Type Of Two-dimensional Material Research Articles

Enhancing the Performance of 2D Ni-Fe Layered Double Hydroxides by Cabbage-Inspired Carbon Conjunction for Oxygen Evolution Reactions.

Layered double hydroxide (LDH) nanosheets as one type of two-dimensional materials have garnered increasing attention in the field of oxygen evolution reaction (OER) in recent decades. To address the challenges associated with poor conductivity and limited electron and charge transfer capability in LDH materials, we have developed a straightforward one-pot synthesis method to successfully fabricate a composite material with a microstructure resembling cabbage, which encompasses NiFe-LDH and nanocarbon (referred as NiFe-LDH@C). Atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM) revealed that the monolayer NiFe-LDH with a height of ~ 0.5-0.8 nm is uniformly distributed and closely bonded to the carbon support, leading to a significant enhancement in conductivity and facilitating faster electron and charge transfer. Moreover, the NiFe-LDH@C exhibits a substantial number of surface defect sites, which enhances the interaction with oxygen species. This dual enhancement in charge transfer and oxygen species-mediated transfer greatly improves the catalytic OER performance, which is further corroborated by theoretical calculations. Notably, the Ni10Fe6-LDH@C with the highest concentration of surface oxygen vacancies demonstrated superior water oxidation performance, surpassing commercially available RuO2 catalysts; an OER overpotential of 231 mV@10 mA cm-2 with a Tafel slope of 71 mV dec-1 was achieved.

SiO2-Decorated-Montmorillonite reinforced Poly(1,3-dioxolane) as a multifunctional solid electrolyte for High-Performance lithium batteries

Solid polymer electrolytes (SPEs) have garnered considerable attention owing to their remarkable flexibility, manufacturability, and cost-effectiveness. However, SPEs are hampered by critical limitations such as inadequate ionic conductivity at room temperature and issues related to lithium-ion migration, which curtail their practical applications. To tackle these challenges, the incorporation of inorganic additives into SPEs is considered as an effective strategy. Montmorillonite (MMT), a typical two-dimensional material, has emerged as an advanced filler for SPEs, displaying increased ionic conductivity, lithium-ion transference, and electrochemical stability. Herein, siliconized-modified montmorillonite (SiO2-MMT) nanosheets are synthesized and incorporated into poly(1,3-dioxolane) (PDOL)-based SPEs, resulting in a multifunctional composite solid electrolyte (CSE). The CSE shows an ionic conductivity as high as 5.58 × 10−4 S cm−1 at 30 °C, with a lithium-ion transference number close to 0.58. Symmetrical Li||Li cells utilizing the CSE exhibits stable performance for over 1200 h at a current density of 0.2 mA cm−2. Additionally, the CSE contributes to the stability of electrolytes, facilitates superior Li+ mobility and uniform deposition, thereby forming a stable solid electrolyte interface (SEI). Density functional theory (DFT) simulation confirms that SiO2-MMT, containing a large number of adsorption sites, facilitated fast reaction kinetics and effective anchoring of lithium polysulfides (LiPSs). As a result, the composite electrolyte is cycled in Lithium-sulfur (Li-S) batteries at 200 mA g−1 and 30 °C for 250 cycles, achieving a high coulombic efficiency (CE > 99.4 %) and a capacity decay rate of 0.15 %. Additionally, when paired with high-voltage Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathodes and LiFePO4 (LFP) cathodes, both display excellent electrochemical performance. This research presents a highly promising approach for constructing multifunctional solid electrolytes for high-performance lithium batteries.

Density functional theory study of adsorption of organic molecules on ZnO monolayers: Implications for conduction type and electrical characteristics

Graphene-like ZnO monolayer, a typical two-dimensional material, has garnered enormous research attention due to its desirable optoelectronic properties and potential broad applications. However, the difficult in fabricating p-type ZnO material is still undergoing. Herein, the atomic and electronic properties of the adsorption of the selected organic molecules including electrophilic molecule tetracyano-p-quinodimethane (TCNQ) and nucleophilic molecule tetrathiafulvalene (TTF) on ZnO monolayers are carried out by the first-principles calculations. The results indicate that the adsorption of TCNQ on the ZnO monolayer leads to typical p-type doping, with a small gap (Ep) between the lowest unoccupied molecular and the valance band maximum with shallow acceptor states in the middle gap. However, the adsorption of TTF can obtain n-type doping of ZnO monolayer with the large gap (En) between the highest occupied molecular and the conduction band minimum with deep donor states. For TCNQ-ZnO monolayer, it exhibits the enhancement absorb in solar energy. There is a considerable charge transfer and strong non-covalent interaction between TCNQ and ZnO monolayer. The work function of TCNQ-ZnO ML is higher than that of pristine ZnO ML. However, the adsorption of TTF can significantly reduce the work function of ZnO ML, turning it into an n-type conduction semiconductor. Additionally, upon the adsorption of organic molecules, the layer thickness and the interlayer coupling as well as the adsorption concentration can modify the band gap of ZnO, and further tune the conduction type of ZnO. Remarkably, applying electric field can alter the number of hole and further greatly tune the electrical characteristic of TCNQ-ZnO ML. The current results can promote the applications of two-dimensional ZnO in nanoelectronics and optoelectronics.

Improved mechanical and thermal properties of polypropylene filled with reduced graphene oxide (rGO) and hexagonal boron nitride (hBN) particles

Improving thermal properties of polymer-based composites by using different types of fillers most of the time also reduces material elasticity and flexural strength, which is a significant problem for application. To address this problem, we have used two types of two-dimensional materials, such as reduced graphene oxide (rGO) and hexagonal boron nitride (hBN) to achieve better thermal and mechanical properties. Great tensile strength and flexibility of both those 2D-materials combined with good thermal conductivity of hBN provided a synergistic effect for the resulting composites. Here we show the composites with 30% of hBN and 10% rGO by weight that have greatly improved flexural strength and flexural modulus as well as more than threefold increased thermal conductivity as compared to pristine polypropylene. Mechanical properties of composites only filled with hBN are significantly lower.

One-step method to control the temperature of S and Mo source and its effect on the size and morphology of MoS2

Molybdenum disulfide (MoS2) is a typical two-dimensional material, which is widely used in many fields because of its excellent electrical and optical properties. In recent years, the high-quality growth of MoS2 has attracted more and more attention from researchers. Many studies have reported a two-step method for the production of MoS2 by pre-deposition of molybdenum (Mo) source and then vulcanization, which is cumbersome and time-consuming, and the preparation temperature is mostly above 800 °C, increasing energy consumption and experimental risk. In this paper, S source and Mo source can be distinguished by double temperature zone tube furnace to prepare MoS2 material in one-step method. The temperatures of S and Mo sources were designed separately, and the effect of each temperature on the quality of MoS2 was investigated. And the monolayer MoS2 with high crystalline quality was obtained at a S source temperature of 165 °C and a Mo source temperature of 680 °C. We produce MoS2 in one-step method at low temperature, which provides a reference for the synthesis of high-quality monolayer MoS2.

Urchin-like Fe3O4@C with core-shell structure modified 2D MXene for high-performance microwave absorption

As a typical two-dimensional material, Ti3C2Tx MXene has been considered a novel potential microwave-absorbing material because of its outstanding metallic-like conductivity and rich surface functional groups. Unfortunately, the microwave absorption performance is constrained by its intrinsic high conductivity and single loss mechanism. Herein, an urchin-like Fe3O4@C hollow sphere with core-shell structure was built by hydrothermal and annealing processes, which was subsequently used to modify MXene via electrostatic self-assembly. The Fe3O4@C/Ti3C2Tx hybrid with 30 wt% Fe3O4@C loading displayed a minimum reflection loss (RLmin) value of –64.0 dB at a thickness of 3.32 mm and a maximum efficient absorption bandwidth (EABmax) of 3.02 GHz at 3.24 mm. The exceptional microwave absorption performance is mainly attributed to the impedance matching brought about by the special urchin-like core-shell structure of Fe3O4@C, as well as the rich interfacial polarization and multiple reflections/scatterings. This work offers a novel idea for the design of efficient MXene-based microwave-absorbing materials.

Machine learning interatomic potentials as efficient tools for obtaining reasonable phonon dispersions and accurate thermal conductivity: A case study of typical two-dimensional materials

The accurate description of phonon dispersion of two-dimensional (2D) materials demonstrates significance in many research fields of condensed matter physics. In this paper, we systematically calculate the phonon spectra and transport properties of six representative 2D materials (encompassing single-element and binary compounds with flat, buckled, and puckered backbone geometries) by means of density functional theory (DFT) and two machine learning interatomic potentials [MLIPs, on-the-fly machine learning potential (FMLP), and moment tensor potential (MTP)]. The results show that the acoustic out-of-plane flexural (ZA) dispersion of the 2D materials are always and easily exhibiting non-quadratic dispersion phenomena near the center of the Brillouin zone by using the pure DFT calculation method. This phenomenon contradicts physics and reflects intuitively from the non-zero group velocity at Γ point. However, no matter which MLIP (FMLP/MTP) the calculation is based on, it could solve such behavior perfectly, where the ZA mode conforms to the quadratic dispersion relationship in the long-wavelength limit. Our results further demonstrate that compared to the pure DFT calculation, the FMLP and MTP method could quickly and relatively accurately obtain the lattice thermal conductivities of graphene, silicene, phosphorene, SiC, MoS2, and GeS. The findings presented in this work provide a solution about the pseudophysical phenomenon of ZA dispersions in 2D materials with the pure DFT calculation, which will greatly facilitate research areas such as phonon thermal transport, flexural mechanics, and electron–acoustic coupling.

MXene-based Membranes for Drinking Water Production.

The soaring development of industry exacerbates the shortage of fresh water, making drinking water production an urgent demand. Membrane techniques feature the merits of high efficiency, low energy consumption, and easy operation, deemed as the most potential technology to purify water. Recently, a new type of two-dimensional materials, MXenes as the transition metal carbides or nitrides in the shape of nanosheets, have attracted enormous interest in water purification due to their extraordinary properties such as adjustable hydrophilicity, easy processibility, antifouling resistance, mechanical strength, and light-to-heat transformation capability. In pioneering studies, MXene-based membranes have been evaluated in the past decade for drinking water production including the separation of bacteria, dyes, salts, and heavy metals. This review focuses on the recent advancement of MXene-based membranes for drinking water production. A brief introduction of MXenes is given first, followed by descriptions of their unique properties. Then, the preparation methods of MXene membranes are summarized. The various applications of MXene membranes in water treatment and the corresponding separation mechanisms are discussed in detail. Finally, the challenges and prospects of MXene membranes are presented with the hope to provide insightful guidance on the future design and fabrication of high-performance MXene membranes.

A Highly Efficient Electromagnetic Wave Absorption System with Graphene Embedded in Hybrid Perovskite.

To cope with the explosive increase in electromagnetic radiation intensity caused by the widespread use of electronic information equipment, high-performance electromagnetic wave (EMW)-absorbing materials that can adapt to various frequency bands of EMW are also facing great demand. In this paper, CH3NH3PbI3/graphene (MG) high-performance EMW-absorbing materials were innovatively synthesized by taking organic-inorganic hybrid perovskite (OIHP) with high equilibrium holes, electron mobility, and accessible synthesis as the main body, graphene as the intergranular component, and adjusting the component ratio. When the component ratio was 16:1, the thickness of the absorber was 1.87 mm, and MG's effective EMW absorption width reached 6.04 GHz (11.96-18.00 GHz), achieving complete coverage of the Ku frequency band. As the main body of the composite, CH3NH3PbI3 played the role of the polarization density center, and the defects and vacancies in the crystal significantly increased the polarization loss intensity; graphene, as a typical two-dimensional material distributed in the crystal gap, built an efficient electron transfer channel, which significantly improved the electrical conductivity loss strength. This work effectively broadened the EMW absorption frequency band of OIHP and promoted the research process of new EMW-absorbing materials based on OIPH.

Metal ions-assisted construction of SiO2/MXene/Fe3O4 aerogel as multifunctional electromagnetic wave absorbing material

Advanced electromagnetic wave absorbing materials are developing towards the directions of lightweight, thin thickness, broad absorption bandwidth, and multifunction. MXene, as a new type of two-dimensional material, has received widespread attention, but it is necessary to address the impedance mismatch problem caused by its high conductivity. In this work, Fe3O4/MXene composite aerogel is prepared by metal ion-assisted crosslinking method without adding additional crosslinking agents. And a layer of hydrophobic fumed silica is further sprayed on the aerogel. Benefiting from the magneto-electric synergistic effect and the porous structure, SiO2/MXene/Fe3O4 aerogels shows excellent electromagnetic wave absorption performances, achieving a quite broad absorption bandwidth up to 8.8 GHz at an extremely thin thickness of 1 mm. The hybrid aerogel also shows superhydrophobic and thermal insulation properties, which are conducive to improving the resistance to harsh environments and thus endow the absorbers with a long service time.

An all-in-one graphene-based ionic actuator with fast switching response

Graphene, as a typical two-dimensional material is widely recognized for its excellent performance to application in many fields such as smart actuation systems. Here, an all-in-one graphene-based smart actuator has been developed for the first time. The graphene oxide film containing with ionic liquid are reduced on both sides via laser writing method. The smart actuator exhibits a promising actuation ability triggered by a low operation voltage of 0.8 V and delivers a deformation in fast switching response (10 Hz for one cycle) and excellent actuation stability. It means the new integrated graphene-based actuator has the potential for practical applications.

Improvement in hydrogen storage performance of Mg by mechanical grinding with molten salt etching Ti3C2Clx

Mg-based materials are currently a hot research topic as hydrogen storage materials due to their considerable theoretical hydrogen storage capacity. However, the kinetic performance of hydrogen absorption and desorption of Mg is too slow and requires high temperature, which seriously hinders the application of this material. MXene is a new type of two-dimensional material with significant role in improving thermodynamics and kinetics. In this experiment, a two-dimensional layered MXene containing Cl functional group was prepared by molten salt etching using the Ti-containing MAX phase as the raw material. Then different ratios of Ti3C2Clx were uniformly dispersed onto the surface of Mg by high energy ball milling. The samples were characterized by hydrogen absorption and desorption kinetics, SEM, XRD, XPS, and DSC to investigate the effect of Ti3C2Clx on the hydrogen absorption and desorption performance of Mg. The onset hydrogen absorption temperature can be reduced to room temperature and the hydrogen release temperature is reduced by 200 ​°C by doping Ti3C2Clx. And there is also 5.4 ​wt% hydrogen storage in the isothermal hydrogen absorption test at 400 ​°C. The results of DSC demonstrate that the Ea of Mg+15 ​wt% Ti3C2Clx was reduced by 12.6% compared to pristine Mg. The ΔH is almost invariable. The results of XPS show that the presence of multivalent Ti promotes electron transfer and thus improves the conversion between Mg2+/Mg and H−/H. This study provides a guideline for further improving the hydrogen absorption and desorption performance of Mg-based hydrogen storage materials.

Hydroxyl-functionalized ZnO monolayers for optoelectronic devices: Atomic structures and electronic properties

Two-dimensional materials have been extensively investigated both experimentally and theoretically due to their appealing physical/chemical properties. Zinc oxide (ZnO) monolayers, as typical two-dimensional materials, have also aroused wide concern. However, the improper bandgap or nonmagnetic limits their applications in optoelectronic or spintronic devices. Herein, based on first-principles calculations, the effects of individual hydroxyl adsorption and hydroxyl group functionalization on the atomic and electronic structures of ZnO monolayers are investigated. The results demonstrated that the most stable structure for individual hydroxyl on the ZnO monolayer is the one in which the hydroxyl is adsorbed on the top of the hollow site with an adsorption energy of −1.448 eV. Furthermore, hydroxyl could easily aggregate on ZnO monolayer with increasing of hydroxyl coverage and form epoxy groups. Upon hydroxyl group functionalization, ZnO monolayers exhibit mechanical and thermal stability. Moreover, OH–ZnO and ZnO–OH monolayers exhibit magnetic semiconductors, while OH–ZnO–OH monolayers are nonmagnetic semiconductor. Additionally, the band gaps of ZnO monolayer with hydroxyl group functionalization could be effectively modulated via applying the strain. This study opens a new avenue for preparing potential high-performance ZnO-based optoelectronic devices.

Plasmon Damping Rates in Coulomb-Coupled 2D Layers in a Heterostructure.

The Coulomb excitations of charge density oscillation are calculated for a double-layer heterostructure. Specifically, we consider two-dimensional (2D) layers of silicene and graphene on a substrate. From the obtained surface response function, we calculated the plasmon dispersion relations, which demonstrate how the Coulomb interaction renormalizes the plasmon frequencies. Most importantly, we have conducted a thorough investigation of how the decay rates of the plasmons in these heterostructures are affected by the Coulomb coupling between different types of two-dimensional materials whose separations could be varied. A novel effect of nullification of the silicene band gap is noticed when graphene is introduced into the system. To utilize these effects for experimental and industrial purposes, graphical results for the different parameters are presented.

Recent Progress in Double-Layer Honeycomb Structure: A New Type of Two-Dimensional Material.

Two-dimensional (2D) materials are no doubt the most widely studied nanomaterials in the past decade. Most recently, a new type of 2D material named the double-layer honeycomb (DLHC) structure opened a door to achieving a series of 2D materials from traditional semiconductors. However, as a newly developed material, there still lacks a timely understanding of its structure, property, applications, and underlying mechanisms. In this review, we discuss the structural stability and experimental validation of this 2D material, and systematically summarize the properties and applications including the electronic structures, topological properties, optical properties, defect engineering, and heterojunctions. It was concluded that the DLHC can be a universal configuration applying to III-V, II-VI, and I-VII semiconductors. Moreover, these DLHC materials indeed have exotic properties such as being excitonic/topological insulators. The successful fabrication of DLHC materials further demonstrates it is a promising topic. Finally, we summarize several issues to be addressed in the future, including further experimental validation, defect engineering, heterojunction engineering, and strain engineering. We hope this review can help the community to better understand the DLHC materials timely and inspire their applications in the future.

Preparation of Zn5Mo2O11·5H2O@Sulfonated Graphene by Template Method and Its Anticorrosion Mechanism in Polyurethane Coatings

Currently, waterborne coatings are widely used, but their poor anticorrosion performance compared with solvent-based coatings hinders their further application. In this study, a series of Zn5Mo2O11·5H2O@sulfonated graphene (SZMO@SG) composites are prepared using the template method. SZMO@SG is a type of two-dimensional material with a large diameter and low thickness compared to traditional zinc molybdate. Combining SZMO@SG with waterborne hydroxy acrylic latex and isocyanate, the polyurethane coatings with 3 wt% SZMO@SG achieve the best anticorrosion performance in the 3.5 wt% NaCl immersion test. In electrochemical impedance spectroscopy (EIS), the charge transfer resistance (Rct) of polyurethane coatings with 3 wt% SZMO@SG reaches 283,100 Ω·cm2 after soaking in a 3.5 wt% NaCl solution for 48 h. Its corrosion potential and corrosion current are only −0.453 V and 1.71 × 10−3 mA/cm2, respectively. After metal substrate corrosion, the metal substrate of polyurethane coatings with SZMO@SG contain more Mo, Zn and low-state Fe atoms. It confirms that a passivation film was deposited on the metal substrate and prevents Fe from oxidation. The elemental content and distribution of the coatings after the NaCl solution immersion test indicate that SZMO@SG may have the Na+ adsorption function.

MoS2 nanosheets fixed on network carbon derived from apple pomace for fast Na storage kinetics

Molybdenum disulfide (MoS 2 ), as a typical two-dimensional material with high theorical capacity (670 mAh g −1 ), is widely used for electrode material in energy storage systems. However, the inferior electronic conductivity, low stability, and sluggish kinetics make it prone to stack during cycling, resulting in a poor lifespan and rate performance. In this work, a 3D network porous structure MoS 2 /OAPC composite was fabricated by carbonizing biowaste apple pomace (AP) collected from concentrated juice factory, then oxidizing apple pomace carbon (APC), and finally sulfurizing (NH 4 ) 6 Mo 7 O 24 ∙4H 2 O/OAPC preform. The oxidization process ensures rich surface oxygen-containing functional groups on OAPC, which will provide necessary nucleation sites for the growth of MoS 2 , enhance the interfacial bonding strength and effectively avoid the agglomeration of MoS 2 sheets resulting in a stable structure and high conductivity. In addition, the 3D porous connectivity structure provides necessary guarantee for the fast kinetics of sodium transport. Therefore, the MoS 2 /OAPC anode exhibits a high capacity of 601.8 mAh g −1 after 50 cycles at a current density of 0.2 A g −1 . When the current density is as high as 2 A g −1 , a promising rate capacity of 297.2 mAh g −1 can still be maintained. • Porous network MoS 2 /OAPC was synthesized by oxidation and sulfurization of method. • Unique C-O-Mo provides stable bonding between MoS 2 and OAPC during cycling. • The OAPC network skeleton ensures a stable structure and accelerates charge transfer. • The MoS 2 /OAPC electrode exhibited fast sodium storage kinetics.

Nonlinear optical properties and photoexcited carrier dynamics of MnPS3 nanosheets.

Here, we systematically report on the preparation of high-quality few-layered MnPS3 nanosheets (NSs) by chemical vapor transport (CVT) and mechanical stripping method, and its carrier dynamics and third-order nonlinear optical properties were studied. Using the classical technique of open aperture Z-scan, a typical phenomenon of saturable absorption (SA) was observed at 475 nm, which indicates that the material is expected to be used as a saturable absorber in ultrafast lasers. The typical phenomenon of reverse saturation absorption (RSA) is observed at 800 and 1550 nm, which shows its potential in the field of broadband optical limiting. Compared with graphene, BP, MXene, MoS2 and other typical two-dimensional materials, MnPS3 NSs has a higher modulation depth. Using the non-degenerate transient absorption spectroscopy technology at room temperature, a slower cooling process of thermal carrier of MnPS3 was observed. Moreover, the carrier lifetime can be tuned according to the wavelength. This work is of great significance to the improvement of MnPS3 based devices, and lays a foundation for the application of MnPS3 in short-wavelength photovoltaic cell, photoelectric detection and other fields.

Research and Application of Terahertz Response Mechanism of Few-Layer Borophene.

The terahertz stealth and shielding performance of a new type of two-dimensional material, borophene, has been studied theoretically and experimentally. Studies have shown that borophene materials have good terahertz stealth and shielding properties. First-principles calculations show that compared with single-layer borophene, few-layer borophene has good terahertz stealth and shielding performance in the range of 0.1~2.7 THz. In the range of 2~4 layers, the terahertz stealth and shielding performance of few-layer borophene increases with the increase of the number of layers. The finite element simulation calculation results also confirmed this point. Using the few-layer borophene prepared by our research group as a raw material, a PDMS composite was prepared to verify the terahertz stealth and shielding performance of the few-layer borophene. In the ultra-wide frequency range of 0.1~2.7 THz, the electromagnetic shielding effectiveness (EMI SE) of the PDMS material mixed with few-layer borophene can reach 50 dB, and the reflection loss (RL) can reach 35 dB. With the concentration of few-layer borophene increasing, the terahertz stealth and shielding effectiveness of the material is enhanced. In addition, the simultaneous mixing of few-layer borophene and few-layer graphene will make the material exhibit better terahertz stealth and shielding performance compared with mixing separately.

Electrode based on porous MXene nanosheets for high-performance supercapacitor

MXenes, a family of the typical two-dimensional materials, that are considered to be an excellent candidate material for supercapacitors, due to their large surface area, high conductivity and high specific pseudocapacitance. However, when assembled into electrode, MXene nanosheets are easy to aggregate because of the strong Van der Waals force. The assembled dense structure will limit the transport of electrolyte, decrease the active sites and electrochemical performance. In this work, in order to suppress the self-restacking of nanosheets and introduce more electrolyte transport channels, Ti3C2Tx nanosheets are partially oxidized and etched to get porous nanosheets. Film electrode based on porous Ti3C2Tx nanosheets shows higher specific surface area (48.3 m2/g) and improved electrochemical performance, including a high specific capacitance of 385 F/g at 1 A/g and good cycle stability of 92 % after 10,000 CV cycles at 100 mV/s.