Scalable fabrication of highly conductive 3D graphene by electrochemical exfoliation of graphite in molten NaCl under Ar/H2 atmosphere

Vacancy-plane-mediated exfoliation of sub-monolayer 2D pyrrhotite

Conventional exfoliation exploits the anisotropy in bonding or compositional character to delaminate 2D materials with large lateral size and atomic thickness. This approach, however, limits the choice to layered host crystals with a specific composition. Here, we demonstrate the exfoliation of a crystal along planes of ordered vacancies as a novel route toward previously unattainable 2D crystal structures. Pyrrhotite, a non-stoichiometric iron sulfide, was utilized as a prototype system due to its complex vacancy superstructure. Bulk pyrrhotite crystals were synthesized by gas-assisted bulk conversion, and their diffraction pattern revealed a 4C superstructure with 3 vacancy interfaces within the unit cell. Electrochemical intercalation and subsequent delamination yield ultrathin 2D flakes with a large lateral extent. Atomic force microscopy confirms that exfoliation occurs at all three supercell interfaces, resulting in the isolation of 2D structures with sub-unit cell thicknesses of 1/2 and 1/4 monolayers. The impact of controlling the morphology of 2D materials below the monolayer limit on 2D magnetic properties was investigated. Bulk pyrrhotite was shown to exhibit ferrimagnetic ordering that agrees with theoretical predictions and that is retained after exfoliation. A complex magnetic domain structure and an enhanced impact of vacancy planes on magnetization emphasize the potential of our synthesis approach as a powerful platform for modulating magnetic properties in future electronics and spintronics.

Porous Graphene Produced by Carbothermal Shock for Green Electromagnetic Interference Shielding in Both Microwave and Terahertz Bands

The prospect of graphene-based shielding materials in the form of fillers is limited by the cumbersome preparation of graphene. Herein, defect-tunable porous graphene prepared by carbothermal shock using low-value sucrose as a precursor is proposed as an effective shielding filler. The resultant porous graphene exhibits 32.5 dB shielding efficiency (SE) and 2.5-18 GHz effective bandwidth at a mass loading of 20 wt%, competing with the shielding performance of graphene fillers prepared by other methods. Particularly, defect-rich graphene synthesized by increasing voltage and prolonging time shows increased electromagnetic (EM) wave absorption, echoing the current concept of green shielding. In addition, the strategy of controlling the discharge conditions to improve the absorption by the shield is developed in the terahertz band. The average SE and reflection loss of the samples in the THz band (0.2-1.2 THz) exhibit 40.7 and 15.9 dB at filler loading of 5 wt%, respectively, achieving effective shielding and absorption of THz waves. This work paves a new way for low-cost preparation of graphene for EM interference shielding fillers. Meanwhile, it supplies a reference for the shielding research of the upcoming applications integrating multiple EM bands (such as sixth-generation based integrated sensing and communication).

Total exfoliation of graphite in molten salts

The exfoliation of graphite to graphene nanoplatelets (GnP) in a molten salt medium is investigated in this study. It is shown that this mechanical force-free process yielded a large-sized GnP product (>15 microns) with a low defect density. The effect of the surface tension of the molten salt on graphite exfoliation efficiency was investigated for a series of alkali chloride salts (CsCl, KCl, NaCl and eutectic NaCl-KCl) at 850 °C. It was demonstrated that the produced GnP could be completely and easily separated from the salt. Molten salt with the lowest value of surface tension (CsCl) displayed the highest wettability of the graphitic layers and hence facilitated total exfoliation of the graphite to GnP. The exfoliation of graphite in molten salts is applicable in the thermal energy storage field, as well as in exfoliation of other layered materials. Herein, it is demonstrated that the thermal conductivity of the GnP-CsCl composite is enhanced by ∼300% compared to the neat salt.

Green syntheses of graphene and its applications in internet of things (IoT)-a status review

Internet of Things (IoT) is a trending technological field that converts any physical object into a communicable smarter one by converging the physical world with the digital world. This innovative technology connects the device to the internet and provides a platform to collect real-time data, cloud storage, and analyze the collected data to trigger smart actions from a remote location via remote notifications, etc. Because of its wide-ranging applications, this technology can be integrated into almost all the industries. Another trending field with tremendous opportunities is Nanotechnology, which provides many benefits in several areas of life, and helps to improve many technological and industrial sectors. So, integration of IoT and Nanotechnology can bring about the very important field of Internet of Nanothings (IoNT), which can re-shape the communication industry. For that, data (collected from trillions of nanosensors, connected to billions of devices) would be the 'ultimate truth', which could be generated from highly efficient nanosensors, fabricated from various novel nanomaterials, one of which is graphene, the so-called 'wonder material' of the 21st century. Therefore, graphene-assisted IoT/IoNT platforms may revolutionize the communication technologies around the globe. In this article, a status review of the smart applications of graphene in the IoT sector is presented. Firstly, various green synthesis of graphene for sustainable development is elucidated, followed by its applications in various nanosensors, detectors, actuators, memory, and nano-communication devices. Also, the future market prospects are discussed to converge various emerging concepts like machine learning, fog/edge computing, artificial intelligence, big data, and blockchain, with the graphene-assisted IoT field to bring about the concept of 'all-round connectivity in every sphere possible'.

Carbon nanofibers derived from cellulose via molten-salt method as supercapacitor electrode

Carbon nanofibers (CNFs) have been paid much attention as supercapacitor electrode due to outstanding chemical stability, high electron transfer rate and large specific surface area. However, the preparation process of CNFs is always stalemated in electrospinning, heat stabilization and carbonization. The problems of solvent pollution in the electrospinning process, complex process and high energy consumption in conventional carbonization process can't be solved. Herein, CNFs have been innovatively prepared from nanofibrillated cellulose by the molten-salt method (NaCl/NaOH). Molten salt penetrates between the fibers, separates and activates the fibers. The obtained carbon nanofibers remain developed branching structures and have a large specific surface area (899 m² g^-1). The electrical properties are tested in a symmetrical two-electrode system. The specific capacitance is 150 F g^-1 at the current density of 1 A g^-1. Low equivalent series resistance (1.13 Ω) indicates that it has high electrode conductivity. This study has taken into account energy conservation, environmental protection, recyclability and simplified preparation process, which has a very far-reaching significance for the industrial production of CNFs.

Constructing Graphitic-Nitrogen-Bonded Pentagons in Interlayer-Expanded Graphene Matrix toward Carbon-Based Electrocatalysts for Acidic Oxygen Reduction Reaction

Metal-free carbon-based materials with high electrocatalytic activity are promising catalysts for the oxygen reduction reaction (ORR) in several renewable energy systems. However, the performance of carbon-based materials is far inferior to that of Pt-based catalysts in acid electrolytes. Here, a novel carbon-based electrocatalyst is reported toward ORR in 0.1 m HClO₄ with half-wave potential of 0.81 V and better durability (100 h reaction time) than commercial 20 wt% Pt/C. It is achieved by constructing graphitic-nitrogen (GN)-bonded pentagons in graphitic carbon to improve the intrinsic activity of the carbon sites and increasing the amount of active sites via expanding the interlayer spacing. X-ray absorption spectroscopy and aberration-corrected electron microscopy characterizations confirm the formation of GN-bonded pentagons in this carbon material. Raman and X-ray photoelectron spectroscopy reveal that the activity is linearly associated with the amounts of both pentagons and adjacent GN atoms. Density function theory further demonstrates that adjacent GN atoms significantly increase the charge density at the carbon atom of a GN-bonded pentagon, which is the activity origin for the ORR.

Anti-pathogenic activity of graphene nanomaterials: A review

Graphene and its derivatives are promising candidates for a variety of biological applications, among which, their anti-pathogenic properties are highly attractive due to the outstanding physicochemical characteristics of these novel nanomaterials. The antibacterial, antiviral and antifungal performances of graphene are increasingly becoming more important due to the pathogen's resistance to existing drugs. Despite this, the factors influencing the antibacterial activity of graphene nanomaterials, and consequently, the mechanisms involved are still controversial. This review aims to systematically summarize the literature, discussing various factors that affect the antibacterial performance of graphene materials, including the shape, size, functional group and the electrical conductivity of graphene flakes, as well as the concentration, contact time and the pH value of the graphene suspensions used in related microbial tests. We discuss the possible surface and edge interactions between bacterial cells and graphene nanomaterials, which cause antibacterial effects such as membrane/oxidative/photothermal stresses, charge transfer, entrapment and self-killing phenomena. This article reviews the anti-pathogenic activity of graphene nanomaterials, comprising their antibacterial, antiviral, antifungal and biofilm-forming performance, with an emphasis on the antibacterial mechanisms involved.

Clean production and utilisation of hydrogen in molten salts

Green and low cost production of strategic materials such as steel and graphene at large scale is a critical step towards sustainable industrial developments. Hydrogen is a green fuel for the future, and a key element for the clean production of steel. However, the sustainable and economic production of hydrogen is a barrier towards its large scale utilisation in iron and steelmaking, and other possible applications. As a key challenge, the water electrolysis, which is commonly used for the carbon-free production of hydrogen, is uneconomic and involves various problems including the corrosion of equipment, the use of expensive catalysts and high over-potentials, limiting its viability. Moreover, the hydrogen transportation from the electrolyser to the utilisation unit is problematic in terms of cost and safety. From a thermodynamic point of view, the potential and efficiency of the water splitting process can greatly be improved at high temperatures. Therefore, a practical approach to resolve the above-mentioned shortcomings can be based on the electro-generation of hydrogen in high temperature molten salts, and the utilisation of the generated hydrogen in situ to produce metals, alloys or other commercially valuable materials. Clean production of alloy powders is particularly interesting due to the rising of advanced manufacturing methods like additive manufacturing. The hydrogen produced in molten salts can also be used for the large scale preparation of high value advanced carbon nanostructures such as single and multi-layer high quality graphene and nanodiamonds. The combination of these findings can lead to the fabrication of hybrid structures with interesting energy and environmental applications. Surprisingly, the production of a large variety of materials such as Fe, Mo, W, Ni and Co-based alloys should be achievable by the electrolytic hydrogen produced in molten salts at a potential of around 1 V, which can easily be powered by advanced photovoltaic cells. This review discusses the recent advancements on these topics.

Preparation of Y2SiO5:Pr3+,Li and Na2NbxTa2−xO6/(Au/RGO) composites and investigation into visible-light driven photocatalytic hydrogen production

A three-component photocatalytic system is constructed by using Na₂Nb_xTa_2−xO₆ as the main catalyst, Y₂SiO₅:Pr³⁺,Li as the up-conversion luminescence agent and Au/RGO as the co-catalyst.