2D Inorganic Materials Research Articles

MXenes as Emerging 2D Materials for Anticorrosive Application: Challenges and Opportunities

AbstractMXenes (MXs) (singular; “MXene” (MX); pronounced “Maxenes”) are a relatively new class of 2D inorganic materials that possess numerous potential biological and industrial applications. After the discovery of the first MXene, Ti3C2Tx, in 2011 plenty of reports on the synthesis and application of MXenes and their derivatives are published in the literature. Generally, MXenes contain heteroatoms at their surface; therefore, they can act as strong ligands and can form coordination bonding with the metal atoms and their ions. Because of this property, recently MXenes are used as nanofillers in polymer‐based coatings. The MXenes possess excellent filler properties. They are extensively used as fillers in epoxy resins and polyurethane‐based coatings but their application as fillers in other polymers is highly limited, which opens an area to explore in the future. The anticorrosive application of MXenes‐filled polymers coatings is extensively reported. The contemporary review designates the assemblies of various reports on the anticorrosive and filler property of the MXenes and their composites. Previous studies suggest that MXenes and their composites not only affect the performance of polymer coatings but also enhance their durability. The present report also describes the synthesis, characterization, chemical structures, and properties of the MXenes and their composites.

Insight into the Nanotribological Mechanism of Two-Dimensional Covalent Organic Frameworks.

Two-dimensional (2D) materials are promising in reducing friction-induced energy loss and wear in automotive and electronics industries because of their superior tribological performance. As a kind of organic 2D materials, the structure and functionality of covalent organic frameworks (COFs) are much easier to tailor compared to other inorganic 2D materials, which expand their potential application in a Micro-Electro-Mechanical System (MEMS). In this manuscript, several kinds of COFs are synthesized and characterized on the surface of highly oriented pyrolytic graphite (HOPG) to investigate the nanotribological mechanism of organic 2D materials. It is surprisingly revealed that the friction coefficients of surface COFs are positively correlated with the pore sizes of honeycomb networks. The COFs with smaller pores would have a smoother potential energy surface and exhibit a lower friction coefficient. Besides, the porous structures of surface COFs make them good candidates to be host templates. The host-guest assembly structures are successfully constructed after introducing coronene molecules, and these host-guest systems display higher friction coefficients because the assembly structure of the guest molecules would be perturbed during the friction process and bring additional slip energy barriers, but the capacity of COFs to form composite assembly with functional guest molecules greatly promotes their further application in the MEMS.

Empirical indication for desalinating properties of porous boron nitride

In recent years, inorganic 2D materials have been recognized as promising candidates for membrane filtration. In particular, theoretical studies predict the excellent desalination performance of nanoporous hexagonal boron nitride. However, studies showing the experimental realization of such systems are to this date missing. In this work, we demonstrate the desalinating properties of sp2-bonded boron nitride. Secondary Ion Mass Spectrometry experiments have shown the clear separation of NaCl and water by the boron nitride film: Na and Cl ions have been retained and trapped in the near-surface region, while water permeated through its whole depth. Analysis based on the diffusion equation revealed that the diffusion coefficient of water is over 3 orders of magnitude higher than the diffusion coefficient of NaCl in the temperature range of 25-65°C, manifesting that boron nitride is a material of high potential for use as a selective layer for membrane filtration.

Monitoring substrate-induced electron–phonon coupling at interfaces of 2D organic/inorganic van der Waals heterostructures with in situ Raman spectroscopy

Multifunctional devices based on 2D organic/inorganic van der Waals heterostructures (2D OIHs) exhibit excellent properties due to extensive and flexible structural tunability. However, how to precisely regulate devices via in situ monitoring technique remains a great challenge, and corresponding development is still in its infancy. In this Letter, we show that Raman spectroscopy can serve as an effective in situ detection strategy to systematically observe the interfacial electron–phonon coupling (IEPC) between substrate and 2D OIHs. Combining non-adiabatic molecular dynamics simulations with ultrafast spectroscopy, we reveal that the different strengths of IEPC between substrates and 2D OIHs can directly modulate the photocarrier lifetimes of inorganic 2D materials, and therefore, indirectly modify the Raman-sensitive photo-induced charge transfer processes at the interface of 2D OIHs. Further in situ Raman evidence demonstrates the unique advantage of Raman spectroscopy with high sensitivity to monitor different substrate-induced IEPC under variable temperature.

Smart Synthetic and Surface‐Engineering Approaches to Functionalize 2D Black Phosphorus for Real‐Setting Applications

AbstractPhosphorene or 2D black phosphorus (2D bP) has attracted increasing attention within material scientists in the last decade due to its electronic and photophysical properties as a pristine material. Furthermore, the high chemical reactivity of 2D bP enables the engineering of the outermost superficial layers. This tailored functionalization allows to obtain 2D bP‐based systems such as heterostructures with multiple and/or nonstandard functional properties that can be straightforwardly exploited for real‐setting applications. The aim of this review is to summarize the state of the art on the different strategies in the functionalization of 2D bP such as chemical reactivity with organic molecules, decoration with metal and metal‐oxide nanoparticles, passivation with thin layers of metal oxides or polymers, van der Waals coupling with different inorganic 2D materials, blending into polymeric composites. The main physical and chemical properties of all the considered heterostructures and as‐realized derivatives of 2D bP, with a particular focus on the increase of stability in air, are described. Finally, the functional characteristics of each system which are correlated to and involved in the development of specific real‐setting applications, spanning from catalysis, to electronics and optoelectronics, to energy conversion and storage and biodiagnostics, are highlighted.

Molecularly "clicking" active moieties to germanium-based inorganic 2D materials.

Two dimensional materials beyond graphene are in forefront research. Two dimensional analogues of graphene of group 14, germanene, are of high importance for their electronic and optical properties. The commonly used deintercalation fabrication approach has reached a major bottleneck in the field due to the lack of versatility derived from the limited library of precursors available for 2D-Ge functionalization with terminal groups. Thus, a chemical procedure that would allow for the on-demand synthesis of functional 2D-Ge derivatives with tuned physicochemical features for task-specific applications is of utmost importance to advance in the field. To fill this gap, click chemistry is herein presented as a straightforward "one-pot" synthetic strategy to simply reach functional 2D-Ge derivatives by covalently assembling ad hoc thiol-rich active molecular components (R'-SH) upon commercially available allyl 2D-Ge (2D-Ge-CH2CHCH2) by taking advantage of a photoinduced thiol-ene click reaction. Consequently, the combination of molecular engineering and Ge-based 2D materials through click chemistry supposes a step forward towards the achievement of a new family of smart 2D-Ge-CH2CH2CH2S-R' derivatives with different (supra)molecular responsiveness, which goes beyond the state-of-the-art in the field. This approach of functionalization of 2D monoelemental post-graphene material germanene is highly innovative and shall provide universal way of functionalization of germananes.

Two-Dimensional Metal-Organic Framework on Superconducting NbSe2.

The combination of two-dimensional (2D) materials into vertical heterostructures has emerged as a promising path to designer quantum materials with exotic properties. Here, we extend this concept from inorganic 2D materials to 2D metal–organic frameworks (MOFs) that offer additional flexibility in realizing designer heterostructures. We successfully fabricate a monolayer 2D Cu-dicyanoanthracene MOF on a 2D van der Waals NbSe2 superconducting substrate. The structural and electronic properties of two different phases of the 2D MOF are characterized by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS), complemented by density-functional theory (DFT) calculations. These experiments allow us to follow the formation of the kagome band structure from Star of David-shaped building blocks. This work extends the synthesis and electronic tunability of 2D MOFs beyond the electronically less relevant metal and semiconducting surfaces to superconducting substrates, which are needed for the development of emerging quantum materials such as topological superconductors.

Memristor Based on Inorganic and Organic Two-Dimensional Materials: Mechanisms, Performance, and Synaptic Applications.

A memristor is a two-terminal device with nonvolatile resistive switching (RS) behaviors. Recently, memristors have been highly desirable for both fundamental research and technological applications because of their great potential in the development of high-density memory technology and neuromorphic computing. Benefiting from the unique two-dimensional (2D) layered structure and outstanding properties, 2D materials have proven to be good candidates for use in gate-tunable, highly reliable, heterojunction-compatible, and low-power memristive devices. More intriguing, stable and reliable nonvolatile RS behaviors can be achieved in multi- and even monolayer 2D materials, which seems unlikely to be achieved in traditional oxides with thicknesses less than a few nanometers because of the leakage currents. Moreover, such two-terminal devices show a series of synaptic functionalities, suggesting applications in simulating a biological synapse in the neural network. In this review article, we summarize the recent progress in memristors based on inorganic and organic 2D materials, from the material synthesis, device structure and fabrication, and physical mechanism to some versatile memristors based on diverse 2D materials with good RS properties and memristor-based synaptic applications. The development prospects and challenges at the current stage are then highlighted, which is expected to inspire further advancements and new insights into the fields of information storage and neuromorphic computing.

Piezotronics in two‐dimensional materials

AbstractThe fascinating two‐dimensional (2D) materials are being potentially applied in various fields from science to engineering benefitting from the charming physical and chemical properties on optics, electronics, and magnetism, compared with the bulk crystal, while piezotronics is a universal and pervasive phenomenon in the materials with broking center symmetry, promoting the new field and notable achievements of piezotronics in 2D materials with higher accuracy and sensitivity. For example, 20 parts per billion of the detecting limitations in NO2 sensor, 500 μm of spatial strain resolution in flexible devices, and 0.363 eV output voltage in nanogenerators. In this review, three categories of 2D piezotronics materials are first introduced ranging from organic to inorganic data, among which six types of 2D inorganic materials are emphasized based on the geometrical arrangement of different atoms. Then, the microscopic mechanism of carrier transport and separation in 2D piezotronic materials is highlighted, accompanied with the presentation of four measured methods. Subsequently, the developed applications of 2D piezotronics are discussed comprehensively including different kinds of sensors, piezo‐catalysis, nanogenerators and information storage. Ultimately, we suggest the challenges and provide the ideas for qualitative–quantitative research of microscopic mechanism and large‐scale integrated applications of 2D piezotronics.image

(Invited) Hybrid Van Der Waals Heterostructures: From Fundamentals to Applications

2D materials are held together by weak interplanar van der Waals (vdW) interactions. The incorporation of molecules in such materials holds an immense potential to understand and modify the fundamental physical properties of the pristine materials while creatin new artificial materials. Whilst nature offers a finite number of 2D materials, an almost unlimited variety of molecules can be designed and synthesized with predictable functionalities. The possibilities offered by systems in which continuous molecular layers are interfaced with inorganic 2D materials to form hybrid organic/inorganic van der Waals heterostructures (H-vdWH) are emphasized. Similar to their inorganic counterpart, the hybrid structures have been exploited to suggest novel device architectures. Moreover, specific molecular groups can be employed to modify intrinsic properties and confer new capabilities to 2D materials. In particular, I will highlight how molecular self-assembly at the surface of 2D materials can be mastered to achieve precise control over position and density of (molecular) functional groups, paving the way for a new class of hybrid functional materials.In particular, within such vdW heterostructures, currently assembled by mechanical superposition of different layers, periodic potentials naturally occur at the interface between the 2D materials. These potentials significantly modify the electronic structure of the individual 2D components within the stack and their alignment, thus offering the possibility to build up hybrid and novel materials with unique properties.Also, I will show how the presence of ordered supramolecular assemblies bearing different functional groups can modify the pristine Shubnikov-De Haas oscillations occurring in graphene.Finally, an example will be given of how a carefully designed H-vdWH could be used for sensing of different biomarkers.

Two-Dimensional Guanidine-Based Hybrid Perovskites with Strong Dichroism for Multiwavelength Polarization-Sensitive Detection.

Two-dimensional (2D) organic-inorganic hybrid perovskites, benefiting from their natural anisotropy of quantum-well motifs and optical properties, have shown remarkable polarization-dependent responses superior to the 3D counterparts. Here, for the first time, multiwavelength polarization-sensitive detectors were fabricated by using single crystals of a guanidine-based 2D hybrid perovskite, (BA)2 (GA)Pb2 I7 (where BA+ is n-butylammonium and GA+ is guanidium). Its unique 2D quantum-well structure results in strong crystallographic-dependence of optical absorption. Strikingly, our crystal-based photodetector exhibits a prominent photocurrent dichroic ratio (Imax /Imin ) of ∼2.2 at 520 nm, higher than the typical 2D inorganic materials (GeSe, ∼1.09, PdSe2 , ∼1.8). In addition, notable dichroic ratios of 1.29 and 1.23 at 405 nm and 637 nm are also created for the multiwavelength polarized-light detection. The prominent detecting performances, including low dark current (1.6×10-11 A), considerable on/off ratio (∼2×103 ), high photodetectivity (∼3.3×1011 Jones) and responsivity (∼12.01 mA W-1 ), make (BA)2 (GA)Pb2 I7 a promising candidate for polarized-light detection. This work sheds light on the rational engineering of new 2D hybrid perovskites for the high-performance optoelectronic device applications.

Стрейнтроника двумерных неорганических материалов для электронных и оптических приложений

Стрейнтроника двумерных неорганических материалов для электронных и оптических приложений

Стрейнтроника двумерных неорганических материалов для электронных и оптических приложений

Стрейнтроника двумерных неорганических материалов для электронных и оптических приложений

Volatile Organic Compound Sensors Based on 2D Materials

AbstractDue to their unique chemical and physical properties, 2D inorganic materials (2DMs) have attracted a lot of attention in recent years as an attractive platform for diverse applications in opto‐electronics, energy generation and storage, and sensing. This article presents the progress being made in sensors designed for measuring volatile organic compounds (VOCs) in ambient air. It considers commercially available sensors, such as the amperometric and conductometric types, and the recent advancements in VOCs sensors employing 2DMs and their nanocomposites. Their performance is summarized in a graphical form and the challenges and possible mitigation methods for these types of VOC sensor are highlighted.

Higher Ultrasonic Frequency Liquid Phase Exfoliation Leads to Larger and Monolayer to Few-Layer Flakes of 2D Layered Materials.

Among the most reliable techniques for exfoliation of two-dimensional (2D) layered materials, sonication-assisted liquid-phase exfoliation (LPE) is considered as a cost-effective and straightforward method for preparing graphene and its 2D inorganic counterparts at reasonable sizes and acceptable levels of defects. Although there were rapid advances in this field, the effect and outcome of the sonication frequency are poorly understood and often ignored, resulting in a low exfoliation efficiency. Here, we demonstrate that simple mild bath sonication at a higher frequency and low power positively contributes to the thickness, size, and quality of the final exfoliated products. We show that monolayer graphene flakes can be directly exfoliated from graphite using ethanol as a solvent by increasing the frequency of the bath sonication from 37 to 80 kHz. The statistical analysis shows that ∼77% of the measured graphene flakes have a thickness below three layers with an average lateral size of 13 μm. We demonstrate that this approach works for digenite (Cu9S5) and silver sulfide (Ag2S), thus indicating that this exfoliation technique can be applied to other inorganic 2D materials to obtain high-quality few-layered flakes. This simple and effective method facilitates the formation of monolayer/few layers of graphene and transition metal chalcogenides for a wide range of applications.

A novel method to fabricate two-dimensional nanomaterial based on electrospinning

Two-dimensional (2D) nanomaterials have been widely used as advanced functional materials due to their special nanostructures and various functionalities. Researchers working on 2D nanomaterials are facing several problems, the difficulties in synthesis, scarcity of species, largely unclear formation mechanism and non-universal preparation method. Herein, this paper reports a new method based on electrospinning to fabricate 2D inorganic materials (titanium dioxide) with thickness around 20 nm and width/thickness ratio of >50. These 2D nanobelts TiO2 could enhance the dielectric performance of PVDF based composites much more significantly, and the energy density of 12.45 J/cm3 could be easily achieved with a small volume fraction (3 vol%) of the nanobelts. Such method has many advantages such as safe production, low production cost, and continuous production. More importantly, this approach is potential to become a universal method to fabricate a range of 2D inorganic nanomaterials in the future due to its universality.

Interface engineering and integration of two-dimensional polymeric and inorganic materials for advanced hybrid structures

Recent progress and future directions in the creation of hybrid structures based on 2D polymers and inorganic 2D materials are discussed.

Mechanics of free-standing inorganic and molecular 2D materials.

The discovery of graphene has triggered a great interest in inorganic as well as molecular two-dimensional (2D) materials. In this review, we summarize recent progress in the mechanical characterization of free-standing 2D materials, such as graphene, hexagonal boron nitride (hBN), transition metal-dichalcogenides, MXenes, black phosphor, carbon nanomembranes (CNMs), 2D polymers, 2D metal organic frameworks (MOFs) and covalent organic frameworks (COFs). Elastic, fracture, bending and interfacial properties of these materials have been determined using a variety of experimental techniques including atomic force microscopy based nanoindentation, in situ tensile/fracture testing, bulge testing, Raman spectroscopy, Brillouin light scattering and buckling-based metrology. Additionally, we address recent advances of 2D materials in a variety of mechanical applications, including resonators, microphones and nanoelectromechanical sensors. With the emphasis on progress and challenges in the mechanical characterization of inorganic and molecular 2D materials, we expect a continuous growth of interest and more systematic experimental work on the mechanics of such ultrathin nanomaterials.

A promising nanoporous Al[formula omitted]Ga[formula omitted]N nanosheet based on octagraphene

A new class of 2D inorganic materials named octa-AlxGa(1-x)N (x=0,0.25,0.5,0.75and1) with the octa-graphene architecture is theoretically investigated by Density Functional Theory simulations. It was found that the energy band gap increased with the introduction of Al atoms. The calculated Young modulus is within the range (46.02 N/m ⩽Y2D⩽53.66 N/m) and Poisson’s ratio within (0.733⩽ν⩽0.783), while frequency calculations reveal that these structures are dynamically stable. Energetic barriers for Li, Na and K diffusion were also studied and were found values lower than those calculated for octa-graphene in a previous work.

Precisely Controlled Two-Dimensional Rhombic Copolymer Micelles for Sensitive Flexible Tunneling Devices

Nanoscale two-dimensional (2D) organic materials have attracted significant interest on account of their unique properties, which result from their ultrathin and flat morphology. Supramolecular 2D ...