Inorganic 2D Research Articles

Synthetic Nanoarchitectonics of Functional Organic-Inorganic 2D Germanane Heterostructures via Click Chemistry.

Succeeding graphene, 2D inorganic materials made of reactive van der Waals layers, like 2D germanane (2D-Ge) derivatives, have attracted great attention because their physicochemical characteristics can be entirely tuned by modulating the nature of the surface substituent. Although very interesting from a scientific point of view, almost all the reported works involving 2D-Ge derivatives are focused on computational studies. Herein, a first prototype of organic-inorganic 2D-Ge heterostructure has been synthesized by covalently anchoring thiol-rich carbon dots (CD-SH) onto 2D allyl germanane (2D-aGe) via a simple and green "one-pot" click chemistry approach. Remarkably, the implanted characteristics of the carbon nanomaterial provide new physicochemical features to the resulting 0D/2D heterostructure, making possible its implementation in yet unexplored optoelectronic tasks-e.g., as a fluorescence resonance energy transfer (FRET) sensing system triggered by supramolecular π-π interactions-that are inaccessible for the pristine 2D-aGe counterpart. Consequently, this work builds a foundation toward the robust achievement of functional organic-inorganic 2D-Ge nanoarchitectonics through covalently assembling thiol-rich carbon nanoallotropes on commercially available 2D-aGe.

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.

Understanding the mechanism of Nb-MXene bioremediation with green microalgae

Rapidly developing nanotechnologies and their integration in daily applications may threaten the natural environment. While green methods of decomposing organic pollutants have reached maturity, remediation of inorganic crystalline contaminants is major problem due to their low biotransformation susceptibility and the lack of understanding of material surface-organism interactions. Herein, we have used model inorganic 2D Nb-based MXenes coupled with a facile shape parameters analysis approach to track the mechanism of bioremediating 2D ceramic nanomaterials with green microalgae Raphidocelis subcapitata. We have found that microalgae decomposed the Nb-based MXenes due to surface-related physicochemical interactions. Initially, single and few-layered MXene nanoflakes attached to microalgae surfaces, which slightly reduced algal growth. But with prolonged surface interaction, the microalgae oxidized MXene nanoflakes and further decomposed them into NbO and Nb2O5. Since these oxides were nontoxic to microalgal cells, they consumed Nb-oxide nanoparticles by an uptake mechanism thus enabling further microalgae recovery after 72 h of water treatment. The uptake-associated nutritional effects were also reflected by cells’ increased size, smoothed shape and changed growth rates. Based on these findings, we conclude that short- and long-term presence of Nb-based MXenes in freshwater ecosystems might cause only negligible environmental effects. Notably, by using 2D nanomaterials as a model system, we show evidence of the possibility of tracking even fine material shape transformations. In general, this study answers an important fundamental question about the surface interaction-associated processes that drive the mechanism of 2D nanomaterials’ bioremediation as well as provides the fundamental basis for further short- and long-term investigations on the environmental effects of inorganic crystalline nanomaterials.

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.

Coordination Chemistry of Anionic Pnictogenylborane Compounds

Novel anionic metallacycles (6: [(1) W(CO)4]; 7: ([(2) W(CO)4])2; 8: [(3) W(CO)4]; 9: [(4) W(CO)4]; and 10: [(5) W(CO)4]) were selectively synthesized from the reaction of the flexible anionic pnictogenylborane derivatives [M(C12H24O6)][H2E-BH2-EH2] [E = P, M = Na (1); E = As, M = K (2)], [Na(C12H24O6)][H2As-BH2-PH2-BH2-AsH2] (3), and [Na(C12H24O6)(thf)2][tBuHE-BH2-EHtBu] [E = P (4); E = As (5)], with [W(CO)4(nbd)] (nbd = bicyclo[2.2.1]hepta-2,5-diene). In addition, the reaction of 1, 4, and 5 with [Cu(MeCN)4][BF4] leads to unique coordination assemblies of the general formula [Cu2Na2(RHE-BH2-EHR)4]n [E = P, R = H (11); E = P, R = tBu (12); E = As, R = tBu (13)]. The solid-state structure of compound 11 possesses an inorganic 3D scaffold with an adamantane-like repeating unit of Cu(I) ions.

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.

Progress and challenges in layered two-dimensional hybrid perovskites

Dimensionality is the game-changer property of a material. The optical and electronic properties of a compound get dramatically influenced by confining dimensions from 3D to 2D. The bulk 3D perovskite materials have shown remarkable up-gradation in the power conversion efficiency, hence grabbing worldwide attention. But instability against moisture, temperature, and ion migration are the factors constantly back-stabbing and hindering from full-scale commercialization. 2D perovskite material has emerged as an excellent bridging entity between structural-chemical stability, and viable commercialization. Organic–inorganic 2D perovskite materials come with a layered structure in which a large organic cation layer as a spacer is sandwiched between two inorganic metal halide octahedra layers. Moreover, hydrophobic spacer cations are employed which isolate inorganic octahedral layers from water molecules. Hydrophobic spacer cations protect the authentic structure from being degraded. These layered structures occur in two phases namely the Ruddlesden–Popper phase and Dion–Jacobson phase, depending on the spacer cation types. Alternating inorganic and organic layers form multiple quantum wells naturally, along with spin–orbit-coupling gives Rashba splitting. 2D perovskite materials are coming up with interesting chemical, physical properties like exciton dynamics, charge carrier transport, and electron–phonon coupling as a result of the quantum confinement effect. Despite appreciable stability, limited charge transport and large bandgap are limiting the application of 2D perovskite materials in solar cells. These limitations can be overcome by using the concept of 2D/3D multidimensional hybrid perovskites, which includes the long-term stability of 2D perovskite and the high performance of 3D perovskite at the same time. Here in this perspective, we have given brief insight on structural versatility, synthesis techniques, some of the unique photophysical properties, potential device fabrication, and recent advancements in the 2D structure to stand against degradation. Certain shortcomings and future outlooks are also discussed to make the perspective more informative.

Improved 3D Printing and Cell Biology Characterization of Inorganic-Filler Containing Alginate-Based Composites for Bone Regeneration: Particle Shape and Effective Surface Area Are the Dominant Factors for Printing Performance

The use of organic–inorganic 3D printed composites with enhanced properties in biomedical applications continues to increase. The present study focuses on the development of 3D printed alginate-based composites incorporating inorganic fillers with different shapes (angular and round), for bone regeneration. Reactive fillers (bioactive glass 13–93 and hydroxyapatite) and non-reactive fillers (inert soda–lime glass) were investigated. Rheological studies and the characterization of various extrusion-based parameters, including material throughput, printability, shape fidelity and filament fusion, were carried out to identify the parameters dominating the printing process. It was shown that the effective surface area of the filler particle has the highest impact on the printing behavior, while the filler reactivity presents a side aspect. Composites with angular particle morphologies showed the same high resolution during the printing process, almost independent from their reactivity, while composites with comparable amounts of round filler particles lacked stackability after printing. Further, it could be shown that a higher effective surface area of the particles can circumvent the need for a higher filler content for obtaining convincing printing results. In addition, it was proven that, by changing the particle shape, the critical filler content for the obtained adequate printability can be altered. Preliminary in vitro biocompatibility investigations were carried out with the bioactive glass containing ink. The 3D printed ink, forming an interconnected porous scaffold, was analyzed regarding its biocompatibility in direct or indirect contact with the pre-osteoblast cell line MC3T3-E1. Both kinds of cell tests showed increased viability and a high rate of proliferation, with complete coverage of the 3D scaffolds’ surface already after 7 d post cell-seeding.

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.

Strain Switching in van der Waals Heterostructures Triggered by a Spin‐Crossover Metal–Organic Framework

AbstractVan der Waals heterostructures (vdWHs) provide the possibility of engineering new materials with emergent functionalities that are not accessible in another way. These heterostructures are formed by assembling layers of different materials used as building blocks. Beyond inorganic 2D crystals, layered molecular materials remain still rather unexplored, with only few examples regarding their isolation as atomically thin layers. Here, the family of van der Waals heterostructures is enlarged by introducing a molecular building block able to produce strain: the so‐called spin‐crossover (SCO). In these metal–organic materials, a spin transition can be induced by applying external stimuli like light, temperature, pressure, or an electric field. In particular, smart vdWHs are prepared in which the electronic and optical properties of the 2D material (graphene and WSe2) are clearly switched by the strain concomitant to the spin transition. These molecular/inorganic vdWHs represent the deterministic incorporation of bistable molecular layers with other 2D crystals of interest in the emergent fields of straintronics and band engineering in low‐dimensional materials.

Review on Organic–Inorganic Two-Dimensional Perovskite-Based Optoelectronic Devices

Organic–inorganic two-dimensional (2D) perovskite is an optoelectronic material, with quantum-well structure and improved moisture stabilities, which has been widely used in various optoelectronic devices recently. In this review, the structure and properties of organic–inorganic 2D perovskite materials are first briefly introduced. After that, according to the different photoelectron coupling mechanisms, the recent progress of typical 2D perovskite-based optoelectronic devices is described in detail: including photodetectors, light-emitting diodes, solar cells, and lasers, as well as some optoelectronic devices (e.g., optical memory and optical synapses). We analyzed the influence of structure, manufacturing process, and material selection on device performance and showed promising progress in different applications. Subsequently, we proposed the possible breakthrough development direction of 2D perovskite-based optoelectronic devices in the coming years. This work points out the way for future progress of 2D perovskite-based optoelectronic devices, which is conducive to further improving device performance and inspiring designs of high-performance organic–inorganic 2D perovskite-based optoelectronic devices.

Laser additive manufacturing of Si/ZrO<sub>2</sub> tunable crystalline phase 3D nanostructures

The current study is directed to the rapidly developing field of inorganic material 3D object production at nano-/micro scale. The fabrication method includes laser lithography of hybrid organic-inorganic materials with subsequent heat treatment leading to a variety of crystalline phases in 3D structures. In this work, it was examined a series of organometallic polymer precursors with different silicon (Si) and zirconium (Zr) molar ratios, ranging from 9:1 to 5:5, prepared via sol-gel method. All mixtures were examined for perspective to be used in 3D laser manufacturing by fabricating nano- and micro-feature sized structures. Their spatial downscaling and surface morphology were evaluated depending on chemical composition and crystallographic phase. The appearance of a crystalline phase was proven using single-crystal X-ray diffraction analysis, which revealed a lower crystallization temperature for microstructures compared to bulk materials. Fabricated 3D objects retained a complex geometry without any distortion after heat treatment up to 1400 °C. Under the proper conditions, a wide variety of crystalline phases as well as zircon (ZrSiO₄ - a highly stable material) can be observed. In addition, the highest new record of achieved resolution below 60 nm has been reached. The proposed preparation protocol can be used to manufacture micro/nano-devices with high precision and resistance to high temperature and aggressive environment.

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.

Dynamic nano-assemblies based on two-dimensional inorganic nanoparticles: Construction and preclinical demonstration.

Dynamic drug delivery systems (DDSs) have the ability of transforming their morphology and functionality in response to the biological microenvironments at the disease site and/or external stimuli, show spatio-temporally controllable drug delivery, and enhance the treatment efficacy. Due to the large surface area and modification flexibility, two-dimensional (2D) inorganic nanomaterials are being increasingly exploited for developing intelligent DDSs for biomedical applications. In this review, we summarize the engineering methodologies used to construct transformable 2D DDSs, including changing compositions, creating defects, and surface dot-coating with polymers, biomolecules, or nanodots. Then we present and discuss dynamic inorganic 2D DDSs whose transformation is driven by the diseased characteristics, such as pH gradient, redox, hypoxia, and enzyme in the tumor microenvironment as well as the external stimuli including light, magnetism, and ultrasound. Finally, the limitations and challenges of current transformable inorganic DDSs for clinical translation and their in vivo safety assessment are discussed.

Interstitial Nature of Mn2+ Doping in 2D Perovskites.

Halide perovskites doped with magnetic impurities (such as the transition metals Mn2+, Co2+, Ni2+) are being explored for a wide range of applications beyond photovoltaics, such as spintronic devices, stable light-emitting diodes, single-photon emitters, and magneto-optical devices. However, despite several recent studies, there is no consensus on whether the doped magnetic ions will predominantly replace the octahedral B-site metal via substitution or reside at interstitial defect sites. Here, by performing correlated nanoscale X-ray microscopy, spatially and temporally resolved photoluminescence measurements, and magnetic force microscopy on the inorganic 2D perovskite Cs2PbI2Cl2, we show that doping Mn2+ into the structure results in a lattice expansion. The observed lattice expansion contrasts with the predicted contraction expected to arise from the B-site metal substitution, thus implying that Mn2+ does not replace the Pb2+ sites. Photoluminescence and electron paramagnetic resonance measurements confirm the presence of Mn2+ in the lattice, while correlated nano-XRD and X-ray fluorescence track the local strain and chemical composition. Density functional theory calculations predict that Mn2+ atoms reside at the interstitial sites between two octahedra in the triangle formed by one Cl- and two I- atoms, which results in a locally expanded structure. These measurements show the fate of the transition metal dopants, the local structure, and optical emission when they are doped at dilute concentrations into a wide band gap semiconductor.

Electro-optic hybrid aligned nematic device utilizing carbon nanotube arrays and two-dimensional hexagonal boron nitride nanosheet as alignment substrates.

Hybrid-aligned nematic (HAN) liquid crystal (LC) devices have both fundamental and technological importance for their applications in LC adaptive lenses, low voltage LC displays, smart windows, and many more. We report the fabrication and characterization of a nanostructure-based HAN device employing vertically aligned carbon nanotube (VA-CNT) arrays as the homeotropic alignment agent on one side and two-dimensional (2D) hexagonal boron nitride (h-BN) as the planar alignment agent on the other side of the LC cell. The LC achieves the HAN configuration in the cell, i.e., homeotropic alignment at the VA-CNT side due to the π-π stacking interaction between the LC and CNTs, and planar alignment at the h-BN side due to the π-π stacking interaction between the LC and h-BN. When an applied electric field is ramped up across this VA-CNT/h-BN HAN cell, the LC (positive anisotropic) obtains a homeotropic state, requiring no threshold voltage to start the reorientation process; this effect is similar to that of a traditional polyimide (PI)-based HAN device. This VA-CNT/h-BN HAN cell successfully demonstrates the optical, electro-optical operations and the electric field-induced dynamic response. This study reveals that two inorganic nanostructured surfaces, VA-CNT arrays and 2D h-BN, can efficiently replace the organic PI alignment agents when needed and retain the HAN device's necessary electro-optical performances. These results substantially expand the fundamental understanding and the scope of utilizing various nanostructured surfaces for LC alignment mechanisms.

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.

Synthesis, characterization and optoelectronic properties of 2D hybrid RPbX4 semiconductors based on an isomer mixture of hexanediamine-based dications

Abstract Three new hybrid two-dimensional (2D) organic–inorganic semiconductors are presented, which contain lead halides and a mixture of hexanediamine-based isomers in the stoichiometry [2,2,4(2,4,4)-trimethyl-1,6-hexanediamine]PbX4 (X = I, Br, Cl). These hexanediamine derivatives, with attached methyl groups at the carbon backbone of both isomers, determine the packing of the organic layers between the inorganic 2D sheets, while the optical absorption and photoluminescence spectra reveal excitonic peaks at T = 77 K and room temperature. The as-synthesized semiconductors were stored for three years in the dark and under low humidity and were examined again and the results were compared to those of the fresh materials. The chloride analogue, after the three year storage, displays white-like luminescence. The use of non-equivalent isomer and racemic mixtures in the organic component to form hybrid organic–inorganic semiconductors is an efficient method to alter the properties of 2D perovskites by tuning the isomers’ chemical functionalities. Finally, a comparison of the observed excitonic absorption and photoluminescence signals to that of analogous 2D compounds is discussed.

Crystal growth and characterisation of organic–inorganic lead-free 2D double perovskite for application in radiation sensing

Crystal growth and characterisation of organic–inorganic lead-free 2D double perovskite for application in radiation sensing

Tailored Lattice "Tape" to Confine Tensile Interface for 11.08%-Efficiency All-Inorganic CsPbBr3 Perovskite Solar Cell with an Ultrahigh Voltage of 1.702V.

The crystal distortion such as lattice strain and defect located at the surfaces and grain boundaries induced by soft perovskite lattice highly determines the charge extraction‐transfer dynamics and recombination to cause an inferior efficiency of perovskite solar cells (PSCs). Herein, the authors propose a strategy to significantly reduce the superficial lattice tensile strain by means of incorporating an inorganic 2D Cl‐terminated Ti3C2 (Ti3C2Cl x ) MXene into the bulk and surface of CsPbBr3 film. Arising from the strong interaction between Cl atoms in Ti3C2Cl x and the under‐coordinated Pb2+ in CsPbBr3 lattice, the expanded perovskite lattice is compressed and confined to act as a lattice “tape”, in which the Pb—Cl bond plays a role of “glue” and the 2D Ti3C2 immobilizes the lattice. Finally, the defective surface is healed and a champion efficiency as high as 11.08% with an ultrahigh open‐circuit voltage up to 1.702 V is achieved on the best all‐inorganic CsPbBr3 PSC, which is so far the highest efficiency record for this kind of PSCs. Furthermore, the unencapsulated device demonstrates nearly unchanged performance under 80% relative humidity over 100 days and 85 °C over 30 days.