Functionalization Of 2D Materials Research Articles

The role of selectively oxidized graphene and MoS2 in enhancing efficiency of spray-coated bulk heterojunction photoactive layers

This study investigates bulk heterojunction photoactive layers constituted of selectively oxidized graphene (SOG), molybdenum disulfide (MoS2), and poly 3-hexyl thiophene (P3HT) deposited by spray coating. The functionalization of these 2D materials was confirmed by X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform infrared spectroscopy, and Raman spectroscopy. The results show that functionalized 2D materials significantly modify the surface morphology and roughness of the photoactive layer, reducing agglomeration. Incorporating SOG and MoS2 leads to a 35% increase in theoretical short circuit current, enhancing wavelength absorption and overall efficiency while maintaining transparency. These results highlight the potential of SOG and MoS2 in scalable semi-transparent solar cell applications, paving the way for further advancements in energy generation and aesthetic architectural integration.

Self-assembly plasmonic gold nanoribbons on few-layer PtSe2 under femtosecond laser irradiation

Functional two-dimensional (2D) materials have been extensively explored for a wide range of applications such as energy generation, low-power computing, and biosensing. In this work, we present an approach involving the integration of six-layer platinum diselenide (PtSe2) as an interlayer between the thin gold film and SiO2 substrate to induce spontaneous formation of plasmonic nanostructures (nanoribbons) on the upper gold film (∼8 nm) under 1030 nm femtosecond laser irradiation. The formation of periodic nanostructures is attributed to the periodic energy deposition that occurs in the PtSe2 layers under intense femtosecond laser pulses. Notably, the self-assembled gold nanostructures exhibit a distinctive polarization-dependent plasmonic response in the near-infrared spectral region and could be directly fabricated in a centimeter scale within several minutes. This straightforward method for self-assembling plasmonic nanostructures using layered materials may expand the utility of functional 2D materials and advance the cost-effective and large-area fabrication of plasmonic thin-film nanostructures in a simplified manner.

When Machine Learning Meets 2D Materials: A Review.

The availability of an ever-expanding portfolio of 2D materials with rich internal degrees of freedom (spin, excitonic, valley, sublattice, and layer pseudospin) together with the unique ability to tailor heterostructures made layer by layer in a precisely chosen stacking sequence and relative crystallographic alignments, offers an unprecedented platform for realizing materials by design. However, the breadth of multi-dimensional parameter space and massive data sets involved is emblematic of complex, resource-intensive experimentation, which not only challenges the current state of the art but also renders exhaustive sampling untenable. To this end, machine learning, a very powerful data-driven approach and subset of artificial intelligence, is a potential game-changer, enabling a cheaper - yet more efficient - alternative to traditional computational strategies. It is also a new paradigm for autonomous experimentation for accelerated discovery and machine-assisted design of functional 2D materials and heterostructures. Here, the study reviews the recent progress and challenges of such endeavors, and highlight various emerging opportunities in this frontier research area.

Testing the Aquatic Toxicity of 2D Few-Layer Graphene Inks Using Rainbow Trout (Oncorhynchus mykiss): In Vivo and In Vitro Approaches to Support an SSbD Assessment.

Graphene-based conductive inks offer attractive possibilities in many printing technology applications. Often, these inks contain a mixture of compounds, such as solvents and stabilizers. For the safe(r) and sustainable use of such materials in products, potentially hazardous components must be identified and considered in the design stage. In this study, the hazards of few-layer graphene (FLG)-based ink formulations were tested in fish using in vitro (RTL-W1 cell line) and in vivo aquatic ecotoxicity tests (OECD TG 203). Five ink formulations were produced using different processing steps, containing varying amounts of solvents and stabilizers, with the end products formulated either in aqueous solutions or in powder form. The FLG ink formulations with the highest contents of the stabilizer sodium deoxycholate showed greater in vitro cytotoxic effects, but they did not provoke mortality in juvenile rainbow trout. However, exposure led to increased activities of the cytochrome P450 1a (Cyp1a) and Cyp3a enzymes in the liver, which play an essential role in the detoxification of xenobiotics, suggesting that any effects will be enhanced by the presence of the stabilizers. These results highlight the importance of an SSbD approach together with the use of appropriate testing tools and strategies. By incorporating additional processing steps to remove identified cytotoxic residual solvents and stabilizers, the hazard profile of the FLG inks improved, demonstrating that, by following the principles of the European Commission's safe(r) and sustainable by design (SSbD) framework, one can contribute to the safe(r) and sustainable use of functional and advanced 2D materials in products.

Detection of decomposed gases in SF6 surge arrester contaminated conditions in ultra-high voltage transmission lines based on Ta-doped defective h-BN nanosheet: A DFT study

SF6 surge arrester on ultra-high voltage transmission lines plays a critical role in the entire power transmission system. They not only protect electrical equipment from the dangers of high transient over voltages, but also bear the responsibility of maintaining the safety and stability of the transmission lines. Detecting the decomposed gases under polluted conditions inside SF6 surge arresters is of paramount importance. In this paper, based on extensive investigations and the application of density functional theory and 2D materials, we conducted a study on the detection of decomposed gases (HF, H2S, SOF2) in SF6 surge arresters for ultra-high voltage transmission lines under polluted conditions using Ta-doped defective h-BN nanosheets gas sensor. Revealing the adsorption and sensing mechanisms of these target gases on h-BN sensors through band structure, density of states, projected density of states, and differential charge density analysis. The results showed that Ta metal particle modification significantly improves the electronic activity of defective h-BN, substantially reducing the band gap values from 4.560 eV to 0.153 eV and 0.912 eV in the B atom and N atom defective oping systems. Meanwhile, Ta-doped defective h-BN exhibits strong selectivity and sensitivity to three decomposition components, with the adsorption capability ranking as SOF2 > H2S > HF, all of which are physical chemisorption types. Furthermore, in terms of various adsorption parameters, defective h-BN’s adsorption ability far surpasses other materials, offering broad prospects for practical applications. The results of this work contribute to the development and application of Ta-doped defective h-BN sensors for the detection of decomposed gases inside SF6 surge arresters under polluted conditions.

Hydrogen storage on the lithium and sodium-decorated inorganic graphenylene

Efficient H2 storage is one of the keys to the energy transition toward global sustainability. Hydrogen energy sources on functionalized 2D materials by metals have been shown as promising alternatives for clean energy systems. In a particular way, we have demonstrated here that the inorganic graphenylene-like silicon carbide (IGP-SiC) weakly adsorbs H2. At the same time, the Li/Na decoration significantly enhances the H2 interaction, accommodating up to 48H2 molecules by a stronger physisorption. Also, scanning bond critical points (BCPs) confirms a great interaction between the Li(Na)@IGP-SiC systems and the hydrogen, a distinct scenario for the pristine IGP-SiC. Gravimetrically, hydrogen densities reach 8.27 wt% (Li) and 6.78 wt% (Na), exceeding the U.S. Department of Energy (5.6 wt%) benchmark. Regarding thermodynamic stability, the desorption temperatures at ambient conditions are suitable for hydrogen storage devices. Therefore, Li(Na)@IGP-SiC systems emerge as high-capacity hydrogen storage materials.

The effect of controlled intercalation on the mechanical performances and dimensional accuracy of material extrusion additive manufactured poly(lactic acid)/organo-montmorillonite nanocomposites

Although the material extrusion-based 3D printing (MEX-3DP) has the ability to construct functional complex nanocomposites based on two-dimensional (2D) nanomaterials, however, the interplay of exfoliation degree of 2D materials and MEX-3DP parameters has not been elucidated, which seriously limits the further design and application of MEX-3DP 2D materials towards low-cost device fabrication. In this report, we use the well-studied organo-montmorillonite (MMT) as model materials and systematically studied the effect of various intercalation degrees on the mechanical and geometrical performance of MEX-3DP organo-MMT reinforced poly (lactic acid) nanocomposites. It was elucidated that, different from traditional injection moulding process, the best performance of MEX-3DP samples is obtained from completely exfoliated organo-MMT. The effect of the intercalation degrees is correlated with the melt flowability, thermal expansion and the resulting voids size that essential for MEX-3DP processes. The structure and rheology analysis demonstrate that the high exfoliation degree of 2D materials is essential to compensate the weak interfacial bonding or shrinkage-induced poor mechanical properties. The findings provide a detailed insight into the 2D materials exfoliation on the MEX-3DP quality, which is meaningful for engineers willing to design MEX-3DP functional 2D materials, for next generation disruptive technologies and applications.

Three-Dimensional MoS2/MXene Heterostructure Aerogel for Chemical Gas Sensors with Superior Sensitivity and Stability.

The concept of integrating diverse functional 2D materials into a heterostructure provides platforms for exploring physics that cannot be accessed in a single 2D material. Here, physically mixing two 2D materials, MXene and MoS2, followed by freeze-drying is utilized to successfully fabricate a 3D MoS2/MXene van der Waals heterostructure aerogel. The low-temperature synthetic approach effectively suppresses significant oxidation of the Ti3C2Tx MXene and results in a hierarchical and freestanding 3D heterostructure composed of high-quality MoS2 and MXene nanosheets. Functionalization of MXene with a MoS2 catalytic layer substantially improves sensitivity and long-term stability toward detection of NO2 gas, and computational studies are coupled with experimental results to elucidate that the mechanism behind enhancements in the gas-sensing properties is effective inhibition of HNO2 formation on the MXene surface, due to the presence of MoS2. Overall, this study has a great potential for expansion of applicability to other classes of two-dimensional materials as a general synthesis method, to be applied in future fields of catalysis and electronics.

Exfoliation of 2D Metal-Organic Frameworks: toward Advanced Scalable Materials for Optical Sensing.

Two-dimensional metal-organic frameworks (MOFs) occupy a special place among the large family of functional 2D materials. Even at a monolayer level, 2D MOFs exhibit unique sensing, separation, catalytic, electronic, and conductive properties due to the combination of porosity and organo-inorganic nature. However, lab-to-fab transfer for 2D MOF layers faces the challenge of their scalability, limited by weak interactions between the organic and inorganic building blocks. Here, comparing three top-down approaches to fabricate 2D MOF layers (sonication, freeze-thaw, and mechanical exfoliation), The technological criteria have established for creation of the layers of the thickness up to 1nm with a record aspect ratio up to 2*10^4:1. The freezing-thaw and mechanical exfoliation are the most optimal approaches; wherein the rate and manufacturability of the mechanical exfoliation rivaling the greatest scalability of 2D MOF layers obtained by freezing-thaw (21300:1vs 1330:1 aspect ratio), leaving the sonication approach behind (with a record 900:1 aspect ratio) have discovered. The high quality 2D MOF layers with a record aspect ratio demonstrate unique optical sensitivity to solvents of a varied polarity, which opens the way to fabricate scalable and freestanding 2D MOF-based atomically thin chemo-optical sensors by industry-oriented approach.

Role of reactive oxygen species in the toxicity of two-dimensional nanomaterials: A study on layered Ti3C2 MXenes

Two-dimensional (2D) materials, such as MXenes and graphene, are tested as catalysts, sensors, and nanomedicine, but their safety and biocompatibility are poorly understood. In this study, Ti3C2 MXenes (single-layer and multilayer) and graphene oxide are prepared to evaluate their inflammatory potential in vivo and in vitro using the read-across approach. Pulmonary exposure of the test materials in mice led to significant dose-dependent increases in several toxicity endpoints of bronchoalveolar lavage fluid. The correlation of the oxidative potential of the test materials and the toxicity endpoints shows that both the intrinsic and intracellular oxidative potentials of 2D materials are key factors for the inflammation and damage of the plasma membrane. Scanning electron microscopy and in vitro studies using the differentiated THP-1 macrophage-like cells support this finding. Furthermore, the toxicity of test items is reduced when treated with N-acetyl cysteine, a scavenger for reactive oxygen species; this finding further supports the oxidative stress paradigm proposed in this study. This oxidative stress paradigm may apply to 2D materials in general and improve the understanding the toxicity mechanism of such materials, which would facilitate the design of safer functional 2D materials.

Measuring complex refractive index through deep-learning-enabled optical reflectometry

Optical spectroscopy is indispensable for research and development in nanoscience and nanotechnology, microelectronics, energy, and advanced manufacturing. Advanced optical spectroscopy tools often require both specifically designed high-end instrumentation and intricate data analysis techniques. Beyond the common analytical tools, deep learning methods are well suited for interpreting high-dimensional and complicated spectroscopy data. They offer great opportunities to extract subtle and deep information about optical properties of materials with simpler optical setups, which would otherwise require sophisticated instrumentation. In this work, we propose a computational approach based on a conventional tabletop optical microscope and a deep learning model called ReflectoNet. Without any prior knowledge about the multilayer substrates, ReflectoNet can predict the complex refractive indices of thin films and 2D materials on top of these nontrivial substrates from experimentally measured optical reflectance spectra with high accuracies. This task was not feasible previously with traditional reflectometry or ellipsometry methods. Fundamental physical principles, such as the Kramers–Kronig relations, are spontaneously learned by the model without any further training. This approach enables in-operando optical characterization of functional materials and 2D materials within complex photonic structures or optoelectronic devices.

Enhanced Supercontinuum Generation in Integrated Waveguides Incorporated with Graphene Oxide Films

AbstractEnhanced supercontinuum generation (SCG) is experimentally demonstrated in integrated silicon nitride (Si3N4) waveguides incorporating highly nonlinear graphene oxide (GO) in the form of 2D films. On‐chip integration of the 2D GO films with precise control of their thickness is realized by using a transfer‐free and layer‐by‐layer coating method. The control of the film length and coating position is achieved via window opening in the upper silica cladding of the photonic integrated chips. Detailed SCG measurements are performed using the fabricated devices with different waveguide geometries and GO film thicknesses, and the results are compared with devices without GO. Significantly improved spectral broadening of ultrashort optical pulses with ultrahigh peak powers exceeding 1000 W is observed for the hybrid devices, achieving up to 2.4 times improvement in the spectral bandwidth relative to devices without GO. Theoretical analyses for the influence of GO film thickness, coating length, coating position, and waveguide geometry are also provided by fitting the experimental results with theory, showing that there is still significant room for further improvement. This work opens up a new avenue toward improving the SCG performance of photonic integrated devices by incorporating functional 2D materials.

A systematic study of work function and electronic properties of MXenes from first principles.

Functional 2D materials are interesting for a wide range of applications. The rapid growth of the MXene family is due to its compositional diversity, which, in turn, allows significant tuning of the properties, and hence their applicability. The properties are to a large extent dictated by surface terminations. In the present work, we demonstrate the influence of termination species (O, NH, N, S, F, Cl, Br, I) on the changes in electronic structure, work function, dynamical stability, and atomic charges and distances of MXenes (Ti2C, Nb2C, V2C, Mo2C, Ti3C2, and Nb4C3). Among these systems, the work function values were not previously reported for ∼60% of the systems, and most of the previously reported MXenes with semiconducting nature are here proven to be dynamically unstable. The results show that the work function generally decreases with a reduced electronegativity of the terminating species, which in turn is correlated to a reduced charge of both the metal and terminating species and an increased metal-termination distance. An exception to this trend is NH terminations, which display a significantly reduced work function due to an intrinsic dipole moment within the termination. Furthermore, the results suggest that halogen terminations improve the electrical conductivity of the materials.

Functionalized 2D materials F–MoS2 and F-g-C3N4 with TiO2 as Composite Electrocatalysts for Electrochemical Hydrogen Evolution

Electrochemical hydrogen evolution is an important research field to produce renewable energy. Nanostructured two dimensional (2D) materials such as g-C3N4 and MoS2 are potential electrocatalysts for hydrogen evolution reaction (HER). The incorporation of semiconducting material into 2D material enhances the hydrogen evolution. Here in, we have developed composite of acid functionalized MoS2 and g-C3N4 with TiO2 (F–MoS2/TiO2, F-g-C3N4/TiO2). The F–MoS2/TiO2 composite exhibited excellent electrochemical HER activity with an overpotential of 103 mV Vs RHE at 20 mA/cm2 compared to pristine F–MoS2 of 232 mV, TiO2 of 455 mV Vs RHE. In addition F-g-C3N4/TiO2 showed high overpotential of 322 mV at 5 mA/cm2 than pristine F-g-C3N4 and TiO2 of 433 mV and 448 mV Vs RHE at 2.7 mA/cm2 respectively.

Engineering of Oxidized Line Defects on CVD-Grown MoS2 Flakes.

Defect engineering is a promising means to create patterns on two-dimensional (2D) materials to enable unconventional properties. However, defects usually exist abundantly and randomly on 2D materials, which makes it difficult to tune the properties in a controllable manner. Therefore, it is highly desirable to find out the formation mechanism and controllable fabrication method of defects on 2D materials. In this report, we systematically investigated the line defects on monolayer MoS2 formed by introducing oxygen during the CVD growth. The line defects were formed due to the overoxidation of the MoS2 flake along crystal boundaries, which bulged out of the surface and had the same surface potential as the basal plane. Therefore, the MoS2 flake with line defects maintained the optical and electrical integrity but exhibited distinct properties as compared to the pristine one. By controlling the oxygen concentration during CVD growth, the density of the line defects can be precisely controlled to implement controllable property tuning. Moreover, during the transfer process, the MoS2 flake was easily broken along the line defects, which increased the active sites to achieve enhanced hydrogen evolution reaction performance. This work is expected to inspire the development of patterned functional 2D materials by defect engineering.

Electrochemical Exfoliation to Produce High-Quality Black Phosphorus.

To obtain high-quality two-dimensional (2D) materials from the bulky crystals, delamination under an externally controlled stimulus is crucial. Electrochemical exfoliation of layered materials requires simple instrumentation yet offers high-quality exfoliated 2D materials with high yields and features straightforward upscalability; therefore, it represents a key technology for advancing fundamental studies and industrial applications. Moreover, the solution processability of functionalized 2D materials enables the fabrication of (opto)electronic and energy devices via different printing technologies such as inkjet printing and 3D printing. This paper presents the electrochemical exfoliation protocol for the synthesis of black phosphorus (BP), one of the most promising emerging 2D materials, from its bulk crystals in a step-by-step manner, namely, cathodic electrochemical exfoliation of BP in the presence of N(C4H9)4∙HSO4 in propylene carbonate, dispersion preparation by sonication and subsequent centrifugation for the separation of flakes, and morphological characterization by scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM).

Scavenging Tumor‐Derived Small Extracellular Vesicles by Functionalized 2D Materials to Inhibit Tumor Regrowth and Metastasis Following Radiotherapy

AbstractRadiotherapy is essential for treating unresectable or metastatic breast cancer, but radiotherapy‐induced tumor cell death generates small extracellular vesicles (sEVs) that promote tumor regrowth and metastasis following treatment. Here cationic nanosheets with a high sEVs‐binding capacity that suppress sEVs‐induced tumor regrowth and metastasis following radiotherapy is developed. Molybdenum disulfide (MoS2) monolayers are prepared by using lithium ions as intercalation agents, and are functionalized with cationic polyamidoamine (PAMAM) dendrimers. The MoS2‐PAMAM particles exhibit a corrugated sheet‐like nanostructure with a larger surface‐to‐volume ratio than spherical PAMAM‐functionalized particles, resulting in greater sEVs binding capacity. Treatment of MDA‐MB‐231 human breast cancer cells with the MoS2‐PAMAM nanosheets reduces sEVs‐induced Toll‐like receptor activation and tumor cell proliferation, migration, and invasion to a greater extent than treatment with spherical PAMAM nanoparticles. In a mouse 4T1 metastatic breast cancer model, the nanosheets exhibit greater inhibition of tumor regrowth and metastasis after radiotherapy than the spherical nanoparticles, demonstrating the potential of these sEVs‐scavenging nanosheets for improving outcomes for breast cancer radiotherapy patients. The work reveals a pivotal role of the 2D sheet‐like materials in binding sEVs, indicating the significance of nanoscale geometry in developing the next‐generation sEVs‐scavenging biomaterials.

Molecular Lego for Functional 2D Materials: Self-Assembly and Ordering of Bi-Molecular 2D Spinlattices of M(II,III) Phthalocyanines and of Highly Crystalline Free Standing Networks

Single layer low-dimensional materials are presently of emerging interest, also in the context of magnetism. We further developed on-surface supra-molecular architecturing to create two-dimensional spin arrays. By chemical programming of the modules, different checkerboards were produced containing metals of different oxidation and spin states, diamagnetic zinc, and a metal-free ‘spacer’. [1] In an in-depth, spectro-microscopy and theoretical account, we correlate the structure and the magnetic properties of these tunable systems and discuss the emergence of 2D Kondo magnetism [2] from the spin-bearing components and via the physico-chemical bonding to the underlying substrate. The contributions of the individual elements, as well as the role of the electronic surface state in the bottom substrate, are discussed. Also we show the the first free-standing single layer networks of calixarenes stabilized via functional groups enabling vdW, coordination and dipole-dipole, interaction. [3]Fig. 1) Graphical animation of the 2D spin arrays built by C--H - F--C bonding of two different magnetic atom bearing phthalocyanines that have been exploited to investigate the assembly and properties of Kondo lattices.[1] M. Baljozovic et al. Magnetochemistry 2021, 7, 119.[2] J. Girovsky et al. Nature Communications 2017 8:15388[3] M. Moradi, N. Opara, L.G. Tulli, C. Wäckerlin, S.J. Dalgarno, S.J. Teat, M. Baljozovic, O. Popova, E. van Genderen, A. Kleibert, H. Stahlberg, J.P. Abrahams, C. Padeste, T.A. Jung, P. Shahgaldian, Sci. Adv. 2019; 5: eaav4489 Figure 1

PEI/PEG functionalized Black Phosphorus prepared by a One-Pot method for a wide detection range CO2 gas sensor

Black Phosphorus (BP) has attracted considerable attention in gas detection fields attributing to layer-dependent direct bandgap, and high carrier mobility. Currently, many researchers use blended polyethyleneimine/polyethylene-glycol (PEI/PEG) functionalized two-dimensional (2D) material to detect carbon dioxide (CO2). However, the detection rage of CO2 sensor based blended PEI/PEG functionalized 2D materials still need further with widen to realize more application. In this paper, a RT (25 °C) CO2 sensor prepared by a One-Pot method based on a PEI/PEG functionalized BP composite material is developed, in which the existence of PEI/PEG onto BP was confirmed by SEM, EDS, etc. The gas-sensing experiment results show that the low limit of detection of PEI/PEG-BP gas sensor is 200 ppm CO2 under air conditions and a high limit of detection of 250,000 ppm CO2 under N2 conditions. Moreover, the PEI/PEG-BP sensor shows high selectivity, and excellent repeatability. The excellent gas-sensing properties of the PEI/PEG-BP sensor can be attributed to the meso-macropores structure, the recognition function of amino groups, and the formation of P-N heterojunction between BP and PEI. The reported results of PEI/PEG-BP sensor can provide a foundation for PEI/PEG functionalized 2D material and understand the sensing mechanism for compositing the 2D materials with polymer semiconductors.

The interfacial adhesion of contacting pairs in van der Waals materials

The interfacial adhesion of contacting pairs between two adjacent layers of 2D van der Waals (vdW) layered materials and between 2D materials and their supporting substrates are essential for manipulating 2D materials and constructing functional 2D materials incorporated devices. Here, the interfacial adhesion forces and energies of various contacting pairs involving 2D materials and their underlying physical mechanisms are investigated by combining atomic force microscopy (AFM) measurements and density functional theory (DFT) calculations. The distinct adhesion forces are verified by selecting various contacting pairs between a bare or graphene-coated Si tip and tungsten disulfide (WS2) or graphene as the 2D materials. When using the bare Si tip, the adhesion forces between tip and monolayer WS2 or bilayer WS2 are determined as 32.07 nN or 38.20 nN, respectively. The adhesion forces between the graphene-coated Si tip and monolayer WS2 or graphene are 14.80 nN or 12.28 nN, respectively. Furthermore, the in-depth density functional theory (DFT) calculation results indicate that a distinctly different charge transfer contributes to the different magnitude of the adhesion forces. Our findings demonstrate that the interfacial interaction is an intrinsic property and critically dependent on the type of 2D materials, suggesting a potential strategy for distinguishing 2D materials by adhesion forces.