Bilayer Nanosheets Research Articles

Living Self-Assembly of Monodisperse Micron-Sized Polymer Vesicles.

Artificial vesicles are recognized as powerful platforms for a large body of research across the disciplines of chemistry, physics and biology. Despite the great progress, control of the size distribution to make uniform vesicles remains fundamentally difficult due to the highly uncontrollable growth kinetics, especially for micron-sized vesicles. Here we report a template-free living self-assembly method to prepare monodisperse vesicles around 1 μm from an alternating copolymer. The polymer forms nanodisks (ca. 9 nm) in N,N-dimethylformamide (DMF), acting as seeds for subsequent growth. By adding water, the nanodisks gradually grow into larger circular bilayer nanosheets, which bend to crowns and continue to grow into uniform micron-sized vesicles. The first-order growth kinetics as well as the small size polydispersity index (<0.1) suggests the living self-assembly characteristics. This work paves a new way in both living self-assembly and monodisperse polymer vesicles.

Living Self‐Assembly of Monodisperse Micron‐Sized Polymer Vesicles

AbstractArtificial vesicles are recognized as powerful platforms for a large body of research across the disciplines of chemistry, physics and biology. Despite the great progress, control of the size distribution to make uniform vesicles remains fundamentally difficult due to the highly uncontrollable growth kinetics, especially for micron‐sized vesicles. Here we report a template‐free living self‐assembly method to prepare monodisperse vesicles around 1 μm from an alternating copolymer. The polymer forms nanodisks (ca. 9 nm) in N,N‐dimethylformamide (DMF), acting as seeds for subsequent growth. By adding water, the nanodisks gradually grow into larger circular bilayer nanosheets, which bend to crowns and continue to grow into uniform micron‐sized vesicles. The first‐order growth kinetics as well as the small size polydispersity index (&lt;0.1) suggests the living self‐assembly characteristics. This work paves a new way in both living self‐assembly and monodisperse polymer vesicles.

Highly sensitive plasmonic biosensor enhanced by perovskite-graphene hybrid configuration

This study theoretically proposes a highly sensitive plasmonic biosensor comprising a silver film, perovskite nanosheets, bi-layer silicon nanosheets, and a graphene overlayer. The introduction of perovskite-graphene hybrid structure can reduce the optical reflectivity of the proposed biosensor configuration so that photons are converted into energy to support surface plasmon resonance (SPR) enhancement. Unlike conventional angular modulation, our proposed biosensor configuration is designed using phase modulation, offering sensitivity enhancements as high as 3 orders of magnitude. Excellent biosensing performances have been examined by optimizing the silver film thickness and the number of perovskite nanosheets. Considering a tiny refractive index change of 0.0012 refractive index unit (RIU) caused by biomolecules adsorption behavior, the optimal plasmonic biosensor configuration of 46-nm silver film–5.7-nm silicon interlayer-1-layer CH3NH3PbI3 perovskite film–0.7-nm silicon interlayer-1-layer graphene can produce the highest detection sensitivity of 1.2314 × 105 degree/RIU. In addition, an excellent linear response in the differential phase can be obtained, as the refractive index variation of the sensing interface can be as low as 10−6 RIU, showing great potential in performing ultrasensitive biosensing.

Synergic effects of FeOOH and CoNi2Se4 bilayer nanosheets as highly efficient electrocatalysts for the oxygen evolution reaction

The substantial growth of nonprecious and inexpensive electrocatalysts for the oxygen evolution reaction (OER) is vital for commercial usage. In this work, cobalt nickel selenide (CoNi2Se4, called CNSe) thin film nanosheet heterojunctions with iron oxyhydroxide (FeOOH) thin film nanosheets were grown directly on a nickel foam substrate (Ni-foam) using an electrodeposition method. The electrocatalytic activity of CNSe/FeOOH bilayer nanosheets was evaluated for OER studies using its CNSe and FeOOH counterparts. The CNSe/FeOOH bilayer thin film exhibited a low overpotential of 222 mV to deliver a benchmark current density of 10 mA cm−2, which was lower than that of the CNSe (327 mV) and FeOOH (276 mV) electrocatalysts. The bilayer electrocatalyst delivered remarkable long-term electrochemical stability for more than 120 h at a constant current density of 10 mA cm−2. The excellent activity was attributed to the synergic effects of CNSe/FeOOH with high electrochemical active sites and feasible charge transfer ability. This study provides new insights for designing a different class of materials using a simple electrochemical deposition route for high-performance OER kinetics.

Architecture-influenced stress and diffusion for hierarchical 3D thick electrodes with multi-layer nanosheets

Hierarchical 3D thick electrodes with multi-layer nanosheets represent an important step in the advancement of electrode design and fabrication that allows more efficient charge transport beyond the limits of traditional electrodes. However, there is still a lack of systematic theoretical investigations of microstructure and kinetic diffusion on the stress development for such electrode at the mesoscale. Therefore, in this work, we propose a comprehensive modeling framework with a light by using plate theory together with a mechanical concept model based on structure constraint that can fully address the chemo-mechanical environment accounting for the failure of electrodes. Through extracting the basic building block of thick electrode, the model can describe the typical characteristics of the elaborated 3D architectures with a compliant backbone. Bilayer and three-layer sandwich-like nanosheets with different mechanical constraints reflecting structure flexibility are considered. Theoretical investigations reveal the influences of the mechanical constraint and heterogeneous electrochemistry on the stress evolution in thick electrodes. Although the analysis of transient ion diffusion in composite solids has been developed for almost 50 years, an exact closed-form solution for general electrochemical conditions is lacking owing to the mathematical difficulty. Here, for transient diffusion in bilayer and three-layer slab under both galvanostatic and potentiostatic charging, theoretical solutions giving a complete description of the spatial and temporal variation of lithium concentration and allowing ion exchange between each layer are derived by using the natural eigenfunction expansion method, which is particularly convenient. Such investigation has potential avenues for guiding design of high performance 3D thick electrodes and catching sight of the underlying mechanisms in the view of mechanics and diffusion considerations.

Rational design of CoP@Ni(OH)2 bilayer nanosheets for high-performance supercapacitors

The CoP@Ni(OH)2 bilayer nanosheets can provide abundant transport paths for electrons and ions, expose more electroactive sites, and enhance structural stability.

Boosting the hydrogen evolution of layered double hydroxide by optimizing the electronic structure and accelerating the water dissociation kinetics

Designing a highly efficient and durable electrocatalyst for hydrogen evolution reactions (HER) is of great significance to promote the development of green hydrogen energy. This work reports a vertical-aligned electrocatalyst of Cu2O/CoCu-LDH inlaid bilayer nanosheets that achieve excellent alkaline HER performance with a low overpotential of 96 mV at 10 mA cm−2 and a low Tafel slope of 76.8 mV dec−1. Notably, Cu2O/CoCu-LDH outperforms Pt/C at a practical current density of 600 mA cm−2. The structural characterizations and theory calculations revealed that the superior HER activity of Cu2O/CoCu-LDH is due to the distinctive morphology, optimized electronic structure and accelerated water dissociation kinetics. Remarkably, the Cu2O/CoCu-LDH acted as the cathode in alkaline Zn-H2O cell demonstrating the potential applications for H2 generation and electricity energy simultaneously. Our work can guide the design of LDH-based electrocatalysts with outstanding HER performance.

Engineering the band gap and optical properties of a two-dimensional molybdenum carbon fluoride MXene

Using first-principles density functional theory, we investigated the electronic and optical properties of monolayer and multilayer nanosheets of molybdenum carbon fluoride (Mo2CF2), a two-dimensional (2D) transition-metal carbide MXene. The indirect band gap of the Mo2CF2 semiconductor can be engineered by controlling the number of layers where the band gap energy changes from 0.278 eV for the monolayer to 0.249 eV for the trilayer nanosheet. The decrease in band gap energy in the multilayer is due to interlayer coupling, which splits the bands according to the number of layers. Mo2CF2 behaves as a metal with an anomalous dispersion and high optical conductivity at incident photon energies of 0.68–2.19, 3.49–6.68 and 7.30–8.31 eV. It has a relatively low reflectivity and is absorbing over a broad range of photon energies from about 0.429 (2890), 0.387 (3204) and 0.345 eV (3594 nm) for the monolayer, bilayer and trilayer nanosheets, respectively, achieving peak absorption in the vacuum ultraviolet region at about 7.9 eV (157 nm). The optical properties of Mo2CF2 can likewise be tuned by varying the number of layers. The unique behavior of its optical properties along with the ability to control its electronic and optical properties enhances the potential of 2D Mo2CF2 for various applications in the fields of electronics and energy storage.

A label-free electrochemical immunosensor based on PdPtCu@BP bilayer nanosheets for point-of-care kidney injury molecule-1 testing

Kidney injury molecule-1 (KIM-1) protein is a vital biomarker for the early diagnosis of acute kidney injury (AKI). Therefore, a rapid and sensitive method for KIM-1 detection is urgently needed. Herein, a novel label-free electrochemical immunosensor constructed on PdPtCu@black phosphorus (BP) bilayer nanosheets (BNSs) is reported for point-of-care (POC) testing of KIM-1. Monolayer-monolayer PdPtCu@BP BNSs, a novel signal substrate, were successfully synthesized using BP nanosheets combined with trimetal PdPtCu nanosheets. Benefiting from the excellent conductivity and peroxidase-like performance of PdPtCu@BP BNSs, the designed label-free electrochemical immunosensor exhibited exceptional detection properties. Under optimal conditions, the facile immunosensor displayed satisfactory linearity from 100 pg/mL to 100 ng/mL with a minimum detection limit of 32 pg/mL. Moreover, it takes 60 min from target addition to measurement completion. Meanwhile, the developed sensing strategy was successfully applied to specifically detect KIM-1 in real samples. The proposed strategy enables rapid and sensitive protein assays, providing a potential versatile platform for POC testing.

Insights from density functional theory calculations on heteroatom P-doped ZnIn2S4 bilayer nanosheets with atomic-level charge steering for photocatalytic water splitting

ZnIn2S4 (ZIS) is an efficient photocatalyst for solar hydrogen (H2) generation from water splitting owing to its suitable band gap, excellent photocatalytic behaviour and high stability. Nevertheless, modifications are still necessary to further enhance the photocatalytic performance of ZIS for practical applications. This has led to our interest in exploring phosphorus doping on ZIS for photocatalytic water splitting, which has not been studied till date. Herein, phosphorus-doped ZnIn2S4 (P-ZIS) was modelled via Density Functional Theory to investigate the effects of doping phosphorus on the structural and electronics properties of ZIS as well as its performance toward photocatalytic water splitting. This work revealed that the replacement of S3 atom by substitutional phosphorus gave rise to the most stable P-ZIS structure. In addition, P-ZIS was observed to experience a reduction in band gap energy, an upshift of valence band maximum (VBM), an increase in electron density near VBM and a reduction of H* adsorption–desorption barrier, all of which are essential for the enhancement of the hydrogen evolution reaction. In overall, detailed theoretical analysis carried out in this work could provide critical insights towards the development of P-ZIS-based photocatalysts for efficient H2 generation via solar water splitting.

Synthesis of bilayer borophene.

As the nearest-neighbour element to carbon, boron is theoretically predicted to have a planar two-dimensional form, named borophene, with novel properties, such as Dirac fermions and superconductivity. Several polymorphs of monolayer borophene have been grown on metal surfaces, yet thicker bilayer and few-layer nanosheets remain elusive. Here we report the synthesis of large-size, single-crystalline bilayer borophene on the Cu(111) surface by molecular beam epitaxy. Combining scanning tunnelling microscopy and first-principles calculations, we show that bilayer borophene consists of two stacked monolayers that are held together by covalent interlayer boron-boron bonding, and each monolayer has β12-like structures with zigzag rows. The formation of a bilayer is associated with a large transfer and redistribution of charge in the first boron layer on Cu(111), which provides additional electrons for the bonding of additional boron atoms, enabling the growth of the second layer. The bilayer borophene is shown to possess metallic character, and be less prone to being oxidized than its monolayer counterparts.

Shape-Shifting Peptide Nanomaterials: Surface Asymmetry Enables pH-Dependent Formation and Interconversion of Collagen Tubes and Sheets.

The fabrication of dynamic, transformable biomaterials that respond to environmental cues represents a significant step forward in the development of synthetic materials that rival their highly functional, natural counterparts. Here, we describe the design and synthesis of crystalline supramolecular architectures from charge-complementary heteromeric pairs of collagen-mimetic peptides (CMPs). Under appropriate conditions, CMP pairs spontaneously assemble into either 1D ultraporous (pore diameter >100 nm) tubes or 2D bilayer nanosheets due to the structural asymmetry that arises from heteromeric self-association. Crystalline collagen tubes represent a heretofore unobserved morphology of this common biomaterial. In-depth structural characterization from a suite of biophysical methods, including TEM, AFM, high-resolution cryo-EM, and SAXS/WAXS measurements, reveals that the sheet and tube assemblies possess a similar underlying lattice structure. The experimental evidence suggests that the tubular structures are a consequence of the self-scrolling of incipient 2D layers of collagen triple helices and that the scrolling direction determines the formation of two distinct structural isoforms. Furthermore, we show that nanosheets and tubes can spontaneously interconvert through manipulation of the assembly pH and systematic adjustment of the CMP sequence. Altogether, we establish initial guidelines for the construction of dynamically responsive 1D and 2D assemblies that undergo a structurally programmed morphological transition.

A Discrete Platinum(II) Amphiphile: Construction, Characterization, and Controllable Self-Assembly in Different Solvents.

"Coordination-driven self-assembly" offers us an efficient method to fabricate 3D metallacages and 2D metallacycles with controllable shape and size via simple building blocks. Herein, a new discrete platinum(II) amphiphile (AOM), which contains hydrophilic tris(ethylene oxide) chains and a hydrophobic porphyrin unit, was constructed successfully by using "coordination-driven self-assembly". From various characterization methods, such as UV-vis spectroscopy, dynamic light scattering, transmission electron microscopy, scanning electron microscopy, and small-angle X-ray scattering, we found that AOM can self-assemble into vesicles, curved vesicles with open ends, and at last stable bilayer nanotubes in aqueous solution at room temperature and flexible cross-linked structures at about 60 °C. In contrast, AOM formed rigid bilayer nanosheets of micrometers in width and millimeters in length in n-hexane. We hope this investigation will pave the way for the fabrication of controllable soft materials.

Bilayer nanosheets of unusual stoichiometric bismuth oxychloride for potassium ion storage and CO2 reduction

Abstract Bilayer-Bi12O17Cl2 nanosheets (BBNs), a kind of unusual stoichiometric bismuth oxychloride, with abundant oxygen vacancies (OVs) were synthesized by a simple but efficient hydrothermal method, and acted as the generalist material for Potassium-ion battery (PIB) anode and CO2 reduction reaction. The BBNs with a thickness of ~1.5 nm offer a large electrode-electrolyte contact interface and a short path for K+ diffusion. Importantly, the abundant OVs not only provide more active sites but also promote ionic transmission and electrical conductivity. As an anode for PIB, it provides a high initial discharge capacity (627.5 mA h g−1 at 500 mA g−1), high rate performance (420 mA h g−1 at 10 A g−1) and outstanding cycle performance (198 mA h g−1 after 1500 cycles at 10 A g−1). When evaluated as the electrocatalyst for CO2 reduction, the BBNs exhibited an impressive activity, selectivity and stability (JHCOO- = 11.5 mA/cm2 at −0.89 V, Faradaic efficiency >92%, and durability for >12 h). Considering the easy preparation, low cost, and fast-kinetics, this promising strategy and associated opportunities demonstrate great potential for energy storage or electrocatalysts.

Buckling of 2D nano hetero-structures with moire patterns

Moire pattern arises from the lattice mismatch between two different nanosheets. The discovery of the Moire pattern has resulted in breakthrough properties in 2D carbon-based nanostructures such as graphene. Here we investigate the impact of a Moire pattern on mechanical properties of bi-layer 2D nanosheets. In particular, buckling instability of 2D carbon-based nano hetero-structures is investigated using atomistic finite element approaches. Nano hetero-structures considered are graphene-hBN (hexagonal Boron Nitride) and graphene-MoS2 (Molybdenum disulphide). Bilayer graphene has also been considered in the buckling analysis, by orienting the individual sheets at moire angle. Atomistic simulation methodology uses elastic beams to represent intra-sheet atomic bonds and elastic springs to represent inter-sheet atomic interactions. The influence of different boundary conditions and sheet length on the buckling of nano hetero-structures has been investigated. The bridged nano hetero-structures are found be displaying higher buckling strength as compared to cantilever sheets.

Evidence for Magnetic Skyrmions at the Interface of Ferromagnet/Topological-Insulator Heterostructures.

The heterostructures of the ferromagnet (Cr2Te3) and topological insulator (Bi2Te3) have been grown by molecular beam epitaxy. The topological Hall effect as evidence of the existence of magnetic skyrmions has been observed in the samples in which Cr2Te3 was grown on top of Bi2Te3. Detailed structural characterizations have unambiguously revealed the presence of intercalated Bi bilayer nanosheets right at the interface of those samples. The atomistic spin-dynamics simulations have further confirmed the existence of magnetic skyrmions in such systems. The heterostructures of ferromagnet and topological insulator that host magnetic skyrmions may provide an important building block for next generation of spintronics devices.

Stepwise Expansion of Layered Metal-Organic Frameworks for Nonstochastic Exfoliation into Porous Nanosheets.

A layered metal-organic framework (MOF) with a porous kagomé lattice, kgmSMe, was synthesized by complexation of 5-methylthioisophthalate (SMe-ip) with Cu2+ in MeOH. As observed by powder XRD, kgmSMe (state I), when immersed in aprotic polar solvents such as THF, underwent stepwise interlayer expansion into a monolayer-expanded state (state III) through a bilayer-expanded state (state II). We successfully obtained the single-crystal structures of states I-III. Of interest, when further immersed in appropriate solvents, state II and III crystals preferentially exfoliated into bilayer and monolayer MOF nanosheets, respectively. The stepwise expansion followed by exfoliation, thus developed, may enable a nonstochastic approach to the selective synthesis of ultrathin porous nanosheets from layered MOF crystals.

Structure, electronic and optical properties of bilayer anatase nanoribbons

The highest surface area anatase TiO2 containing two layers of titanium atoms and exposing facets (0 0 1) is investigated. The material has maximal theoretical surface area of 1080 m2/g, but its stability has been questionable so far. Nanoribbons of this material were considered with the lateral size of 0.4–4.6 nm with varied length of the hydroxylated and non-hydroxylated edges. All the nanoribbons were stable and had flat (0 0 1) surface according to both computational methods used PM6 and SCC-DFTB. The nanoribbons had electronic band gap of around 3.4–3.6 eV and optical band gap of 3.7 eV. They possessed XRD patterns different from those of anatase nanoparticles showing different peaks. Distribution of top orbitals of valence band and bottom orbitals of conduction band as representation for locations of photogenerated holes and electrons showed that orbitals are localized differently depending on the width of nanoribbons, but HOMO and LUMO always occupied different space. Hence, the bilayer nanoribbons are expected to be excellent photocatalysts and sensor materials with good separation of charges. The effect of different conformations of hydroxyl groups on properties of nanoribbons was studied. Interestingly, alignment of all hydroxyl groups in each edge to form hydrogen bonds changes the HOMO, LUMO positions and electronic band gap by up to 0.5 eV, while the optical band gap remained unchanged. It was demonstrated that nanoribbons with even number of layers of Ti atoms had flat structure, while odd-layer nanoribbons showed curvature radius equal to or larger than 3 nm and they can form nanotubes. Given the unique adsorptive and photocatalytic properties of the bilayer nanosheets they are expected to be of great importance in sensors, photocatalysts and adsorbents.

Heterostructured WO3@CoWO4 bilayer nanosheets for enhanced visible-light photo, electro and photoelectro-chemical oxidation of water

Novel WO3@CoWO4 bilayer nanosheets exhibit largely enhanced water oxidation performances compared with WO3 in electrocatalysis, visible-light photocatalysis and photoelectrochemistry.

Ambipolar thermoelectric power of chemically-exfoliated RuO2 nanosheets

The electrical conductivity and Seebeck coefficient of RuO2 nanosheets are enhanced by metal nanoparticle doping using Ag-acetate solutions. In this study, RuO2 monolayer and bilayer nanosheets exfoliated from layered alkali metal ruthenates are transferred to Si substrates for device fabrication, and the temperature dependence of their conductivity and Seebeck coefficients is investigated. For pristine RuO2 nanosheets, the sign of the Seebeck coefficient changes with temperature from 350–450 K. This indicates that the dominant type of charge carrier is dependent on the temperature, and the RuO2 nanosheets show ambipolar carrier transport behavior. By contrast, the sign of the Seebeck coefficient for Ag nanoparticle-doped RuO2 nanosheets does not change with temperature, indicating that the extra charge carriers from metal nanoparticles promote n-type semiconductor behavior.