Chemistry Makes Graphene beyond Graphene

Protecting Li-metal anode with LiF-enriched solid electrolyte interphase derived from a fluorinated graphene additive

As the holy-grail material, the Li-metal anode has been considered the potential anode of the next generation of Li-metal batteries (LMBs). However, issues of undesirable dendrite growth and unsatisfactory reversibility of the Li-plating/stripping process during the electrochemical cycling impede further application of LMBs. Herein, we innovatively introduce fluorinated graphene (F-Gr) species as a sacrificial effective electrolyte additive into EC/EMC-based electrolyte, which effectively triggers LiF-enriched (composition) and organic/inorganic species uniform-distributed (structure) SEI film architecture that features robustness and denseness, as well as good stability. With the F-Gr additive, efficient Li-metal anode protection (dendrite-free morphology on Li-metal surface and improved Li plating/stripping reversibility during electrochemical cycling) and significantly enhanced long-term lifespan of LMBs is achieved. Remarkably, classical electrochemical techniques, combined with the surface-sensitive characterizations (XPS and TOF-SIMS), comprehensively and systematically highlight critical structure-activity relationships between the SEI architecture (both composition and structure) and electrochemical performance. These techniques provide deep insights into the optimal electrolyte designation of Li-metal anode in LMBs.

Tunable Ultrafast Charge Transfer across Homojunction Interface

Charge transfer at heterojunction interfaces is a fundamental process that plays a crucial role in modern electronic and photonic devices. The essence of such charge transfer lies in the band offset, making charge transfer uncommon in a homojunction. Recently, sliding ferroelectricity has been proposed and confirmed in two-dimensional van der Waals stacked materials such as bilayer boron nitride. During the sliding of these layers, the band alignment shifts, creating conditions for charge separation at the interface. We employ ab initio nonadiabatic molecular dynamics simulations to elucidate the excited state carrier dynamics in bilayer boron pnictides. We propose that, akin to ferroelectric polarization flipping, the precise modulation of the distribution of excited state carriers can also be reached by sliding. Our results demonstrate that sliding induces a reversal of the frontier orbital distribution on the upper and lower layers, facilitating a robust interlayer carrier transfer. Notably, the interlayer carrier transfer is more pronounced in boron phosphide than in boron nitride, attributed to strong electron scattering in momentum space in boron nitride. We propose this novel method to manipulate carrier distribution and dynamics in a homojunction exhibiting sliding ferroelectricity, in general, paving a new way for developing advanced electronic and photonic devices.

Emerging Nanomaterials as Versatile Nanozymes: A New Dimension in Biomedical Research

The enzyme-mimicking nature of versatile nanomaterials proposes a new class of materials categorized as nano-enzymes, ornanozymes. They are artificial enzymes fabricated by functionalizing nanomaterials to generate active sites that can mimic enzyme-like functions. Materials extend from metals and oxides to inorganic nanoparticles possessing intrinsic enzyme-like properties. High cost, low stability, difficulty in separation, reusability, and storage issues of natural enzymes can be well addressed by nanozymes. Since 2007, more than 100 nanozymes have been reported that mimic enzymes like peroxidase, oxidase, catalase, protease, nuclease, hydrolase, superoxide dismutase, etc. In addition, several nanozymes can also exhibit multi-enzyme properties. Vast applications have been reported by exploiting the chemical, optical, and physiochemical properties offered by nanozymes. This review focuses on the reported nanozymes fabricated from a variety of materials along with their enzyme-mimicking activity involving tuning of materials such as metal nanoparticles (NPs), metal-oxide NPs, metal-organic framework (MOF), covalent organic framework (COF), and carbon-based NPs. Furthermore, diverse applications of nanozymes in biomedical research are discussed in detail.

Calcium oxide adsorption of gas phase PCDD/Fs and its impact on the adsorption properties of activated carbon

Calcium oxide (CaO), utilized in semi-dry/dry desulfurization systems at municipal solid waste incineration (MSWI) plants, demonstrates some capability to remove polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). This study assessed the gas-phase PCDD/F removal performance of CaO, activated carbon (AC) and CaO-AC mixtures. Alone, CaO achieved removal efficiencies of only 31.9% for mass and 50.8% for I-TEQ concentration. However, CaO-AC mixtures exhibited significantly higher efficiencies, reaching 96.0% and 92.5% for mass and I-TEQ concentrations, respectively, surpassing those of AC alone, which were 74.7% and 58.5%. BET analysis indicated that CaO's limited surface area and pore structure are major constraints on its adsorption performance. Density functional theory (DFT) calculations revealed that the π-π electron donor-acceptor (EDA) interaction enhances the adsorption between AC and PCDD/F, with adsorption energies ranging from -1.02 to -1.24 eV. Additionally, the induced dipole interactions between CaO and PCDD/F contribute to adsorption energies ranging from -1.13 to -1.43 eV. Moreover, with increasing chlorination levels, PCDD/F molecules are more predisposed to accept electron transfers from the surfaces of AC or CaO, thereby facilitating adsorption. The calculation for mixed AC and CaO showed that CaO modifies AC's properties, enhancing its ability to adsorb gas phase PCDD/Fs, with the higher adsorption energy and more electrons transfer, aligning with gas phase PCDD/Fs adsorption experiments. This study provides a comprehensive understanding of how CaO influences the PCDD/F adsorption performance of AC.

Emerging Advances around Nanofluidic Transport and Mass Separation under Confinement in Atomically Thin Nanoporous Graphene

Membrane separation stands as an environmentally friendly, high permeance and selectivity, low energy demand process that deserves scientific investigation and industrialization. To address intensive demand, seeking appropriate membrane materials to surpass trade-off between permeability and selectivity and improve stability is on the schedule. 2D materials offer transformational opportunities and a revolutionary platform for researching membrane separation process. Especially, the atomically thin graphene with controllable porosity and structure, as well as unique properties, is widely considered as a candidate for membrane materials aiming to provide extreme stability, exponentially large selectivity combined with high permeability. Currently, it has shown promising opportunities to develop separation membranes to tackle bottlenecks of traditional membranes, and it has been of great interest for tremendously versatile applications such as separation, energy harvesting, and sensing. In this review, starting from transport mechanisms of separation, the material selection bank is narrowed down to nanoporous graphene. The study presents an enlightening overview of very recent developments in the preparation of atomically thin nanoporous graphene and correlates surface properties of such 2D nanoporous materials to their performance in critical separation applications. Finally, challenges related to modulation and manufacturing as well as potential avenues for performance improvements are also pointed out.

Covalent Organic Framework/Graphene Hybrids: Synthesis, Properties, and Applications

To address current energy crises and environmental concerns, it is imperative to develop and design versatile porous materials ideal for water purification and energy storage. The advent of covalent organic frameworks (COFs), a revolutionary terrain of porous materials, is underscored by their superlative features such as divinable structure, adjustable aperture, and high specific surface area. However, issues like inferior electric conductivity, inaccessible active sites impede mass transfer and poor processability of bulky COFs restrict their wider application. As a herculean stride forward, COF/graphene hybrids amalgamate the strengths of their constituent components and have in consequence, enticed significant scientific intrigue. Herein, the current progress on the structure and properties of graphene-based materials and COFs are systematically outlined. Then, synthetic strategies for preparing COF/graphene hybrids, including one-pot synthesis, ex situ synthesis, and in situ growth, are comprehensively reviewed. Afterward, the pivotal attributes of COF/graphene hybrids are dissected in conjunction with their multifaceted applications spanning adsorption, separation, catalysis, sensing, and energy storage. Finally, this review is concluded by elucidating prevailing challenges and gesturing toward prospective strides within the realm of COF/graphene hybrids research.

Moiré band renormalization due to lattice mismatch in bilayer graphene

We investigated the band renormalization caused by the compressive-strain-induced lattice mismatch in parallel AA stacked bilayer graphene using two complementary methods: the tight-binding approach and the low-energy continuum theory. While a large mismatch does not alter the low-energy bands, a small one reduces the bandwidth of the low-energy bands along with a decrease in the Fermi velocity. In the tiny-mismatch regime, the low-energy continuum theory reveals that the long-period moiré pattern extensively renormalizes the low-energy bands, resulting in a significant reduction of bandwidth. Meanwhile, the Fermi velocity exhibits an oscillatory behavior and approaches zero at specific mismatches. However, the resulting low-energy bands are not perfectly isolated flat, as seen in twisted bilayer graphene at magic angles. These findings provide a deeper understanding of moiré physics and offer valuable guidance for related experimental studies in creating moiré superlattices using two-dimensional van der Waals heterostructures.

Unravelling the formation of carbyne nanocrystals from graphene nanoconstrictions through the hydrothermal treatment of agro-industrial waste molasses

The delicate synthesis of one-dimensional (1D) carbon nanostructures from two-dimensional (2D) graphene moiré layers holds tremendous interest in materials science owing to its unique physiochemical properties exhibited during the formation of hybrid configurations with sp-sp2 hybridization. However, the controlled synthesis of such hybrid sp-sp2 configurations remains highly challenging. Therefore, we employed a simple hydrothermal technique using agro-industrial waste as the carbon source to synthesize 1D carbyne nanocrystals from the nanoconstricted zones of 2D graphene moiré layers. By employing suite of characterization techniques, we delineated the mechanism of carbyne nanocrystal formation, wherein the origin of carbyne nanochains was deciphered from graphene intermediates due to the presence of a hydrothermally cut nanoconstriction regime engendered over well-oriented graphene moiré patterns. The autogenous hydrothermal pressurization of agro-industrial waste under controlled conditions led to the generation of epoxy-rich graphene intermediates, which concomitantly gave rise to carbyne nanocrystal formation in oriented moiré layers with nanogaps. The unique growth of carbyne nanocrystals over a few layers of holey graphene exhibits excellent paramagnetic properties, the predominant localization of electrons and interfacial polarization effects. Further, we extended the application of the as-synthesized carbyne product (Cp) for real-time electrochemical-based toxic metal (As3+) sensing in groundwater samples (from riverbanks), which depicted superior sensitivity (0.22 mA μM-1) even at extremely lower concentrations (0.0001 μM), corroborating the impedance spectroscopy analysis.

Interfacial Electronic States of GeC/g-C3N4 van der Waal Heterostructure with Promising Photocatalytic Activity via Hydrogenation

The bandgap of most known two-dimensional materials can be tuned by hydrogenation, although certain 2D materials lack a sufficient wide bandgap. Currently, it would be perfect to design non-toxic, low-cost, and high-performance photocatalysts for photocatalytic water splitting via hydrogenation. We systematically examine the impact of hydrogenation on the optical and electronic characteristics of GeC/g-C3N4 vdW heterostructures (vdWHs) with four different stacking patterns using first-principles calculations. The phonon spectra, interlayer distance, binding energies and ab initio molecular dynamics calculations show the kinetic, mechanical, and thermal stability of GeC/g-C3N4 vdWH after hydrogenation at 300, 500 and 800 K and possesses anisotropic Poisson's ratio, Young's and bulk modulus, suggesting that it's a promising candidate for experimental fabrication. According to an investigation of its electronic properties, GeC/g-C3N4 vdWH has a bandgap of 1.28 eV, but hydrogenation dramatically increases it to 2.47 eV. As a result of interface-induced electronic doping, the electronic states in g-C3N4 might be significantly adjusted by coming into contact with hydrogenated GeC sheets. The vdWH exhibits a type-II semiconductor, which can enhance the spatial separation of electron-hole pairs and has a strong red-shift of absorption coefficient than those of the constituent monolayers. The high potential drop caused by the significant valence and conduction band offsets effectively separated the charge carriers. The absorption coefficient of GeCH2/g-C3N4 vdWH is highly influenced by a biaxial compressive strain more than the biaxial tensile strain. Our theoretical research implies that the hydrogenated GeCH2/g-C3N4 vdWH possesses tunable optical and electronic behaviour for use as a hole-transport material in solar energy harvesting, nanoelectronic and optoelectronic devices.

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Modulation of transport at the interface in the microporous layer for high power density proton exchange membrane fuel cells

The proton exchange membrane (PEM) fuel cell is a device that demonstrates a significant potential for environmental sustainability, since it efficiently converts chemical energy into electrical energy. The microporous layer (MPL) in PEM fuel cells promotes gas transport and eliminates water. Nevertheless, the power density of PEM fuel cells is restricted by ohmic losses and mass transport losses in conventional MPLs. In this study, we enhanced the power density of proton exchange membrane (PEM) fuel cells through the identification of appropriate materials and the mitigation of mass transport losses occurring at the interface between the microporous layer and the catalyst layer. The incorporation of high electron conductivity, slip behavior at the interface between graphene and water, and rapid water evaporation facilitated by nanoporous graphene effectively address transport-related challenges. We evaluated two types of graphene as potential substitutes for carbon black in the microporous layer (MPL). The enhanced power density (up to 1.1 W cm-2) under all humidity conditions and reduced mass transport resistance (a 75 % reduction compared to carbon black MPL) make them promising candidates for next-generation PEM fuel cells. Furthermore, these findings provide guidance for controlling interfacial mass transport in colloidal systems.

The chimera of 2D- and 1D-graphene magnetization by hydrogenation or fluorination: critically revisiting old schemes and proposing new ones by ab initio methods

Graphene is an ideal candidate material for spintronics due to its layered structure and peculiar electronic structure. However, in its pristine state, the production of magnetic moments is not trivial. A very appealing approach is the chemical modification of pristine graphene. The main obstacle is the control of the geometrical features and the selectivity of functional groups. The lack of a periodic functionalization pattern of the graphene sheet prevents, therefore, the achievement of long-range magnetic order, thus limiting its use in spintronic devices. In such regards, the stability and the magnitude of the instilled magnetic moment depending on the size and shape of in silico designed graphane islands and ribbons embedded in graphene matrix will be computed and analysed. Our findings thus suggest that a novel and magneto-active graphene derivative nanostructure could become achievable more easily than extended graphone or nanoribbons, with a strong potential for future spintronics applications with a variable spin-current density.

Graphene Pseudoreference Electrode for the Development of a Practical Paper-Based Electrochemical Heavy Metal Sensor

Paper-based electrochemical devices (PEDs) have emerged as versatile platforms that bridge analytical chemistry and materials science, demonstrating advantages of portability, cost-effectiveness, and environmental sustainability. This study investigates the integration of a graphene pseudoreference electrode (GPRE) into a PED, and it exhibits potential advantages over the traditional Ag/AgCl pseudoreference electrode (PRE). In addition, the electrochemical properties and stability of GPRE are compared with those of the traditional Ag/AgCl PRE. The results demonstrate that GPRE exhibits a stable and reproducible potential during electrochemical measurement throughout 180 days, demonstrating its suitability as an alternative to an expensive metal PRE. Furthermore, a GPRE-incorporated paper-based device is designed and evaluated for use in the electrochemical detection of cadmium (Cd) and lead (Pb) using an in situ bismuth-modified electrode. The GPRE-incorporated PED exhibited good analytical performance, with a low limit of detection of 0.69 and 5.77 ng mL-1 and electrochemical sensitivities of 70.16 and 38.34 μA·mL·μg-1·cm-2 for Cd(II) and Pb(II), respectively. More than 99.9% accuracy of the sensor was obtained for both ions with respect to conventional inductively coupled plasma-mass spectrometry. The results highlight the effectiveness and suitability of the GPRE-incorporated PED as a sensor for various applications, such as environmental monitoring, food quality control, and medical diagnostics.

Click and Detect: Versatile Ampicillin Aptasensor Enabled by Click Chemistry on a Graphene-Alkyne Derivative

Tackling the current problem of antimicrobial resistance (AMR) requires fast, inexpensive, and effective methods for controlling and detecting antibiotics in diverse samples at the point of interest. Cost-effective, disposable, point-of-care electrochemical biosensors are a particularly attractive option. However, there is a need for conductive and versatile carbon-based materials and inks that enable effective bioconjugation under mild conditions for the development of robust, sensitive, and selective devices. This work describes a simple and fast methodology to construct an aptasensor based on a novel graphene derivative equipped with alkyne groups prepared via fluorographene chemistry. Using click chemistry, an aptamer is immobilized and used as a successful platform for the selective determination of ampicillin in real samples in the presence of interfering molecules. The electrochemical aptasensor displayed a detection limit of 1.36 nM, high selectivity among other antibiotics, the storage stability of 4 weeks, and is effective in real samples. Additionally, structural and docking simulations of the aptamer shed light on the ampicillin binding mechanism. The versatility of this platform opens up wide possibilities for constructing a new class of aptasensor based on disposable screen-printed carbon electrodes usable in point-of-care devices.

Acrylates Polymerization on Covalent Plasma-Assisted Functionalized Graphene: A Route to Synthesize Hybrid Functional Materials

The modification of the surface properties of graphene with polymers provides a method for expanding its scope into new applications as a hybrid material. Unfortunately, the chemical inertness of graphene hinders the covalent functionalization required to build them up. Developing new strategies to enhance the graphene chemical activity for efficient and stable functionalization, while preserving its electronic properties, is a major challenge. We here devise a covalent functionalization method that is clean, reproducible, scalable, and technologically relevant for the synthesis of a large-scale, substrate-supported graphene-polymer hybrid material. In a first step, hydrogen-assisted plasma activation of p-aminophenol (p-AP) linker molecules produces their stable and covalent attachment to large-area graphene. Second, an in situ radical polymerization reaction of 2-hydroxyethyl acrylate (HEA) is carried out on the functionalized surface, leading to a graphene-polymer hybrid functional material. The functionalization with a hydrophilic and soft polymer modifies the hydrophobicity of graphene and might enhance its biocompatibility. We have characterized these hybrid materials by atomic force microscopy (AFM), X-Ray photoelectron spectroscopy (XPS) and Raman spectroscopy and studied their electrical response, confirming that the graphene/p-AP/PHEA architecture is anchored covalently by the sp3 hybridization and controlled polymerization reaction on graphene, retaining its suitable electronic properties. Among all the possibilities, we assess the proof of concept of this graphene-based hybrid platform as a humidity sensor. An enhanced sensitivity is obtained in comparison with pristine graphene and related materials. This functional nanoarchitecture and the two-step strategy open up future potential applications in sensors, biomaterials, or biotechnology fields.

Nanoantibiotic effect of carbon-based nanocomposites: epicentric on graphene, carbon nanotubes and fullerene composites: a review

Carbon in many different forms especially, Graphene, Carbon nanotubes (CNTs), and Fullerene is emerging as an important material in the areas of the biomedical field for various applications. This review comprehensively describes the nano antibiotic effect of carbon-based nanocomposites: epicenter on graphene, carbon nanotubes, and fullerene Composites. It summarises the studies conducted to evaluate their antimicrobial applications as they can disrupt the cell membrane of bacteria resulting in cell death. The initial section gives a glimpse of both "Gram"-positive and negative bacteria, which have been affected by Graphene, CNTs, and Fullerene-based nanocomposites. These bacteria include Staphylococcus Aureus, Bacillus Thuringiensis, Enterococcus faecalis, Enterococcus faecium, Bacillus subtilis, Escherichia coli, Klebseilla pneumoniae, Pseudomonas aeroginosa, Pseudomonas syringae , Shigella flexneri,Candida Albicans, Mucor. Another section is dedicated to the insight of Graphene, and its types such as Graphene Oxide (GO), Reduced graphene oxide (rGO), Graphene Nanoplatelets (GNPs), Graphene Nanoribbons (GNRs), and Graphene Quantum Dots (GQDs). Insight into CNT, including both the types SWCNT and MWCNT, studied, followed by understanding fullerene is also reported. Another section is dedicated to the antibacterial mechanism of Graphene, CNT, and Fullerene-based nanocomposites. Further, an additional section is dedicated to a comprehensive review of the antibacterial characteristics of Graphene, CNT, and nanocomposites based on fullerene. Future perspectives and recommendations have also been highlighted in the last section.

Can Metal-Nitrogen-Carbon Single-Atom Catalysts Boost the Electroreduction of Carbon Monoxide?

Metal-nitrogen-carbon single-atom catalysts (SACs) have exhibited substantial potential for CO2 electroreduction. Unfortunately, the SACs generally cannot generate chemicals other than CO, while deep reduction products are more appealing because of their higher market potential, and the origin of governing CO reduction (COR) remains elusive. Here, by using constant-potential/hybrid-solvent modeling and revisiting Cu catalysts, we show that the Langmuir-Hinshelwood mechanism is of importance for *CO hydrogenation, and the pristine SACs lack another site to place *H, thus preventing their COR. Then, we propose a regulation strategy to enable COR on the SACs: (I) the metal site has a moderate CO adsorption affinity; (II) the graphene skeleton is doped by a heteroatom to allow *H formation; and (III) the distance between the heteroatom and the metal atom is appropriate to facilitate *H migration. We discover a P-doped Fe-N-C SAC with promising COR reactivity and further extend this model to other SACs. This work provides mechanistic insight into the limiting factors of COR and highlights the rational design of the local structures of active centers in electrocatalysis.

Bio-inspired conductive adhesive based on calcium-free alginate hydrogels for bioelectronic interfaces

Electrode impedance is one of the greatest challenges facing neural interfacing medical devices and the use of electrical stimulation-based therapies in the fields of neurology and regenerative medicine. Maximizing contact between electronics and tissue would allow for more accurate recordings of neural activity and to stimulate with less power in implantable devices as electric signals could be more precisely transferred by a stable interfacial area. Neural environments, inherently wet and ion-rich, present a unique challenge for traditional conductive adhesives. As such, we look to marine mussels that use a 3,4-dihydroxyphenyl-L-analine (DOPA)-containing proteinaceous excretion to adhere to a variety of substrates for inspiration. By functionalizing alginate, which is an abundantly available natural polymer, with the catechol residues DOPA contains, we developed a hydrogel-based matrix to which carbon-based nanofiller was added to render it conductive. The synthesized product had adhesive energy within the range of previously reported mussel-based polymers, good electrical properties and was not cytotoxic to brain derived neural precursor cells.

Examining the Long-Range Effect in Very Long Graphene Nanoribbons: A First-Principles Study

The role of long-range effect on the modulation of the electronic structure of graphene nanoribbons has been little studied due to the limitations of existing theoretical and computational methods. By splitting a molecule top-down and calculating and jointing the Fock matrix of fragments, we developed a computational method suitable for large-size molecules with random doping and arbitrary geometry. Utilizing this method, we achieved the study of the effects of dopants and curvature on graphene nanoribbons (GNRs). It reveals that both dopants and curvature can change the charge distribution of GNRs, while the influence of dopants is more significant and can extend up to 1-3 nm. The electronic excitation properties of GNRs are also largely modified by the doping state or nonuniform curvature. Our findings provide not only a feasible approach for studying the electronic structure of large-size molecules but also the possibility to improve the properties of graphene-based materials by dopants and local curvature.

Interfacial thermal transport of graphene/β-Ga2O3 heterojunctions: a molecular dynamics study with a self-consistent interatomic potential

Graphene/β-Ga₂O₃ heterojunctions are widely used in high-power and high-frequency devices, for which thermal management is vital to the device operation and life. Here we apply molecular dynamics simulation to calculate the interfacial thermal resistance (ITR) between graphene and β-Ga₂O₃. Based on the rigid ion model, a self-consistent interatomic potential with a set of parameters that can well reproduce the basic physical properties of crystal β-Ga₂O₃ is fitted. Using this potential, the effects of model size, interface type, temperature, vacancy defects and graphene hydrogenation on the ITR of graphene/β-Ga₂O₃ heterojunctions are evaluated. The results show that there is no obvious dependence of ITR on the size of graphene and β-Ga₂O₃. It is reported that the ITR values of the (100), (010) and (001) interfaces are 7.28 ± 0.35 × 10^-8 K m² W^-1, 6.69 ± 0.44 × 10^-8 K m² W^-1 and 5.22 ± 0.35 × 10^-8 K m² W^-1 at 300 K, respectively. Both temperature increase and vacancy defect increase can prompt the energy propagation across graphene/β-Ga₂O₃ interfaces due to the enhancement of phonon coupling. In addition, graphene hydrogenation provides new channels for in-plane and out-of-plane phonon coupling, and thus reduces the ITR between graphene and β-Ga₂O₃. This study provides basic strategies for the thermal design and management of graphene/β-Ga₂O₃ based photoelectric devices.

Recent Progress in Graphene-Based Electrocatalysts for Hydrogen Evolution Reaction

Hydrogen is regarded as a key renewable energy source to meet future energy demands. Moreover, graphene and its derivatives have many advantages, including high electronic conductivity, controllable morphology, and eco-friendliness, etc., which show great promise for electrocatalytic splitting of water to produce hydrogen. This review article highlights recent advances in the synthesis and the applications of graphene-based supported electrocatalysts in hydrogen evolution reaction (HER). Herein, powder-based and self-supporting three-dimensional (3D) electrocatalysts with doped or undoped heteroatom graphene are highlighted. Quantum dot catalysts such as carbon quantum dots, graphene quantum dots, and fullerenes are also included. Different strategies to tune and improve the structural properties and performance of HER electrocatalysts by defect engineering through synthetic approaches are discussed. The relationship between each graphene-based HER electrocatalyst is highlighted. Apart from HER electrocatalysis, the latest advances in water electrolysis by bifunctional oxygen evolution reaction (OER) and HER performed by multi-doped graphene-based electrocatalysts are also considered. This comprehensive review identifies rational strategies to direct the design and synthesis of high-performance graphene-based electrocatalysts for green and sustainable applications.

Facile Gold-Nanoparticle Boosted Graphene Sensor Fabrication Enhanced Biochemical Signal Detection

Graphene has been considered as an excellent biochemical sensors’ substrate material because of its excellent physical and chemical properties. Most of these sensors have employed enzymes, antibodies, antigens, and other biomolecules with corresponding recognition ability as recognition elements, to convert chemical signals into electrical signals. However, oxidoreductase enzymes that grow on graphene surfaces are affected significantly by the environment and are easily inactivated, which hinders the further improvement of detection sensitivity and robusticity. A gold-boosted graphene sensor was fabricated by the in situ electrochemical deposition of inorganic gold nanoparticles on vertical graphene nanosheets. This approach solves the instability of biological enzymes and improves the detection performance of graphene-based sensors. The uric acid sensitivity of the gold-boosted electrode was 6230 µA mM−1 cm−2, which is 6 times higher than the original graphene electrode. A 7 h GNSs/CC electrode showed an impressive detection performance for ascorbic acid, dopamine, and uric acid, simultaneously. Moreover, it exhibited a reliable detection performance in human serum in terms of uric acid. The possible reason could be that the vertical aliened graphene nanosheet acts as a reaction active spot. This 3D graphene-nanosheet-based doping approach can be applied to a wide variety of inorganic catalytic materials to enhance their performance and improve their durability in aspects such as single-atom catalysis and integration of multiple catalytic properties.

Manifestations of Laser-Induced Graphene under Ultraviolet Irradiation of Polyimide with Varied Optical Fluence

In this work, we put forward a rigorous study on ultraviolet (355-nm) laser irradiation of polyimide for the realization of high-quality laser-induced graphene (LIG) with micron-scale features. High-quality material and micron-scale features are desirable—but often at odds—given that small features demand tightly focused beam spots, with a predisposition to ablation. As such, we investigate the synthesis of LIG by correlating the material characteristics, as gleaned from scanning electron microscopy and Raman spectroscopy, to the incident optical fluence, as a measure of applied optical energy per unit area. The study reveals that high-quality LIG, with ratios of Raman 2D-to-G peak heights approaching 0.7, can be synthesized with micron-scale features, down to 18 ± 2 μm, given suitable attention to the optical fluence. Optimal characteristics are seen at optical fluences between 40 and 50 J/cm2, which promote graphenization and minimize ablation. It is hoped that these findings will lay a foundation for the application of LIG in future integrated technologies.

Evaluation of N doped rGO-ZnO-CoPc(COOH)8 nanocomposite in cyanide degradation and its bactericidal activities

In the present study, an attempt has been made to design a solar light driven N-rGO-ZnO- CoPc(COOH)₈ nanocomposite for the degradation of cyanide. The morphological and structural characterization of the synthesized nanocomposite was performed by XRD, FT-IR, XPS, UV-vis DRS, FESEM, TEM, EDS, PL spectra and BET surface area. The results revealed that almost 91% degradation and 86% toxicity removal occurred at 25 mgL^-1 of initial cyanide concentration by the N-rGO-ZnO-CoPc(COOH)₈ nanocomposite under illumination of solar light within 120 min. Analysis of free radicals reveals that the generation of OH^. radicals was the predominant species in the photocatalytic degradation process. The cyanide degradation follows pseudo-first order kinetics. The estimated apparent rate constant (K_app) of the above nanocomposite was 3 times higher than that of the ZnO photocatalyst alone together with a very good recycle activities. This might be due to the application of metallpthalocyanine photosensitizer CoPc(COOH)₈ which enhances the rate of visible light absorption efficiency and activates the higher band gap ZnO photocatalyst under visible light. In addition, the presence of residual oxygen in N-rGO also promotes nucleation and anchor sites for interfacial contact between ZnO and N-rGO for effective charge transfer. Further, the N-rGO-ZnO-CoPc(COOH)₈ photocatalytic system showed significant antibacterial activities against mixed culture systems. Therefore, the N-rGO-ZnO-CoPc(COOH)₈ nanocomposite may be an alternative solar light driven photocatalyst system for the removal of cyanide from the wastewater along with its strong disinfectant activities.

Two-Dimensional Biphenylene: A Graphene Allotrope with Superior Activity toward Electrochemical Oxygen Reduction Reaction

Developing efficient and inexpensive catalysts for the oxygen reduction reaction (ORR) is a key for sustainable development of fuel cell technologies. Herein, by means of density functional theory calculations and microkinetic modeling, we demonstrate that two-dimensional (2D) biphenylene, a recently synthesized allotrope of graphene composed of tetragonal, hexagonal, and octagonal rings, is a metal-free candidate for facilitating the electrochemical ORR. Different from semimetallic graphene, 2D biphenylene is metallic, and carbon atoms of its tetragonal rings are substantially positively charged, resulting in good ORR activity due to the enhanced binding strength with reaction intermediates. In particular, the ORR activity of 2D biphenylene is pH-dependent, and it can be significantly boosted under alkaline conditions. Moreover, 2D biphenylene possesses rather good electrochemical stability, rendering it attractive for alkaline fuel cells.

Preparation of Carbon Nanowall and Carbon Nanotube for Anode Material of Lithium-Ion Battery

Carbon nanowall (CNW) and carbon nanotube (CNT) were prepared as anode materials of lithium-ion batteries. To fabricate a lithium-ion battery, copper (Cu) foil was cleaned using an ultrasonic cleaner in a solvent such as trichloroethylene (TCE) and used as a substrate. CNW and CNT were synthesized on Cu foil using plasma-enhanced chemical vapor deposition (PECVD) and water dispersion, respectively. CNW and CNT were used as anode materials for the lithium-ion battery, while lithium hexafluorophosphate (LiPF₆) was used as an electrolyte to fabricate another lithium-ion battery. For the structural analysis of CNW and CNT, field emission scanning electron microscope (FE-SEM) and Raman spectroscopy analysis were performed. The Raman analysis showed that the carbon nanotube in composite material can compensate for the defects of the carbon nanowall. Cyclic voltammetry (CV) was employed for the electrochemical properties of lithium-ion batteries, fabricated by CNW and CNT, respectively. The specific capacity of CNW and CNT were calculated as 62.4 mAh/g and 49.54 mAh/g. The composite material with CNW and CNT having a specific capacity measured at 64.94 mAh/g, delivered the optimal performance.

Biotransformations and cytotoxicity of eleven graphene and inorganic two-dimensional nanomaterials using simulated digestions coupled with a triculture in vitro model of the human gastrointestinal epithelium

Background

Engineered nanomaterials (ENMs) have already made their way into myriad applications and products across multiple industries. However, the potential health risks of exposure to ENMs remain poorly understood. This is particularly true for the emerging class of ENMs know as 2-dimensional nanomaterials (2DNMs), with a thickness of one or a few layers of atoms arranged in a planar structure.

Methods

The present study assesses the biotransformations and in vitro cytotoxicity in the gastrointestinal tract of 11 2DNMs, namely graphene, graphene oxide (GO), partially reduced graphene oxide (prGO), reduced graphene oxide (rGO), hexagonal boron nitride (h-BN), molybdenum disulphide (MoS2), and tungsten disulphide (WS2). The evaluated pristine materials were either readily dispersed in water or dispersed with the use of a surfactant (Na-cholate or PF108). Materials dispersed in a fasting food model (FFM, water) were subjected to simulated 3-phase (oral, gastric, and small intestinal) digestion to replicate the biotransformations that would occur in the GIT after ingestion. A triculture model of small intestinal epithelium was used to assess the effects of the digested products (digestas) on epithelial layer integrity, cytotoxicity, viability, oxidative stress, and initiation of apoptosis.

Results

Physicochemical characterization of the 2DNMs in FFM dispersions and in small intestinal digestas revealed significant agglomeration by all materials during digestion, most prominently by graphene, which was likely caused by interactions with digestive proteins. Also, MoS2 had dissolved by ~75% by the end of simulated digestion. Other than a low but statistically significant increase in cytotoxicity observed with all inorganic materials and graphene dispersed in PF108, no adverse effects were observed in the exposed tricultures.

Conclusions

Our results suggest that occasional ingestion of small quantities of 2DNMs may not be highly cytotoxic in a physiologically relevant in vitro model of the intestinal epithelium. Still, their inflammatory or genotoxic potential after short- or long-term ingestion remains unclear and needs to be studied in future in vitro and in vivo studies. These would include studies of effects on co-ingested nutrient digestion and absorption, which have been documented for numerous ingested ENMs, as well as effects on the gut microbiome, which can have important health implications.

Direct growth of crystalline triazine-based graphdiyne using surface-assisted deprotection-polymerisation

Graphdiyne polymers have interesting electronic properties due to their π-conjugated structure and modular composition. Most of the known synthetic pathways for graphdiyne polymers yield amorphous solids because the irreversible formation of carbon–carbon bonds proceeds under kinetic control and because of defects introduced by the inherent chemical lability of terminal alkyne bonds in the monomers. Here, we present a one-pot surface-assisted deprotection/polymerisation protocol for the synthesis of crystalline graphdiynes over a copper surface starting with stable trimethylsilylated alkyne monomers. In comparison to conventional polymerisation protocols, our method yields large-area crystalline thin graphdiyne films and, at the same time, minimises detrimental effects on the monomers like oxidation or cyclotrimerisation side reactions typically associated with terminal alkynes. A detailed study of the reaction mechanism reveals that the deprotection and polymerisation of the monomer is promoted by Cu(ii) oxide/hydroxide species on the as-received copper surface. These findings pave the way for the scalable synthesis of crystalline graphdiyne-based materials as cohesive thin films.

We present a one-pot deprotection/polymerisation protocol for the synthesis of crystalline graphdiynes on top of a copper surface starting with stable trimethylsilylated alkyne monomers.

Graphene-Based Nanocomposites: Synthesis, Mechanical Properties, and Characterizations

Graphene-based nanocomposites possess excellent mechanical, electrical, thermal, optical, and chemical properties. These materials have potential applications in high-performance transistors, biomedical systems, sensors, and solar cells. This paper presents a critical review of the recent developments in graphene-based nanocomposite research, exploring synthesis methods, characterizations, mechanical properties, and thermal properties. Emphasis is placed on characterization techniques and mechanical properties with detailed examples from recent literature. The importance of characterization techniques including Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) for the characterization of graphene flakes and their composites were thoroughly discussed. Finally, the effect of graphene even at very low loadings on the mechanical properties of the composite matrix was extensively reviewed.

Theoretical Understanding of Structure-Property Relationships in Luminescence of Carbon Dots

Carbon dots (CDs) have excellent luminescence characteristics, such as good light stability, high quantum yield (QY), long phosphorescence lifetime, and a wide emission wavelength range, resulting in CDs' great success in optical applications. Understanding the structure-property relationships in CDs is essential for their use in optoelectronic applications. However, because of the complex nature of CD structures and synthesis processes, understanding the luminescence mechanism and structure-property relationships of CDs is a big challenge. This Perspective reviews the theoretical efforts toward the understanding of structure-property relationships and discusses the challenges that need to be overcome in future development of CDs.

A Simplified Method for Patterning Graphene on Dielectric Layers

The large-scale formation of patterned, quasi-freestanding graphene structures supported on a dielectric has so far been limited by the need to transfer the graphene onto a suitable substrate and contamination from the associated processing steps. We report μm scale, few-layer graphene structures formed at moderate temperatures (600-700 °C) and supported directly on an interfacial dielectric formed by oxidizing Si layers at the graphene/substrate interface. We show that the thickness of this underlying dielectric support can be tailored further by an additional Si intercalation of the graphene prior to oxidation. This produces quasi-freestanding, patterned graphene on dielectric SiO₂ with a tunable thickness on demand, thus facilitating a new pathway to integrated graphene microelectronics.

Preparation and Applications of Fluorinated Graphenes

The present review focuses on the numerous routes for the preparation of fluorinated graphene (FG) according to the starting materials. Two strategies are considered: (i) addition of fluorine atoms on graphenes of various nature and quality and (ii) exfoliation of graphite fluoride. Chemical bonding in fluorinated graphene, related properties and a selection of applications for lubrication, energy storage, and gas sensing will then be discussed.

Edge-Functionalized Nanographenes

Nanographenes (NGs) have recently emerged as new carbon materials. Their nanoscale size results in a size-dependent quantum confinement effect, opening the band gap by a few eV. This energy gap allows NGs to be applied as optical materials. This property has attracted researchers across multiple scientific fields. The photophysical properties of NGs can be manipulated by introducing organic groups onto their basal planes and/or into their edges. In addition, the integration of organic functional groups into NGs results in NG-based hybrid materials. These features make the post-synthetic modification of NGs an active research area. As obtainable information on chemically functionalized NGs is limited owing to their nonstoichiometry and structural uncertainty, their structural characterization requires a combination of multiple spectroscopic methods. Therefore, information on the characterization procedures of recently published chemically functionalized NGs is of value for advancing the field of NG-based hybrid materials. The present review focuses on the structural characterization of chemically functionalized NGs. It is hoped that this review will help to advance this field.

Hydrogen-induced tunable electronic and optical properties of a two-dimensional penta-Pt2N4 monolayer

Most known two-dimensional materials lack a suitable wide-bandgap, and hydrogenation can be effectively utilized to tune the bandgap of some 2D materials. By employing density functional theory calculations, we investigate the effect of hydrogenation on the electronic and optical properties of a recently reported anisotropic penta-Pt2N4 monolayer. The results show that penta-Pt2N4 is thermally and mechanically stable after hydrogenation and also possesses anisotropic Young's modulus and Poisson's ratio. The electronic property analysis using the hybrid functional reveals that penta-Pt2N4 exhibits a bandgap of 1.10 eV, and the hydrogenation significantly enhances the bandgap to 2.70 eV. Furthermore, the hydrogenated Pt2N4 displays a strong optical absorption of up to 6.45 × 105 cm-1 in the ultraviolet region, and low absorption and low reflectivity in the visible region. Our results strongly suggest that the hydrogenated Pt2N4 has tunable electronic and optical properties for applications as a hole-transport material layer in solar cells in the visible region, and as an ultraviolet detector in the ultraviolet region of the electromagnetic spectrum.

Regulation of Electronic Structure of Graphene Nanoribbon by Tuning Long-Range Dopant-Dopant Coupling at Distance of Tens of Nanometers

Long-range dopant-dopant coupling in graphene nanoribbon (GNR) has been under intensive study for a very long time. Using a newly developed dopant central insertion scheme (DCIS), we performed first-principles study on multiple H, O, OH, and FeN₄ dopants in long (up to 1000 nm) GNRs and found that, although potential energy of the dopant decays exponentially as a function of distance to the dopant, GNR's electronic density of states (DOS) exhibits wave-like oscillation modulated by dopants separated at a distance up to 100 nm. Such an oscillation strongly infers the purely quantum mechanical resonance states constrained between double quantum wells. This has been unambiguously confirmed by our DCIS study together with a one-dimensional quantum well model study, leading to a proof-of-principle protocol prescribing on-demand GNR-DOS regulation. All these not only reveal the underlining mechanism and importance of long-range dopant-dopant coupling specifically reported in GNR, but also open a novel highway for rationally optimizing and designing two-dimensional materials.

Toxicity Studies on Graphene-Based Nanomaterials in Aquatic Organisms: Current Understanding

Graphene and its oxide are nanomaterials considered currently to be very promising because of their great potential applications in various industries. The exceptional physiochemical properties of graphene, particularly thermal conductivity, electron mobility, high surface area, and mechanical strength, promise development of novel or enhanced technologies in industries. The diverse applications of graphene and graphene oxide (GO) include energy storage, sensors, generators, light processing, electronics, and targeted drug delivery. However, the extensive use and exposure to graphene and GO might pose a great threat to living organisms and ultimately to human health. The toxicity data of graphene and GO is still insufficient to point out its side effects to different living organisms. Their accumulation in the aquatic environment might create complex problems in aquatic food chains and aquatic habitats leading to debilitating health effects in humans. The potential toxic effects of graphene and GO are not fully understood. However, they have been reported to cause agglomeration, long-term persistence, and toxic effects penetrating cell membrane and interacting with cellular components. In this review paper, we have primarily focused on the toxic effects of graphene and GO caused on aquatic invertebrates and fish (cell line and organisms). Here, we aim to point out the current understanding and knowledge gaps of graphene and GO toxicity.

Structural, electronic, and energetic investigations of acrolein adsorption on B36 borophene nanosheet: a dispersion-corrected DFT insight

The adsorption of acrolein (AC) onto the surface of B₃₆ borophene nanosheet was studied using dispersion-corrected density functional theory (DFT). The structural and electronic properties were scrutinized by several quantum chemical parameters such as HOMO-LUMO gap, condensed Fukui function, molecular electrostatic potential (ESP), and the density of states (DOS). The non-covalent interactions (NCI) were explored by combined reduced density gradient (RDG-NCI) and energy decomposition analysis (EDA) techniques. It was found that the adsorption of acrolein on both convex and concave surfaces of borophene is mainly governed by van der Waals interactions. Our calculations showed that the adsorption energy is strengthened and favored when multiple acrolein molecules adsorb on the edge sides of borophene through their terminal carbonyl oxygen atom. Furthermore, the calculated HOMO-LUMO energy gaps were significantly reduced upon adsorption affecting, therefore, the electrical conductance of borophene. These results should be useful in designing acrolein sensors.

Graphene Quantum Dots with High Yield and High Quality Synthesized from Low Cost Precursor of Aphanitic Graphite

It is difficult to keep the balance of high quality and high yield for graphene quantum dots (GQDs). Because the quality is uncontrollable during cutting large 2D nanosheets to small 0D nanodots by top-down methods and the yield is low for GQDs with high quality obtained from bottom-up strategy. Here, aphanitic graphite (AG), a low-cost graphite contains a large amount of small graphite nanocrystals with size of about 10 nm is used as the precursor of graphene oxide quantum dots (GO-QDs) for the first time. GO-QDs with high yield and high quality were successfully obtained directly by liquid phase exfoliating AG without high strength cutting. The yield of these GO-QDs can reach up to 40 wt. %, much higher than that obtained from flake graphite (FG) precursor (less than 10 wt. %). The size of GO-QDs can be controlled in 2-10 nm. The average thickness of GO-QDs is about 3 nm, less than 3 layer of graphene sheet. Graphene quantum dots (GQDs) with different surface properties can be easily obtained by simple hydrothermal treatment of GO-QDs, which can be used as highly efficient fluorescent probe. Developing AG as precursor for GQDs offers a way to produce GQDs in a low-cost, highly effective and scalable manner.

Photochemical reaction on graphene surfaces controlled by substrate-surface modification with polar self-assembled monolayers

The unique thinness of two-dimensional materials enables control over chemical phenomena at their surfaces by means of various gating techniques. For example, gating methods based on field-effect-transistor configurations have been achieved. Here, we report a molecular gating approach that employs a local electric field generated by a polar self-assembled monolayer formed on a supporting substrate. By performing Raman scattering spectroscopy analyses with a proper data correction procedure, we found that molecular gating is effective for controlling solid phase photochemical reactions of graphene with benzoyl peroxide. Molecular gating offers a simple method to control chemical reactions on the surfaces of two-dimensional materials because it requires neither the fabrication of a transistor structure nor the application of an external voltage.

Immobilized Enzymes on Graphene as Nanobiocatalyst

Using enzymes as bioelectrocatalysts is an important step toward the next level of biotechnology for energy production. In such biocatalysts, a sacrificial cofactor as an electron and proton source is needed. This is a great obstacle for upscaling, due to cofactor instability and product separation issues, which increase the costs. Here, we report a cofactor-free electroreduction of CO2 to a high energy density chemical (methanol) catalyzed by enzyme-graphene hybrids. The biocatalyst consists of dehydrogenases covalently bound on a well-defined carboxyl graphene derivative, serving the role of a conductive nanoplatform. This nanobiocatalyst achieves reduction of CO2 to methanol at high current densities, which remain unchanged for at least 20 h of operation, without production of other soluble byproducts. It is thus shown that critical improvements on the stability and rate of methanol production at a high Faradaic efficiency of 12% are possible, due to the effective electrochemical process from the electrode to the enzymes via the graphene platform.