Stable Nanosheets Research Articles

Evolution of Supramolecular Coordination Assemblies Visually Monitored by Time‐Dependent Multicolor Fluorescence

Supramolecular coordination assemblies play an important role in both material science and biological systems. Despite significant efforts in their development, most existing examples are thermodynamically controlled, which lack the adaptability and autonomy essential for the creation of advanced materials. In this work, we have developed non‐equilibrium coordination assembly systems that can evolve over time through a combination of thermodynamic and kinetic controls. The introduction of zinc ions resulted in the formation of metastable fiber assemblies in a kinetically trapped state, which autonomously converted to thermodynamically stable nanosheets over time. This evolution process can be regulated by external stimuli and visually monitored by the time‐dependent multicolor fluorescence. The construction strategy was versatile across other various ions such as Ca2+, Mg2+, and Al3+, offering inspiring insights for the design of complex systems that operated both in and out of their thermodynamic equilibrium

Nanostructured Fe-Doped Ni3S2 Electrocatalyst for the Oxygen Evolution Reaction with High Stability at an Industrially-Relevant Current Density.

A novel oxygen evolution reaction (OER) electrocatalyst was prepared by a synthesis strategy consisting of the solvothermal growth of Ni3S2 nanostructures on Ni foam, followed by hydrothermal incorporation of Fe species (Fe-Ni3S2/Ni foam). This electrocatalyst displayed a low OER overpotential of 230 mV at 100 mA·cm-2, a low Tafel slope of 43 mV·dec-1, and constant performance at an industrially relevant current density (500 mA·cm-2) over 100 h in a 1.0 M KOH electrolyte, despite a minor loss of Fe in the process. Based on a detailed characterization by (in situ) Raman spectroscopy, (quasi-in situ) XPS, SEM, TEM, XRD, ICP-AES, EIS, and Cdl analysis, the high OER activity and stability of Fe-Ni3S2/Ni foam were attributed to the nanostructuring of the surface in the form of stable nanosheets and to the combination of Ni3S2 granting suitable electrical conductivity with newly formed NiFe-based (oxy)hydroxides at the surface of the material providing the active sites for OER.

Supramolecular Hydrolase Mimics in Equilibrium and Kinetically Trapped States

AbstractThe folding of proteins into intricate three‐dimensional structures to achieve biological functions, such as catalysis, is governed by both kinetic and thermodynamic controls. The quest to design artificial enzymes using minimalist peptides seeks to emulate supramolecular structures existing in a catalytically active state. Drawing inspiration from the nuanced process of protein folding, our study explores the enzyme‐like activity of amphiphilic peptide nanosystems in both equilibrium and non‐equilibrium states, featuring the formation of supramolecular nanofibrils and nanosheets. In contrast to thermodynamically stable nanosheets, the kinetically trapped nanofibrils exhibit dynamic characteristics (e.g., rapid molecular exchange and relatively weak intermolecular packing), resulting in a higher hydrolase‐mimicking activity. We emphasize that a supramolecular microenvironment characterized by an optimal local polarity, microviscosity, and β‐sheet hydrogen bonding is conducive to both substrate binding and ester bond hydrolysis. Our work underscores the pivotal role of both thermodynamic and kinetic control in impacting biomimetic catalysis and sheds a light on the development of artificial enzymes.

Supramolecular Hydrolase Mimics in Equilibrium and Kinetically Trapped States.

The folding of proteins into intricate three-dimensional structures to achieve biological functions, such as catalysis, is governed by both kinetic and thermodynamic controls. The quest to design artificial enzymes using minimalist peptides seeks to emulate supramolecular structures existing in a catalytically active state. Drawing inspiration from the nuanced process of protein folding, our study explores the enzyme-like activity of amphiphilic peptide nanosystems in both equilibrium and non-equilibrium states, featuring the formation of supramolecular nanofibrils and nanosheets. In contrast to thermodynamically stable nanosheets, the kinetically trapped nanofibrils exhibit dynamic characteristics (e.g., rapid molecular exchange and relatively weak intermolecular packing), resulting in a higher hydrolase-mimicking activity. We emphasize that a supramolecular microenvironment characterized by an optimal local polarity, microviscosity, and β-sheet hydrogen bonding is conducive to both substrate binding and ester bond hydrolysis. Our work underscores the pivotal role of both thermodynamic and kinetic control in impacting biomimetic catalysis and sheds a light on the development of artificial enzymes.

Hydrolytically stable nanosheets of Cu–imidazolate MOF for selective trapping and simultaneous removal of multiple heavy metal ions

This study reports stable and sustainable material for mitigating the multifaceted challenges presented by toxic metal contamination in water.

Gram-Scale Mechanochemical Synthesis of Atom-Layer MoS2 Semiconductor Electrocatalyst via Functionalized Graphene Quantum Dots for Efficient Hydrogen Evolution.

The development of advanced and efficient synthetic methods is pivotal for the widespread application of 2D materials. In this study, a facile and scalable solvent-free mechanochemical approach is approached, employing graphene quantum dots (GQDs) as exfoliation agents, for the synthesis and functionalization of nearly atom-layered MoS2 nanosheets (ALMS). The resulting ALMS exhibits an ultrathin average thickness of 4nm and demonstrates high solvent stability. The impressive yield of ALMS reached 63%, indicating its potential for scalable production of stable nanosheets. Remarkably, the ALMS catalyst exhibits excellent HER performance. Moreover, the ALMS catalyst showcases exceptional long-term durability, maintaining stable performance for nearly 200 h, underscoring its potential as a highly efficient and durable electrocatalyst. Significantly, the catalytic properties of ALMS are significantly influenced by ball milling production conditions. The GQD-assisted large-scale machinery synthesis pathway provides a promising avenue for the development of efficient and high-performance ultrathin 2D materials.

Temperature-Dependent Preparation of Hydrogen-Bond Organic Frameworks: Ultrathin and Stable Nanosheets for Fluorescent Sensing toward Uranyl

A series of hydrogen-bond organic frameworks (HOFs) (HOF-TCPB-x, x = 298, 333, 343, 353, and 373) with different crystalline structures were prepared by a temperature-dependent method. Among them, HOF-TCPB-373 shows stable duplex H-bonds and a 2-fold interpenetrating layered structure. HOF-TCPB-373 exhibits high thermal, hydrolytic, acid, and base stabilities. Its thermal decomposition temperature in the air is 450 °C, and it can maintain the original crystal structure after being immersed in 6 M H2SO4, 6 M HCl, 6 M HNO3, 0.01 M NaOH, and boiling water. It is noteworthy that the inborn structural features of HOF-TCPB-373, including the robust and dense layers and the weak interactions between layers, make it easy to be stripped into 2D nanomaterials. Successfully, the bulk HOF-TCPB-373 was exfoliated into uniform ultrathin nanosheets with a thickness of 1.5 nm, which can be used as a sensitive UO22+ fluorescence sensor. The quantum yield of Nano-HOF-TCPB-373 is 58.40%, and the fluorescence lifetime is 1.8 ns. It can exhibit almost identical fluorescence-emission intensities under broad pH 2–9 conditions. The detection limit of Nano-HOF-TCPB-373 aqueous suspension toward uranium is 0.13 μg·L–1. Also, Nano-HOF-TCPB-373 shows apparent selectivity toward UO22+ over the common metal ions in water, such as Na+, K+, Ca2+, Sr2+, Zn2+, Ba2+, and Al3+.

Lysozyme-assisted ultrasonic exfoliation of graphitic carbon nitride into highly stable nanosheets with enhanced bactericidal capacity

Graphitic carbon nitride (g-C3N4) is a visible light-responsive photocatalytic material with important application prospects in many fields. However, the interaction between g-C3N4 monolayers makes it easy to aggregate and precipitate in aqueous solutions, and it is necessary to prepare stable g-C3N4 aqueous dispersions for their applications. Here we propose a facile, green, and low-cost method for the preparation of stable g-C3N4 dispersions by ultrasonicating g-C3N4 in lysozyme (LYZ) solution. The LYZ was adsorbed on the surface of g-C3N4 through non-covalent interactions such as electrostatic interaction, hydrogen bonding and π-cation interaction to prevent the aggregation of g-C3N4 nanolayers. The LYZ/g-C3N4 could quickly re-form a uniform aqueous dispersion solution after freeze-drying, and exhibit good stability. Further, the results of photocatalytic sterilization showed that the assisted dispersion of LYZ enhanced the bactericidal activity of g-C3N4 and exhibited promising application prospects in the field of biomedicine and water disinfection.

Ab initio study of anisotropic mechanical and electronic properties of strained carbon-nitride nanosheet with interlayer bonding

Due to the noticeable structural similarity and being neighborhood in periodic table of group-IV and -V elemental monolayers, whether the combination of group-IV and -V elements could have stable nanosheet structures with optimistic properties has attracted great research interest. In this work, we performed first-principles simulations to investigate the elastic, vibrational and electronic properties of the carbon nitride (CN) nanosheet in the puckered honeycomb structure with covalent interlayer bonding. It has been demonstrated that the structural stability of CN nanosheet is essentially maintained by the strong interlayer σ bonding between adjacent carbon atoms in the opposite atomic layers. A negative Poisson’s ratio in the out-of-plane direction under biaxial deformation, and the extreme in-plane stiffness of CN nanosheet, only slightly inferior to the monolayer graphene, are revealed. Moreover, the highly anisotropic mechanical and electronic response of CN nanosheet to tensile strain have been explored.

A Multifunctional Dysprosium‐Carboxylato 2D Metall–Organic Framework

AbstractWe report the microwave assisted synthesis of a bidimensional (2D) MOF of formula [Dy(MeCOO)(PhCOO)2]n (1) and its magnetically diluted analogue [La0.9Dy0.1(MeCOO)(PhCOO)2] (1 d). 1 is a 2D material with single‐ion‐magnet (SIM) behaviour and 1 d is a multifunctional, magnetic and luminescent 2D material. 1 can be exfoliated into stable nanosheets by sonication.

A Multifunctional Dysprosium-Carboxylato 2D Metall-Organic Framework.

We report the microwave assisted synthesis of a bidimensional (2D) MOF of formula [Dy(MeCOO)(PhCOO)2 ]n (1) and its magnetically diluted analogue [La0.9 Dy0.1 (MeCOO)(PhCOO)2 ] (1 d). 1 is a 2D material with single-ion-magnet (SIM) behaviour and 1 d is a multifunctional, magnetic and luminescent 2D material. 1 can be exfoliated into stable nanosheets by sonication.

Pressure-Driven Transformation of CsPbBrI2 Nanoparticles into Stable Nanosheets in Solution through Self-Assembly.

Very recently, two-dimensional (2D) perovskite nanosheets (PNSs), taking the advantages of perovskite as well as the 2D structure properties, have received an enormous level of interest throughout the scientific community. In spite of this incredible success in perovskite nanocrystals (NCs), self-assembly of many nanostructures in metal halide perovskites has not yet been realized, and producing highly efficient red-emitting PNSs remains challenging. In this Letter, we show that by using CsPbBrI2 perovskite nanoparticles (NPs) as a building block, PNSs can emerge spontaneously under high ambient pressure via template-free self-assembly without additional complicated operation. It is found that the formation of PNSs is ascribed to the high pressure that provides the driving force for the alignment of NPs in solution. Because of the disappearance of the grain boundaries between the adjacent NPs and increased crystallinity, these PNSs self-assembled from NPs exhibit enhanced properties compared to the initial NPs, including higher PL intensity and remarkable chemical stability toward light and water.

Ultrasound-assisted exfoliation of a layered 2D coordination polymer with HER electrocatalytic activity

Large blue rectangular crystals of the 2D layered coordination polymer 1 have been obtained. The interest for this complex is two-fold. First, complex 1 is made of 2D layers packing along the (0–11) direction favored by the presence of lattice and coordinated water molecules. And second, nanostructures that could be derived by delamination are potentially suitable for catalytic purposes. Therefore it represents an excellent example to study the role of interlayer solvent molecules on the ultrasound-assisted delamination of functionally-active 2D metal-organic frameworks in water, a field of growing interest. With this aim, ultrasound-assisted delamination of the crystals was optimized with time, leading to stable nanosheet colloidal water suspensions with very homogeneous dimensions. Alternative bottom-up synthesis of related nanocrystals under ultrasound sonication yielded similar shaped crystals with much higher size dispersions. Finally, experimental results evidence that the nanostructures have higher catalytic activities in comparison to their bulk counterparts, due to larger metallic center exposition. These outcomes confirm that the combination of liquid phase exfoliation and a suitable synthetic design of 2D coordination polymers represents a very fruitful approach for the synthesis of functional nanosheets with an enhancement of catalytic active sites, and in general, with boosted functional properties.

Clariant increases catalyst production capacity in China

Despite the rapid development of mass production methods of two-dimensional (2D) transition metal dichalcogenide (TMD) materials in liquid media, long-term stability of these materials in aqueous solution is a major issue. In this study, the instability of chemically exfoliated niobium diselenide (NbSe2) nanosheets (NSs) dispersed in aqueous solution is systematically investigated, and it is revealed that the instability originates from the oxidation of NbSe2 NSs in the aqueous solution, which leads to the precipitation of selenium and restacking of NbSe2 NSs, degrading the electrical property of the NbSe2 NSs. On the basis of the results, for the first time, we propose an efficient method to prevent the oxidation of NbSe2 NSs using an antioxidant (L-ascorbic acid) that effectively consumes the oxygen dissolved in the aqueous solution, rendering the NbSe2 NSs antioxidative during the redox reaction in the aqueous solution, and thereby, improving the long-term stability of the NbSe2 NS ink. Finally, we demonstrate the fabrication of a thermoelectric generator by printing process with our long-term stable NbSe2 NS ink. The thermoelectric power factor was nearly maintained up to 87% regardless of ink storage time even for 30 days.

Long-term stable NbSe2 nanosheet aqueous ink for printable electronics

Despite the rapid development of mass production methods of two-dimensional (2D) transition metal dichalcogenide (TMD) materials in liquid media, long-term stability of these materials in aqueous solution is a major issue. In this study, the instability of chemically exfoliated niobium diselenide (NbSe2) nanosheets (NSs) dispersed in aqueous solution is systematically investigated, and it is revealed that the instability originates from the oxidation of NbSe2 NSs in the aqueous solution, which leads to the precipitation of selenium and restacking of NbSe2 NSs, degrading the electrical property of the NbSe2 NSs. On the basis of the results, for the first time, we propose an efficient method to prevent the oxidation of NbSe2 NSs using an antioxidant (L-ascorbic acid) that effectively consumes the oxygen dissolved in the aqueous solution, rendering the NbSe2 NSs antioxidative during the redox reaction in the aqueous solution, and thereby, improving the long-term stability of the NbSe2 NS ink. Finally, we demonstrate the fabrication of a thermoelectric generator by printing process with our long-term stable NbSe2 NS ink. The thermoelectric power factor was nearly maintained up to 87% regardless of ink storage time even for 30 days.

Two-dimensional ZrB2C2 with multiple tunable Dirac states

In this paper, we designed a two-dimensional honeycomb monolayer ZrB2C2, which is predicted to be a stable nanosheet and exhibits favorable mechanical and thermal properties. The Young's modulus of ZrB2C2 is 122.3 N m-1, which is about one third of that of graphene. The ab initio molecular dynamics (AIMD) results show that ZrB2C2 can sustain up to 500 K. In addition, ZrB2C2 is semi-metallic and it exhibits twelve Dirac cones in the first Brillouin zone; the six pairs of Dirac cones form compensated electron-hole pockets, and the maximum Fermi velocity is about 6.3 × 105 m s-1, which is about 60% of that of graphene. Compared with other transition metal borides which possess Dirac states, the twelve Dirac cones are all robust under different types of external strains, and the Dirac states could be shifted along the opposite direction crossing the Fermi energy barrier by external strains and the gap of the two Dirac cones could be opened around the Fermi energy level with the effect of spin-orbit coupling.

Ostwald Ripening Driven Exfoliation to Ultrathin Layered Double Hydroxides Nanosheets for Enhanced Oxygen Evolution Reaction.

As a key half-reaction in water splitting, the oxygen evolution reaction (OER) process is kinetically sluggish. Layered double hydroxides (LDHs) are regarded as the highly promising electrocatalysts to promote the OER kinetics. However, the closely stacking layered structure of pristine bulk LDHs restricts the exposure of electrocatalytically active sites, and it remains a great challenge to find an efficient strategy to exfoliate the bulk LDHs into ultrathin and stable nanosheets with increased surface area and exposed active sites. Herein, a novel Ostwald ripening driven exfoliation (ORDE) of NiFe LDHs has been achieved in situ on the electrodes by spontaneously self-etching and redepositing via a simple hydrothermal treatment without the assistance of any exfoliating reagent or surfactant. The thermodynamically driven Ostwald ripening has been expanded to the exfoliation of two-dimensional layered materials for the first time. Compared with conventional exfoliation methods, this ORDE is a time-saving and green strategy that avoids the serious adsorption of surfactant molecules. The ORDE of NiFe LDHs is accomplished in situ on a Cu mesh electrode, which not only exhibits excellent electrical contact between LDHs catalyst and electrodes but also prevents the restacking of the exfoliated LDHs. As a result, the exfoliated ultrathin, clean, and vertically aligned NiFe nanosheets with much higher surface area and numerous exposed active edges and sites demonstrated significantly enhanced OER performances with low overpotential of 292 mV at 10 mA cm-2 and long-term stability for more than 60 h, as well as remarkable flexibility. Additionally, bulk Ni(OH)2 nanosheets on Ni foams have also been exfoliated by a similar mechanism, indicating this ORDE strategy can be widely extended to other 2D layered materials for novel applications.

First-principles study of the nanotubes from the TiO2 hexagonal sheet

Using the method based on the density functional theory, the geometric and electronic properties of the TiO2 single-wall nanotubes, constructed by rolling the most stable nanosheet along the (n, 0) and (n, n) directions, have been investigated systematically. The nanotubes with size from n = 6 up to n = 20 have been modeled and studied. The strain energies of the nanotubes decrease monotonically as the radii of the nanotubes increase, regardless of the rolling direction. The band gaps of the nanotubes are increasing with the increase of the n value, approaching the value of the nanosheet. However, there is one nanotube significantly different from the others, i.e., the (6, 0) nanotube. The substantial structural change of (6, 0) nanotube causes a reduction of the band gap. Then, the isovalent sulfur (S) substitution and adsorption with the (6, 0) nanotube have been studied. Energetically, S adsorption at the inner surface is preferred. Electronically, the band gaps are further reduced by 35% for S substitution of oxygen and 22% for S adsorption, respectively, making the nanotube visible light-sensitive.

Two-dimensional bismuth-rich nanosheets through the evaporative thinning of Se-doped Bi2Te3

High bulk conductance obscures the behavior of surface states in the prototypical topological insulators Bi2Te3 and Bi2Se3. However, ternary phases of Bi2Te3−ySey with balanced donor and acceptor levels may lead to large bulk resistivity, allowing for the observation of the surface states. Additionally, the contribution of the bulk conductance may be further suppressed by nanostructuring, increasing the surface-to-volume ratio. Herein we report the synthesis of a ternary tetradymite newly confined to two dimensions. Ultra-thin large-area stable nanosheets were fabricated via evaporative thinning of a Bi2Te2.9Se0.1 original phase. Owing to vapor pressure differences, a compositional shift to a final Bi-rich phase is observed. The Se/Te ratio of the nanosheet increases tenfold, due to the higher stability of the Bi–Se bonds. Hexagonal crystal symmetry is maintained despite dramatic changes in thickness and stoichiometry. Given that small variations in stoichiometry of this ternary system can incur large changes in carrier concentration and switch majority carrier type, the large compositional shifts found in this case imply that compositional analysis of similar CVD and PVD grown materials is critical to correctly interpret topological insulator performance. Further, the characterization techniques deployed, including STEM-EDS and ToF-SIMS, serve as a case study in determining such compositional shifts in two-dimensional form.

Synthesis and Photo-Catalytic Properties of M<sub>O</sub>O<sub>3 </sub>Nanosheets

Layered Molybdenum trioxide MOO3, with a two-dimensional (2D) structure was successfully delaminated into colloidal nanosheets in n-butanol via a soft-chemical process involving intercalation of dodecylamine. X-ray diffration (XRD) showd that: after intercalation spacing of the layered material expend from 1.38nm to 2.69nm. Furthermore, stable nanosheet sol was obtained after exfoliation under ultrasonic condition, Characterizations by transmission electron microscopy (TEM) and scan electron microscopy (SEM) confirmed the formation of unilamellar 2D nanosheet crystallites with an average lateral size of 400 nm, those also suggests that the samples we got is Lamellar structured. Selected Area Electron Diffraction (SEDA) indicates that the obtained nanosheets were crystalline. And the obtained nanosheets exhibited photo-catalytic decolorization properties. Which was evaluated by monitoring the degradation of Methylene Blue, after 40 minutes 90% methylene blue was degradated.