Emerging 2D Materials Research Articles

35 2D-Hexagonal Boron Nitride and Lung Exposure: Exploring Long-Term Effects in Healthy Versus Asthmatic Human Lung in Vitro Model

Abstract Inhalation is one of the most pertinent routes of exposure to nanoscale materials in occupational settings. Hexagonal boron nitride (hBN) is an emerging 2D material attracting significant attention due to its superior electrical, chemical, and thermal properties. For a successful commercial application of 2D-hBN, it is of key importance to understand their safety in occupational settings. However, long-term toxicity profile of this material is largely unknown. Here, an investigation of how 2D-hBN (obtained from Graphene Flagship consortium) interacts with lung cells of healthy versus diseased individuals has been performed. We used air−liquid interface-based exposure models to investigate the potential long-term toxicity of 2D-hBN in human lung airway epithelial cells (Calu-3) and 3D reconstituted airway epithelia (MucilairTM) of healthy and asthmatic subjects. Our results revealed that 2D-hBN was taken up by cells but did not trigger cytotoxicity at occupationally relevant repeated dose exposure for five weeks. However, screening of an immuno-cytokine/chemokine panel indicated an enhanced release of certain cytokines after exposure to 2D-hBN. In addition, we observed a pronounced intracellular accumulation of lipids in lipid droplets after exposure to 2D-hBN. Since lipid intermediates can play important roles in immune-cell activation and the development of lung diseases, we are currently analysing whether 2D-hBN induces alterations in lipid composition in healthy and asthmatic cells by applying global lipidomic profiling. Overall, our data indicate a potential correlation of certain lipid accumulation with enhanced immune signaling, highlighting the need for further studies to understand if 2D-hBN can sensitize for or aggravate pulmonary diseases.

Microenvironment Restruction of Emerging 2D Materials and their Roles in Therapeutic and Diagnostic Nano-Bio-Platforms.

Engineering advanced therapeutic and diagnostic nano-bio-platforms (NBPFs) have emerged as rapidly-developed pathways against a wide range of challenges in antitumor, antipathogen, tissue regeneration, bioimaging, and biosensing applications. Emerged 2D materials have attracted extensive scientific interest as fundamental building blocks or nanostructures among material scientists, chemists, biologists, and doctors due to their advantageous physicochemical and biological properties. This timely review provides a comprehensive summary of creating advanced NBPFs via emerging 2D materials (2D-NBPFs) with unique insights into the corresponding molecularly restructured microenvironments and biofunctionalities. First, it is focused on an up-to-date overview of the synthetic strategies for designing 2D-NBPFs with a cross-comparison of their advantages and disadvantages. After that, the recent key achievements are summarized in tuning the biofunctionalities of 2D-NBPFs via molecularly programmed microenvironments, including physiological stability, biocompatibility, bio-adhesiveness, specific binding to pathogens, broad-spectrum pathogen inhibitors, stimuli-responsive systems, and enzyme-mimetics. Moreover, the representative therapeutic and diagnostic applications of 2D-NBPFs are also discussed with detailed disclosure of their critical design principles and parameters. Finally, current challenges and future research directions are also discussed. Overall, this review will provide cutting-edge and multidisciplinary guidance for accelerating future developments and therapeutic/diagnostic applications of 2D-NBPFs.

In Silico Investigation on the Selective Nanotoxicity of Two-Dimensional Materials to Hen Egg White Lysozyme Protein

Inspired by the urge to determine the underlying mechanism of the induction of toxic effects of state-of-the-art two-dimensional (2D) nanomaterials such as graphene and hexagonal boron nitride (h-BN) toward biomolecules, herein we study the interactions between these nanomaterials with a model protein hen egg white lysozyme (HEWL), employing classical molecular dynamics simulations. It is revealed that the protein gets easily adsorbed on both of the 2D materials, with the interaction energy being much higher in the case of h-BN, suggesting a significantly stronger adsorption affinity. The interactions of aromatic amino acid residues such as tyrosine and tryptophan along with few aliphatic residues such as arginine, lysine, and asparagine with the 2D materials are found to be pronounced, and most of the residues taking part in adsorption are nearly the same for both materials. While the secondary structure of HEWL remains nearly unaltered upon adsorption on graphene, h-BN massively perturbs both the α-helix and β-sheet components through the disruption of intraprotein hydrogen bonds, which are in turn sine quo non for the preservation of the structural integrity. It is demonstrated that the disruption of the secondary structure is due to pronounced thermodynamic preference for the adsorption of the constituent amino acid residues on h-BN compared to their spatial disposition within the proteins. The calculated release times from the adsorbed state are found to be orders of magnitude higher in the case of h-BN compared to graphene, and it is unlikely that the protein would get released in accessible time scales unless dislodged by the application of an external force. The present study contributes to the fundamental understanding of the nanotoxicity of emerging 2D materials toward proteins, thereby aiding experimentalists to design biocompatible 2D materials for nano-biomedical usage and device fabrication.

2D Materials in the Display Industry: Status and Prospects.

With advances in flexible electronics, innovative foldable, rollable, and stretchable displays have been developed to maintain their performance under various deformations. These flexible devices can develop more innovative designs than conventional devices due to their light weight, high space efficiency, and practical convenience. However, developing flexible devices requires material innovation because the devices must be flexible and exhibit desirable electrical insulating/semiconducting/metallic properties. Recently, emerging 2D materials such as graphene, hexagonal boron nitride, and transition metal dichalcogenides have attracted considerable research attention because of their outstanding electrical, optical, and mechanical properties, which are ideal for flexible electronics. The recent progress and challenges of 2D material growth and display applications are reviewed and perspectives for exploring 2D materials for display applications are discussed.

Numerical Analysis of Black Phosphorus‐Assisted Copper‐Based Bimetallic‐Enhanced Surface Plasmon Resonance Biosensor

Atomically thin black phosphorus (BP) is an emerging 2D material with excellent optical and electrical properties. Copper (Cu) and platinum (Pt) are plasmonic metals due to their outstanding electrical properties. Here, Cu–Pt as the plasmonic bimetal is used, BP as the sensing substrate combined with a composite layer of titanium dioxide–silicon dioxide (TiO2–SiO2) to achieve significant enhancement in sensitivity. All of the calculations are based on the transfer matrix method and Fresnel equations. Through systematic optimization of all parameters, the configuration of TiO2(15 nm)/SiO2 (5 nm)/Cu (26 nm)/Pt (9 nm)/BP (4 layers) is achieved, where the sensitivity of 533° RIU−1 reaches 390% of pure copper-based biosensor. There is a linear range of sensitivity with the change of refractive index for this optimal configuration. The detection limit of the refractive index change can be as low as 2 × 10−7 RIU, two orders of magnitude lower compared with that of pure copper-based sensors, indicating great potential to detect trace biomolecules.

Growth of Large‐Sized 2D Ultrathin SnSe Crystals with In‐Plane Ferroelectricity

AbstractTin (II) selenide (SnSe) is an emerging 2D material with many intriguing properties, such as record‐high thermoelectric figure of merit (ZT), purely in‐plane ferroelectricity, and excellent nonlinear optical properties. To explore these functional properties and related applications, a crucial step is to develop controllable routes to synthesize large‐area, ultrathin, and high‐quality SnSe crystals. Physical vapor deposition (PVD) constitutes a reliable method to synthesize 2D SnSe, however, effects of various growth parameters have not yet been systematically investigated, and current PVD‐synthesized flakes are often thick (>10 nm) with small lateral sizes (<10 µm). In this work, high‐quality 2D SnSe crystals are synthesized via low‐pressure PVD, which display in‐plane ferroelectric domains observed by piezoresponse force microscopy and polarization‐dependent reflection spectroscopy. Detailed studies regarding the roles of various parameters are further carried out, including substrate pre‐annealing, growth duration, temperature, and pressure, which enable to rationally optimize the growth and obtain 2D SnSe crystals with lateral sizes up to ≈23.0 µm and thicknesses down to ≈2.0 nm (3–4 layers). This work paves the way for the controlled growth of large‐area 2D SnSe, facilitating the future exploration of many interesting multiferroic properties and applications with atomic thickness.

Intercalation Engineering of 2D Materials at Macroscale for Smart Human–Machine Interface and Double‐Layer to Faradaic Charge Storage for Ions Separation

Abstract2D materials have attracted considerable attention in the past decade for their superlative physical properties. Lightweight foam from 2D materials can reduce the use of raw materials, save energy in processing the material and downregulate the carbon emission. Self‐assembling of graphene nanosheets results in 3D porous lightweight foam resembling hydrogels, aerogels, and xerogels. Hierarchical graphene architecture provides an uninterrupted path to electrons and phonon transport conforms to eligibility for developing sensor, energy storage, and energy conversion devices. Artificial intelligence (AI) originates from human–machine interaction and physiological signal reception which requires a large sensing range that illustrates to healthcare surveillance with wearable devices. Spongy architectures with flexibility and reversible compressibility act as a good candidate for pressure sensing for a wide range of real‐time human health monitoring systems by using artificial intelligence. In this review, the new perspective of emerging 2D materials (such as MXene, and borophene) along with the investigation of the graphene foam structure is demonstrated. Electrosorption of salt‐ions under foam electrode are reviewed in the context of electrochemical stability recycling ability, and efficiency of adsorption‐desorption. Beyond these, remaining challenges are depicted for emerging 2D‐materials of interest for health monitoring sensors and flexible supercapacitors for promising research directions.

Synthesis and Functionalization of Graphene Materials for Biomedical Applications: Recent Advances, Challenges, and Perspectives.

Since its discovery in 2004, graphene is increasingly applied in various fields owing to its unique properties. Graphene application in the biomedical domain is promising and intriguing as an emerging 2D material with a high surface area, good mechanical properties, and unrivalled electronic and physical properties. This review summarizes six typical synthesis methods to fabricate pristine graphene (p-G), graphene oxide (GO), and reduced graphene oxide (rGO), followed by characterization techniques to examine the obtained graphene materials. As bare graphene is generally undesirable in vivo and in vitro, functionalization methods to reduce toxicity, increase biocompatibility, and provide more functionalities are demonstrated. Subsequently, in vivo and in vitro behaviors of various bare and functionalized graphene materials are discussed to evaluate the functionalization effects. Reasonable control of dose (<20mg kg-1 ), sizes (50-1000nm), and functionalization methods for in vivo application are advantageous. Then, the key biomedical applications based on graphene materials are discussed, coupled with the current challenges and outlooks of this growing field. In a broader sense, this review provides a comprehensive discussion on the synthesis, characterization, functionalization, evaluation, and application of p-G, GO, and rGO in the biomedical field, highlighting their recent advances and potential.

High-Performance and Polarization-Sensitive Imaging Photodetector Based on WS2 /Te Tunneling Heterostructure.

Next-generation imaging systems require photodetectors with high sensitivity, polarization sensitivity, miniaturization, and integration. By virtue of their intriguing attributes, emerging 2D materials offer innovative avenues to meet these requirements. However, the current performance of 2Dphotodetectors is stillbelow the requirements forpractical application owing to the severe interfacial recombination, the lack of photoconductive gain, and insufficient photocarrier collection. Here, a tunneling dominant imaging photodetector based on WS2 /Te heterostructure is reported. This device demonstrates competitive performance, including a remarkable responsivity of 402 A W-1 , an outstanding detectivity of 9.28 × 1013 Jones, a fast rise/decay time of 1.7/3.2ms, and a high photocurrent anisotropic ratio of 2.5. These outstanding performances can be attributed to the type-I band alignment with carrier transmission barriers and photoinduced tunneling mechanism, allowing reduced interfacial trapping effect, effective photoconductive gains, and anisotropic collection of photocarriers. Significantly, the constructed photodetector is successfully integrated into a polarized light imaging system and an ultra-weak light imaging system to illustrate the imaging capability. These results suggest the promising application prospect of the device in future imaging systems.

Nano Flex Screen Protectors for 2D Material Piezotronics

We propose nano flex film, a commercially available mobile screen protector, as a prospective flexible substrate for piezotronic devices. Reliable fabrication methods on flexible substrates and robust testing methods are essential to explore piezotronic properties in emerging 2D materials. Unlike conventional rigid substrates, flexible substrates are challenging to handle during fabrication and subsequent testing. The fabrication process on the proposed flexible substrate is as seamless as on rigid substrates. The optimized methods to fabricate 2D material devices on nano flex films are presented. Inorganic dielectric materials such as silicon dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) offer good adhesion, better lifetime, and optical contrast to the 2D material flakes compared to polymer alternatives. The devices made on nano flex films with SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> have shown almost three-fold improvement in open circuit voltage generated (50 mV) and strain gauge values (1997 at 0.44% strain). Also, a simple setup proposed for strain-dependent electrical measurements enables us to characterize the piezotronic properties of different 2D materials without wire bonding or probe needles.

Emerging two-dimensional materials for the electrocatalytic nitrogen reduction reaction to yield ammonia

We summarize the important progress in the electroreduction of N2 to NH3 using state-of-the-art two-dimensional (2D) electrocatalysts. Emerging 2D materials that could potentially serve as viable NRR electrocatalysts are presented.

Graphene-like emerging 2D materials: recent progress, challenges and future outlook.

Owing to the unique physical and chemical properties of 2D materials and the great success of graphene in various applications, the scientific community has been influenced to explore a new class of graphene-like 2D materials for next-generation technological applications. Consequently, many alternative layered and non-layered 2D materials, including h-BN, TMDs, and MXenes, have been synthesized recently for applications related to the 4th industrial revolution. In this review, recent progress in state-of-the-art research on 2D materials, including their synthesis routes, characterization and application-oriented properties, has been highlighted. The evolving applications of 2D materials in the areas of electronics, optoelectronics, spintronic devices, sensors, high-performance and transparent electrodes, energy conversion and storage, electromagnetic interference shielding, hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and nanocomposites are discussed. In particular, the state-of-the-art applications, challenges, and outlook of every class of 2D material are also presented as concluding remarks to guide this fast-progressing class of 2D materials beyond graphene for scientific research into next-generation materials.

Lattice Transformation from 2D to Quasi 1D and Phonon Properties of Exfoliated ZrS2 and ZrSe2.

Recent reports on thermal and thermoelectric properties of emerging 2D materials have shown promising results. Among these materials are Zirconium-based chalcogenides such as zirconium disulfide (ZrS2 ), zirconium diselenide (ZrSe2 ), zirconium trisulfide (ZrS3 ), and zirconium triselenide (ZrSe3 ). Here, the thermal properties of these materials are investigated using confocal Raman spectroscopy. Two different and distinctive Raman signatures of exfoliated ZrX2 (where X = S or Se) are observed. For 2D-ZrX2 , Raman modes are in alignment with those reported in literature. However, for quasi 1D-ZrX2 , Raman modes are identical to exfoliated ZrX3 nanosheets, indicating a major lattice transformation from 2D to quasi-1D. Raman temperature dependence for ZrX2 are also measured. Most Raman modes exhibit a linear downshift dependence with increasing temperature. However, for 2D-ZrS2 , a blueshift for A1g mode is detected with increasing temperature. Finally, phonon dynamics under optical heating for ZrX2 are measured. Based on these measurements, the calculated thermal conductivity and the interfacial thermal conductance indicate lower interfacial thermal conductance for quasi 1D-ZrX2 compared to 2D-ZrX2 , which can be attributed to the phonon confinement in 1D. The results demonstrate exceptional thermal properties for Zirconium-based materials, making them ideal for thermoelectric device applications and future thermal management strategies.

Supercritical etching method for the large-scale manufacturing of MXenes

MXenes as an emerging 2D materials have attracted significant attention in the fields of energy storage, sensing, etc. However, superlong time-consuming (several days) and low-production (⁓ 1 g) of dangerously F-contained acid etching method intrinsically make it inapplicable for large-scale manufacture of MXenes. Herein, we propose a supercritical etching method for the mass preparation of various MXenes assisted by supercritical carbon dioxide. The enhanced thermal power of supercritical carbon dioxide molecules helps significantly accelerate the etching rate of the MAX phase and increase the layer spacing of MXenes. As a result, five typical MAX materials (Ti3AlC2, Nb2AlC, Ti2AlC, Mo2Ga2C, and Ti3AlCN) can be exfoliated into the corresponding MXenes (Ti3C2Tx, Nb2CTx, Ti2CTx, Mo2CTx, and Ti3CNTx) with the yield of ∼ 1 Kg within 2–5 h. We further developed a Ti3C2Tx-based Na-ion battery with a remarkable capacity of 100 mAh g−1 at 100 mA g−1 (70 mAh g−1 at 1000 mA g−1) and excellent coulombic efficiency of nearly 100%. The proposed supercritical etching strategy provides a platform for the commercial production of MXenes.

Machine learning assisted synthetic acceleration of Ruddlesden-Popper and Dion-Jacobson 2D lead halide perovskites

Two-dimensional lead halide perovskites (2D LHPs) can be generally categorized into the Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases, with unbiased and biased structural packing manners, respectively. To distinguish the two different phases during materials discovery, the synthesis has heavily relied on the traditional trial-and-error methods which severely delay the rapid development of these emerging 2D materials. In this work, we applied machine learning (ML) to accelerate the synthetic development of (100)-oriented 2D A2BX4 and ABX4 LHPs (A = organic amine cation, B = Pb, X = halide). The experimentally available 264 crystal structures were used as training data for our ML model to identify the descriptors influencing the formation of the RP- and DJ-phases. The number of nitrogen atoms able to be protonated, the heteroatom type, and the nitrogen content of the organic amine are identified as the most influential factors. To validate our model, three organic amines were tested by growing single crystals and two of the three new structures are consistent with our ML results. This study takes one step further toward the rational synthesis of RP- and DJ-phase hybrid 2D LHPs via an approach of ML.

The Covalent Functionalization of Surface‐Supported Graphene: An Update

AbstractIn the last decade, the use of graphene supported on solid surfaces has broadened its scope and applications, and graphene has acquire a promising role as a major component of high‐performance electronic devices. In this context, the chemical modification of graphene has become essential. In particular, covalent modification offers key benefits, including controllability, stability, and the facility to be integrated into manufacturing operations. In this Review, we critically comment on the latest advances in the covalent modification of supported graphene on substrates. We analyze the different chemical modifications with special attention to radical reactions. In this context, we review the latest achievements in reactivity control, tailoring electronic properties, and introducing active functionalities. Finally, we extended our analysis to other emerging 2D materials supported on surfaces, such as transition metal dichalcogenides, transition metal oxides, and elemental analogs of graphene.

The Covalent Functionalization of Surface-Supported Graphene: An Update.

In the last decade, the use of graphene supported on solid surfaces has broadened its scope and applications, and graphene has acquire a promising role as a major component of high-performance electronic devices. In this context, the chemical modification of graphene has become essential. In particular, covalent modification offers key benefits, including controllability, stability, and the facility to be integrated into manufacturing operations. In this Review, we critically comment on the latest advances in the covalent modification of supported graphene on substrates. We analyze the different chemical modifications with special attention to radical reactions. In this context, we review the latest achievements in reactivity control, tailoring electronic properties, and introducing active functionalities. Finally, we extended our analysis to other emerging 2D materials supported on surfaces, such as transition metal dichalcogenides, transition metal oxides, and elemental analogs of graphene.

B3O3 monolayer an emerging 2D material in as a carrier for anticancer delivery system

We undertook density functional theory (DFT) computations for evaluating the capability of a B3O3 monolayer as a carrier for delivering cyclophosphamide (CP). Also, the properties of CP, the B3O3 monolayer carrier, and those of the complex of the CP-B3O3 monolayer were measured for determining the efficacy of the B3O3 monolayer as a carrier of CP. The interaction between the monolayer and CP demonstrated that the adsorption of CP over the monolayer is favorable in terms of energy and the adsorption energy ranged from −7.89 to −43.11 kcal/mol and −5.02 to −32.66 kcal/mol in the gas phase and in the water media respectively. Moreover, the change in the band gap of the B3O3 monolayer was considerable. According to frontier molecular orbital (FMO) analysis which was also confirmed by the results of NBO, the excitation from the HOMO to the LUMO involved charge transport from CP to the B3O3 monolayer. We can conclude that the B3O3 monolayer can be utilized as a highly efficient carrier for delivering CP.

Mm-band surface acoustic wave devices utilizing two-dimensional boron nitride

The simple structure, low power consumption, and small form factor have made surface acoustic wave (SAW) devices essential to mobile communication as RF filters. For instance, the latest 5G smartphones are equipped with almost 100 acoustic wave filters to select a specific frequency band and increase communication capacity. On the arrival of the newest communication standard, 5G, mm-band up to 39 GHz is supposed to be utilized, whereas the conventional SAW filters are limited to below 3 GHz, leaving a critical component missing. Here, we show an emerging 2D material—hexagonal boron nitride—can become a key enabler of mm-band SAW filter. Our study, based on first principles analysis and acousto-electric simulation, shows the operating frequency of SAW devices can reach over 20 GHz in its fundamental mode and 40 GHz in its interface mode with high electromechanical coupling coefficient (K2) and low insertion loss. In addition to the orders of magnitude improvement compared to the conventional SAW devices, our study provides a systematic approach to utilizing van der Waals crystals with highly anisotropic acoustic properties for practical applications.

An All-in-One Bioinspired Neural Network.

In spite of recent advancements in artificial neural networks (ANNs), the energy efficiency, multifunctionality, adaptability, and integrated nature of biological neural networks remain largely unimitated by hardware neuromorphic computing systems. Here, we exploit optoelectronic, computing, and programmable memory devices based on emerging two-dimensional (2D) layered materials such as MoS2 to demonstrate a monolithically integrated, multipixel, and "all-in-one" bioinspired neural network (BNN) capable of sensing, encoding, learning, forgetting, and inferring at minuscule energy expenditure. We also demonstrate learning adaptability and simulate learning challenges under specific synaptic conditions to mimic biological learning. Our findings highlight the potential of in-memory computing and sensing based on emerging 2D materials, devices, and integrated circuits to not only overcome the bottleneck of von Neumann computing in conventional CMOS designs but also to aid in eliminating the peripheral components necessary for competing technologies such as memristors.