Atomic layers of hybridized boron nitride and graphene domains

Unveiling the potential of a BCN-biphenylene monolayer as a high-performance anode material for alkali metal ion batteries: a first-principles study

Inspired by a freshly synthesized two-dimensional biphenylene carbon network, which features a captivating combination of hexagonal, square, and octagonal rings, we explored a similar biphenylene network composed of boron, carbon, and nitrogen (bpn-BCN) using first-principles calculations. There are six possible phases of borocarbonitrides, which are isoelectronic to biphenylene carbon networks with a stoichiometric ratio of 1 : 1 : 1 for boron (B), carbon (C), and nitrogen (N) atoms. All possible isoelectronic structures of the BCN combination of biphenylene networks are found to be stable, according to first-principles calculations. However, the geometry has a relatively large number of robust C-C and B-N bonds and strong partially ionic-covalent B-C and C-N bonds inside these bpn-BCN monolayers are effectively more stable. Furthermore, we employed first-principles calculations to investigate the electrochemical properties of the most stable geometry of BCN biphenylene as a potential anode material for alkali metal (AM) ion batteries. A global search has been made to find the most favourable alkali metal ion adsorption sites. The biphenylene monolayer has octagonal, square, and hexagonal motifs with different adsorption strengths. Furthermore, the partially ionic bond of B-N (due to the electronegativity difference) also supports the alkali metal ions for adsorption. The electronic properties of the stable phase of bpn-BCN reveal its narrow bandgap semiconductor nature. The ion diffusion calculations show a low activation barrier for Li, Na, and K of 0.65 eV, 0.26 eV, and 0.23 eV, respectively, indicating a fast charge/discharge rate. Furthermore, the theoretical capacities of the BCN biphenylene monolayer for Li (1057.33 mA h g-1), Na (647.27 mA h g-1), and K (465.98 mA h g-1) are found to be greater than those of commercial graphite. The average open-circuit voltage for AM decreases with increasing metal ion concentrations. It falls within a reasonable range of 0.34-1.89 V. Our results show that the BCN biphenylene monolayer could be a promising anode material in alkali metal ion rechargeable batteries.

Tuning Properties of Layered Materials Based on Hexagonal Boron Nitride by Methylation: A Density Functional Theory Study

In this work, the rational design of optoelectronic properties of two-dimensional materials based on hexagonal boron nitride (h-BN) by functionalization by methyl (CH3) groups is proposed. Using density functional theory, we examine the functionalization of single- or double-layer systems with either CH3 radicals alone or with both CH3 (cations) and chlorine (anions), i. e., under conditions of homolytic or heterolytic splitting of CH3Cl precursor molecules, respectively. Different degrees of methylation (coverages) are considered. The methylation of pure h-BN leads to a reduction of the band gap, while in h-BN/G heterostructures (with methylated graphene layer), methylation increases the band gap. As a consequence, h-BN/G heterostructures offer a high tunability of their optoelectronic properties. To guide possible experiments, vibrational properties and spectra of methylated h-BN and methylated h-BN/G are determined.

Enhancing the energetic and magnetic stability of atomic hydrogen chemisorbed on graphene using (non)compensated B-N pairs

In this pioneering study for identifying atomic scale magnetic moment, a single hydrogen atom chemisorbed on pristine graphene exhibits distinct spin polarization. Using first-principles calculations and analyses, we demonstrate that the binding between a H adsorbate and a C substrate is substantially enhanced via compensated B-N pairs embedded into graphene. Surprisingly, the interaction can be further enhanced via non-compensated B-N pair doping. Our established prototype of orbital intercoupling between H 1s and hybridized pz of gapped band edges gives an insight into the enhancing mechanism. For compensated B-N doping, the conduction band minimum (CBM) is pushed upward, which induces stronger interaction between the H 1s and hybridized pz orbitals of the CBM. For non-compensated B-N doping, the orbital interaction occurs between H 1s and hybridized pz orbitals of valence band maximum, thus further lowering the resulting bonding energy due to the enlarged gap. This significantly enhanced interaction between H and C atoms agrees well with the results of charge localization at the gapped band edges. More importantly, the corresponding magnetic moments can be well maintained or even enhanced in both doping; here, one more H atom is needed for non-compensated doping, where its electron occupies the empty CBM. Our findings might provide an effective and practical way to enhance the energetic and magnetic stability of atomic scale magnetic moment on graphene and extensively expand the conception of non-compensated doping.

Borocarbonitride Catalyzed Ethylbenzene Oxidative Dehydrogenation: Activity Enhancement via Encapsulation of Mn Clusters inside the Tube

Borocarbonitride (BCN) catalysts, boasting multiple redox sites, have shown considerable potential in alkane oxidative dehydrogenation (ODH) to olefin molecules. However, their catalytic efficiency still lags behind that of leading commercial catalysts, primarily due to the limited reactivity of oxygen functional groups. In this study, a groundbreaking hybrid catalyst is developed, featuring BCN nanotubes (BCNNTs) encapsulated with manganese (Mn) clusters, crafted through a meticulous supramolecular self-assembly and postcalcination strategy. This novel catalyst demonstrates a remarkable enhancement in activity, achieving 30% conversion and ≈100% selectivity toward styrene in ethylbenzene ODH reactions. Notably, its performance surpasses both pure BCNNTs and those hosting Mn nanoparticles. Structural and kinetic analyses unveil a robust interaction between BCNNTs and the Mn component, substantially boosting the catalytic activity of BCNNTs. Furthermore, density functional theory (DFT) calculations elucidate that BCNNTs encapsulated with Mn clusters not only stabilize key intermediates (─B─O─O─B─) but also enhance the nucleophilicity of active sites through electron transfer from the Mn cluster to the BCNNTs. This electron transfer mechanism effectively lowers the energy barrier for ─C─H cleavage, resulting in a 13% improvement in catalytic activity compared to pure BCNNTs.

Recent advances in the functionalization, substitutional doping and applications of graphene/graphene composite nanomaterials

Recently, graphene and graphene-based nanomaterials have emerged as advanced carbon functional materials with specialized unique electronic, optical, mechanical, and chemical properties. These properties have made graphene an exceptional material for a wide range of promising applications in biological and non-biological fields. The present review illustrates the structural modifications of pristine graphene resulting in a wide variety of derivatives. The significance of substitutional doping with alkali-metals, alkaline earth metals, and III-VII group elements apart from the transition metals of the periodic table is discussed. The paper reviews various chemical and physical preparation routes of graphene, its derivatives and graphene-based nanocomposites at room and elevated temperatures in various solvents. The difficulty in dispersing it in water and organic solvents make it essential to functionalize graphene and its derivatives. Recent trends and advances are discussed at length. Controlled reduction reactions in the presence of various dopants leading to nanocomposites along with suitable surfactants essential to enhance its potential applications in the semiconductor industry and biological fields are discussed in detail.

Optical and electronic properties of BCN films deposited by magnetron sputtering

Boron carbonitride (BCN) films containing hybridized bonds involving B, C, and N over wide compositional ranges enable an abundant variety of new materials, properties, and applications; however, their electronic performance is still limited by the presence of structural and electronic defects, yielding sluggish mobility and electrical conductivity. This work reports on mechanically stable BCN films and their corresponding optical and electronic properties. The ternary BCN films consisting of hybridized B-C-N bonds have been achieved by varying N2 flow by the radio frequency magnetron sputtering method. The BCN films show a bandgap value ranging from 3.32 to 3.82 eV. Hall effect measurements reveal an n-type conductivity with an improved hall mobility of 226 cm2/V s at room temperature for the optimal film. The n-BCN/p-Si heterojunctions exhibit a nonlinear rectifying characteristic, where the tunneling behavior dominates the injection regimes due to the density of defects, i.e., structural disorder and impurities. Our work demonstrates the tunable electrical properties of BCN/Si p-n diodes and, thus, is beneficial for the potential application in the fields of optics, optoelectronics, and electrics.

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.

Emerging Two-Dimensional Carbonaceous Materials for Electrocatalytic Energy Conversions: Rational Design of Active Structures through High-Temperature Chemistry

Electrochemical energy conversion and storage technologies involving controlled catalysis provide a sustainable way to handle the intermittency of renewable energy sources, as well as to produce green chemicals/fuels in an ecofriendly manner. Core to such technology is the development of efficient electrocatalysts with high activity, selectivity, long-term stability, and low costs. Here, two-dimensional (2D) carbonaceous materials have emerged as promising contenders for advancing the chemistry in electrocatalysis. We review the emerging 2D carbonaceous materials for electrocatalysis, focusing primarily on the fine engineering of active structures through thermal condensation, where the design, fabrication, and mechanism investigations over different types of active moieties are summarized. Interestingly, all the recipes creating two-dimensionality on the carbon products also give specific electrocatalytic functionality, where the special mechanisms favoring 2D growth and their consequences on materials functionality are analyzed. Particularly, the structure-activity relationship between specific heteroatoms/defects and catalytic performance within 2D metal-free electrocatalysts is highlighted. Further, major challenges and opportunities for the practical implementation of 2D carbonaceous materials in electrocatalysis are summarized with the purpose to give future material design guidelines for attaining desirable catalytic structures.

Ti-B-O System for Catalyzing Boron Nitride Nanotube Growth

Chemical vapor deposition (CVD) stands out as the most promising method for cost-effective production of high-quality boron nitride nanotubes (BNNTs). Catalysts play a crucial role in BNNT synthesis. This work delves into the impact of oxygen (O) on Ti-based catalysts during the CVD growth of BNNTs. In contrast to the B/TiB2 nanoparticles (NPs) and B/TiN NPs systems, the oxygen-containing precursor B/TiO2 NPs remarkably catalyzes the growth of high-quality and high-purity BNNTs across a wider range of synthesis parameters. Subsequent analyses reveal that TiBO3 acts as an active catalyst, facilitating BNNT growth in Ti-based catalyst systems. Moreover, the nanocomposite film synthesized from BNNTs and PVDF-HFP exhibits excellent mechanical properties and heat dissipation capabilities. Utilizing the nanocomposite film as a thermal interface material effectively enhances the heat dissipation for a 5 W light-emitting diode (LED) chip. Consequently, our research confirms the effectiveness of the Ti-B-O system in catalyzing BNNT growth.

Advances in boron nitride-based nanomaterials for environmental remediation and water splitting: a review

Boron nitride has gained wide-spread attention globally owing to its outstanding characteristics, such as a large surface area, high thermal resistivity, great mechanical strength, low density, and corrosion resistance. This review compiles state-of-the-art synthesis techniques, including mechanical exfoliation, chemical exfoliation, chemical vapour deposition (CVD), and green synthesis for the fabrication of hexagonal boron nitride and its composites, their structural and chemical properties, and their applications in hydrogen production and environmental remediation. Additionally, the adsorptive and photocatalytic properties of boron nitride-based nanocomposites for the removal of heavy metals, dyes, and pharmaceuticals from contaminated waters are discussed. Lastly, the scope of future research, including the facile synthesis and large-scale applicability of boron nitride-based nanomaterials for wastewater treatment, is presented. This review is expected to deliver preliminary knowledge of the present state and properties of boron nitride-based nanomaterials, encouraging the future study and development of these materials for their applications in various fields.

Circular dichroism in two-dimensional BC6N and B3C2N3in absence of intervalley excitonic coupling

Two-dimensional (2D) noncentrosymmetric systems offer potential opportunities for exploiting the valley degrees of freedom for advanced information processing, owing to non-zero Berry curvature. However, such valley polarization in 2D materials is crucially governed by the intervalley excitonic scattering in momentum space due to reduced electronic degrees of freedom and consequent enhanced electronic correlation. Here, we study the valley excitonic properties of two 2D noncentrosymmetric complementary structures, namely, BC6N and B3C2N3using first principles-based GW calculations combined with the Bethe-Salpeter equation, that brings the many-body interactions among the quasiparticles. Thek-resolved oscillator strength of their first bright exciton indicates their ability to exhibit valley polarization under the irradiation of circularly polarized light of different chiralities. Both the systems show significant singlet excitonic binding energies of 0.74 eV and 1.31 eV, respectively. Higher stability of dark triplet excitons as compared to the singlet one can lead to higher quantum efficiency in both the systems. The combination of large excitonic binding energies and the valley polarization ability with minimal intervalley scattering make them promising candidates for applications in advanced optical devices and information storage technologies.

Structural evolution of in-plane hybrid graphene/hexagonal boron nitride heterostructure upon heating

In-plane hybrid graphene/hexagonal boron nitride (h-BN) heterostructure (graphene/hBN/graphene) is studied via molecular dynamics simulation. The initial configuration (6400-atom graphene/6200-atom h-BN/6400-atom graphene) is heated up from 50 K to 7500 K via Tersoff potential. To study the structural evolution, some thermal dynamics quantities are calculated such as the coordination number, the total energy per atom, the heat capacity, the angular distribution, and the distribution of rings. Some main results are calculated and presented as follows: i) The sudden increase of total energy per atom at the melting point (5500 K) exhibits the first order phase transition from the crystalline state to a liquid state of the hybrid graphene/h-BN/graphene heterostructure; ii) The heat capacity shows two peaks. The first peak (at 5500 K) represents the phase transition from the crystalline to a liquid states while the second one (at 6300 K) represents the formation of gaseous atoms of B and N in the h-BN sheet; iii) The coordination number of three decreases dramatically at temperature of 5500 K (about 10% lefts for each type of atoms) leading to the formation of the first peak in the graph of the heat capacity. The coordination number of zero for B and N in the h-BN layer increases significantly (over 55%) at 6300 K causing the formation of the second peak in the graph of the heat capacity; iv) The influence of the relative number of atoms of h-BN to graphene in the hybrid graphene/h-BN/graphene heterostructure on the structural evolution upon heating is considered as follows. The number of atoms in the graphene sheets remains constant (6400 atoms per sheet) while the one of the h-BN sheet varies in size (780, 1560, 3120, 4680, 5490, 5880, 6080, and 6200 atoms). The results show that although the phase transition is still the first order type, the phase transition temperature decreases as the size of the h-BN layer in the hybrid heterostructure increases.

Colossal electrocaloric effect in an interface-augmented ferroelectric polymer

The electrocaloric effect demands the maximized degree of freedom (DOF) of polar domains and the lowest energy barrier to facilitate the transition of polarization. However, optimization of the DOF and energy barrier-including domain size, crystallinity, multiconformation coexistence, polar correlation, and other factors in bulk ferroelectrics-has reached a limit. We used organic crystal dimethylhexynediol (DMHD) as a three-dimensional sacrificial master to assemble polar conformations at the heterogeneous interface in poly(vinylidene fluoride)-based terpolymer. DMHD was evaporated, and the epitaxy-like process induced an ultrafinely distributed, multiconformation-coexisting polar interface exhibiting a giant conformational entropy. Under a low electric field, the interface-augmented terpolymer had a high entropy change of 100 J/(kg·K). This interface polarization strategy is generally applicable to dielectric capacitors, supercapacitors, and other related applications.

Density functional theory studies on graphene/h-boron nitride hybrid nanosheets for supercapacitor electrode applications

Pristine graphene (C32), hexagonal boron nitride (h-BN), and graphene/h-BN hybrid nanosheets were examined using density functional theory calculations in order to find their suitability as an electrode material for supercapacitor applications. The stability of the structure, charge density, electronic properties, and quantum capacitance of pristine graphene and graphene/h-BN hybrid nanosheets were studied. The structural optimization results reveal that all the nanosheets are stable with zero transverse displacement of atoms along the z-direction. Further, replacing the C-C pair with B-N altered the average bond length and angle, thereby maintaining structural stability. The interaction between graphene and h-BN is higher for C16B8N8 compared to other hybrid nanosheets because of the delocalized distribution of the electron density cloud. The doping of the B-N pair into the graphene nanosheet shifts the Fermi level into either the valence band or the conduction band based on the concentration of the B-N pair. Meanwhile, the effective mass is increased and is relatively high for the hybrid nanosheets with a localized state. The pristine B16N16 nanosheet exhibits a quantum capacitance of 31.539 μF cm-2, while among the hybrid nanosheets, the C4B14N14 nanosheet exhibits a maximum quantum capacitance of 22.518 μF cm-2, and from the outcomes, they are suitable as an electrode for asymmetric supercapacitors.

Interfacial engineering of a vertically stacked graphene/h-BN heterostructure as an efficient electrocatalyst for hydrogen peroxide synthesis

Recently, it was reported that an in-plane graphene (G)/hexagonal boron nitride (h-BN) (G/h-BN) heterostructure provided the catalytic activity for H2O2 synthesis by the 2 e- oxygen reduction reaction (ORR). However, there are few reports on the vertically stacked G/h-BN heterostructure, which refers to the stacking of graphene domains on the surface of h-BN. Herein, a simulated chemical vapor deposition method is proposed for fabricating a heterostructure of abundant vertically stacked G/h-BN by in situ growing graphene quantum dots (GQDs) on porous h-BN sheets. The performance of our vertically stacked heterostructure catalyst is superior to that of reported carbon-based electrocatalysts under an alkaline environment, with an H2O2 selectivity of 90-99% in a wide potential range (0.35 V-0.7 V vs. RHE), over 90% faradaic efficiency, and high mass activity of 1167 mmol gcatalyst-1 h-1. The experimental results and density functional theory (DFT) simulation verified that the vertically stacked heterostructure exhibits an excellent catalytic performance for the 2 e- ORR, and the edge B atoms in the B-centered AB stacking model are the most active catalytic sites. This research adequately demonstrates the promising catalytic activity of the vertically stacked G/h-BN heterostructure and provides a facile route for fabricating other vertically stacked heterostructures.

Investigation of the adsorption behavior of the anti-cancer drug hydroxyurea on the graphene, BN, AlN, and GaN nanosheets and their doped structures via DFT and COSMO calculations

To reduce the direct side effects of chemotherapy, researchers are trying to establish a new approach of a drug-delivery system using nanomaterials. In this study, we investigated graphene and its derivative nanomaterials for their favorable adsorption behavior with the anti-cancer drug hydroxyurea (HU) using DFT calculations. Initially, different pristine and doped graphene and its derivatives were taken into consideration as HU drug carriers. Among them, AlN, GaN, GaN-doped AlN, and AlN-doped GaN nanosheets exhibited favorable adsorption behavior with HU. The HU adsorbed on these four nanosheets with adsorption energies of -0.92, -0.75, -0.83, and -0.69 eV, transferring 0.16, 0.032, 0.108, and 0.230 e charges to the nanosheets, respectively, in air medium. In water solvent media, these four nanosheets interacted with HU by -0.56, -0.45, -0.58, and -0.56 eV by accepting a significant amount of charge of about 0.125, 0.128, 0.192, and 0.126 e from HU. The dipole moment and COSMO analysis also indicated that these nanosheets, except for GaN-doped AlN, show high asymmetricity and solubility in water solvent media due to the increased values of the dipole moment by two or three times after the adsorption of the HU drug. Quantum molecular descriptors also suggest that the sensitivity and reactivity of the nanosheets are enhanced during the interaction with HU. Therefore, these nanosheets can be used as anti-cancer drug carriers.

Investigating the thermoelectric properties of the (6, 6) two sided-closed single-walled boron nitride nanotubes ((6, 6) TSC-SWBNNTs) due to the impurity of a single carbon atom and temperature changes

In this research, the thermoelectric properties of the (6, 6) two sided-closed single-walled boron nitride nanotube ((6, 6) TSC-SWBNNT) was investigated in the state without impurity and carbon atom impurity instead of boron and nitrogen atoms in the center, left, and right the nanotube. The test conditions were the energy range of -5.5 to 5.5 eV and temperatures of 200, 300, 500, 700, 900, 1100, and 1300 K. Based on the obtained results, with an increase in temperature and the creation of impurities, the band gap is affected and becomes noticeably smaller. At the temperature of 1300 K, the band gap shows the greatest decrease and the peak height shows the least decrease. With increasing temperature, the number of peaks has decreased, suggesting an increase in the mobility of electrons and holes and a decrease in their localization. The Seebeck coefficient figures also changed by replacing carbon atoms with boron and nitrogen atoms in different parts of the nanotube. In addition, the height of the heat conduction peaks increased with increasing temperature. However, the heat conduction values are generally in the range of 9-10 nm, which are small values. With the increase in temperature, ZT values increased such that the highest values corresponded to the temperature of 1300 K. The ZT values higher than 1, especially at high temperatures, show that (6, 6) TSC-SWBNNT nanotubes are suitable candidates for thermoelectric materials.

Carbon-Hybridized Hydroxides for Energy Conversion and Storage: Interface Chemistry and Manufacturing

Carbon-hybridized hydroxides (CHHs) have been intensively investigated for uses in the energy conversion/storage fields. Nevertheless, the intrinsic structure-activity relationships between carbon and hydroxides within CHHs are still blurry, which hinders the fine modulation of CHHs in terms of practical applications to some degree. This review aims to figure out the intrinsic role of carbon materials in CHHs with a focus on the interface chemistry and the engineering strategy in-between two components. The fundamental effects of the carbon materials in enhancing the charge/mass transfer kinetics are first analyzed, particularly the extra electron pathways for fast charge transfer and the anchoring sites for boosting the mass transfer. Subsequently, the surface-guided/confined effects of carbon materials in CHHs to modify the morphology and tailor the hydroxides, and functional heterojunction for regulating the inner electronic structure are decoupled. The methods to efficiently construct a stable yet robust solid-solid heterointerface are summarized, including oxygen functional groups engrafting, topological defective sites construction and heteroatom incorporation to activate the inert carbon surface. The smart CHHs in some typical energy applications are demonstrated. Additionally, the methodologies that can reveal the hybridization electron configuration between two components are summed up. At last, the perspective and challenges faced by the CHHs for energy-related applications are outlined.

Paramagnetic States in Oxygen-Doped Boron Nitride Extend Light Harvesting and Photochemistry to the Deep Visible Region

A family of boron nitride (BN)-based photocatalysts for solar fuel syntheses have recently emerged. Studies have shown that oxygen doping, leading to boron oxynitride (BNO), can extend light absorption to the visible range. However, the fundamental question surrounding the origin of enhanced light harvesting and the role of specific chemical states of oxygen in BNO photochemistry remains unanswered. Here, using an integrated experimental and first-principles-based computational approach, we demonstrate that paramagnetic isolated OB₃ states are paramount to inducing prominent red-shifted light absorption. Conversely, we highlight the diamagnetic nature of O-B-O states, which are shown to cause undesired larger band gaps and impaired photochemistry. This study elucidates the importance of paramagnetism in BNO semiconductors and provides fundamental insight into its photophysics. The work herein paves the way for tailoring of its optoelectronic and photochemical properties for solar fuel synthesis.

Reduced Graphene Oxide-Polydopamine-Gold Nanoparticles: A Ternary Nanocomposite-Based Electrochemical Genosensor for Rapid and Early Mycobacterium tuberculosis Detection

Tuberculosis (TB) has been a devastating human illness for thousands of years. According to the WHO, around 10.4 million new cases of tuberculosis are identified every year, with 1.8 million deaths. To reduce these statistics and the mortality rate, an early and accurate TB diagnosis is essential. This study offers a highly sensitive and selective electrochemical biosensor for Mycobacterium tuberculosis (MTB) detection based on a ternary nanocomposite of reduced graphene oxide, polydopamine, and gold nanoparticles (rGO-PDA-AuNP). Avidin-biotin coupling was used to bind the MTB probe DNA onto the rGO-PDA-AuNP modified glassy carbon electrode (ssDNA/avidin/rGO-PDA-AuNP). UV-Visible, Raman, XRD, and TEM were used to evaluate the structural and morphological characteristics of rGO-PDA-AuNP. Furthermore, DNA immobilization is validated using FESEM and FT-IR techniques. The modified electrodes were electrochemically analyzed using cyclic voltammetry (CV) and linear sweep voltammetry (LSV), and the results indicate that the produced electrode can detect target DNA up to 0.1 × 10^-7 mM with 2.12 × 10^-3 mA µM^-1 sensitivity and a response time of 5 s. The constructed genosensor displayed high sensitivity and stability, and it also provides a unique strategy for diagnosing MTB at an early stage. Furthermore, our rGO-PDA-AuNP/GCE-based electrochemical platform has broad potential for creating biosensor systems for detecting various infectious pathogens and therapeutically significant biomarkers.

Transparent and high-performance electromagnetic interference shielding composite film based on single-crystal graphene/hexagonal boron nitride heterostructure

The multiple requirements of optical transmittance, high shielding effectiveness, and long-term stability bring considerable challenge to electromagnetic interference (EMI) shielding in the fields of visualization windows, transparent optoelectronic devices, and aerospace equipment. To this end, attempts were hereby made, and based on high-quality single crystal graphene (SCG)/hexagonal boron nitride (h-BN) heterostructure, transparent EMI shielding films with weak secondary reflection, nanoscale ultra-thin thickness and long-term stability were finally realized by a composite structure. In this novel structure, SCG was adopted as the absorption layer, while sliver nanowires (Ag NWs) film acted as the reflection layer. These two layers were placed on different sides of the quartz to form a cavity, which achieved the dual coupling effect, so that the electromagnetic wave was reflected multiple times to form more absorption loss. Among the absorption dominant shielding films, the composite structure in this work demonstrated stronger shielding effectiveness of 28.76 dB with a higher light transmittance of 80.6%. In addition, under the protection of the outermost h-BN layer, the decline range of the shielding performance of the shielding film was extensively reduced after 30 days of exposure to air and maintained long-term stability. Overall, this study provides an outstanding EMI shielding material with great potential for practical applications in electronic devices protection.

Theoretical Analysis of Magnetic Coupling in the Ti2C Bare MXene

The nature of the electronic ground state of the Ti₂C MXene is unambiguously determined by making use of density functional theory-based calculations including hybrid functionals together with a stringent computational setup providing numerically converged results up to 1 meV. All the explored density functionals (i.e., PBE, PBE0, and HSE06) consistently predict that the Ti₂C MXene has a magnetic ground state corresponding to antiferromagnetic (AFM)-coupled ferromagnetic (FM) layers. A spin model, with one unpaired electron per Ti center, consistent with the nature of the chemical bond emerging from the calculations, is presented in which the relevant magnetic coupling constants are extracted from total energy differences of the involved magnetic solutions using an appropriate mapping approach. The use of different density functionals enables us to define a realistic range for the magnitude of each of the magnetic coupling constants. The intralayer FM interaction is the dominant term, but the other two AFM interlayer couplings are noticeable and cannot be neglected. Thus, the spin model cannot be reduced to include nearest-neighbor interactions only. The Néel temperature is roughly estimated to be in the 220 ± 30 K, suggesting that this material can be used in practical applications in spintronics and related fields.

Synthesis and Properties of B4 N4 -Heteropentalenes Fused with Polycyclic Hydrocarbons

Hybrid molecules of π-conjugated carbon rings and BN-heterocyclic rings (h-CBNs) fused with each other have been a rare class of compounds due to the limited availability of their synthetic methods. Here we report the synthesis of new h-CBNs featuring a B₄ N₄ -heteropentalene core and polycyclic aromatic hydrocarbon wings. Using 1,2-azaborinine derivatives as a building block, we developed a rational synthetic protocol that allows the formation of a B₄ N₄ ring in a stepwise manner, resulting in the fully fused ABA-type triblock molecules. Thus, three derivatives of 1 bearing naphthalene (1_Naph ), anthracene (1_Anth ), or phenanthrene (1_Phen ) wings fused with the B₄ N₄ core were synthesized and characterized. Among them, 1_Phen , which displays the highest triplet-state energy, was found to serve a host material for phosphorescent OLED devices, for which a maximum external quantum efficiency of 13.7 % was recorded. These findings may promote the synthesis of various types of h-CBNs aiming at new properties arising from the synergy of two different π-electronic systems.

Tuning functionalized hexagonal boron nitride quantum dots for full visible-light fluorescence emission

Tunable photoluminescence has been observed in hexagonal boron nitride quantum dots (BNQDs), but the underlying luminescence mechanism remains elusive. In this study, we examine excited-state properties of several functionalized BNQDs models using density functional theory (DFT), time-dependent DFT, and multistate complete active space second-order perturbation theory (MS-CASPT2) methods. Unlike reported graphene quantum dots, photoluminescence of BNQDs is not affected by their sizes (<2.5 nm). Instead, the embedded single sp³ carbon atom connecting different functional groups can tune emission colors of BNQDs, whose emission wavelength cover full range of visible light and even extend toward near-infrared region. Further analysis reveals that both exciton self-trapping and electron-hole separation decrease HOMO-LUMO energy gaps, leading to large Stokes shifts. Moreover, uneven and even hybridizations induce blue- and red-shifted emission spectra. These findings provide novel insights into full-spectrum emission of BNQDs modified with functional groups.

Optimization of reduced Graphene oxide synthesis using central composite design analysis-A waste to value approach

In recent times, reduced graphene oxide has gained more attention in various fields. In our study, a direct synthesis of reduced graphene oxide using a novel carbon-rich agro-waste from Pennisetum glaucum was used. Ferrocene acted as an oxidizing agent during thermal degradation at 300 °C for 15 and 20 min to promote graphene oxide and reduced graphene oxide formation. The X-ray diffraction peak at 2θ indicating a shift from 16.86 to 24.28°, presence of functional groups like -OH stretching, -C = C-, C = O, C-O, and C-OH by Fourier transmission infrared spectroscopy, prominent D and G bands at 1308 cm^-1 and 1578 cm^-1 by Raman spectra and UV-visible spectroscopy peak shift from 235 to 245 nm (π-π*, C = C bonds) confirmed the reduction of graphene oxide to reduced graphene oxide. The average particle size values 233.3 nm for graphene oxide and 63.57 nm for reduced graphene oxide illustrate the nanoscale range of our synthesized material. The negative zeta potential values in the range - 45.5 mV and - 29.5 mV for graphene oxide and its reduced forms infer the dispersion stability along with surface oxygen group presence. We have also highlighted the formation of graphene oxide quantum dots by magnetic stirring and confirmed by UV transilluminator and photoluminescence spectra. The photodegradation efficiency was optimized using central composite design for dosage, dye concentration, pH, and time for both malachite green and reactive blue dye. The kinetic studies report pseudo-first-order kinetic model for catalytic degradation and statistical Analysis of variance proved the significance of the process for p value < 0.05. Thus, the synthesized graphene materials could be used as a potential candidate for environmental applications.

A Review of Scalable Hexagonal Boron Nitride (h-BN) Synthesis for Present and Future Applications

Hexagonal boron nitride (h-BN) is a layered inorganic synthetic crystal exhibiting high temperature stability and high thermal conductivity. As a ceramic material it has been widely used for thermal management, heat shielding, lubrication, and as a filler material for structural composites. Recent scientific advances in isolating atomically thin monolayers from layered van der Waals crystals to study their unique properties has propelled research interest in mono/few layered h-BN as a wide bandgap insulating support for nanoscale electronics, tunnel barriers, communications, neutron detectors, optics, sensing, novel separations, quantum emission from defects, among others. Realizing these futuristic applications hinges on scalable cost-effective high-quality h-BN synthesis. Here, the authors review scalable approaches of high-quality mono/multilayer h-BN synthesis, discuss the challenges and opportunities for each method, and contextualize their relevance to emerging applications. Maintaining a stoichiometric balance B:N = 1 as the atoms incorporate into the growing layered crystal and maintaining stacking order between layers during multi-layer synthesis emerge as some of the main challenges for h-BN synthesis and the development of processes to address these aspects can inform and guide the synthesis of other layered materials with more than one constituent element. Finally, the authors contextualize h-BN synthesis efforts along with quality requirements for emerging applications via a technological roadmap.

A BC2N/blue phosphorene heterostructure as an anode material for high-performance sodium-ion batteries: first principles insights

Blue phosphorene (Blu-Pn) is a new phosphorene allotrope capable of hosting a substantial amount of sodium (Na) atoms. However, it has been reported to exhibit low electrical conductivity, chemical sensitivity, and structural stability, thus limiting its utility as an anode material for Na-ion batteries (NIBs). In this work, we introduce BC₂N as a protective layer for Blu-Pn. Based on van der Waals (vdW) corrected density functional theory (DFT), we conduct a comprehensive first-principles study to explore the main electrochemical properties of the BC₂N/Blu-Pn vdW heterostructure. The BC₂N/Blu-Pn system exhibits a small band-gap of 0.03 eV that fades away and indicates metallic behavior upon Na adsorption. Furthermore, the binding energy of Na incorporated into the inter-layer of the BC₂N/Blu-Pn system is lower (-2.03 eV) compared with those of free-standing BC₂N (-1.25 eV) and Blu-Pn monolayer (-1.52 eV). Therefore, the growth of Na dendrites can be avoided. Furthermore, the migration energy barrier for the BC₂N/Blu-Pn system is about 0.11 eV, indicating fast Na diffusion and excellent rate performance. Moreover, the theoretical storage capacity is 763 mA h g^-1. Finally, we show that the intercalation of Na in the BC₂N/Blu-Pn system has the advantage of a small average voltage of approximately 0.24 V. Besides these properties, the proposed heterostructure is based on chemical elements that are widely available and technologically established and have low atomic mass, which are all advantages for Na-ion battery applications.

M. SK, Baek KH. Assessing the Food Quality Using Carbon Nanomaterial Based Electrodes by Voltammetric Techniques

The world is facing a global financial loss and health effects due to food quality adulteration and contamination, which are seriously affecting human health. Synthetic colors, flavors, and preservatives are added to make food more attractive to consumers. Therefore, food safety has become one of the fundamental needs of mankind. Due to the importance of food safety, the world is in great need of developing desirable and accurate methods for determining the quality of food. In recent years, the electrochemical methods have become more popular, due to their simplicity, ease in handling, economics, and specificity in determining food safety. Common food contaminants, such as pesticides, additives, and animal drug residues, cause foods that are most vulnerable to contamination to undergo evaluation frequently. The present review article discusses the electrochemical detection of the above food contaminants using different carbon nanomaterials, such as carbon nanotubes (CNTs), graphene, ordered mesoporous carbon (OMC), carbon dots, boron doped diamond (BDD), and fullerenes. The voltammetric methods, such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV), have been proven to be potential methods for determining food contaminants. The use of carbon-based electrodes has the added advantage of electrochemically sensing the food contaminants due to their excellent sensitivity, specificity, large surface area, high porosity, antifouling, and biocompatibility.

Recent progress of two-dimensional heterostructures for thermoelectric applications

The rapid development of synthesis and fabrication techniques has opened up a research upsurge in two-dimensional (2D) material heterostructures, which have received extensive attention due to their superior physical and chemical properties. Currently, thermoelectric energy conversion is an effective means to deal with the energy crisis and increasingly serious environmental pollution. Therefore, an in-depth understanding of thermoelectric transport properties in 2D heterostructures is crucial for the development of micro-nano energy devices. In this review, the recent progress of 2D heterostructures for thermoelectric applications is summarized in detail. Firstly, we systematically introduce diverse theoretical simulations and experimental measurements of the thermoelectric properties of 2D heterostructures. Then, the thermoelectric applications and performance regulation of several common 2D materials, as well as in-plane heterostructures and van der Waals heterostructures, are also discussed. Finally, the challenges of improving the thermoelectric performance of 2D heterostructures materials are summarized, and related prospects are described.

Wrinkle-mediated CVD synthesis of wafer scale Graphene/h-BN heterostructures

The combination of two-dimensional materials (2D) into heterostructures enables their integration in tunable ultrathin devices. For applications in electronics and optoelectronics, direct growth of wafer-scale and vertically stacked graphene/hexagonal boron nitride (h-BN) heterostructures is vital. The fundamental problem, however, is the catalytically inert nature of h-BN substrates, which typically provide a low rate of carbon precursor breakdown and consequently a poor rate of graphene synthesis. Furthermore, out-of-plane deformations such as wrinkles are commonly seen in 2D materials grown by chemical vapor deposition (CVD). Herein, a wrinkle-facilitated route is developed for the fast growth of graphene/h-BN vertical heterostructures on Cu foils. The key advantage of this synthetic pathway is the exploitation of the increased reactivity from inevitable line defects arising from the CVD process, which can act as active sites for graphene nucleation. The resulted heterostructures are found to exhibit superlubric properties with increased bending stiffness, as well as directional electronic properties, as revealed from atomic force microscopy measurements. This work offers a brand-new route for the fast growth of Gr/h-BN heterostructures with practical scalability, thus propelling applications in electronics and nanomechanical systems.

Graphene and Its Derivatives: Synthesis and Application in the Electrochemical Detection of Analytes in Sweat

Wearable sensors and invasive devices have been studied extensively in recent years as the demand for real-time human healthcare applications and seamless human-machine interaction has risen exponentially. An explosion in sensor research throughout the globe has been ignited by the unique features such as thermal, electrical, and mechanical properties of graphene. This includes wearable sensors and implants, which can detect a wide range of data, including body temperature, pulse oxygenation, blood pressure, glucose, and the other analytes present in sweat. Graphene-based sensors for real-time human health monitoring are also being developed. This review is a comprehensive discussion about the properties of graphene, routes to its synthesis, derivatives of graphene, etc. Moreover, the basic features of a biosensor along with the chemistry of sweat are also discussed in detail. The review mainly focusses on the graphene and its derivative-based wearable sensors for the detection of analytes in sweat. Graphene-based sensors for health monitoring will be examined and explained in this study as an overview of the most current innovations in sensor designs, sensing processes, technological advancements, sensor system components, and potential hurdles. The future holds great opportunities for the development of efficient and advanced graphene-based sensors for the detection of analytes in sweat.

Exploration of Chemical Space for Designing Functional Molecules Accounting for Geometric Stability

The design of functional molecules is regarded as searching for molecules with desired functionalities in chemical space populated by candidate molecules. Considering the geometric stability of molecules during the search process is crucial for designing realistic molecules. Here, we propose a method for designing functional molecules by exploring chemical space while explicitly accounting for geometric stability based on computational quantum alchemy. The proposed design method allows the simultaneous prediction of functional molecule in the equilibrium structure and its target desired property in an inverse design fashion without preparing the molecular geometries and performing brute-force screening. The applicability of the design method is proven by obtaining molecules with the desired atomization and electronic energies in various chemical spaces: (BF, CO), (CH₄, NH₃), 18 BN-doped benzene derivatives, and 3.1 × 10⁵ BN-doped phenanthrene derivatives.

Constructing Interfacial Boron‐Nitrogen Moieties in Turbostratic Carbon for Electrochemical Hydrogen Peroxide Production

The electrochemical oxygen reduction reaction (ORR) provides a green route for decentralized H₂O₂ synthesis, where a structure–selectivity relationship is pivotal for the control of a highly selective and active two‐electron pathway. Here, we report the fabrication of a boron and nitrogen co‐doped turbostratic carbon catalyst with tunable B−N−C configurations (CNB‐ZIL) by the assistance of a zwitterionic liquid (ZIL) for electrochemical hydrogen peroxide production. Combined spectroscopic analysis reveals a fine tailored B−N moiety in CNB‐ZIL, where interfacial B−N species in a homogeneous distribution tend to segregate into hexagonal boron nitride domains at higher pyrolysis temperatures. Based on the experimental observations, a correlation between the interfacial B−N moieties and HO₂⁻ selectivity is established. The CNB‐ZIL electrocatalysts with optimal interfacial B−N moieties exhibit a high HO₂⁻ selectivity with small overpotentials in alkaline media, giving a HO₂⁻ yield of ≈1787 mmol g_catalyst⁻¹ h⁻¹ at −1.4 V in a flow‐cell reactor.

Direct growth of hBN/Graphene heterostructure via surface deposition and segregation for independent thickness regulation

Hexagonal boron nitride/graphene (hBN/G) vertical heterostructures have attracted extensive attention, owing to the unusual physical properties for basic research and electronic device applications. Here we report a facile deposition-segregation technique to synthesize hBN/G heterostructures on recyclable platinum (Pt) foil via low pressure chemical vapor deposition. The growth mechanism of the vertical hBN/G is demonstrated to be the surface deposition of hBN on top of the graphene segregated from the Pt foil with pre-dissolved carbon. The thickness of hBN and graphene can be controlled separately from sub-monolayer to multilayer through the fine control of the growth parameters. Further investigations by Raman, scanning Kelvin probe microscopy and transmission electron microscope show that the hBN/G inclines to form a heterostructure with strong interlayer coupling and with interlayer twist angle smaller than 1.5°. This deposition-segregation approach paves a new pathway for large-scale production of hBN/G heterostructures and could be applied to synthesize of other van der Waals heterostructures.

Turbostratic Boron-Carbon-Nitrogen and Boron Nitride by Flash Joule Heating

Turbostratic layers in 2D materials have an interlayer misalignment. The lack of alignment expands the intrinsic interlayer distances and weakens the optical and electronic interactions between adjacent layers. This introduces properties distinct from those structures with well-aligned lattices and strong coupling interactions. However, direct and rapid synthesis of turbostratic materials remains a challenge owing to their thermodynamically metastable properties. Here, a flash Joule heating (FJH) method to achieve bulk synthesis of boron-carbon-nitrogen ternary compounds with turbostratic structures by a kinetically controlled ultrafast cooling process that takes place within milliseconds (10³  to 10⁴ K s^-1 ) is reported. Theoretical calculations support the existence of turbostratic structures and provide estimates of the energy barriers with respect to conversion into the corresponding well-aligned counterparts. When using non-carbon conductive additives, a direct synthesis of boron nitride is possible. The turbostratic nature facilitates mechanical exfoliation and more stable dispersions. Accordingly, the addition of flash products to a poly(vinyl alcohol) nanocomposite film coating a copper surface greatly improves the copper's resistance to corrosion in 0.5 m sulfuric acid or 3.5 wt% saline solution. FJH allows the use of bulk materials as reactants and provides a rapid approach to large quantities of the hitherto hard-to-access turbostratic materials.

Electronic property modulation in two-dimensional lateral superlattices of monolayer transition metal dichalcogenides

Fabricating lateral heterostructures (HSs) and superlattices (SLs) provides a unique degree of freedom for modulating the physical properties of two-dimensional (2D) materials by varying the chemical component, geometric size and interface structure in the ultra-thin atomic thickness limit. While a variety of 2D lateral HSs/SLs have been synthesized, especially for transition metal dichalcogenides (TMDs), how such structures affect quantitatively the physical properties of 2D materials has not yet been established. We herein explore electronic property modulation in 2D lateral SLs of monolayer TMDs through first-principles high-throughput calculations. The dependence of the electronic structure, bandgap, carrier effective masses, charge density overlap on chemical components, interface type, and sub-lattice size of lateral TMD-SLs are investigated. We find that by comparison with their random alloy counterparts, the lateral TMD-SLs exhibit generally type-II band alignment, a wider range of bandgap tunability, larger carrier effective masses, and stronger electron-hole charge separation tendency. The bandgap variation with a sub-lattice size shows larger bowing parameters for the SLs with heterogeneous anions, by comparison with the homogeneous anion cases. A similar behavior is observed for the SLs with an armchair-type interface, by comparison with the zigzag-type interface cases. Further analyses reveal that the underlying physical mechanism can be attributed to the synergistic interplay among the band offset of sub-lattices, quantum confinement effect, and existing internal strain.

Efficient CO2 Capture and Activation on Novel Two-Dimensional Transition Metal Borides

The large-scale production of CO₂ in the atmosphere has triggered global warming, the greenhouse effect, and ocean acidification. The CO₂ conversion to valuable chemical products or its capture and storage are of fundamental importance to mitigate the greenhouse effect on the environment. Therefore, exploring new two-dimensional (2D) materials is indispensable due to their potential intriguing properties. Here, we report a new family of 2D transition metal borides (M₂B₂, M = Sc, Ti, V, Cr, Mn, and Fe; known as MBenes) and demonstrate their static and dynamic stability. These MBenes show a metallic nature and exhibit excellent electrical conductivity. The CO₂ adsorption energy on MBenes ranges from -1.04 to -3.95 eV and exhibits the decreasing order as Sc₂B₂ > Ti₂B₂ > V₂B₂ > Cr₂B₂ > Mn₂B₂ > Fe₂B₂. The spin-polarization calculation shows a reduction in the adsorption energy for magnetic systems. Bader charge transfer indicates the formation of CO₂^δ- moiety on the MBene surface, so-called activated CO₂, which is essential for its reaction with other surface chemicals. Differential charge density plots reveal a significant charge accumulation around the CO₂ molecule. Our theoretical results predict the usage of new MBenes as a cost-effective catalyst for CO₂ capture and activation.

Influence of Hexagonal Boron Nitride on Electronic Structure of Graphene

By performing first-principles calculations, we studied hexagonal-boron-nitride (hBN)-supported graphene, in which moiré structures are formed due to lattice mismatch or interlayer rotation. A series of graphene/hBN systems has been studied to reveal the evolution of properties with respect to different twisting angles (21.78°, 13.1°, 9.43°, 7.34°, 5.1°, and 3.48°). Although AA- and AB-stacked graphene/hBN are gapped at the Dirac point by about 50 meV, the energy gap of the moiré graphene/hBN, which is much more asymmetric, is only about several meV. Although the Dirac cone of graphene residing in the wide gap of hBN is not much affected, the calculated Fermi velocity is found to decrease with the increase in the moiré super lattice constant due to charge transfer. The periodic potential imposed by hBN modulated charge distributions in graphene, leading to the shift of graphene bands. In agreement with experiments, there are dips in the calculated density of states, which get closer and closer to the Fermi energy as the moiré lattice grows larger.