Few-layer Sheets Research Articles

Characterization of Rice Husk for Graphene Extraction and Metallization

Rice husk, an underutilized agricultural waste product, serves as a potential precursor for graphene synthesis. This study focuses on synthesizing and characterizing graphene through the chemical exfoliation method, employing advanced analytical techniques to explore its potential applications in metallization. Graphene was produced by chemically activating rice husk ash (RHA) with potassium hydroxide (KOH) at 800 ºC. The extracted graphene underwent analysis using various techniques. X-ray Diffraction (XRD) confirmed the material's crystalline nature and graphitic structure. Fourier-Transform Infrared Spectroscopy (FTIR) identified typical functional groups present in the synthesized graphene. Raman Spectroscopy revealed significant defects and confirmed that the graphene consists of single or few-layer thin sheets. Transmission Electron Microscopy (TEM) showed the presence of thin graphene sheets and nanoparticles with sizes ranging from 1.47 nm to 5.80 nm. Ultraviolet-Visible Spectroscopy (UV-Vis) confirmed electronic structure and optical properties, essential for metallization. X-ray Fluorescence (XRF) confirmed the purity of the graphene, while Brunauer-Emmett-Teller (BET) analysis revealed a high specific surface area, making the material suitable for surface-based applications. Electrical conductivity tests demonstrated good conductivity in the lower to moderate current range. The study underscores the potential of rice husk-derived graphene for metallization, offering a cost-effective and eco-friendly synthesis method for industrial and commercial applications.

Tuning the Active Oxygen Species of Two-Dimensional Borophene Oxide toward Advanced Metal-Free Catalysis.

Two-dimensional (2D) borophene materials are predicted to be ideal catalytic materials due to their structural analogy to graphene. However, the lack of chemical functionalization of borophene hinders its practical application in catalysis. Herein, we reported a massive production of freestanding few-layer 2D borophene oxide (BO) sheets with tunable active oxygen species by a moderate oxidation-assisted exfoliation method. State-of-the-art characterizations demonstrated the evolution of active oxygen species from surface B-O species at the initial stage to the intermediate BxOy (1.5 < x/y < 3) species and eventually to bulk B2O3 with an increasing oxidation duration. As a result, the 2D BO sheet with enhanced B-O species exhibited a strikingly high catalytic activity for the aerobic oxidation of benzylamine into N-benzylidenebenzylamine. The formation rate of imine reaches as high as 29.7 mmol gcatal-1 h-1 under mild reaction conditions, higher than that of pristine borophene, boron oxides, graphene oxide, and other metal/metal-free catalysts in the reported literature. Density functional theory calculations further revealed the critical role of surface B-O species, which favor the adsorption and N-H activation of benzylamine for high activity and suppress the deep dehydrogenation, yielding an outstanding imine selectivity (>90%). This work paves the route for a moderate and scalable synthesis of few-layer BO sheets with highly active B-O species toward advanced metal-free catalysis beyond graphene.

Ex Situ Covalent Functionalization of Germanene via 1,3-Dipolar Cycloaddition: A Promising Approach for the Bandgap Engineering of Group-14 Xenes.

Group-14 Xenes beyond graphene such as silicene, germanene, and stanene have recently gained a lot of attention for their peculiar electronic properties, which can be tuned by covalent functionalization. Up until now, reported methods for the top-down synthesis of covalently functionalized silicene and germanene typically yield multilayered flakes with a minimum thickness of 100nm. Herein, the ex situ covalent functionalization of germanene (fGe) is reported via 1,3-dipolar cycloaddition of the azomethine ylide generated by the decarboxylative condensation of 3,4-dihydroxybenzaldehyde and sarcosine. Amorphous few-layered sheets (average thickness of ≈6nm) of dipolarophile germanene (GeX) are produced by thermal dehydrogenation of its fully saturated parent precursor, germanane (GeH). Spectroscopic evidence confirmed the emergence of the dipolarophilic sp2 domains due to the dehydrogenation of germanane, and their sp3 hybridization due to the covalent functionalization of germanene. Elemental mapping of the functionalized germanene revealed flakes with a very high abundance of carbon uniformly covering the germanium backbone. The 500meV increase of the optical bandgap of germanene observed upon functionalization paves the way toward bandgap engineering of other group-14 Xenes, which could potentially be a major turning point in the fields of electronics, electrocatalysis, and photocatalysis.

Synthesis of Few-Layer Hexagonal Boron Nitride for Magnetic Tunnel Junction Application.

Hexagonal boron nitride (hBN), a wide-gap two-dimensional (2D) insulator, is an ideal tunneling barrier for many applications because of the atomically flat surface, high crystalline quality, and high stability. Few-layer hBN with a thickness of 1-2 nm is an effective barrier for electron tunneling, but the preparation of few-layer hBN relies on mechanical exfoliation from bulk hBN crystals. Here, we report the large-area growth of few-layer hBN by chemical vapor deposition on ferromagnetic Ni-Fe thin films and its application to tunnel barriers of magnetic tunnel junction (MTJ) devices. Few-layer hBN sheets mainly consisting of two to three layers have been successfully synthesized on a Ni-Fe catalyst at a high growth temperature of 1200 °C. The MTJ devices were fabricated on as-grown hBN by using the Ni-Fe film as the bottom ferromagnetic electrode to avoid contamination and surface oxidation. We found that trilayer hBN gives a higher tunneling magnetoresistance (TMR) ratio than bilayer hBN, resulting in a high TMR ratio up to 10% at ∼10 K.

Harnessing niobium-based MXenes for sensors and energy storage applications: The past, the present and the future

Niobium carbide MXenes belong to a class of metal carbide MXenes with niobium as the early transition metal. The transformation of niobium carbide MXene sheets in to few-layer MXene sheets, the combination of the niobium-based MXene with other materials, delamination, intercalation, and partial oxidation of the niobium carbide MXene sheets have resulted in the formation of a material with excellent energy storage and sensing potentials. Herein, the synthesis and classification of the niobium-based MXenes (NBM), their application as sensing materials for a wide range of analytes, and their energy storage potentials are discussed exhaustively. The various transformations of niobium carbide MXenes over the last two decades are also established in this timely review. Essentially, this review is a searchlight on the prospects of NBM, the current state of their application, and their relevance in the materials research community.

GO/ZnO Biosensor Synthesis and Characterization for Biosensors

In this study, GO/ZnO nanoparticles were synthesized using the solvothermal method and characterized for potential biosensor applications. The synthesized nanoparticles exhibited a high degree of crystalline structural purity, as confirmed by XRD analysis. The XRD pattern revealed characteristic peaks corresponding to the crystal planes of ZnO, indicating a typical wurtzite hexagonal structure. In addition, the synthesized nanoparticles were evaluated for their physical characteristics using transmission electron microscopy. The TEM analysis showed that the ZnO nanoparticles had a narrow size distribution, with an average particle size of approximately 25.19 ± 4.1 nm. The morphology of the nanoparticles was further examined, revealing that the ZnO nanoparticles were uniformly dispersed and localized within the GO sheets. Furthermore, the exfoliation of GO into single or few-layered sheets was achieved, as evidenced by its transparency in the TEM images. These findings suggest that the solvothermal synthesis method is effective in producing highly dispersed GO/ZnO nanoparticles with a narrow size distribution. The synthesized GO/ZnO nanoparticles showed promise for biosensor applications due to their uniform shape and distribution, as well as their small size.

Electrochemical detection of sulfanilamide using tannic acid exfoliated MoS2 nanosheets combined with reduced graphene oxide/graphite

Sulfonamides are a family of synthetic drugs with a broad-spectrum of antimicrobial activity. Like other antimicrobials, they have been found in aquatic environments, making their detection important. Herein, an electrochemical sensor was designed using tannic acid exfoliated few-layered MoS2 sheets, which were combined with a mixture of reduced graphene oxide (rGO) and graphite flakes (G). The rGO/G was formed using electrodeposition, by cycling from −0.5 to −1.5 V in an acidified sulfate solution with well dispersed GO and G. The exfoliated MoS2 sheets were drop cast over the wrinkled rGO/G surface to form the final sensor, GCE/rGO/G/ta-MoS2. The mixture of rGO/G was superior to pure rGO in formulating the sensor. The fabricated sensor exhibited an extended linear range from 0.1 to 566 μM, with a LOD of 86 nM, with good selectivity in the presence of various salts found in water and structurally related drugs from the sulfonamide family. The sensor showed very good reproducibility with the RSD at 0.48 %, repeatability and acceptable long term stability over a 10-day period. Good recovery from both tap and river water was achieved, with recovery ranging from 90.4 to 98.9 % for tap water and from 83.5 to 94.4 % for real river water samples.

Quantum octets in high mobility pentagonal two-dimensional PdSe2

Two-dimensional (2D) materials have drawn immense interests in scientific and technological communities, owing to their extraordinary properties and their tunability by gating, proximity, strain and external fields. For electronic applications, an ideal 2D material would have high mobility, air stability, sizable band gap, and be compatible with large scale synthesis. Here we demonstrate air stable field effect transistors using atomically thin few-layer PdSe2 sheets that are sandwiched between hexagonal BN (hBN), with large saturation current > 350 μA/μm, and high field effect mobilities of ~ 700 and 10,000 cm2/Vs at 300 K and 2 K, respectively. At low temperatures, magnetotransport studies reveal unique octets in quantum oscillations that persist at all densities, arising from 2-fold spin and 4-fold valley degeneracies, which can be broken by in-plane and out-of-plane magnetic fields toward quantum Hall spin and orbital ferromagnetism.

Two-dimensional architecture of N,S-codoped nanocarbon composites embedding few-layer MoS2 for efficient lithium storage.

The exploration and advancement of highly efficient anode materials for lithium-ion batteries (LIBs) are critical to meet the growing demands of the energy storage market. In this study, we present an easily scalable synthesis method for the one-pot formation of few-layer MoS2 nanosheets on a N,S dual-doped carbon monolith with a two-dimensional (2D) architecture, termed MoS2/NSCS. Systematic electrochemical measurements demonstrate that MoS2/NSCS, when employed as the anode material in LIBs, exhibits a high capacity of 681 mA h g-1 at 0.2 A g-1 even after 110 cycles. The exceptional electrochemical performance of MoS2/NSCS can be attributed to its unique porous 2D architecture. The few-layer MoS2 sheets with a large interlayer distance reduce ion diffusion pathways and enhance ion mobility rates. Additionally, the N,S-doped porous carbon matrix not only preserves structural integrity but also facilitates electronic conductivity. These combined factors contribute to the reversible electrochemical activities observed in MoS2/NSCS, highlighting its potential as a promising anode material for high-performance LIBs.

Revealing enhanced X-Ray radiation shielding of 2D layered materials and their laminar heterostructures

This paper demonstrates a new concept of using two-dimensional (2D) layered materials and their heterostructures for enhanced X-ray radiation shielding. This phenomenon is revealed by characterization on the X-ray shielding performances of several 2D materials with high atomic numbers (Z), including MoS2, antimonene (Sb), and MXene prepared as multi-layered and heterostructure films by assembly their few-layer sheets. Results showed considerable X-ray shielding enhancement of (40–50%) at 30 kVp for individual 2D multi-layered films compared with their bulk structures of these materials. Furthermore, when these multi-layered films were combined into laminar heterostructures structures (e.g., MoS2 + MXene), further enhancement of 60% was achieved. The mechanism of the observed X-ray shielding enhancement by these multi-layered 2D structures is not clear at this stage. It is postulated to be the result of an additional multiple scattering and reflections of photons between multiple layers of 2D crystals inside the film, which does not occur in their uniform bulk materials. The presented results suggest that multi-layered 2D materials with high atomic numbers (Z) and their laminar heterostructures could offer a new and promising strategy for designing of a new generation of Pb-free radiation-shielding materials, which is urgently needed across broad sectors.Graphical abstract

Direct Solution Phase Synthesis and Functionalization of 2D WSe2 for Ambient Stability.

2H phase tungsten diselenide (WSe2) is a p-type 2D semiconductor from the transition metal dichalcogenides (TMDs) family with unique opto-electrical properties. Solution phase production of atomically thin WSe2is challenging due to its instability under ambient conditions. We present a highly efficient and scalable solution method for simultaneously exfoliating and functionalizingWSe2by leveraging the noncovalent interaction between mercapto-group and bulk WSe2.Single and few-layer 2H phase pure WSe2sheets of lateral size up to 5µm with minimal basal plane defects, as revealed by XPS, Raman and FTIR spectroscopy, are produced in water-ethanol mixture. Remarkably, WSe2dispersion remains stable even at high concentrations (10 mg/ml) and exhibited high colloidal stability with shelf-life exceeding a year. The findings from our study suggest that through precise manipulation of intercalation chemistry, mass production of solution processable phase-sensitive 2D materials such as WSe2can be achieved. This advancement holds great potential for facilitating their practical utilization in various real-world applications.

Synthesis of Large-Area Single- to Few-Layered MoS2 on an Ionic Liquid Surface.

Large-area fabrication of transition metal dichalcogenides via environmentally friendly and efficient processes has been a long-standing issue in the field of two-dimensional (2D) materials. Here, we report that single- to few-layered MoS2 sheets with an average size of the order of micrometers have been successfully synthesized on an ionic liquid surface by a modified low-pressure chemical vapor deposition (LP-CVD) method without the assistance of catalysts. It is found that the MoS2 sheets grown on the liquid substrate exhibit a complete molecular crystal structure, which is confirmed by transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectroscopy measurements. The interlayer spacing does not change significantly with the increase of the MoS2 layers, corresponding to a layer-by-layer growth pattern. The growth mechanism of the MoS2 sheets is presented according to the experimental results. The work provides a new and simple method of preparing more molecular crystals on liquid substrates and will contribute to further research in this field.

Post-Ammonia-Treated V2CTx MXene at Different Pressures: Effects on Morphology, Electronic, and Optical Properties

In the present work, vanadium carbide (V2CTx) MXene was synthesized successfully and then treated with an ammonia solution (NH4OH) under different pressures using a hydrothermal process. The sample morphology reveals that the V2CTx MXene gradually changed from uneven multilayered micrometre-size sheets to uniform few-layered nanometer-size sheets as the pressure increased. The optical emission spectra show broad emission and a blue shift due to nitrogen-related defects and quantum confinement. X-ray photoelectron spectroscopy shows the presence of nitrogen in all of the samples. The ultraviolet photoelectron spectroscopy study shows a modified density of states near the Fermi level and a maximum of ∼0.6 eV valence band edge shift towards a higher binding energy side after post-treatment with ammonia. More interestingly, the E1g Raman band becomes degenerate and the E1g band upshifts (∼15 cm–1) with increasing pressure treatment. The Raman results suggest that the induced lattice strain due to post-ammonia treatment plays a crucial role in deciding the optical and electronic properties.

Single-Atom Sn-Loaded Exfoliated Layered Titanate Revealing Enhanced Photocatalytic Activity in Hydrogen Generation.

Green H2 generation through layered materials plays a significant role among a wide variety of materials owing to their high theoretical surface area and distinctive features in (photo)catalysis. Layered titanates (LTs) are a class of these materials, but they suffer from large bandgaps and a layers' stacked form. We first address the successful exfoliation of bulk LT to exfoliated few-layer sheets via long-term dilute HCl treatment at room temperature without any organic exfoliating agents. Then, we demonstrate a substantial photocatalytic activity enhancement through the loading of Sn single atoms on exfoliated LTs (K0.8Ti1.73Li0.27O4). Comprehensive analysis, including time-resolved photoluminescence spectroscopy, revealed the modification of electronic and physical properties of the exfoliated layered titanate for better solar photocatalysis. Upon treating the exfoliated titanate in SnCl2 solution, a Sn single atom was successfully loaded on the exfoliated titanate, which was characterized by spectroscopic and microscopic techniques, including aberration-corrected transmission electron microscopy. The exfoliated titanate with an optimal Sn loading exhibited a good photocatalytic H2 evolution from water containing methanol and from ammonia borane (AB) dehydrogenation, which was not only enhanced from the pristine LT, but higher than conventional TiO2-based photocatalysts like Au-loaded P25.

Modification of Ti3C2Tx MXene with hyperbranched polyethylene ionomers: stable dispersions in nonpolar/low-polarity organic solvents, oxidation protection, and potential application in supercapacitors

Hydrophilic MXene nanosheets are intercalated with hydrophobic hyperbranched polyethylene ionomers containing quaternary ammonium ions to render ionomer-modified multi- or few-layer MXene sheets with marked changed physiochemical properties.

Sea-urchin-like NiCo2S4 modified MXene hybrids with enhanced microwave absorption performance

The development of electromagnetic wave absorbing materials with lightweight and high absorption capacity is an effective way to solve electromagnetic wave pollution. Although the two-dimensional MXene material has become one of the most attractive electromagnetic wave absorbing materials due to its unique structure, the poor impedance matching makes it difficult to obtain both lightweight and efficient absorption capacity. Herein, few-layer MXene sheets and sea-urchin-like NiCo2S4 (NCS) hybrids were successfully synthesized by a simple electrostatic self-assembly method. MXene/NCS hybrids achieve good absorption performances. The maximum absorption bandwidth is 5.6 GHz at a matching thickness of only 1.53 mm with a filling ratio of only 10 wt%. In addition, the excellent microwave absorption performance is attributed to the improved impedance matching of MXene and the synergistic effects of dielectric loss and interfacial polarization. This work provides new ideas for the design and synthesis of materials with lightweight and efficient electromagnetic wave absorption.

In-Situ Chemical Thinning and Surface Doping of Layered Bi2Se3.

As a promising topological insulator, two-dimensional (2D) bismuth selenide (Bi2Se3) attracts extensive research interest. Controllable surface doping of layered Bi2Se3 becomes a crucial issue for the relevant applications. Here, we propose an efficient method for the chemical thinning and surface doping of layered Bi2Se3, forming Se/Bi2Se3 heterostructures with tunable thickness ranging from a few nanometers to hundreds of nanometers. The thickness can be regulated by varying the reaction time and large-size few-layer Bi2Se3 sheets can be obtained. Different from previous liquid-exfoliation methods that require complex reaction process, in-situ and thickness-controllable exfoliation of large-size layered Bi2Se3 can be realized via the developed method. Additionally, the formation of Se nanomeshes coated on the Bi2Se3 sheets remarkably enhance the intensity of Raman vibration peaks, indicating that this method can be used for surface-enhanced Raman scattering. The proposed chemical thinning and surface-doping method is expected to be extended to other bulk-layered materials for high-efficient preparation of 2D heterostructures.

Laser-induced galfenol embedded multi-layer graphene-oxide in solution

The proposed work demonstrates the direct synthesis of nanomaterial-embedded laser-induced few-layer graphene-oxide by directly ablating galfenol in a water-based solution for the first time. Laser-induced multilayer graphene-oxide (GO) embedded with galfenol (gallium–iron alloy) nanoparticles (NPs) is created through a method of direct laser inscription of bulk galfenol in deionized (DI) water with femtosecond laser ablation. The NP-embedded GO is achieved by irradiating a near-infrared (near-IR) femtosecond laser at 1040 nm on a bulk galfenol material submerged in a solution comprising DI water and a small concentration (5%/wt.) of polyvinylpyrrolidone followed by a second ablation in pure DI water. Results show nanoparticles with a mean diameter of ∼30 nm embedded in GO sheets with visible folds spaced at ∼0.63 nm. The composition of iron and gallium shifts by less than 2% during the laser ablation process, and the few-layer GO sheets exhibit similar Raman peaks to bulk graphite.

Improvement of mechanical property for BNNSs/PAN composite films via electro-spinning with high filtration performance

People increasingly need air filters with ultra-high efficiency due to air pollution. In this work, BNNSs (boron nitride nanosheets) were prepared by chemical method using potassium permanganate and sulphuric acid. This functionalization induced the exfoliation of the layered structure of h-BN into monolayer or few-layer sheets. Infrared spectrum analysis shows that the oxidation functional group was introduced into hexagonal boron nitride. Further investigation of the crystallization property was accomplished by XRD analysis in conclusion that the crystal structure was not changed for the introduction of oxidation functional group. The polyacrylonitrile (PAN) and BNNSs/PAN nanofiber films were constructed by electrospinning. It is found that the electrospun nanofiber films had good filtration effect and could capture the most particles in the air because of electrostatic adsorption. The removal rate of particle by the filters reached 99.8% for BNNSs/PAN nanofiber films. Addition of BNNSs increaed the mechanical property of the nanofiber films.

Facile preparation and characterization of MXene@Platinum nanocomposite for energy conversion applications

The 2D transition metal carbide, MXene (MX - TixCxTx) and MX@Pt nanocomposites was prepared from MAX (Ti3AlC2) precursor. The effective nanocomposite (MXene/Pt) photocatalysts are prepared by facile water bath sonication and CVD tubular furnace thermal annealing treatment at 600 °C. The successfully prepared MAX into MXene (MX) flakes are also compared to structural conformation of MX@Pt nanocomposites through XRD results and revealed good crystalline diffracted peaks. The micro-RAMAN results explored with excelent connection of 106.49 and 612.78 cm−1. The FT-IR substantiation for Ti-C and Ti-O-C stretching for MXene (TixCxTx) functional groups confirm the MAX, MX, MX@Pt materials formation. The surface FE-SEM morphology explored MXene few-layer sheets with ‘Pt’ decorated (MX@Pt) nanocomposites. Further, FE-SEM with EDAX elemental characterization system confirm materials atomic percentage as ‘Ti’– 48.36 at. %, ‘C”– 48.63 at. % and platinum ‘Pt’– 3.01 at. %. Finally, MX@Pt nanocomposites explored to HER studies, which exhibited 165 mV to attain 10 mA/cm2 and it exhibited 477 mV overpotential to reach 100 mA/cm2. MX@Pt nanocomposites revealed for H2 and HER activity applications will demonstrate future potential H2 productions and water splitting applications.