processes of assembly and growth of “flowing” carbon nanostructures take place. Therefore, by tailoring the temperature gradients, the density of carbon molecules and atoms as well as their residence time, selective synthesis of graphene/N-graphene (nitrogen doped graphene) sheets in a narrow range of operational parameters can be achieved. Two different experimental strategies to deliver the nitrogen precursors to the plasma environment, i.e., top-to-down and down-to-top injection, have been applied. The top-to-down approach provides injection of both the carbon and the nitrogen precursors mixed with argon gas into the “hot” plasma zone, while down-to-top approach provides injection of nitrogen precursor into the “mild” plasma zone against the main flux.In this report we demonstrate an operational plasma-based proof-of-concept machine for a controllable, continuous fabrication of graphene and N-graphene at a gram scale ensuring high-degree of single layer selectivity (~50 %), high yield (~30 mg/min) and repeatability while using cheap starting materials (e.g., ethanol, methane, acetonitrile, etc.). The plasma machine provides high level of control and customization via the application of special protocols, resulting in a controllable level of N-doping, oxygen impurities and sheets size (~300 – 400 nm). The fabricated graphene/N-graphene flakes possess high quality as evidenced by comprehensive physicochemical analyses made (for pure graphene C/O ratio: > 50; sp2 carbons~ 70%; for N-graphene C/O ratio: > 40; sp2 carbons >60%).The microwave plasma driven synthesis is controllable at a single step and atmospheric pressure conditions, allows continuous production in an environmentally friendly manner.

DABCO Derived Nitrogen-Doped Carbon Nanotubes for Oxygen Reduction Reaction (ORR) and Removal of Hexavalent Chromium from Contaminated Water.

Though chemically-derived reduced graphene oxide (CDG) from graphite oxide (GO) precursors is a widely practiced procedure for the large-scale production of graphene, the quality and quantity of thus obtained CDG is dependent on the reduction strategy used. In this work, we report an all-solid-state, residue-free, microwave process for the reduction of graphene oxide and subsequent growth of carbon nanotube ‘separators’ from a single precursor, namely DABCO (1,4-diazabicyclo[2.2.2]octane). The utility of our newly developed technique in efficiently and effectively reducing graphene oxide and in growing nitrogen-doped carbon nanotubes via catalysts like palladium and iron into unique mesoporous, 3-D hierarchical carbon nanostructures is demonstrated. The applicability of the thus obtained palladium embedded in Pd@NCNT-rGO nanoarchitectures for the oxygen reduction reaction (ORR) is investigated. When carbon fiber (CF) was used as the substrate, three-dimensional Fe@NCNT-CF were obtained, whose capability as versatile adsorbents for hexavalent chromium ion removal from contaminated waters was also demonstrated.