Precise determination of graphene functionalization by in situ Raman spectroscopy

Caramel doped with aromatic compounds as halogen- and phosphorus-free flame-retardant strategy for wool fabric

The development of halogen- and phosphorus-free flame-retardant strategies is urgently needed in textile industry. In this study, a caramel product doped with aromatic compounds was developed via caramelization and aldol reactions using glucose and p-phthaldialdehyde. The modified caramel (Car@PDA) was subsequently used as a sustainable approach to improve flame retardancy of wool fabric. The flame retardancy, washing durability, heat generation, and flame-retardant mode of action of Car@PDA on wool fabric were investigated. The modified wool fabrics showed excellent flame retardancy, with the limiting oxygen index increasing to 32.5 % and the damaged length decreasing to 10.1 cm, with good self-extinguishing capacity. Car@PDA could combine with wool fibers through Schiff base reaction and electrostatic attraction, so the modified wool fabrics still self-extinguished and met the B1 flame-retardant requirements after 10 washing cycles. The modified wool showed significantly decreased heat release capacity and fire growth rate, suggesting high fire safety. Car@PDA promoted the decomposition of the fabric to form char barrier, thereby achieving an effective flame-retardant effect. In addition, the Car@PDA modification had a minimal effect on the tensile strength and handle of wool fabric. This study provides an innovative way to create bio-based, halogen- and phosphorus-free flame-retardants for protein wool fabrics.

One-Pot Synthesis of Functionalised rGO/AgNPs Hybrids as Pigments for Highly Conductive Printing Inks

This work provides a method for the development of conductive water-based printing inks for gravure, flexography and screen-printing incorporating commercial resins that are already used in the printing industry. The development of the respective conductive materials/pigments is based on the simultaneous (in one step) reduction of silver salts and graphene oxide in the presence of 2,5-diaminobenzenesulfonic acid that is used for the first time as the common in-situ reducing agent for these two reactions. The presence of aminophenylsulfonic derivatives is essential for the reduction procedure and in parallel leads to the enrichment of the graphene surface with aminophenylsulfonic groups that provide a high hydrophilicity to the final materials/pigments.

Toward the Production of Super Graphene

The quality requirements of graphene depend on the applications. Some have a high tolerance for graphene quality and even require some defects, while others require graphene as perfect as possible to achieve good performance. So far, synthesis of large-area graphene films by chemical vapor deposition of carbon precursors on metal substrates, especially on Cu, remains the main way to produce high-quality graphene, which has been significantly developed in the past 15 years. However, although many prototypes are demonstrated, their performance is still more or less far from the theoretical property limit of graphene. This review focuses on how to make super graphene, namely graphene with a perfect structure and free of contaminations. More specially, this study focuses on graphene synthesis on Cu substrates. Typical defects in graphene are first discussed together with the formation mechanisms and how they are characterized normally, followed with a brief review of graphene properties and the effects of defects. Then, the synthesis progress of super graphene from the aspects of substrate, grain size, wrinkles, contamination, adlayers, and point defects are reviewed. Graphene transfer is briefly discussed as well. Finally, the challenges to make super graphene are discussed and a strategy is proposed.

Nitrogen-Doped Hierarchical Porous Carbon Derived from Coal for High-Performance Supercapacitor

The surface properties and the hierarchical pore structure of carbon materials are important for their actual application in supercapacitors. It is important to pursue an integrated approach that is both easy and cost-effective but also challenging. Herein, coal-based hierarchical porous carbon with nitrogen doping was prepared by a simple dual template strategy using coal as the carbon precursor. The hierarchical pores were controlled by incorporating different target templates. Thanks to high conductivity, large electrochemically active surface area (483 m² g^-1), hierarchical porousness with appropriate micro-/mesoporous channels, and high surface nitrogen content (5.34%), the resulting porous carbon exhibits a high specific capacitance in a three-electrode system using KOH electrolytes, reaching 302 F g^-1 at 1 A g^-1 and 230 F g^-1 at 50 A g^-1 with a retention rate of 76%. At 250 W kg^-1, the symmetrical supercapacitor assembled at 6 M KOH shows a high energy density of 8.3 Wh kg^-1, and the stability of the cycling is smooth. The energy density of the symmetric supercapacitor assembled under ionic liquids was further increased to 48.3 Wh kg^-1 with a power output of 750 W kg^-1 when the operating voltage was increased to 3 V. This work expands the application of coal-based carbon materials in capacitive energy storage.

Morphology Effect of Photoconverted Silver Nanoparticles on the Performance of Surface-Enhanced Raman Spectroscopy Substrates

Nowadays, surface-enhanced Raman spectroscopy (SERS) substrates are of great interest for many researchers, aiming to fabricate substrates with high sensitivity and low fabrication costs. In this study, we photoconverted Ag nanoparticles by using a simple and affordable red-green-blue light-emitting diode photoreactor. The obtained dispersions were transformed into a paste of nanoparticles and used to fabricate SERS substrates by a simple drop-casting process under controlled humidity conditions. The performance of these substrates was tested using p-aminothiophenol as a Raman probe. The results indicate that the particle shape has an influence on the Raman intensities and substrate sensitivity, showing a significant enhancement as the number of faces and vertices in the particle increases.

Electrochemical Exfoliation of Graphite to Graphene-Based Nanomaterials

Here, we report on a new automated electrochemical process for the production of graphene oxide (GO) from graphite though electrochemical exfoliation. The effects of the electrolyte and applied voltage were investigated and optimized. The morphology, structure and composition of the electrochemically exfoliated GO (EGO) were probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy and Raman spectroscopy. Important metrics such as the oxygen content (25.3 at.%), defect density (I_D/I_G = 0.85) and number of layers of the formed EGO were determined. The EGO was also compared with the GO prepared using the traditional chemical method, demonstrating the effectiveness of the automated electrochemical process. The electrochemical properties of the EGO, CGO and other carbon-based materials were further investigated and compared. The automated electrochemical exfoliation of natural graphite powder demonstrated in the present study does not require any binders; it is facile, cost-effective and easy to scale up for a large-scale production of graphene-based nanomaterials for various applications.

Excitation and detection of acoustic phonons in nanoscale systems

Phonons play a key role in the physical properties of materials, and have long been a topic of study in physics. While the effects of phonons had historically been considered to be a hindrance, modern research has shown that phonons can be exploited due to their ability to couple to other excitations and consequently affect the thermal, dielectric, and electronic properties of solid state systems, greatly motivating the engineering of phononic structures. Advances in nanofabrication have allowed for structuring and phonon confinement even down to the nanoscale, drastically changing material properties. Despite developments in fabricating such nanoscale devices, the proper manipulation and characterization of phonons continues to be challenging. However, a fundamental understanding of these processes could enable the realization of key applications in diverse fields such as topological phononics, information technologies, sensing, and quantum electrodynamics, especially when integrated with existing electronic and photonic devices. Here, we highlight seven of the available methods for the excitation and detection of acoustic phonons and vibrations in solid materials, as well as advantages, disadvantages, and additional considerations related to their application. We then provide perspectives towards open challenges in nanophononics and how the additional understanding granted by these techniques could serve to enable the next generation of phononic technological applications.

Bacterial Peroxidase on Electrochemically Reduced Graphene Oxide for Highly Sensitive H2 O2 Detection

Peroxidase enzymes enable the construction of electrochemical sensors for highly sensitive and selective quantitative detection of various molecules, pathogens and diseases. Herein, we describe the immobilization of a peroxidase from Bacillus s. (BsDyP) on electrochemically reduced graphene oxide (ERGO) deposited on indium tin oxide (ITO) and polyethylene terephthalate (PET) layers. XRD, SEM, AFM, FT-IR and Raman characterization of the sensor confirmed its structural integrity and a higher enzyme surface occupancy. The BsDyP-ERGO/ITO/PET electrode performed better than other horseradish peroxidase-based electrodes, as evinced by an improved electrochemical response in the nanomolar range (linearity 0.05-280 μM of H2 O2 , LOD 32 nM). The bioelectrode was mechanically robust, active in the 3.5-6 pH range and exhibited no loss of activity upon storage for 8 weeks at 4 °C.

Thermogravimetric Analysis on a Resonant Microcantilever

Thermogravimetric analysis (TGA) is a widely applied classic method for material characterization. However, the existing TGA method has reached its technical ceiling in regard to its sensitivity, efficiency, application scope, and extensibility. With temperature-programming and a picogram (10^-12 g) mass resoluble measurement function, an integrated resonant microcantilever is proposed and developed into micro-electromechanical system-based TGA (MEMS TGA) technology to satisfy the significantly higher TGA requirements. With only a nanogram (10^-9 g) level of a loaded sample, the microcantilever can conduct ultrasensitive mass-loss analysis along with ultrafast and controllable heating up to 1200 °C. Experiments have verified that MEMS TGA can improve heating efficiency by at least one order of magnitude compared to conventional TGA while maintaining measurement accuracy. The trace sample requirement also enables MEMS TGA to directly test explosive substances in an air atmosphere, while conventional TGA with a larger amount of sample has difficulty in avoiding explosion-induced equipment damage during heating. The silicon MEMS TGA microchip also exhibits functional combination (even integration) with other analytical techniques such as Raman spectroscopy to realize operando characterization.

Laser-Triggered Bottom-Up Transcription of Chemical Information: Toward Patterned Graphene/MoS2 Heterostructures

Efficiently assembling heterostructures with desired interface properties, stability, and facile patternability is challenging yet crucial to modern device fabrication. Here, we demonstrate an interface coupling concept to bottom-up construct covalently linked graphene/MoS₂ heterostructures in a spatially defined manner. The covalent heterostructure domains are selectively created in analogy to the traditional printmaking technique, enabling graphic patterns at the bottom MoS₂ layer to be precisely transferred to the top graphene layer. This bottom-up connection and transcription of chemical information is achieved simply via laser beam irradiation. Our approach opens up a new paradigm for heterostructure construction and integration. It enables the efficient generation and real-time visualization of spatially well-resolved covalent graphene/MoS₂ heterostructures, facilitating further design and integration of patterned heterostructures into new generations of high-performance devices.

Solution-Processable Semiconducting Conjugated Planar Network

After the emergence of graphene in the material science field, top-down and bottom-up studies to develop semiconducting organic materials with layered structures became highly active. However, most of them have suffered from poor processability, which hampers device fabrication and frustrates practical applications. Here, we suggest an unconventional approach to fabricating semiconducting devices, which avoids the processability issue. We designed a soluble amorphous network using a solution process to form a thin film on a substrate. We then employed heat treatment to develop a flattened organic structure in the thin film, as an active layer for organic thin-film transistors (TFTs). The fabricated TFTs showed good performance in both horizontal and vertical charge transport, suggesting a versatile and useful approach for the development of organic semiconductors.

Evaluation of photodegradation performance by paper microzones

Currently, the performance evaluation of catalysts usually requires expensive instruments. Hence, it is imperative to develop an alternative, green and sustainable method to investigate the photocatalytic reaction processes. Herein, the variation of degradation performance of different wastewaters with different dosage of P25 TiO₂ was evaluated to verify the reliability of the paper microzones method (PMZs). The optimum P25 TiO₂ dosage of 1 g/L for the degradation of methylene blue (MB) (UV light for 6 mins) and 0.5 g/L for the degradation of fuchsin basic (FB) (UV light for 5 mins) was obtained by the PMZs method. For the photocatalytic degradation of trivalent iron ion complexed salicylic acid (Fe(III)-SA) solution, the R² values of 0.904 and 0.801 were obtained for the photocatalytic reaction kinetics by PMZs and spectrophotometry, respectively, which again indicated the high reliability of PMZs. The accuracy of the results obtained by PMZs method relative to the spectrophotometric method ranged from 68.80% to 87.54% when degrading MB, FB, mixture of MB and FB, and Fe(III)-SA by P25 TiO₂. Therefore, the PMZs method is all in line with the requirements of low-carbon environmental protection and green chemistry, and has broad application prospects in the future.

Self-Healing Graphene-Templated Platinum-Nickel Oxide Heterostructures for Overall Water Splitting

Electrocatalysts with dramatically enhanced water splitting efficiency, derived from controlled structures, phase transitions, functional activation, etc., have been developed recently. Herein, we report an in situ observation of graphene-based self-healing, in which this functional activation is induced by a redox reaction. Specifically, graphene on stainless steel (SUS) switches between graphene (C-C) and graphene oxide (C-O) coordination via an electrical redox reaction to activate water splitting. A heterostructure comprising Pt-NiO thin films on single-layer graphene directly grown on a SUS substrate (Pt-NiO/Gr-SUS) was also synthesized by electrodeposition. Pt-NiO/Gr-SUS exhibited water splitting activity with low Pt loading (<1 wt %). The findings provide valuable insight for designing robust electrodes based on reversible redox-induced self-healable graphene to develop more efficient catalysts.

Amine-Functionalized Carbon Nanodot Electrocatalysts Converting Carbon Dioxide to Methane

The electrochemical conversion of carbon dioxide (CO₂ ) to methane (CH₄ ), which can be used not only as fuel but also as a hydrogen carrier, has drawn great attention for use in supporting carbon capture and utilization. The design of active and selective electrocatalysts with exceptional CO₂ -to-CH₄ conversion efficiency is highly desirable; however, it remains a challenge. Here a molecular tuning strategy-in situ amine functionalization of nitrogen-doped graphene quantum dots (GQDs) for highly efficient CO₂ -to-CH₄ conversion is presented. Amine functionalized nitrogen-doped GQDs achieve a CH₄ Faradic efficiency (FE) of 63% and 46%, respectively, at CH₄ partial current densities of 170 and 258 mA cm^-2 , approximating to or even outperforming state-of-the-art Cu-based electrocatalysts. These GQDs also convert CO₂ to C₂ products mainly including C₂ H₄ and C₂ H₅ OH with a maximum FE of ≈10%. A systematic analysis reveals that the CH₄ yield varies linearly with amine group content, whereas the C₂ production rate is positively dependent on pyridinic N dopant content. This work provides insight into the rational design of carbon catalysts with CO₂ -to-CH₄ conversion efficiency at the industrially relevant level.

Nanofabrication route to achieve sustainable production of next generation defect-free graphene: analysis and characterisation

In the past two decades, graphene has been one of the most studied materials due to its exceptional properties. The scalable route to cost-effective manufacture defect-free graphene has continued to remain a technical challenge. Intrinsically defect-free graphene changes its properties dramatically, and it is a challenging task to control the defects in graphene production using scaled-down subtractive manufacturing techniques. In this work, the exfoliation of graphite was investigated as a sustainable low-cost graphene manufacturing technique. The study made use of a simple domestic appliance e.g., a kitchen blender to churn graphene in wet conditions by mixing with N-Methyl-2-pyrrolidone (NMP). It was found that the centrifugal force-induced turbulent flow caused by the rotating blades exfoliates graphite flakes to form graphene. The technique is endowed with a high yield of defect-free graphene (0.3 g/h) and was deemed suitable to remove 10% fluoride content from the water and color absorption from fizzy drinks.

Studying 2D materials with advanced Raman spectroscopy: CARS, SRS and TERS

Raman spectroscopy has been established as a valuable tool to study and characterize two-dimensional (2D) systems, but it exhibits two drawbacks: a relatively weak signal response and a limited spatial resolution. Recently, advanced Raman spectroscopy techniques, such as coherent anti-Stokes spectroscopy (CARS), stimulated Raman scattering (SRS) and tip-enhanced Raman spectroscopy (TERS), have been shown to overcome these two limitations. In this article, we review how useful physical information can be retrieved from different 2D materials using these three advanced Raman spectroscopy and imaging techniques, discussing results on graphene, hexagonal boron-nitride, and transition metal di- and mono-chalcogenides, thus providing perspectives for future work in this early-stage field of research, including similar studies on unexplored 2D systems and open questions.

Theoretical study of small aromatic molecules adsorbed in pristine and functionalised graphene

Small aromatic molecules are precursors for several biological systems such as DNA, proteins, drugs, and are also present in several pollutants. The understanding of the interaction of these small aromatic molecules with pristine and functionalised graphene (fGr) can generate different applications. We performed ab initio simulations based on the density functional theory to evaluate the interaction between the aromatic compounds, benzene, benzoic acid, aniline and phenol, with pristine and fGr. The results show that the binding energy for all cases is less than 103.24 kJ/mol (1.07 eV) without substantial modification of the electronic properties, indicating that the interaction occurs through a physical adsorption regime. The results are promising because they suggest that pristine graphene and functionalised graphene are suitable for removing these pollutants, or for carrying molecules for biological applications influenced by π-π and H-bonds interaction.

Benzofurazan derivatives modified graphene oxide nanocomposite: Physico-chemical characterization and interaction with bacterial and tumoral cells

Two novel graphene oxide-benzofuran derivatives composites were obtained through the covalent immobilization of [4-hydrazinyl-7nitrobenz-[2,1,3-d]-oxadiazole (NBDH) and respectively, N1-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)benzene-1,2-diamine (NBD-PD), on graphene oxide. This covalent functionalization was achieved by activating the carboxylic groups on the surface of graphene oxide by the reaction with thionyl chloride followed by coupling with the amino group of benzofurazane derivatives to obtain the NBD derivatives grafted on graphene oxide. The formation of new materials was check by Raman spectroscopy, fluorescence, infrared spectroscopy and X-ray photoelectron spectroscopy, thermal analysis, scanning electron microscopy, and elemental mapping. The antimicrobial effect of the new composites was evaluated on Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, both on planktonic and adherent biofilm populations. The cytotoxic effects of the materials on human colon cancer HCT-116 cell line and the normal human fibroblast BJ cell line were evaluated by investigating cell viability and membrane integrity. Apoptosis and colony forming ability of tumor cells were also investigated following exposure to new materials. The biological results of this study have shown that the new materials have potential in combating biofilm formation and also, the tested materials induced cytotoxicity in human colon cancer HCT-116 cell line with limited effects on normal BJ fibroblasts, suggesting their antitumor potential.

Tuning the Oxygen Content of Reduced Graphene Oxide and Effects on Its Properties

The need to recover the graphene properties in terms of electrical and thermal conductivity calls for the application of reduction processes leading to the removal of oxygen atoms from the graphene oxide sheet surface. The recombination of carbon-carbon double bonds causes a partial recovery of the original graphene properties mainly limited by the presence of residual oxygen atoms and lattice defects. However, the loss of polar oxygen-based functional groups renders the material dispersibility rather complicated. In addition, oxygen-containing functional groups are reaction sites useful to further bind active molecules to engineer the reduced graphene sheets. For these reasons, a variety of chemical processes are described in the literature to reduce the graphene oxide. However, it is greatly important to select a chemical process enabling a thin modulation of the residual oxygen content thus tuning the properties of the final product. In this work, we will present a chemical-processing technique based on the hydroiodic acid to carefully control the degree of residual oxidation. Graphene oxides were reduced using hydroiodic acid with concentrations from 0.06 to 0.95 mol L-1. Their properties were characterized in detail and tested, and the results showed that their oxygen content was finely tuned from 33.6 to 10.7 atom %. This allows carefully tailoring the material properties with respect to the desired application, which is exemplified by the variation of the bulk resistance from 92 Ω to 14.8 MΩ of the film from the obtained rGO.

Growth and in situ characterization of 2D materials by chemical vapour deposition on liquid metal catalysts: a review

2D materials (2DMs) have now been established as unique and attractive alternatives to replace current technological materials in a number of applications. Chemical vapour deposition (CVD), is undoubtedly the most renowned technique for thin film synthesis and meets all requirements for automated large-scale production of 2DMs. Currently most CVD methods employ solid metal catalysts (SMCat) for the growth of 2DMs however their use has been found to induce structural defects such as wrinkles, fissures, and grain boundaries among others. On the other hand, liquid metal catalysts (LMCat), constitute a possible alternative for the production of defect-free 2DMs albeit with a small temperature penalty. This review is a comprehensive report of past attempts to employ LMCat for the production of 2DMs with emphasis on graphene growth. Special attention is paid to the underlying mechanisms that govern crystal growth and/or grain consolidation and film coverage. Finally, the advent of online metrology which is particularly effective for monitoring the chemical processes under LMCat conditions is also reviewed and certain directions for future development are drawn.

In situ laser annealing as pathway for the metal free synthesis of tailored nanographenes

Tailored synthesis of nanographenes, and especially graphene nanoribbons (GNR), has been achieved on metal substrates via a bottom-up approach from organic precursors, which paves the way to their application in nanoelectronics and optoelectronics. Since quantum confinement in nanographenes leads to the creation of peculiar band structures, strongly influenced by their topological characteristics, it is important to be able to exactly engineer them in order to precisely tune their electronic, optical and magnetic properties. However practical application of these materials requires post-synthesis transfer to insulating substrates. Recently, cyclodehydrofluorination of fluorinated organic precursors has been shown to be a promising pathway to achieve metal-free bottom-up synthesis of nanographenes. Here we present how to apply in situ laser annealing to induce cyclodehydrofluorination leading to nanographene formation directly on non-metallic surfaces. In this work, we analyze the changes in the Raman fingerprint of the fluorinated precursor tetrafluoro-diphenyl-quinquephenyl (TDQ) during the laser annealing process in high vacuum (HV), demonstrating that both heating and photo-induced processes influence the cyclization process. Hence, in situ laser annealing allows not only to influence chemical reactions, but also to have a fast and contact-free monitoring of the reaction products. Optimization of the laser annealing process adds a new level of control in the tailored synthesis of nanographenes on non-metallic substrates. This is a very promising pathway to unravel the full application potential of nanographenes in general and GNR in particular, enabling a fast optimization of precursor molecules and substrate geometry engineered for specific applications.

The fate of oxygen on graphene-catalyst in the photocatalytic water splitting reaction

This paper reveals the transformation of oxygen on graphene in the water splitting process and for the first time, points out a step by step dehydrogenation process with the intermediates OH–C and O–C, and finally CO2.

Optimized and scalable synthesis of magnetic nanoparticles for RNA extraction in response to developing countries' needs in the detection and control of SARS-CoV-2

Ecuador is one of the most affected countries, with the coronavirus disease 2019 (COVID-19) infection, in Latin America derived from an ongoing economic crisis. One of the most important methods for COVID-19 detection is the use of techniques such as real time RT-PCR based on a previous extraction/purification of RNA procedure from nasopharyngeal cells using functionalized magnetic nanoparticles (MNP). This technique allows the processing of ~ 10,000 tests per day in private companies and around hundreds per day at local Universities guaranteeing to reach a wide range of the population. However, the main drawback of this method is the need for specialized MNP with a strong negative charge for the viral RNA extraction to detect the existence of the SARS-CoV-2 virus. Here we present a simplified low cost method to produce 10 g of nanoparticles in 100 mL of solution that was scaled to one litter by parallelizing the process 10 times in just two days and allowing for the possibility of making ~ 50,000 COVID-19 tests. This communication helps in reducing the cost of acquiring MNP for diverse biomolecular applications supporting developing country budgets constraints and chemical availability specially during the COVID-19 International Health Emergency.

Aryl Migration on Graphene

The design and synthesis of molecular systems able to carry out movements resembling macroscopic objects is an exciting and challenging endeavor. Molecules that can walk covalently on a track have been demonstrated, and we now report how aryl groups that can migrate over a graphene surface. Specifically, we describe a system comprised of covalently functionalized aryl groups on graphene that undergo continuous aryl shifts. The dynamic aryl shift allows the aryl groups on graphene to effectively migrate step-by-step wherein each step involves reversible bond breaking and making that is initiated by a combination of an activated arene and p-doping of the graphene surface. Raman spectroscopic mapping of the distribution of the covalent attachment revealed that activated 4-methoxyphenyl groups migrate several microns from regions of high functionalization to regions with no prior functionalization.

Electrocatalytic Properties of 3D Hierarchical Graphitic Carbon-Cobalt Nanoparticles for Urea Oxidation

A 3D hierarchical graphitic carbon nanostructure encapsulating cobalt(0)/cobalt oxide nanoparticles (CoGC) has been prepared by solid-state pyrolysis of a mixture of anthracene and cobalt 2,2'-bipyridine terephthalate complex at 850 °C. Based on the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, the prepared material has high surface area (186.8 m² g^-1) with an average pore width of 205.5 Å. XPS reveals the functionalization of carbon with different oxygen-containing groups, such as carboxylic acid groups. The presence of metallic cobalt nanoparticles with cubic and hexagonal crystalline structures encapsulated in graphitized carbon is confirmed using XRD and TEM. Raman spectroscopy indicates a graphitization degree of I _D/I _G = 1.02. CoGC was cast onto a glassy carbon electrode and used for urea electrooxidation in an alkaline solution. The electrochemical investigation shows that the newly prepared CoGC has a promising electrocatalytic activity toward urea. The specific activity is 128 mA cm^-1 mg^-1 for the electrooxidation of 0.3 M urea in 1 M KOH at a relatively low onset potential (0.31 V vs Ag/AgCl). It can be mainly attributed to the morphological structure of carbon and the high reactivity of cobalt nanoparticles. The calculated charge-transfer resistance, R _ct, of the modified electrode in the presence of urea (10.95 Ω) is significantly lower than that in the absence of urea (113.5 Ω), which indicates electrocatalytic activity. The value of charge-transfer rate constant, k _s, for the anodic reaction is 0.0058 s^-1. Electrocatalytic durability in 1000 s chronoamperometry of the modified electrode suggests high structure stability. The modified electrode retained about 60% of its activity after 100 cycles as indicated by linear sweep voltammetry.

New Limits for Stability of Supercapacitor Electrode Material Based on Graphene Derivative

Supercapacitors offer a promising alternative to batteries, especially due to their excellent power density and fast charging rate capability. However, the cycling stability and material synthesis reproducibility need to be significantly improved to enhance the reliability and durability of supercapacitors in practical applications. Graphene acid (GA) is a conductive graphene derivative dispersible in water that can be prepared on a large scale from fluorographene. Here, we report a synthesis protocol with high reproducibility for preparing GA. The charging/discharging rate stability and cycling stability of GA were tested in a two-electrode cell with a sulfuric acid electrolyte. The rate stability test revealed that GA could be repeatedly measured at current densities ranging from 1 to 20 A g-1 without any capacitance loss. The cycling stability experiment showed that even after 60,000 cycles, the material kept 95.3% of its specific capacitance at a high current density of 3 A g-1. The findings suggested that covalent graphene derivatives are lightweight electrode materials suitable for developing supercapacitors with extremely high durability.

Intriguing Carbon Flake Formation during Microwave-Assisted Hydrothermal Carbonization of Sodium Lignosulfonate

Elongated carbon structures, here denoted as carbon flakes (CF), are revealed after microwave-assisted hydrothermal carbonization of sodium lignosulfonate. The morphology of formed CF is investigated by transmission electron microscopy and atomic force microscopy. Interestingly, a wide range of length distributions (between 100 and 700 nm) and a relatively constant aspect ratio and thickness are observed, indicating structures clearly different from the carbon spheres commonly formed during hydrothermal carbonization of lignocellulosic biomass. Moreover, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy provide further information of the chemical structure, which consist mainly of nanographitic domains with a high degree of defects such as oxygenated functional groups, hybridized sp3 carbon, and aliphatic side chains. Furthermore, new insights into the formation mechanisms are uncovered and the formation is speculated to proceed through the combined effect of microwave irradiation and a heterogeneous solid-solid conversion. The formed CF are anticipated as highly interesting products for a variety of material applications.

Ultralong Spin Lifetime in Light Alkali Atom Doped Graphene

Today's great challenges of energy and informational technologies are addressed with a singular compound, Li- and Na-doped few-layer graphene. All that is impossible for graphite (homogeneous and high-level Na doping) and unstable for single-layer graphene works very well for this structure. The transformation of the Raman G line to a Fano line shape and the emergence of strong, metallic-like electron spin resonance (ESR) modes attest the high level of graphene doping in liquid ammonia for both kinds of alkali atoms. The spin-relaxation time in our materials, deduced from the ESR line width, is 6-8 ns, which is comparable to the longest values found in spin-transport experiments on ultrahigh-mobility graphene flakes. This could qualify our material as a promising candidate in spintronics devices. On the other hand, the successful sodium doping, this being a highly abundant metal, could be an encouraging alternative to lithium batteries.

Understanding the Electron-Doping Mechanism in Potassium-Intercalated Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) can be doped with potassium, similar to graphite, leading to intercalation compounds. These binary systems exhibit a clear metallic character. However, the entire picture of how electron doping (e-doping) modifies the SWCNTs' vibrational spectra as a function of their diameter, chirality, and metallicity is still elusive. Herein, we present a detailed study of the intercalation and solid state reduction of metallic and semiconducting enriched HiPco SWCNTs. We performed a combined experimental and theoretical study of the evolution of their Raman response with potassium exposure, focusing specifically on their radial breathing mode (RBM). We found the charge donated from the potassium atoms occupies antibonding π orbitals of the SWCNTs, weakening their C-C bonds, and reducing the RBM frequency. This RBM downshift with increasing doping level is quasi-linear with a steplike behavior when the Fermi level crosses a van Hove singularity for semiconducting species. Moreover, this weakening of the C-C bonds is greater with decreasing curvature, or increasing diameter. Overall, this suggests the RBM downshift with e-doping is proportional to both the SWCNT's integrated density of states (DOS) ϱ(ε) and diameter d. We have provided a precise and complete description of the complex electron doping mechanism in SWCNTs up to a charge density of -18 me/C, far beyond that achievable by standard gate voltage studies, not being the highest doping possible, but high enough to track the effects of doping in SWCNTs based on their excitation energy, diameter, band gap energy, chiral angle, and metallicity. This work is highly relevant to tuning the electronic properties of SWCNTs for applications in nanoelectronics, plasmonics, and thermoelectricity.

Characterizing the maximum number of layers in chemically exfoliated graphene

An efficient route to synthesize macroscopic amounts of graphene is highly desired and bulk characterization of such samples, in terms of the number of layers, is equally important. We present a Raman spectroscopy-based method to determine the typical upper limit of the number of graphene layers in chemically exfoliated graphene. We utilize a controlled vapour-phase potassium intercalation technique and identify a lightly doped stage, where the Raman modes of undoped and doped few-layer graphene flakes coexist. The spectra can be unambiguously distinguished from alkali doped graphite, and modeling with the typical upper limit of the layers yields an upper limit of flake thickness of five layers with a significant single-layer graphene content. Complementary statistical AFM measurements on individual few-layer graphene flakes find a consistent distribution of the layer numbers.

Preparation and in-situ Raman characterization of binder-free u-GF@CFC cathode for rechargeable aluminum-ion battery

We provide a method for preparation of binder-free cathode for rechargeable aluminum-ion batteries (AIBs). Ultrasonicated natural graphite (u-NG) flakes in N-methylpyrrolidone (NMP) is drop-casted to a carbon fiber cloth (CFC) to obtain binder-free u-GF@CFC cathode for AIBs. We also provide an in-situ Raman spectral technology and the corresponding in-situ Raman cell to determine the mechanism of intercalation/deintercalation reactions of the chloroaluminate ions at cathode of AIBs. The in-situ Raman spectra are recorded using a Raman spectrometer combined with a potentiostat/galvanostat model electrochemical workstation.

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A simple preparation method of a binder-free u-GF@CFC cathode is suggested.

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The u-GF@CFC cathode is obtained by drop-casting ultrasonicated graphite flakes on the surface and internal gaps of the carbon fiber cloth.

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The method includes the in-situ Raman spectral technology and the corresponding in-situ Raman cell.

Raman spectroscopy of bottom-up synthesized graphene quantum dots: size and structure dependence

Graphene quantum dots (GQDs) have attracted significant interest as synthetically tunable optoelectronic and photonic materials that can also serve as model systems for understanding size-dependent behaviors of related graphene structures such as nanoribbons. We present a Raman spectroscopy study of bottom-up synthesized GQDs with lateral dimensions between 0.97 to 1.62 nm, well-defined (armchair) edge type, and fully benzenoid structures. For a better understanding of observed size-dependent trends, the study is extended to larger graphene structures including nano-graphene platelets (>25 nm) and large-area graphene. Raman spectra of GQDs reveal the presence of D and G bands, as well as higher order modes (2D, D + G, and 2G). The D and G band frequencies and intensity were found to increase as GQD size increases, while higher order modes (2D, D + G, and 2G) also increased in intensity and became more well-defined. The integrated intensity ratios of D and G bands (I_D/I_G) increase as the size of the GQDs approaches 2 nm and rapidly decrease for larger graphene structures. We present a quantitative comparison of I_D/I_G ratios for the GQDs and for defects introduced into large area graphenes through ion bombardment, for which inter-defect distances are comparable to the sizes of GQDs studied here. Close agreement suggests the I_D/I_G ratio as a size diagnostic for other nanographenes. Finally, we show that Raman spectroscopy is also a good diagnostic tool for monitoring the formation of bottom-up synthesized GQDs.

Lattice Opening upon Bulk Reductive Covalent Functionalization of Black Phosphorus

The chemical bulk reductive covalent functionalization of thin-layer black phosphorus (BP) using BP intercalation compounds has been developed. Through effective reductive activation, covalent functionalization of the charged BP by reaction with organic alkyl halides is achieved. Functionalization was extensively demonstrated by means of several spectroscopic techniques and DFT calculations; the products showed higher functionalization degrees than those obtained by neutral routes.

The correlation between electrical conductivity and second-order Raman modes of laser-reduced graphene oxide

Second-order Raman modes correlate with the electrical properties of reduced graphene oxide measured at the nanoscale by atomic force microscopy.