Ultrathin 2D Research Articles

The lithiation mechanism of ultrathin 2D ZnO systems working as anode materials for lithium-ion batteries: From Wurtzite to graphene-like structures

Several ZnO nanostructures such as nanosheets, nanotubes and quantum dots with Wurtzite structure have been prepared and studied as lithium-ion anode materials revealing that the increasing interface is a key aspect to improve their performance. To the best of our knowledge, up to now, there are no reports in the literature that deal directly with lithium-ion transport and charge transfer on ultrathin 2D ZnO exhibiting graphene-like and Wurtzite structures working as anode materials for lithium-ion batteries. Here, we present a DFT study on the lithiation of ultrathin 2D ZnO nanostructures including graphene-like (monolayer and bilayer) and Wurtzite (trilayer) structures. We focus on the ionic-electronic transport properties addressing the ionic transport through the different surfaces as well as charge transfer, equilibrium voltages, and work function variations due to lithiation for all systems. We reveal interesting features regarding how deep the reduction of Zn ions is still observed allowing more efficient charge transfer for graphene-like and Wurtzite systems working as anode material for a lithium-ion battery.

Exfoliation of a Coordination Polymer Based on a Linear π-Conjugated Ligand into an Ultrathin Nanosheet for Glyphosate Sensing.

Owing to the large-scale consumption of pesticides and their potential threats to the environment and human health, the development of sensing materials for pesticides has attracted considerable attention in recent years. In this work, a novel Cd(II)-based coordination polymer (CP) with the formula [Cd(H2O)2(L)]·DMF (Cd-1, DMF = N,N-dimethylformamide, H2L = 4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-benzoic acid) was synthesized under solvothermal conditions. Structural analysis revealed that coordination between central Cd2+ cations and the ligand L2- formed two-dimensional (2D) networks, which were further assembled by noncovalent hydrogen bonds into a three-dimensional (3D) supramolecular framework. Through ultrasonic treatment in isopropyl alcohol, Cd-1 was exfoliated to afford an ultrathin CP-based 2D nanosheet (Cd-1-NS) with a thickness of less than 1.8 nm. Compared to the bulk materials, the prepared Cd-1-NS exhibited enhanced fluorescence emission properties and superior sensing performance toward glyphosate (Glyph) in water with high selectivity, sensitivity, anti-interference, fast response, and good recyclability via the turn-off effect. The limit of detection (LOD) of Cd-1-NS for Glyph was as low as 41 nM (7 ppb) in the low-concentration range of 0-2.4 μM. In addition, the Cd-1-NS also showed excellent practicability and reliability for the detection of Glyph in real samples, including lake water, tap water, cabbage, and watermelon skin, and could realize the rapid visualized sensing of Glyph residues on the surfaces of vegetables and fruits.

Large anomalous transverse transport properties in atomically thin 2D Fe3GaTe2

Anomalous transverse conductivities, such as anomalous Hall conductivity (AHC), anomalous Nernst conductivity (ANC), and anomalous thermal Hall conductivity (ATHC), play a crucial role in the emerging field of spintronics. Motivated by the recent fabrication of two-dimensional (2D) ferromagnetic thin film Fe3GaTe2, we investigate the thickness-dependent anomalous transverse conductivities of the 2D Fe3GaTe2 system (from one to four layers). The atomically ultrathin 2D Fe3GaTe2 system shows above-room-temperature ferromagnetism with a large perpendicular magnetic anisotropy energy. Furthermore, we obtain a large AHC of −485 S/cm in the four-layer thickness, and this is further enhanced to −550 S/cm with small electron doping. This AHC is seven times larger than the measured AHC in thicker 2D Fe3GaTe2 (178 nm). The ANC also reaches 0.55 A/K.m in the four-layer structure. Along with these, the four-layer system exhibits a large ATHC (−0.105 ~ −0.135 W/K.m). This ATHC is comparable to the large ATHC found in Weyl semimetal Co3Sn2S2. Based on our results, the atomically ultrathin 2D Fe3GaTe2 system shows outstanding anomalous transverse conductivities and can be utilized as a potential platform for future spintronics and spin caloritronic device applications.

Nonconventional Strain Engineering for Uniform Biaxial Tensile Strain in MoS2 Thin Film Transistors.

Strain engineering has been employed as a crucial technique to enhance the electrical properties of semiconductors, especially in Si transistor technologies. Recent theoretical investigations have suggested that strain engineering can also markedly enhance the carrier mobility of two-dimensional (2D) transition-metal dichalcogenides (TMDs). The conventional methods used in strain engineering for Si and other bulk semiconductors are difficult to adapt to ultrathin 2D TMDs. Here, we report a strain engineering approach to apply the biaxial tensile strain to MoS2. Metal-organic chemical vapour deposition (MOCVD)-grown large-area MoS2 films were transferred onto SiO2/Si substrate, followed by the selective removal of the underneath Si. The release of compressive residual stress in the oxide layer induces strain in MoS2 on top of the SiO2 layer. The amount of strain can be precisely controlled by the thickness of oxide stressors. After the transistors were fabricated with strained MoS2 films, the array of strained transistors was transferred onto plastic substrates. This process ensured that the MoS2 channels maintained a consistent tensile strain value across a large area.

Tunable electronic and optical properties of h-BP/MoS2 van der Waals heterostructures toward optoelectronic applications

The integration of two-dimensional materials (2D) into van der Waals heterostructures (vdWHs) is widely recognized as an effective strategy for the development of multifunctional devices. This study aims to construct stable ultrathin 2D vdWHs using h-BP and MoS2 monolayers, and analyze the impact of strain on the electronic properties of h-BP/MoS2 vdWHs, with a specific focus on the mechanism of biaxial strain regulation. The h-BP/MoS2 vdWHs demonstrate the type II band alignment and possess direct bandgap, which can be effectively controlled through appropriate application of biaxial strain. The power conversion efficiency (PCE) can reach 21.85 % achieved suggests that the material under consideration has potential as a suitable candidate for 2D excitonic solar cells. The observed decrease in effective mass for both electrons and holes implies an enhanced carrier mobility, thereby facilitating the utilization of h-BP/MoS2 vdWHs in the development of high-efficiency excitonic solar cells. These findings indicate that the h-BP/MoS2 vdWHs possess the capability to serve as a reconfigurable system in the construction of highly efficient solar cells.

Controlled Growth of Submillimeter-Scale Cr5Te8 Nanosheets and the Domain Wall Nucleation Governed Magnetization Reversal Process.

Two-dimensional (2D) ferromagnets have attracted widespread attention for promising applications in compact spintronic devices. However, the controlled synthesis of high-quality, large-sized, and ultrathin 2D magnets via facile, economical method remains challenging. Herein, we develop a hydrogen-tailored chemical vapor deposition approach to fabricating 2D Cr5Te8 ferromagnetic nanosheets. Interestingly, the time period of introducing hydrogen was found to be crucial for controlling the lateral size, and a Cr5Te8 single-crystalline nanosheet of lateral size up to ∼360 μm with single-unit-cell thickness has been obtained. These samples exhibit a leading role of domain wall nucleation in governing the magnetization reversal process, providing important references for optimizing the performances of associated devices. The nanosheets also show notable magnetotransport response, including nonmonotonous magnetic-field-dependent magnetoresistance and sizable anomalous Hall resistivity, demonstrating Cr5Te8 as a promising material for constructing high-performance magnetoelectronic devices. This study presents a breakthrough of large-sized CVD-grown 2D magnetic materials, which is indispensable for constructing 2D spintronic devices.

In-situ Ni-doped V-MOF ultra-thin nanosheet arrays on Ni foam for high-performance hybrid supercapacitors

Bimetallic organic frameworks possess distinctive structural and component benefits that make them essential materials for energy storage devices with outstanding capabilities. Here, ultra-thin 2D VNi-MOF nanosheet arrays (NSAs) have been in-situ grown on nickel foam (NF) which served as both the current collector and the Ni source by pretreatment and one-step solvothermal method and used as an efficient electrode material for high performance supercapacitors. Benefiting from its ultra-thin 2D NSAs structure and the synergy of bimetallic ions, the VNi-MOF NSAs/NF exhibits a high specific capacity performance (516.5 C g−1 at 1 A g−1) and outstanding cycling stability (85.6 % capacity retention over 12, 000 cycles at 20 A g−1). Battery-type VNi-MOF NSAs/NF and capacitive-type AC are integrated to assemble a HSC. The prototype HSC achieves a remarkably high energy density of 43 Wh kg−1 (at 800 W kg−1), which demonstrates the great potential of VNi-MOF (bimetallic organic framework) as a HSC electrode.

Engineering of Ultra-Thin Layer of MIL-125(Ti) Nanosheet\Zn-Tetracarboxy-Phthalocyanine S-Scheme Heterojunction as Photocatalytic CO2 Reduction Catalyst.

Metal-organic frameworks (MOFs) with ultrathin 2D structure have attracted remarkable attention in photocatalytic application owing to the accessibility of abundant active sites on the surface. But high charge recombination results in poor photocatalytic activity. Herein, the synthesis of ultrathin MIL-125(Ti) nanosheets is reported with a thickness of 1.3nm through a simple chemical reaction route of precursor solution aging and subsequent solvothermal process for photocatalytic CO2 production. The maximal CO evolution rate achieves 200.8µmol g-1 h-1, which is prominently higher than that (78.6µmol g-1 h-1) of the bulk MIL-125(Ti) counterpart. Furthermore, the structurally stable Zn (II) tetracarboxy phthalocyanine (ZnTcPc) molecules assembly on ultrathin MIL-125(Ti) nanosheet (NS) to form MIL-125(Ti) NS\ZnTcPc S-scheme heterojunction through the strong interaction between the Ti3+ in MIL-125(Ti) and the COOH in ZnTcPc. The introduction of ZnTcPc greatly extends light absorption range and increases charge separation rate. The experimental and density functional theory calculation results validate that the MIL-125(Ti) NS\ZnTcPc S-scheme heterojunction can favor CO2 adsorption and effectively depress the formation energy of the intermediates, achieving a high CO evolution rate of 450.8µmol g-1 h-1. This work provides a strategy of engineering 2D MOF-based heterostructure systems for photocatalytic application.

Biotene: Earth-Abundant 2D Material as Sustainable Anode for Li/Na-Ion Battery.

Natural ores are abundant, cost-effective, and environmentally friendly. Ultrathin (2D) layers of a naturally abundant van der Waals mineral, Biotite, have been prepared in bulk via exfoliation. We report here that this 2D Biotene material has shown extraordinary Li-Na-ion battery anode properties with ultralong cycling stability. Biotene shows 302 and 141 mAh g-1 first cycle-specific charge capacity for Li- and Na-ion battery applications with ∼90% initial Coulombic efficiency. The electrode exhibits significantly extended cycling stability with ∼75% capacity retention after 4000 cycles even at higher current densities (500-2000 mA g-1). Further, density functional theory studies show the possible Li intercalation mechanism between the 2D Biotene layers. Our work brings new directions toward designing the next generation of metal-ion battery anodes.

Integrating Photoactive Ligands into Crystalline Ultrathin 2D Metal-Organic Framework Nanosheets for Efficient Photoinduced Energy Transfer.

3D metal-organic frameworks (MOFs) have gained attention as heterogeneous photocatalysts due to their porosity and unique host-guest interactions. Despite their potential, MOFs face challenges, such as inefficient mass transport and limited light penetration in photoinduced energy transfer processes. Recent advancements in organic photocatalysis have uncovered a variety of photoactive cores, while their heterogenization remains an underexplored area with great potential to build MOFs. This gap is bridged by incorporating photoactive cores into 2D MOF nanosheets, a process that merges the realms of small-molecule photochemistry and MOF chemistry. This approach results in recyclable heterogeneous photocatalysts that exhibit an improved mass transfer efficiency. This research demonstrates a bottom-up synthetic method for embedding photoactive cores into 2D MOF nanosheets, successfully producing variants such as PCN-641-NS, PCN-643-NS, and PCN-644-NS. The synthetic conditions were systematically studied to optimize the crystallinity and morphology of these 2D MOF nanosheets. Enhanced host-guest interactions in these 2D structures were confirmed through various techniques, particularly solid-state NMR studies. Additionally, the efficiency of photoinduced energy transfer in these nanosheets was evidenced through photoborylation reactions and the generation of reactive oxygen species (ROS).

Ultrathin Cu2MoS4/g-C3N4 nanosheets for promoting charge separation with strong redox ability and enhanced photocatalytic hydrogen production activity

Hydrogen energy stands out as one of the most auspicious clean energy prospects, with photocatalytic water splitting emerging as the preeminent method for the efficient production of hydrogen. Combining carbon nitride (g-C3N4) with an oxidized cocatalyst Cu2MoS4 significantly enhances the process for separation of photoinduced holes and photoinduced electrons. In this study, 2D–2D Cu2MoS4/g-C3N4 heterostructure materials using the oil bath method was successfully achieved. The hydrogen production rate of ultrathin 2D–2D Cu2MoS4/g-C3N4 nanosheets is increased by 66 times, reaching 2385 μmol·h−1·g−1. Additionally, insights have been provided through density functional theory (DFT) calculations, showing that the S-type heterojunction formation is a critical factor, which made it possible for photogenerated electrons in g-C3N4 and photogenerated holes in Cu2MoS4 with excellent redox ability to be efficiently separated spatially. This article underscores the significance of interface engineering strategies to control the disjunction of photoinduced holes and electrons.

The electrocatalytic self-reconstruction of ultrathin 2D MOF nanoarrays supported on alloy foam improves the oxygen evolution reaction

Investigating the self-reconstruction process of MOF-supported electrodes is of significant importance for understanding the reaction mechanisms in electrocatalytic oxygen evolution reaction (OER). By using 1,1′-ferrocenedicarboxylic acid (FcDA) as the ligand and NiFe foam (NFF) as the current collector, a self-supported T50NiFc-MOF/NFF electrode was synthesized through the introduction of triethylamine (TEA) to regulate the deprotonation process. The optimized T50NiFc-MOF/NFF exhibited excellent electrocatalytic OER performance, requiring only 217 mV to drive a current density of 10 mA cm−2, surpassing commercial RuO2. Additionally, the T50NiFc-MOF/NFF showed a remarkable electrocatalytic stability of over 70 h. The unique 2D MOF nanoarrays and strong coordination bonds between the metal and ligand in the as-prepared self-supported electrode contribute to the enrichment of electrochemical active sites and catalytic stability. Through a self-construction process, the 2D MOF nanoarrays on the electrode surface were in-situ converted into a more active metal-LDH during alkaline electrocatalysis, which played a crucial role in improving the electronic structure of the electrode, demonstrating its importance in achieving efficient OER processes.

Wafer-scale synthesis of two-dimensional ultrathin films.

Two-dimensional (2D) materials, consisting of atomically thin layered crystals, have attracted tremendous interest due to their outstanding intrinsic properties and diverse applications in electronics, optoelectronics, and catalysis. The large-scale growth of high-quality ultrathin 2D films and their utilization in the facile fabrication of devices, easily adoptable in industrial applications, have been extensively sought after during the last decade; however, it remains a challenge to achieve these goals. Herein, we introduce three key concepts: (i) the microwave assisted quick (∼1 min) synthesis of wafer-scale (6-inch) anisotropic conducting ultrathin (∼1 nm) amorphous carbon and 2D semiconducting metal chalcogenide atomically thin films, (ii) a polymer-assisted deposition process for the synthesis of wafer-scale (6-inch) 2D metal chalcogenide and pyrolyzed carbon thin films, and (iii) the surface diffusion and epitaxial self-planarization induced synthesis of wafer-scale (2-inch) single crystal 2D binary and large-grain 2D ferromagnetic ternary metal chalcogenide thin films. The proposed synthesis concepts can pave a new way for the manufacture of wafer-scale high quality 2D ultrathin films and their utilization in the facile fabrication of devices.

Crystallinity regulation induced organics degradation on Ultra-thin 2D Co3O4/SiO2 Nanosheets: the critical trigger of oxygen vacancy

As an antibiotic drug, sulfamethoxazole (SMX) is a nitrogen-containing and sulfur-containing heterocyclic compound, which is an endocrine disruptor and difficult to be biodegraded. Not only can it exist stably in...

In situ conversion of Co–CoN nanowires into ultrathin 2D nanosheets for highly effective catalytic hydrogenation

Ultrathin 2D Co–CoN heterojunction nanosheets were prepared by a novel route based on in situ conversion of Co–CoN nanowires. The nanosheets exhibit excellent catalytic activity and stability towards aromatic nitro compounds.

Mild chemistry synthesis of ultrathin Bi2O2S nanosheets exhibiting 2D-ferroelectricity at room temperature.

Modern technology demands miniaturization of electronic components to build small, light, and portable devices. Hence, discovery and synthesis of new non-toxic, low cost, ultra-thin ferroelectric materials having potential applications in various electronic and optoelectronic devices are of paramount importance. However, achieving room-temperature ferroelectricity in two dimensional (2D) ultra-thin systems remains a major challenge as conventional three-dimensional ferroelectric materials lose their ferroelectricity when the thickness is brought down below a critical value owing to the depolarization field. Herein, we report room-temperature ferroelectricity in ultra-thin single-crystalline 2D nanosheets of Bi2O2S synthesized by a simple, rapid, and scalable solution-based soft chemistry method. The ferroelectric ground state of Bi2O2S nanosheets is confirmed by temperature-dependent dielectric measurements as well as piezoelectric force microscopy and spectroscopy. High resolution transmission electron microscopy analysis and density functional theory-based calculations suggest that the ferroelectricity in Bi2O2S nanosheets arises due to the local distortion of Bi2O2 layers, which destroys the local inversion symmetry of Bi2O2S.

Pyridine-induced caused structural reconfiguration forming ultrathin 2D metal–organic frameworks for the oxygen evolution reaction

2D Co MOF-Py3 is synthesized by a bottom-up structural reconfiguration strategy by using pyridine for the oxygen evolution reaction.

Ultrathin MOF nanosheets and their mixed-matrix membranes for ammonia and aliphatic amine sensing in water.

Ultrathin 2D metal-organic frameworks (MOFs) exhibit a myriad of unparalleled properties, rendering them extensively applicable across various fields. Despite this, developing a 2D MOF sensor for detecting hazardous amines in water remains a formidable challenge. To address this issue, we synthesized Ni-btc MOF ultrathin nanosheets with a thickness of approximately 4.15 nm for the detection of amines in water. These nanosheets demonstrated a notable "turn-on" fluorescence response in the presence of ammonia and aliphatic amines. The detection limit for aliphatic amines ranged from 297 to 424 nM, while for ammonia, it reached an impressive low limit of around 42 nM, which is an excellent value compared to other reported MOFs for ammonia sensing in water. Density functional theory calculations elucidated the mechanism underlying fluorescence enhancement. Additionally, a mixed matrix membrane based on MOF nanosheets was fabricated for real-time sensing that exhibits an immediate color change in the presence of ammonia and aliphatic amines.

Two-dimensional layered MOF nanosheets with multiple binding sites for selective detection and removal of Fe(III) ions

Heavy metal contamination has become an urgent global concern, posing a significant threat to our environment and health. Hence, it is critical to exploit functional materials for heavy metal ions sensing and elimination. However, the development of multifunctional materials that can simultaneously accomplish the selective detection and removal of the metal ions remains a significant challenge. In this work, a two-dimensional (2D) layered metal–organic framework (LMOF) functionalized with diverse binding sites has been utilized to concurrently detect and remove Fe3+ ions. The LMOF [Zn(hsb-2) (5-aipa)](HSB-W15) was rationally designed and constructed from the mixed ligands of hsb-2 (1,2-bis(4′-pyridylmethylamino)-ethane) and 5-aipa (5-aminoisophthate) under mild condition. In addition, the corresponding ultrathin nanosheets HSB-W15-NS were also obtained by adapting the instant in situ exfoliation (IISEM) method. Owing to the ultrathin nanosheet morphology and an abundance of active sites on the surface, HSB-W15-NS nanosheets can function as an effective fluorescent sensor to detect Fe3+ and Cr3+ ions. Exceptionally, HSB-W15-NS can also be used to selectively capture Fe3+ ions from water, with up to 93 % removal efficiency, and the adsorption equilibrium attained in 5 min. The sensing and adsorption processes were investigated based on kinetic model analysis, Fourier transform infrared spectroscopy, Raman spectrum analysis, density functional theory calculations, and control experiments. This work inspired the development of ultrathin 2D MOF nanosheets for applications in environmental protection.

Ultrathin 2D IZO film transistors printed via liquid InZn alloys: insights into the oxidation behavior and enhanced mobility properties

Atomically ultra-thin Zn-doped In2O3 films with high transparency and superior electronic properties were obtained by a liquid In–Zn printing approach.