High-quality thin graphene films from fast electrochemical exfoliation

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.

Ultrasensitive detection of 5-hydroxymethylcytosine in genomic DNA using a graphene-based sensor modified with biotin and gold nanoparticles

Ten-eleven translocation (TET) proteins orchestrate deoxyribonucleic acid (DNA) methylation-demethylation dynamics by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC) and are frequently inactivated in various cancers. Due to the significance of 5hmC as an epigenetic biomarker for cancer diagnosis, pathogenesis, and treatment, its rapid and precise quantification is essential. Here, we report a highly sensitive electrochemical method for quantifying genomic 5hmC using graphene sheets that were electrochemically exfoliated and functionalized with biotin and gold nanoparticles (Bt-AuNPs) through a single-step electrical method. The attachment of Bt-AuNPs to graphene enhances the specificity of 5hmC-containing DNA and augments the oxidation of 5hmC to 5-formylcytosine in DNA. When coupled to a gold electrode, the Bt-AuNP-graphene-based sensor exhibits exceptional sensitivity and specificity for detecting 5hmC, with a detection limit of 63.2 fM. Furthermore, our sensor exhibits a remarkable capacity to measure 5hmC levels across a range of biological samples, including preclinical mouse tissues with varying 5hmC levels due to either TET gene disruption or oncogenic transformation, as well as human prostate cancer cell lines. Therefore, our sensing strategy has substantial potential for cancer diagnostics and prognosis.

Improved Mechanical Properties of Graphene/Carbon Fiber Composites via Silanization

Despite their excellent mechanical performance, carbon fiber-reinforced polymer (CFRP) composites are limited by the interfacial properties due to the inherent nature of laminated structures. One way to modify the interface is by the inclusion of nanomaterials. Here, we use electrochemical exfoliation to produce graphene (EEG) flakes that have hydroxyl and epoxy functional groups. To further improve the interfacial bonding, silanization was carried out on graphene with 3-aminopropyl triethoxysilane, and then, EEA flakes were achieved. Both flakes were dispersed in ethanol and spray-coated onto carbon fibers, followed by vacuum-assisted resin infusion to make hybrid composites. Testing of their mechanical properties showed that EEG flakes tend to act as points of stress concentration, which accelerated the delamination, while the EEA flakes improved interfacial properties owing to the covalent bonding. As a result, with only 0.5 wt % EEA flakes spray-coated onto the carbon fibers, the tensile and flexural strength of graphene/carbon fiber composites improved by 17.6 and 5.4%, respectively. The combination of electrochemical exfoliation, silanization, spray coating, and vacuum-assisted resin infusion enables large-scale hybrid composite fabrication without size or shape limitations, without weakening the CFs or carbon fabric patterns, and is suitable for continuous production. This process has proven to be practical and attractive for engineering applications.

Electrochemical exfoliation of graphene from pencil lead

Addressing an ever-increasing demand for graphene in recent years, simple, accessible, and effective graphene synthesis methods are essential. One of such methods is to use a highly oriented pyrolytic graphite (HOPG) to perform an electrochemical exfoliation. While this is one of the simplest and most cost-effective methods, the limited availability and price of HOPG hinders its usage. Our study proposed a simple and economical electrochemical exfoliation of pencil lead, producing graphene with properties comparable to that produced from HOPG. The electrical properties are determined by depositing graphene onto a screen-printed electrode. Graphene from pencil leads can achieve an electrical resistance as low as 1.86 kΩ, marking over 80% improvement in electrical performance compared to bare electrodes. This finding provides an alternative for the synthesis of graphene, increasing its availability and the cost-effectiveness as well as contributing towards a potential commercialization of the method in the future.

Intercalation in 2D materials and in situ studies

Intercalation of atoms, ions and molecules is a powerful tool for altering or tuning the properties - interlayer interactions, in-plane bonding configurations, Fermi-level energies, electronic band structures and spin-orbit coupling - of 2D materials. Intercalation can induce property changes in materials related to photonics, electronics, optoelectronics, thermoelectricity, magnetism, catalysis and energy storage, unlocking or improving the potential of 2D materials in present and future applications. In situ imaging and spectroscopy technologies are used to visualize and trace intercalation processes. These techniques provide the opportunity for deciphering important and often elusive intercalation dynamics, chemomechanics and mechanisms, such as the intercalation pathways, reversibility, uniformity and speed. In this Review, we discuss intercalation in 2D materials, beginning with a brief introduction of the intercalation strategies, then we look into the atomic and intrinsic effects of intercalation, followed by an overview of their in situ studies, and finally provide our outlook.

Molecularly Imprinted Polymer Biosensor Based on Nitrogen-Doped Electrochemically Exfoliated Graphene/Ti3 CNTX MXene Nanocomposite for Metabolites Detection

Rapid and accurate quantification of metabolites in different bodily fluids is crucial for a precise health evaluation. However, conventional metabolite sensing methods, confined to centralized laboratory settings, suffer from time-consuming processes, complex procedures, and costly instrumentation. Introducing the MXene/nitrogen-doped electrochemically exfoliated graphene (MXene@N-EEG) nanocomposite as a novel biosensing platform in this work addresses the challenges associated with conventional methods, leveraging the concept of molecularly imprinted polymers (MIP) enables the highly sensitive, specific, and reliable detection of metabolites. To validate our biosensing technology, we utilize agmatine as a significant biologically active metabolite. The MIP biosensor incorporates electrodeposited Prussian blue nanoparticles as a redox probe, facilitating the direct electrical signaling of agmatine binding in the polymeric matrix. The MXene@N-EEG nanocomposite, with excellent metal conductivity and a large electroactive specific surface area, effectively stabilizes the electrodeposited Prussian blue nanoparticles. Furthermore, increasing the content of agmatine-imprinted cavities on the electrode enhances the sensitivity of the MIP biosensor. Evaluation of the designed MIP biosensor in buffer solution and plasma samples reveals a wide linear concentration range of 1.0 nM-100.0 μM (R2 = 0.9934) and a detection limit of 0.1 nM. Notably, the developed microfluidic biosensor offers low cost, rapid response time to the target molecule (10 min of sample incubation), good recovery results for detecting agmatine in plasma samples, and acceptable autonomous performance for on-chip detection. Moreover, its high reliability and sensitivity position this MIP-based biosensor as a promising candidate for miniaturized microfluidic devices with the potential for scalable production for point-of-care applications.

Spatially Confined Radical Addition Reaction for Electrochemical Synthesis of Carboxylated Graphene and its Applications in Water Desalination and Splitting

Due to the chemical stability of graphene, synthesis of carboxylated graphene still remains challenging during the electrochemical exfoliation of graphite. In this work, a spatially confined radical addition reaction which occurs in the sub-nanometer scaled interlayers of the expanded graphene sheets for the electrochemical synthesis of highly stable carboxylated graphene is reported. Here, formate anions act as both intercalation ions and co-reactant acid for the confinement of electro-generated carboxylic radical (●COOH) in the sub-nanometer scaled interlayers, which facilitates the radical addition reaction on graphene sheets. The controllable carboxylation of graphene is realized by tuning the concentration of formate anions in the electrolyte solution. The high crystallinity of the obtained product indicates the occurrence of spatially confined ●COOH addition reaction between the sub-nanometer interlayers of expanded graphite. In addition, the carboxylated graphene have been used for water desalination and hydrogen/oxygen reduction reaction. Therefore, this work provides a new method for the in situ preparation of functionalized graphene through the electrolysis and its applications in water desalination and hydrogen/oxygen reduction reactions.

Mechanical Properties of Conducting Printed Nanosheet Network Thin Films Under Uniaxial Compression

Thin film networks of solution processed nanosheets show remarkable promise for use in a broad range of applications including strain sensors, energy storage, printed devices, textile electronics, and more. While it is known that their electronic properties rely heavily on their morphology, little is known of their mechanical nature, a glaring omission given the effect mechanical deformation has on the morphology of porous systems and the promise of mechanical post processing for tailored properties. Here, this work employs a recent advance in thin film mechanical testing called the Layer Compression Test to perform the first in situ analysis of printed nanosheet network compression. Due to the well-defined deformation geometry of this unique test, this work is able to explore the out-of-plane elastic, plastic, and creep deformation in these systems, extracting properties of elastic modulus, plastic yield, viscoelasticity, tensile failure and sheet bending vs. slippage under both out of plane uniaxial compression and tension. This work characterizes these for a range of networks of differing porosities and sheet sizes, for low and high compression, as well as the effect of chemical cross linking. This work explores graphene and MoS2 networks, from which the results can be extended to printed nanosheet networks as a whole.

Two-dimensional materials as catalysts, interfaces, and electrodes for an efficient hydrogen evolution reaction

Two-dimensional (2D) materials have been significantly investigated as electrocatalysts for the hydrogen evolution reaction (HER) over the past few decades due to their excellent electrocatalytic properties and their structural uniqueness including the atomically thin structure and abundant active sites. Recently, 2D materials with various electronic properties have not only been used as active catalytic materials, but also employed in other components of the HER electrodes including a conductive electrode layer and an interfacial layer to maximize the HER efficiency or utilized as templates for catalytic nanostructure growth. This review provides the recent progress and future perspectives of 2D materials as key components in electrocatalytic systems with an emphasis on the HER applications. We categorized the use of 2D materials into three types: a catalytic layer, an electrode for catalyst support, and an interlayer for enhancing charge transfer between the catalytic layer and the electrode. We first introduce various scalable synthesis methods of electrocatalytic-grade 2D materials, and we discuss the role of 2D materials as HER catalysts, an interface for efficient charge transfer, and an electrode and/or a growth template of nanostructured noble metals.

The Influence of Reaction Conditions on the Properties of Graphene Oxide

The present study focuses on correlations between three parameters: (1) graphite particle size, (2) the ratio of graphite to oxidizing agent (KMnO4), and (3) the ratio of graphite to acid (H2SO4 and H3PO4), with the reaction yield, structure, and properties of graphene oxide (GO). The correlations are a challenge, as these three parameters can hardly be separated from each other due to the variations in the viscosity of the system. The larger the graphite particles, the higher the viscosity of GO. Decreasing the ratio of graphite to KMnO4 from 1:4 to 1:6 generally leads to a higher degree of oxidation and a higher reaction yield. However, the differences are very small. Increasing the graphite-to-acid-volume ratio from 1 g/60 mL to 1 g/80 mL, except for the smallest particles, reduced the degree of oxidation and slightly reduced the reaction yield. However, the reaction yield mainly depends on the extent of purification of GO by water, not on the reaction conditions. The large differences in the thermal decomposition of GO are mainly due to the bulk particle size and less to other parameters.

Ultrafast alternating-current exfoliation toward large-scale synthesis of graphene and its application for flexible supercapacitors

To facilitate the transition of laboratory research to industrial applications, it is critical to establish a reliable protocol for the mass synthesis of high-quality graphene. Here, we present an efficient electrochemical intercalation-based exfoliation approach utilizing alternating current that allows for the production of sub-kilogram quantities of graphene. This strategy involves repeatedly intercalating foreign anions and cations into the interlayer gaps of dual-graphite electrodes, accelerating the graphite expansion process and maximizing the exfoliation efficiency of both electrodes while inhibiting excessive anodic oxidation. The exfoliation process leads to high-yield graphene nanosheets (92 %, primarily 1-3 layers) with minimal structural deterioration (ID/IG ratio of 0.05), high purity (2.1 at% oxygen), and outstanding electrical property (7.28 × 104 S m-1). Notably, our scaled-up manufacturing technique produces a record-breaking throughput of 135 g h-1, improving on the best-reported exfoliation efficiency with direct current by 35%. Furthermore, the as-made graphene demonstrates a large reversible capacity of 102 mF cm-2 for flexible supercapacitors, with robust cyclability with 99.5% after 10,000 cycles, excellent mechanical flexibility, and exceptional serial integration for adjustable voltage output. The efficient and scalable method presents a significant advancement in the large-scale manufacture of graphene, with potential for widespread industrial applications.

Nitrogen-Doped Graphene Materials with High Electrical Conductivity Produced by Electrochemical Exfoliation of Graphite Foil

Nitrogen-doped graphene-based materials are of utmost importance in sensing and energy conversion devices due to their unique physicochemical properties. However, the presence of defects such as pyrrolic nitrogen and oxygenated functional groups reduces their electrical conductivity. Herein, a two-step approach based on the electrochemical exfoliation of graphite foils in aqueous mixed electrolytes followed by thermal reduction at 900 °C is used to prepare high-quality few layers of N-doped graphene-based materials. The exfoliations were conducted in 0.1 M (NH4)2SO4 or H2SO4 and HNO3 (5 mM or 0.1 M) electrolytes mixtures and the HNO3 vol% varied. Chemical analysis demonstrated that the as-prepared graphene oxides contain nitro and amine groups. Thermal reduction is needed for substitutional N-doping. Nitrogen and oxygen surface concentrations vary between 0.23-0.96% and 3-8%, respectively. Exfoliation in (NH4)2SO4 and/or 5 mM HNO3 favors the formation of pyridinic-N (10-40% of the total N), whereas 1 M HNO3 favors the formation of graphitic-N (≈60%). The electrical conductivity ranges between 166-2705 Scm-1. Raman spectroscopy revealed a low density of defects (ID/IG ratio between 0.1 and 0.7) and that most samples are composed of mono-to-bilayer graphene-based materials (IG/I2D integrated intensities ratio). Structural and compositional stability of selected samples after storage in air for three months is demonstrated. These results confirm the high quality of the synthesized undoped and N-doped graphene-type materials.

Electrochemical Exfoliation of Graphene Oxide: Unveiling Structural Properties and Electrochemical Performance

An electrochemical exfoliation method for the production of graphene oxide and its characterization by electrochemical techniques are presented here. Graphite rods are used as working electrode in a three-electrode electrochemical cell, and electro-exfoliation is achieved by applying anodic polarization in a sulfuric acid solution. The electrochemical process involved two steps characterized by an intercalation at lower potential and an exfoliation at higher potential. The electrochemical behavior of the produced GO is studied through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). X ray Photoelectronic Spectroscopy (XPS), Raman spectroscopy, Transmission Electron Microscopy (TEM), and Atomic Force Microscopy (AFM) are employed to characterize the structural and chemical properties of the exfoliated GO. The results demonstrate that the electrochemical exfoliation method yields GO materials with varying degrees of oxidation, defect density, and crystallite size, depending on the applied potential and acid concentration. The graphene oxide samples exhibited distinct electrochemical properties, including charge transfer resistance, interfacial capacitance, and relaxation times for the charge transfer, as revealed by CV and EIS measurements with a specifically selected redox probe. The comprehensive characterization performed provides valuable insights into the structure-property relationships of the GO materials synthesized through electrochemical exfoliation of graphite.

Producing Bilayer Graphene Oxide via Wedge Ion-Assisted Anodic Exfoliation: Implications for Energy and Electronics

Electrochemical synthesis has emerged as a promising approach for the large-scale production of graphene-based two-dimensional (2D) materials. Electrochemical intercalation of ions and molecules between graphite layers plays a key role in the synthesis of graphene with controllable thickness. However, there is still a limited understanding regarding the impact of intercalant molecules. Herein, we investigated a series of anionic species (i.e., ClO4-, PF6-, BF4-, HSO4-, CH3SO3-, and TsO-) and examined their wedging process between the weakly bonded layered materials driven by electrochemistry. By combining cyclic voltammetry, X-ray diffraction (XRD), and Raman spectroscopy, along with density functional theory (DFT) calculations, we found that stage-2 graphite intercalation compounds (GICs) can be obtained through intercalation of ClO4-, PF6-, or BF4- anions into the adjacent graphene bilayers. The anodic exfoliation step based on ClO4--GIC in (NH4)2SO4 (aq.) resulted in the formation of bilayer-rich (>57%) electrochemically exfoliated graphene oxide (EGO), with a high yield (∼85 wt %). Further, the physicochemical properties of these EGO can be readily customized through electrochemical reduction and modification with different surfactants. This versatility allows for precise tailoring of EGO, making it feasible for energy and electronic applications such as electrodes in electrochemical capacitors and functional composites in wearable electronics.

Applications of Carbon-Based Materials in Activated Peroxymonosulfate for the Degradation of Organic Pollutants: A Review

In recent years, water pollution has posed a serious threat to aquatic organisms and humans. Advanced oxidation processes (AOPs) based on activated peroxymonosulfate (PMS) show high oxidation, good selectivity, wide pH range and no secondary pollution in the removal of organic pollutants in water. Carbon-based materials are emerging green catalysts that can effectively activate persulfates to generate radical and non-radical active species to degrade organic pollutants. Compared with transition metal catalysts, carbon-based materials are widely used in SR-AOPs because of their low cost, non-toxicity, acid and alkali resistance, large specific surface area, and scalable surface charge, which can be used for selective control of specific water pollutants. This paper mainly presents several carbon-based materials used to activate PMS, including raw carbon materials and modified carbon materials (heteroatom-doped and metal-doped), analyzes and summarizes the mechanism of activating PMS by carbon-based catalysts, and discusses the influencing factors (temperature, pH, PMS concentration, catalyst concentration, inorganic anions, inorganic cations and dissolved oxygen) in the activation process. Finally, the future challenges and prospects of carbon-based materials in water pollution control are also presented.

Effect of graphite oxide electrochemically exfoliated over a multimode interference filter

In this work, we study multimodal interference filters with a graphite oxide coating. Use of the multimodal interference filter shows a distinctive peak in the signal spectrum, and when using the exfoliated graphite coated multimodal interference filter, the signal shows different spectral changes, such as the full width at half maximum of the curve, the maximum power, and central wavelength, which indicates that graphite oxide absorbs part of the energy. In addition, microscope observations when a He-Ne laser is passed through the filter confirm that graphite oxide is adhered to the filter.

Realizing Highly-Ordered Laser-Reduced Graphene for High-Performance Flexible Microsupercapacitor

Laser reduction of graphene oxide (GO) with direct-write technology is promising to develop miniaturized energy storage devices because of highly flexible, mask-free, and chemical-free merits. However, laser reduction of GO is often accompanied with deflagration (spectacular and violent deoxygenating reaction), leading reduced graphene oxide (rGO) films into brittle and irregular internal structure which is harmful to the applications. Here, a pre-reduction strategy is demonstrated to avoid this deflagration and realize a uniform laser-reduced GO (LrGO) matrix for the application of flexible micro-supercapacitors (MSCs).The pre-reduction process with ascorbic acid decreases the content of oxygen-containing functional groups on GO in advance, and thus relieves gases emission and avoids unconstrained expansion during the laser reduction process. In addition, a self-assembled skeleton with pre-reduced GO (PGO) nanosheets could be constructed which is a more appropriate aforehand framework for laser reduction to establish controllable rGO films with the homogenous porosity. The quasi-solid-state MSCs assembled with laser-reduced PGO exhibit the maximum areal capacitance of 88.32 mF cm-2 , good cycling performance (capacitance retention of 82% after 2000 cycles), and outstanding flexibility (no capacitance degradation after bending for 5000 times). This finding provides opportunities to enhance quality of LrGO which is promising for micro-power devices and beyond.

Insights into the Conductive Network of Electrochemical Exfoliation with Graphite Powder as Starting Raw Material for Graphene Production

Electrochemical exfoliation starting with graphite powder as the raw material for graphene production shows superiority in cost effectiveness over the popular bulk graphite. However, the crucial conductive network inside the graphite powder electrode along with its formation and influence mechanisms remains blank. Here, an adjustable-pressure graphite powder electrode with a sandwich structure was designed for this. Appropriate encapsulation pressure is necessary and conducive to constructing a continuous and stable conductive network, but overloaded encapsulation pressure is detrimental to the exfoliation and graphene quality. With an initial encapsulation pressure (IEP) of 4 kPa, the graphite powders expand rapidly to a final stable expansion pressure of 49 kPa with a final graphene yield of 46.3%, where 84% of the graphene sheets are less than 4 layers with I_D/I_G values between 0.22 and 1.24. Increasing the IEP to 52 kPa, the expansion pressure increases to 73 kPa, but the graphene yield decreases to 39.3% with a worse graphene quality including higher layers and I_D/I_G values of 1.68-2.13. In addition, small-size graphite powders are not suitable for the electrochemical exfoliation. With the particle size decreasing from 50 to 325 mesh, the graphene yield decreases almost linearly from 46.3% to 5.5%. Conductive network and electrolyte migration synergize and constrain each other, codetermining the electrochemical exfoliation. Within an encapsulated structure, the electrochemical exfoliation of the graphite powder electrode proceeds from the outside to the inside. The insights revealed here will provide direction for further development of electrochemical exfoliation of graphite powder to produce graphene.

Stepwise rapid electrolytic synthesis of graphene oxide for efficient adsorption of organic pollutants

Graphene oxide (GO) has been widely used in energy devices, biomedicine, environmental protection, composite materials and other fields. Hummers' method is currently one of the most powerful strategies for the preparation of GO. However, many deficiencies, including severe environmental pollution, operation safety issues and low oxidation efficiency are major obstacles for the large-scale green synthesis of GO. Here, we report a stepwise electrochemical method for the fast preparation of GO using spontaneous persulfate intercalation followed by anodic electrolytic oxidation. Such a step-by-step process not only avoids uneven intercalation and insufficient oxidation in traditional one-pot methods, but also largely shortens the overall duration by two orders of magnitude. In particular, the oxygen content of the obtained GO is as high as 33.7 at%, almost double that from Hummers' method (17.4 at%). The abundant surface functional groups render this GO an excellent adsorption platform for methylene blue with an adsorption capacity of 358 mg g^-1, 1.8-fold higher than conventional GO.

Controllable Synthesis of 2D Materials by Electrochemical Exfoliation for Energy Storage and Conversion Application

2D materials have captured much recent research interest in a broad range of areas, including electronics, biology, sensors, energy storage, and others. In particular, preparing 2D nanosheets with high quality and high yield is crucial for the important applications in energy storage and conversion. Compared with other prevailing synthetic strategies, the electrochemical exfoliation of layered starting materials is regarded as one of the most promising and convenient methods for the large-scale production of uniform 2D nanosheets. Here, recent developments in electrochemical delamination are reviewed, including protocols, categories, principles, and operating conditions. State-of-the-art methods for obtaining 2D materials with small numbers of layers-including graphene, black phosphorene, transition metal dichalcogenides and MXene-are also summarized and discussed in detail. The applications of electrochemically exfoliated 2D materials in energy storage and conversion are systematically reviewed. Drawing upon current progress, perspectives on emerging trends, existing challenges, and future research directions of electrochemical delamination are also offered.

Investigating the Extracellular-Electron-Transfer Mechanisms and Kinetics of Shewanella decolorationis NTOU1 Reducing Graphene Oxide via Lactate Metabolism

Microbial graphene oxide reduction is a developing method that serves to reduce both production costs and environmental impact in the synthesis of graphene. This study demonstrates microbial graphene oxide reduction using Shewanella decolorationis NTOU1 under neutral and mild conditions (pH = 7, 35 °C, and 1 atm). Graphene oxide (GO) prepared via the modified Hummers’ method is used as the sole solid electron acceptor, and the characteristics of reduced GO (rGO) are investigated. According to electron microscopic images, the surface structure of GO was clearly changed from smooth to wrinkled after reduction, and whole cells were observed to be wrapped by GO/rGO films. Distinctive appendages on the cells, similar to nanowires or flagella, were also observed. With regard to chemical-bonding changes, after a 24-h reaction of 1 mg mL−1, GO was reduced to rGO, the C/O increased from 1.4 to 3.0, and the oxygen-containing functional groups of rGO were significantly reduced. During the GO reduction process, the number of S. decolorationis NTOU1 cells decreased from 1.65 × 108 to 1.03 × 106 CFU mL−1, indicating the bactericide effects of GO/rGO. In experiments adding consistent concentrations of initial bacteria and lactate, it was shown that with the increase of GO additions (0.5–5.0 mg mL−1), the first-order reaction rate constants (k) of lactate metabolism and acetate production increased accordingly; in experiments adding consistent concentrations of initial bacteria and GO but different lactate levels (1 to 10 mM), the k values of lactate metabolism did not change significantly. The test results of adding different electron transfer mediators showed that riboflavin and potassium ferricyanide were able to boost GO reduction, whereas 2,6-dimethoxy-1,4-benzoquinone and 2,6-dimethyl benzoquinone completely eliminated bacterial activity.

Antimonene: a tuneable post-graphene material for advanced applications in optoelectronics, catalysis, energy and biomedicine

The post-graphene era is undoubtedly marked by two-dimensional (2D) materials such as quasi-van der Waals antimonene. This emerging material has a fascinating structure, exhibits a pronounced chemical reactivity (in contrast to graphene), possesses outstanding electronic properties and has been postulated for a plethora of applications. However, chemistry and physics of antimonene remain in their infancy, but fortunately recent discoveries have shed light on its unmatched allotropy and rich chemical reactivity offering a myriad of unprecedented possibilities in terms of fundamental studies and applications. Indeed, antimonene can be considered as one of the most appealing post-graphene 2D materials reported to date, since its structure, properties and applications can be chemically engineered from the ground up (both using top-down and bottom-up approaches), offering an unprecedented level of control in the realm of 2D materials. In this review, we provide an in-depth analysis of the recent advances in the synthesis, characterization and applications of antimonene. First, we start with a general introduction to antimonene, and then we focus on its general chemistry, physical properties, characterization and synthetic strategies. We then perform a comprehensive study on the allotropy, the phase transition mechanisms, the oxidation behaviour and chemical functionalization. From a technological point of view, we further discuss the applications recently reported for antimonene in the fields of optoelectronics, catalysis, energy storage, cancer therapy and sensing. Finally, important aspects such as new scalable methodologies or the promising perspectives in biomedicine are discussed, pinpointing antimonene as a cutting-edge material of broad interest for researchers working in chemistry, physics, materials science and biomedicine.

Recent Advances for the Synthesis and Applications of 2-Dimensional Ternary Layered Materials

Layered materials with unique structures and symmetries have attracted tremendous interest for constructing 2-dimensional (2D) structures. The weak interlayer interaction renders them to be readily isolated into various ultrathin nanosheets with exotic properties and diverse applications. In order to enrich the library of 2D materials, extensive progress has been made in the field of ternary layered materials. Consequently, many brand-new materials are derived, which greatly extend the members of 2D realm. In this review, we emphasize the recent progress made in synthesis and exploration of ternary layered materials. We first classify them in terms of stoichiometric ratio and summarize their difference in interlayer interaction, which is of great importance to produce corresponding 2D materials. The compositional and structural characteristics of resultant 2D ternary materials are then discussed so as to realize desired structures and properties. As a new family of 2D materials, we overview the layer-dependent properties and related applications in the fields of electronics, optoelectronics, and energy storage and conversion. The review finally provides a perspective for this rapidly developing field.

Promising Nitrogen-Doped Graphene Derivatives; A Case Study for Preparations, Fabrication Mechanisms, and Applications in Perovskite Solar Cells

Graphene (G) has been a game-changer for conductive optical devices and has shown promising aspects for its implementation in the power industry due to its diverse structures. Graphene has played an essential role as electrodes, hole transport layers (HTLs), electron transport layers (ETLs), and a chemical modulator for perovskite layers in perovskite solar cells (PSCs) over the past decade. Nitrogen-doped graphene (N-DG) derivatives are frequently evaluated among the existing derivatives of graphene because of their versatility of design, easy synthesis process, and high throughput. This review presents a state-of-the-art overview of N-DG preparation methods, including wet chemical process, bombardment, and high thermal treatment methods. Furthermore, it focuses on different structures of N-DG derivatives and their various applications in PSC applications. Finally, the challenges and opportunities for N-DG derivatives for the continuous performance improvement of PSCs have been highlighted.

Progress on TiO2-based materials for solar water interfacial evaporation

Solar water interfacial evaporation (SWIE) has attracted much attention for harvesting clean water. Over the last few decades, researchers have developed an innovative photo-thermal material for high-performance solar water interfacial evaporation. For higher evaporation performance, TiO2-based materials gain attention as a promising photo-thermal material due to their light absorption capacity. This study compared conceptual designs of TiO2-based materials for SWIE. Structural design and engineering strategies for improving evaporation rates and higher thermal conversion efficiency were reviewed. In addition, the material’s thermal stability and heat management were analyzed. This review provides an overview of the current advances in photo-thermal TiO2 materials to motivate research and translation efforts from the laboratory to large-scale solar water clean water production. Additional benefits of TiO2 materials on solar water interfacial evaporation should be investigated beyond containers to solve interconnected water, environmental, and energy progression.

One-Step Synthesis of Aminobenzoic Acid Functionalized Graphene Oxide by Electrochemical Exfoliation of Graphite for Oxygen Reduction to Hydrogen Peroxide and Supercapacitors

Graphene-based materials have attracted considerable attention as promising electrocatalysts for the oxygen reduction reaction (ORR) and as electrode materials for supercapacitors. In this work, electrochemical exfoliation of graphite in the presence of 4-aminebenzoic acid (4-ABA) is used as a one-step method to prepare graphene oxide materials (EGO) functionalized with aminobenzoic acid (EGO-ABA). The EGO and EGO-ABAs materials were characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction and scanning electron microscopy. It was found that the EGO-ABA materials have smaller flake size and higher density of oxygenated functional groups compared to bare EGO. The electrochemical studies showed that the EGO-ABA catalysts have higher activity for the ORR to H2O2 in alkaline medium compared to EGO due to their higher density of oxygenated functional groups. However, bare EGO has a higher selectivity for the 2-electron process (81%) compared to the EGO-ABA (between 64 and 72%) which was related to a lower content of carbonyl groups. The specific capacitance of the EGO-ABA materials was higher than that of EGO, with an increase by a factor of 3 for the materials prepared from exfoliation in 5 mM 4-ABA/0.1 M H2SO4. This electrode material also showed a remarkable cycling capability with a loss of only 19.4% after 5000 cycles at 50 mVs−1.

2D Layers of Group VA Semiconductors: Fundamental Properties and Potential Applications

Members of the 2D group VA semiconductors (phosphorene, arsenene, antimonene, and bismuthine) present a new class of 2D materials, which are recently gaining a lot of research interest. These materials possess layered morphology, tunable direct bandgap, high charge carrier mobility, high stability, unique in-plane anisotropy, and negative Poisson's ratio. They prepare the ground for novel and multifunctional applications in electronics, optoelectronics, and batteries. The most recent analytical and empirical developments in the fundamental characteristics, fabrication techniques, and potential implementation of 2D group VA materials in this review, along with presenting insights and concerns for the field's future are analyzed.

Recent development and challenges in fuel cells and water electrolyzer reactions: an overview

Water electrolysis is the most promising method for the production of large scalable hydrogen (H2), which can fulfill the global energy demand of modern society. H2-based fuel cell transportation has been operating with zero greenhouse emission to improve both indoor and outdoor air quality, in addition to the development of economically viable sustainable green energy for widespread electrochemical applications. Many countries have been eagerly focusing on the development of renewable as well as H2-based energy storage infrastructure to fulfill their growing energy demands and sustainable goals. This review article mainly discusses the development of different kinds of fuel cell electrocatalysts, and their application in H2 production through various processes (chemical, refining, and electrochemical). The fuel cell parameters such as redox properties, cost-effectiveness, ecofriendlyness, conductivity, and better electrode stability have also been highlighted. In particular, a detailed discussion has been carried out with sufficient insights into the sustainable development of future green energy economy.

Review on the Effects of Electrochemical Exfoliation Parameters on the Yield of Graphene Oxide

Recent years have witnessed many breakthroughs in research on graphene as well as a significant improvement in the electrochemical synthesis methods of graphene oxide (GO). GO is a derivative of graphene which has attracted the focus of worldwide scientists and researchers because of its hydrophilic and easily functionalized properties. The electrochemical approach is popular because it saves time, creates zero explosion risk, releases no hazardous gases, and avoids environmental pollution. Although recent publications show that the green, rapid, and mass electrochemical synthesis of GO has more advantages as compared with the traditional Hummers method, it is crucial to study the effects of reaction parameters. Herein, we review recent various works regarding the influences of various reaction parameters on the synthesis of GO sheets. The advancement, current challenges, and solutions of electrochemical synthesis methods of GO are also outlined. Through this review, we hope to spark some clear ideas for anyone who wants to scale up the yield of GO.

Concentrated Solar Induced Graphene

Graphene is one of the most promising nanomaterials with many extraordinary properties and numerous exciting applications. In this work, a green, facile, and rapid method was developed to prepare graphene directly from common biomass materials such as banana peels, cantaloupe peels, coconut peels, and orange peels by using concentrated solar radiation. The basic principle of this method is photothermal conversion. On a sunny day, the sunlight was concentrated by a biconvex lens to form a focused light spot with a high temperature above 1000 °C, which can directly convert fruit peels into graphene nanosheets within 2-3 s. The product is named concentrated-solar-induced graphene (CSIG) based on the process employed to generate it. The resulting CSIG was characterized using a range of analytical techniques. The Raman spectrum of the CSIG displayed two distinct peaks corresponding to the D and G bands at ∼1343 and ∼1568 cm-1, respectively. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction were used to confirm that the CSIG consists of a few layers of turbostratic graphene nanosheets. Atomic force microscopy characterization revealed that the CSIG nanosheets have a thickness of ∼4 nm. The antibacterial potential of the CSIG was also explored. The CSIG had a strong inhibitory effect on the growth of Escherichia coli. This simple, green, and straightforward method for producing graphene may open a new route for turning waste into useful materials: an inexhaustible and pollution-free natural resource can be readily exploited by using a solar tracker-lens system for the large-scale production of graphene materials directly from low-cost biomass materials.

Reliable fabrication of transparent conducting films by cascade centrifugation and Langmuir-Blodgett deposition of electrochemically exfoliated graphene

Electrochemical exfoliation is an efficient and scalable method to obtain liquid-phase graphene. Graphene in solution, obtained through electrochemical exfoliation or other methods, is typically polydisperse, containing particles of various sizes, which is not optimal for applications. We employed cascade centrifugation to select specific particle sizes in solution and prepared thin films from those graphene particles using the Langmuir-Blodgett assembly. Employing centrifugation speeds of 3, 4, and 5 krpm, further diluting the solutions in different volumes of solvent, we reliably and consistently obtained films of tunable thickness. We show that there is a limit to how thin these films can be, which is imposed by the percolation threshold. The percolation threshold is quantitatively compared to results found in literature that are obtained using other, more complex graphene film fabrication methods, and is found to occur with a percolation exponent and percolative figure of merit that are of the same order as results in literature. A maximum optical transparency of 82.4% at a wavelength of 660 nm is obtained for these films, which is in agreement with earlier works on Langmuir-Blodgett assembled ultrasonic-assisted liquid-phase exfoliated graphene. Our work demonstrates that films that are in all respects on par with films of graphene obtained through other solution-based processes can be produced from inexpensive and widely available centrifugal post-processing of existing commercially available solutions of electrochemically exfoliated graphene. The demonstrated methodology will lower the entry barriers for new research and industrial uses, since it allows researchers with no exfoliation experience to make use of widely available graphene materials.

Effect of mixing conditions and polymer particle size on the properties of polypropylene/graphite nanoplatelets micromoldings

In this study, properties of polypropylene/graphite nanoplatelets (PP/GNP) composites and corresponding micromoldings were systematically studied in terms of filler loading concentrations and mixing methods. PP of different forms, i.e., PP pellets and powders, were adopted to fabricate PP/GNP composites. Additionally, a comparative study of precoating GNP and PP powders using solvent-based solution blending and ultrasonication-assisted mixing was performed. Results showed that PP/GNP composites prepared using powder form PP resulted in at least one order of magnitude higher electrical conductivity than using pellet form PP and further reduced the percolation threshold from 12.5 to 10 wt%, which was related to the state of filler distribution within corresponding moldings. Morphology observations revealed that microparts prepared with powder-PP/GNP composites exhibited less preferential alignment of GNP particles along the flow direction when compared with those molded using pellet-PP/GNP counterparts, which was helpful in improving the overall electrical conductivity for PP/GNP micromoldings.

Improved Dispersibility of Graphene in an Aqueous Solution by Reduced Graphene Oxide Surfactant: Experimental Verification and Density Functional Theory Calculation

It is difficult to disperse graphene flakes well in an aqueous solution while maintaining conductivity due to its high hydrophobicity. Herein, we demonstrated that a well-dispersed state of graphene in an aqueous solution was realized by using reduced graphene oxide (rGO) with a suitable content of oxygen-functional groups. A rGO-dispersed graphene (rGO/G) film was fabricated from the graphene dispersion with good conductivity by using rGO with a C/O ratio of 2.48 as the surfactant. Also, the prepared rGO/G aerogel has a broad prospect. Density functional theory calculation revealed that the strong electrostatic repulsion, which was more potent than the van der Waals force and the π-π interaction, was the primary driving force promoting the dispersibility of graphene in an aqueous solution. Furthermore, the repulsion of the rGO/G dispersion decreased with the reduction of the oxygen-functional groups of rGO. Therefore, applying rGO with an appropriate content of oxygen-functional groups is an alternative option to improve the dispersibility of graphene in an aqueous medium while maintaining its original properties, from which many potential applications could be expected.

Facile Synthesis of Ag/Carbon Quantum Dots/Graphene Composites for Highly Conductive Water-Based Inks

The development of graphene conductive inks with a high conductivity and dispersion stability in water poses considerable challenges. Herein, a highly conductive Ag/carbon quantum dots (CQDs)/graphene (G) composite with good dispersity and stability in water was prepared for the first time through the in situ photoreduction of AgNO3 and deposition of Ag onto graphene nanosheets obtained via CQD-assisted liquid-phase exfoliation. Ag nanoparticles with an average size of ∼1.88 nm were uniformly dispersed on graphene nanosheets. The Ag/CQDs/G composite exhibited good dispersity and stability in water for 30 days. The formation mechanism of the Ag/CQDs/G composites was also discussed. CQDs played a vital role in coordinating with Ag+ and reducing it under visible light conditions. The addition of only 1.58 wt % of Ag NPs to the CQDs/G film resulted in a significant decrease in the electrical resistivity by approximately 89.5%, reaching a value of 0.054 Ω cm for a 40 μm thick Ag/CQDs/G film. A low resistivity of 2.15 × 10-3 Ω cm for the Ag/CQDs/G film was achieved after rolling compression with a compression ratio of 78%. The Ag/CQDs/G film exhibited good conductivity and durability when bent, rolled, or twisted. Moreover, the resistivity of the film displayed a slight deviation after 5000 bending cycles, indicating its outstanding stability. This study provides an efficient strategy for preparing graphene-based conductive composites with good dispersibility and stability in water as well as novel high-performance conductive inks for application in flexible printed electronics.

Structural evolution of MXenes and their composites for electromagnetic interference shielding applications

Nowadays, the extensive utilization of electronic devices and equipment inevitably leads to severe electromagnetic interference (EMI) issues. Therefore, EMI shielding materials have drawn considerable attention, and great effort has been devoted to the exploration of high-efficiency EMI shielding materials. As a novel kind of 2D transition metal carbide material, MXenes have been widely investigated for EMI shielding in the past few years due to their extraordinary electrical conductivity, large specific surface area, light weight, and easy processability. In view of the great achievements in MXene-based materials for EMI shielding, herein, we reviewed the recent studies on the structural design and evolution of MXenes and their composites for EMI shielding. First, the methods for structural control of MXenes, including HF etching, in situ HF etching, fluorine-free etching, electrochemical etching, and molten salt etching, are systematically summarized. Then we illustrate the fundamental relationship between the microstructure of MXenes and the EMI shielding mechanism. In the following, the effects of different synthesis methods and structures of MXene-based composite materials as well as their EMI shielding performances are comprehensively discussed. Lastly, future prospects for the development of MXene-based composite materials in EMI shielding applications are commented on.

Preparation of multi-function graphene materials through electrode-distance controlled electrochemical exfoliation

Preparation of graphene materials with different microstructures is of great significance for the specific applications in various areas. Here, a modified electrochemical exfoliation method with controlled electrode distance is proposed to prepare exfoliated graphene, graphene quantum dots, and graphene oxide (EGr, EGQD, and EGO). Compared with electrolysis at a fixed location, the modified electrode distance can effectively tune the insertion speed and direction, as well as the kinetic rates of exfoliation processes. Specifically, at a short electrode distance of 3 cm, it produced high-quality EGr with the size above 5μm and thickness below 5 layers; when the electrode distance increased to 30 cm, EGQD with the size below 5 nm was produced. Further, the distance between 3 and 30 cm facilitates producing EGO with ca. 15% O content. In addition, it is found that the reaction temperature, optimized electrolyte, and controlled potential can further optimize the exfoliation processes, which can achieve a high exfoliation rate of ca. 2000, 140, and 1500 g h^-1for EGr, EGQD, and EGO preparation in an industrial-scale system, respectively. These modified graphene materials can be directly applied in various areas. For example, EGr can act as an effective component to increase one order of the dielectric property of PVDF; EGQD can effectively generate a PL spectrum at ca. 550 nm; EGO can facilely form a conductive and flexible film through self-assembly.

Surface Modification of 2D Photocatalysts for Solar Energy Conversion

2D materials show many particular properties, such as high surface-to-volume ratio, high anisotropic degree, and adjustable chemical functionality. These unique properties in 2D materials have sparked immense interest due to their applications in photocatalytic systems, resulting in significantly enhanced light capture, charge-transfer kinetics, and surface reaction. Herein, the research progress in 2D photocatalysts based on varied compositions and functions, followed by specific surface modification strategies, is introduced. Fundamental principles focusing on light harvesting, charge separation, and molecular adsorption/activation in the 2D-material-based photocatalytic system are systemically explored. The examples described here detail the use of 2D materials in various photocatalytic energy-conversion systems, including water splitting, carbon dioxide reduction, nitrogen fixation, hydrogen peroxide production, and organic synthesis. Finally, by elaborating the challenges and possible solutions for developing these 2D materials, the review is expected to provide some inspiration for the future research of 2D materials used on efficient photocatalytic energy conversions.

Corrosion performance of a steel surface modified by a robust graphene-based superhydrophobic film with hierarchical roughness

Potentiostatic deposition of cobalt film and cobalt-graphene, Co-G, composite, followed by modification with low surface energy stearic acid (SA), was used to fabricate superhydrophobic films on a steel substrate successfully. A scanning electron microscope was used to analyze the surface morphology of the prepared superhydrophobic cobalt film modified by stearic acid, Co-SA, and the cobalt-graphene film modified by stearic acid, Co-G-SA. The findings show that both the fabricated films have micro-nanostructures. The Co-G-SA film shows a higher roughness due to the network structures of graphene and so exhibits higher superhydrophobicity. The Fourier transform infrared spectrophotometer, FTIR, results confirm the formation of Co-SA and Co-G-SA films on the steel surface. The wettability of the prepared films shows that they exhibit superhydrophobicity, where the Co-SA and Co-G-SA films have contact angles of 155° and 158°, respectively. The Potentiodynamic polarization results show that the value of the corrosion current density for steel coated with Co-SA (0.7094 µA) is lower than that of bare steel (0.1457 mA), while the coated steel with Co-G-SA film has the lowest value (0.1732 µA). The electrochemical impedance spectroscopy, EIS, results show that the charge transfer resistance for steel coated with Co-SA is 38 times that of bare steel, while steel coated with Co-SA is 57 times that of bare steel. Potentiodynamic polarization and EIS results show that the prepared Co-G-SA film superhydrophobic films exhibit higher corrosion resistance. Co-G-SA film has higher mechanical stability (maintains superhydrophobicity until 900 abrasion cycles), chemical stability (has superhydrophobicity in the pH range 1–13), and long-term stability (retains superhydrophobicity after 30 days in a 0.5 M NaCl solution) in 0.5 M NaCl solution.

Self-assembly of graphene oxide flakes for smart and multifunctional coating with reversible formation of wrinkling patterns

One of the main purposes of smart and multifunctional coatings is to have the versatility to be applied in a wide range of applications. However, the functions of smart materials are often highly limited. In particular, the stimuli-responsive lateral expansion of coatings based on 2D materials has not been reported before. This manuscript describes small two-dimensional graphene oxide (GO) flakes (e.g., thin sheets with a thickness of a few nanometers and much larger lateral dimensions) that act as elementary agents for the formation of smart and multifunctional coatings. The coating can be self-assembled from the GO flakes and disassembled flexibly when required. The coating is stimuli-responsive: upon localized contact with water, it expands and forms wrinkling patterns throughout its whole surface. Evaporating the water allows the wrinkles to disappear; hence, the process is reversible. This stimuli-responsiveness can be controlled to be reduced or completely switched off by temperature or pressure. These features are fundamentally due to the reversible intermolecular interactions among the flakes and favorable packing structure of the coating. The smart coating is shown to be useful for patterned fluidic systems of the desired shapes and the development of channels between fluidic reservoirs via the shortest path. Importantly, these results showed that a simple collection of uniquely 2D elementary agents with small nanoscale thickness can self-assemble into macroscopic materials that perform interactive and multifunctional operations.

Highly Conductive Networks of Silver Nanosheets

Although printed networks of semiconducting nanosheets have found success in a range of applications, conductive nanosheet networks are limited by low conductivities (<10⁶ S m^-1 ). Here, dispersions of silver nanosheets (AgNS) that can be printed into highly conductive networks are described. Using a commercial thermal inkjet printer, AgNS patterns with unannealed conductivities of up to (6.0 ± 1.1) × 10⁶  S m^-1 are printed. These networks can form electromagnetic interference shields with record shielding effectiveness of >60 dB in the microwave region at thicknesses <200 nm. High resolution patterns with line widths down to 10 µm are also printed using an aerosol-jet printer which, when annealed at 200 °C, display conductivity >10⁷  S m^-1 . Unlike conventional Ag-nanoparticle inks, the 2D geometry of AgNS yields smooth, short-free interfaces between electrode and active layer when used as the top electrode in vertical nanosheet heterostructures. This shows that all-printed vertical heterostructures of AgNS/WS₂ /AgNS, where the top electrode is a mesh grid, function as photodetectors demonstrating that such structures can be used in optoelectronic applications that usually require transparent conductors.

Barium titanate-enhanced hexagonal boron nitride inks for printable high-performance dielectrics

Printed electronics have been attracting significant interest for their potential to enable flexible and wearable electronic applications. Together with printable semiconductors, solution-processed dielectric inks are key in enabling low-power and high-performance printed electronics. In the quest for suitable dielectrics inks, two-dimensional materials such as hexagonal boron nitride (h-BN) have emerged in the form of printable dielectrics. In this work, we report barium titanate (BaTiO₃) nanoparticles as an effective additive for inkjet-printable h-BN inks. The resulting inkjet printed BaTiO₃/h-BN thin films reach a dielectric constant (ε_r) of ∼16 by adding 10% of BaTiO₃nanoparticles (in their volume fraction to the exfoliated h-BN flakes) in water-based inks. This result enabled all-inkjet printed flexible capacitors withC ∼ 10.39 nF cm^-2, paving the way to future low power, printed and flexible electronics.