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Mechanical nonreciprocity, or the asymmetric transmission of mechanical quantities between two points in space, is crucial for developing systems that can guide, damp, and control mechanical energy. We report a uniform composite hydrogel that displays substantial mechanical nonreciprocity, owing to direction-dependent buckling of embedded nanofillers. This material exhibits an elastic modulus more than 60 times higher when sheared in one direction compared with the opposite direction. Consequently, it can transform symmetric vibrations into asymmetric ones that are applicable for mass transport and energy harvest. Furthermore, it exhibits an asymmetric deformation when subjected to local interactions, which can induce directional motion of various objects, including macroscopic objects and even small living creatures. This material could promote the development of nonreciprocal systems for practical applications such as energy conversion and biological manipulation.

This review focuses on the synthetic strategies and characterization methods of atomic cation vacancies in 2D nanosheets and their energy-related applications.

The separation of layered MFI into unilamellar nanosheets in solution confirms the general validity of soft-chemical exfoliation for zeolites and allows top-down production of films with potential applications in separation and catalysis.

Anion-exchange membranes (AEMs) with high conductivity are crucial for realizing next-generation energy storage and conversion systems in an alkaline environment, promising a huge advantage in cost reduction without using precious platinum group metal catalysts. Layered double hydroxide (LDH) nanosheets, exhibiting a remarkably high hydroxide ion (OH

A method for creating genuine nanopores in high area density on monolayer two-dimensional (2D) metallic oxides has been developed. By use of the strong reduction capability of hydroiodic acid, active metal ions, such as Fe

A pelletized self-supported cathode based on a pairwise/sandwich-like assembly of a TaO3 nanomesh and reduced graphene oxide for high-areal-capacity Li–S batteries.

Layered rare-earth hydroxides (LREHs) are promising optical and magnetic materials, while it is hard to obtain monolayer nanosheets through a direct exfoliation. In this study, organic dodecyl sulfate (C12H25SO4-, DS-) was used to prepare LREHs. In-plane lattice parameters of the LREHs decreased from Sm3+ to Er3+, correlating well with the monotonically decreasing ionic radius. Conversely, the interlayer spacing slightly increased with the increase of host layer charge density and corresponding intercalated DS- contents. By a direct sonication of the LREHs in formamide, nanosheets were obtained with a thickness of ∼1 nm and size of ∼500 nm. Compared to the bulk crystals, exfoliation resulted in a slight elongation of in-plane lattice constants and a more asymmetric coordination environment. The suspension of europium hydroxide nanosheets exhibited a remarkably high red-light emission purity (91.4%). This work demonstrated an important strategy toward an efficient synthesis of well-defined LREH nanosheets with high color purity.

Neat (dense and nonoverlapped) monolayer tiling of 2D nanosheets on a substrate surface is very important because we can conduct artificial lattice-engineering by repeating the tiling process in a designed sequence to tailor various hierarchical nanostructures, leading to a range of sophisticated functions. It is recently reported that a facile spin-coating technique realizes the neat monolayer tiling of various 2D nanosheets. Establishing universal guidelines to neatly tile 2D nanosheets on substrates of various materials and size/shape is of essential importance to fully apply this technique, but the mechanism of how the nanosheets are tiled has not been clarified yet. In the present study, we have systematically examined the nanosheet deposition process at various rotation speeds by microscopic observations and found that the neat monolayer tiling of nanosheets is attained on the solvent surface during the spin-coating, and then the monolayer film is deposited onto the substrate surface from its center toward the edges upon evaporation of the solvent. Furthermore, we have clarified how the rotation speed and the nanosheet concentration govern the deposition behaviors in terms of neat tiling, overlap, or noncoverage in a such process. On the basis of the guidelines, we can predict the optimum spin-coating conditions for attaining the neat monolayer tiling of various nanosheets over an entire surface of the substrate.

Molecularly thin two-dimensional (2D) nanomaterials are attractive building blocks for constructing anticorrosion nanocoatings as an ultimate pursuit in the metal-related industry. However, the nanocoating of prefocused graphene is far from industrial demands due to its high cost, low scalability, and insufficient quality. We propose all requirements to realize rational anticorrosion nanocoating of metal oxide nanosheets. The proof-of-concept study with Ti0.87O2 and Ca2Nb3O10 nanosheets demonstrates that the 10 and 20 nm thick coatings fabricated by a facile layer-by-layer (LbL) self-assembly on stainless steel (SUS) give perfect inhibition efficiency (IE) values of 99.92% and 99.89%, respectively. A driving test with a nanosheet-coated car-baffle demonstrated suitable corrosion resistance and mechanical and thermal robustness for industrial applications. The revealed and controlled thermal oxidation mechanisms are critical toward high-temperature application of the 2D oxide anticorrosion nanocoating. The advantages of nanosheet coating and extensible materials design will open a solid but exciting route to anticorrosion nanotechnology.

The regulation of anions and cations at the atomic scale is of great significance in membrane-based separation technologies. Ionic transport regulation techniques could also play a crucial role in developing high-performance alkali metal batteries such as alkali metal-sulfur and alkali metal-selenium batteries, which suffer from the non-uniform transport of alkali metal ions (e.g., Li+ or Na+) and detrimental shuttling effect of polysulfide/polyselenide anions. These drawbacks could cause unfavourable growth of alkali metal depositions at the metal electrode and irreversible consumption of cathode active materials, leading to capacity decay and short cycling life. Herein, we propose the use of a polypropylene separator coated with negatively charged Ti0.87O2 nanosheets with Ti atomic vacancies to tackle these issues. In particular, we demonstrate that the electrostatic interactions between the negatively charged Ti0.87O2 nanosheets and polysulfide/polyselenide anions reduce the shuttling effect. Moreover, the Ti0.87O2-coated separator regulates the migration of alkali ions ensuring a homogeneous ion flux and the Ti vacancies, acting as sub-nanometric pores, promote fast alkali-ion diffusion., An optimized transport of anions and cations is essential for the development of practical alkali metal batteries. Here, the authors report the use of Ti0.87O2 nanosheets as coating material of polypropylene separators for Li-S, Li-Se and Na-Se cells.

A 29-year-old male patient underwent laparoscopic sleeve gastrectomy (LSG) for morbid obesity and was discharged without any complications. Thirteen months later, he visited the emergency room with epigastric pain. A few hours before onset, he had had a larger-than-usual meal and vomited afterwards. Enhanced abdominal computed tomography revealed a hematoma 127 × 63 mm in diameter around the stomach. Angiography revealed no extravasation or pseudoaneurysm. Upper gastrointestinal endoscopy found no ulcers or abnormality of the stapler line scar from the LSG. The patient's vital signs were stable, and his hemoglobin had not fallen below the previous day's value. Conservative treatment was therefore chosen. The patient was discharged in stable condition after 11 days of hospitalization. However, the exact source of the hemorrhage was unable to be detected on the imaging findings. In view of his clinical course and the hematoma location, omental vessels were suspected of being the source of the hemorrhage.

As atomically thin oxide layers deposited on flat (noble) metal surfaces have been proven to have a significant influence on the electronic structure and thus the catalytic activity of the metal, we sought to mimic this architecture at the bulk scale. This could be achieved by intercalating small positively charged Pd nanoparticles of size 3.8 nm into a nematic liquid crystalline phase of lepidocrocite-type layered titanate. Upon intercalation the galleries collapsed and Pd nanoparticles were captured in a sandwichlike mesoporous architecture showing good accessibility to Pd nanoparticles. On the basis of X-ray photoelectron spectroscopy (XPS) and CO diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) Pd was found to be in a partially oxidized state, while a reduced Ti species indicated an electronic interaction between nanoparticles and nanosheets. The close contact of titanate sandwiching Pd nanoparticles, moreover, allows for the donation of a lattice oxygen to the noble metal (inverse spillover). Due to the metal–support interactions of this peculiar support, the catalyst exhibited the oxidation of CO with a turnover frequency as high as 0.17 s–1 at a temperature of 100 °C.

Europium and terbium doped layered gadolinium hydroxides were prepared by microwave assisted hydrothermal precipitation. They were subsequently exfoliated into nanosheets by sonication treatment in formamide. The thickness of the nanosheets (LGdH:Eu and LGdH:Tb) was found to be approximately 1 nm, exemplifying a single-layer feature. Multilayer and superlattice films were prepared through layer-by-layer (LbL) deposition of exfoliated hydroxide nanosheets with a polyanionic electrolyte (polystyrene sulfonate, PSS) and heteroassembly with semiconducting oxide nanosheets (Ti0.87O20.52- and TaO3-), respectively. Compared to the multilayers of (LGdH:Eu/PSS)n and (LGdH:Tb/PSS)n, the superlattices of (LGdH:Eu/Ti0.87O20.52-)n and (LGdH:Tb/TaO3-)n exhibited significantly enhanced photoluminescence intensity, ∼14 times and ∼5 times, respectively. The photoenergy absorbed by the semiconducting nanosheets can be transferred to the excited states of rare-earth hydroxide nanosheets for enhanced photoluminescence emission. Further investigation on the stacking sequence of the nanosheets revealed that direct neighboring and energy level matching with semiconducting nanosheets was essential for realizing efficient energy transfer across the nanosheet interface. Annealing at 600 °C could further enhance the emission intensity of the superlattice structured films. The current work demonstrates an important strategy for hetero-assembling nanosheets at the molecular level with a carefully designed interface for tunable and enhanced functionalities.

Lithium–sulfur batteries have high promise for applications in next-generation energy storage. However, further advances have been hindered by various intractable challenges, particularly three notorious problems: the “shuttle effect”, sluggish kinetics of lithium polysulfide conversion, and nonuniform nucleation of Li2S. In this study, a three-in-one cathode host based on a superlattice of two-dimensional (2D) materials is designed to tackle these three issues. Alternately restacked Nb3O8 nanosheets with Lewis acid surface and reduced graphene oxide (rGO) with high electrical conductivity give rise to a unique superlattice structure without the self-restacking, thereby maximizing the synergistic effect that stems from the inherent advantages of each component. The Nb3O8/rGO superlattice cathode host is characterized by its high affinity, excellent catalytic activity, abundance of exposed active sites, and high electrical conductivity, effectively confining lithium polysulfides and reducing the overpotentials for lithium polysulfide conversion and Li2S nucleation. As a result, high-performance lithium–sulfur batteries were achieved with an initial capacity of 1529 mA h g−1 at 0.1C and a slow capacity decay of 0.064% per cycle at 1C over 1000 cycles. This work provides a novel strategy of heteroassembling 2D nanosheets as a cathode host, opening a promising avenue for advanced lithium–sulfur batteries.

Atomic interfacial electric fields hold great potential for boosting ionic and charge transfer and accelerating electrochemical reaction kinetics. Here, built-in electric fields within the heterostructure are created by electrostatic assembly of unilamellar titano-niobate/graphene (reduced graphene oxide) nanosheets as building blocks. Scanning Kelvin probe microscopy confirms the existence of built-in electric fields by detecting the unbalanced surface potential of disparate nanosheets in the heterostructure, which facilitates ion and electron transfer, thus enabling an excellent reversible sodium storage capacity of 245 mAh g

Although various biomimetic soft materials that display structural hierarchies and stimuli responsiveness have been developed from organic materials, the creation of their counterparts consisting entirely of inorganic materials presents an attractive challenge, as the properties of such materials generally differ from those of living organisms. Here, we have developed a hydrogel consisting of inorganic nanosheets (14 wt%) and water (86 wt%) that undergoes thermally induced reversible and abrupt changes in its internal structure and mechanical elasticity (23-fold). At room temperature, the nanosheets in water electrostatically repel one another and self-assemble into a long-periodic lamellar architecture with mutually restricted mobility, forming a physical hydrogel. Upon heating above 55 °C, the electrostatic repulsion is overcome by competing van der Waals attraction, and the nanosheets rearrange into an interconnected 3D network of another hydrogel. By doping the gel with a photothermal-conversion agent, the gel-to-gel transition becomes operable spatiotemporally on photoirradiation., Inorganic soft materials are an attractive concept but challenging to make. Here the authors have developed a hydrogel consisting of inorganic nanosheets (14 wt%) and water (86 wt%) that undergoes thermally induced reversible and abrupt changes in its internal structure and mechanical elasticity (23-fold).

Recent advances in two-dimensional (2D) materials offer an opportunity for atomic layer engineering of functional thin films and superlattices. For future applications of 2D materials, there is an urgent need to develop convenient deposition processes that enable precise control of thin-film architectures while reducing the time, cost, and energy/sample consumption. Here, we demonstrate a strategy for nanosheet assembly using a simple drop casting with a pipet and a hot plate. By controlled thermal convection of a single droplet on a hot plate, a range of 2D nanosheets, such as Ti

Flexible and wearable electronics have recently sparked intense interest in both academia and industry because they can greatly revolutionize human lives by impacting every aspect of our daily routine. Therefore, developing compatible energy storage devices has become one of the most important research frontiers in this field. Particularly, the development of flexible electrodes is of great significance when considering their essential role in the performance of these devices. Although there is no doubt that transition metal oxide nanomaterials are suitable for providing electrochemical energy storage, individual oxides generally cannot be developed into freestanding electrodes because of their intrinsically low mechanical strength.Two-dimensional sheets with genuine unilamellar thickness are perfect units for the assembly of freestanding and mechanically flexible devices, as they have the advantages of low thickness and good flexibility. Therefore, the development of metal oxide materials into a two-dimensional sheet morphology analogous to graphene is expected to solve the above-mentioned problems. In this Account, we summarize the recent progress on two-dimensional molecular sheets of transition metal oxides for wearable energy storage applications. We start with our understanding of the principle of producing two-dimensional metal oxides from their bulk-layered counterparts. The unique layered structure of the precursors inspired the exploration of their interlayer chemistry, which helps us to understand the processes of swelling and delamination. Rational methods for tuning the chemical composition, size/thickness, and surface chemistry of the obtained nanosheets and how physicochemical properties of the nanosheets can be modulated are then briefly introduced. Subsequently, the orientational alignment of the anisotropic sheets and the origins of their liquid-crystalline characteristics are discussed, which are of vital importance for their subsequent macroscopic assembly. Finally, macroscopic electrodes with geometric diversity ranging from one-dimensional macroscopic fibers to two-dimensional films/papers and three-dimensional monolithic foams are summarized. The intrinsically low mechanical stiffness of metal oxide sheets can be effectively overcome by wisely designing the assembly mode and sheet interfaces to obtain decent mechanical properties integrated with superior electrochemical performance, thereby providing critical advantages for the fabrication of wearable energy storage devices.We expect that this Account will stimulate further efforts toward fundamental research on interface engineering in metal oxide sheet assembly and facilitate wide applications of their designed assemblies in future new-concept energy conversion devices and beyond. In the foreseeable future, we believe that there will be a big explosion in the application of transition metal oxide sheets in flexible electronics.

Efficient electrocatalysts are highly demanded for oxygen evolution reaction (OER) in water splitting and metal–air batteries. Here, superlattice structured materials composed of CoNiFe layered dou...

Molecularly thin two-dimensional (2D) semiconductors are emerging as photocatalysts owing to their layer-number-dependent quantum effects and high charge separation efficiency. However, the correlation among the dimensionality, crystallinity, and photocatalytic activity of such 2D nanomaterials remains unclear. Herein, a Ag photoreduction technique coupled with microscopic analyses is employed to spatially resolve the photocatalytic activity of MoS2 as a model catalyst. Interestingly, we find that only monolayer (1L)-MoS2 is active for a Ag photoreduction reaction. The photocatalytic activity of 1L-MoS2 is enhanced by a built-in electrical field originated from the MoS2/SiO2 interface, instead of by the specific surface structure and quantum electronic state of 1L-MoS2. Furthermore, we observe photocatalytic active sites to be geometrically distributed on triangular 1L-MoS2 crystals, wherein the Ag particles are preferentially deposited on the outermost zigzag edges and defective inner parts of the triangular grains. The degradation of photocatalytic activity and electron mobility with the formation of Mo(VI) species indicates that the species inhibit the in-plane diffusion of the photogenerated electrons to the reductive sites. The monolayer-selectivity, activation, and inactivation mechanisms, unveiled in this work, will offer future directions in designing 2D nanophotocatalysts.

Layered double hydroxides (LDHs) with di-/trivalent metal cations are considered as one of the most promising materials for high-performance electrocatalysts. On the other hand, α-type hydroxides, ...

Rutile-type fluorides have been proven to be active components in the context of emerging antiferr-omagnetic devices. However, controlled synthesis of low-dimensional, in particular two-dimensional (2D), fluorides in a predictable and deterministic manner remains unrealized because of a lack of efficient anisotropic control, which impedes their further development in reduced dimensions. We report here that altered passivation of {110} growing facets can direct the synthesis of rutile-type fluoride nanocrystals into well-defined zero-dimensional (0D) particulates, one-dimensional (1D) rods and 2D sheets in a colloidal approach. The obtained nanocrystals show positive exchange bias and enhanced magnetic transition temperature from the coexistence of long-range antiferromagnetic order and disordered surface spins, making them strong alternatives for flexible magnetic devices and sensors., The altered passivation of growing facets can direct the colloidal synthesis of rutile-type fluorides nanocrystals into 0D particulates, 1D rods, and 2D sheets.

Two-dimensional (2D) superlattices, assembled from vertically stacked inorganic 2D nanosheets, are a new class of artificial 2D materials of significant scientific and technological importance. The incorporation of an infinite number of organic molecules within these systems further provides unlimited possibilities for the design and synthesis of 2D organic–inorganic hybrid superlattices with predictable functionalities. Herein, the recent research progress in 2D organic–inorganic hybrid superlattices is summarized. Many facile strategies have been developed for the fabrication of 2D organic–inorganic hybrid superlattices, in which continuous organic layers are intercalated in the interlayer galleries of inorganic 2D nanosheets at an atomic/molecular scale. The advantages of these 2D superlattices are discussed for some typical energy storage applications, such as supercapacitors, lithium/sodium/potassium ion batteries, and multivalent-ion rechargeable batteries. The challenges and perspectives for future research are also outlined.

Flocculation or restacking of different kinds of two-dimensional (2D) nanosheets into heterostructure nanocomposites is of interest for the development of high-performance electrode materials and catalysts. However, lacking a molecular-scale control on the layer sequence hinders enhancement of electrochemical activity. Herein, we conducted electrostatic layer-by-layer (LbL) assembly, employing oxide nanosheets (e.g., MnO

Just like in living organisms, if precise coherent operation of tiny movable components is possible, one may generate a macroscopic mechanical motion. Here we report that ~1010 pieces of colloidally dispersed nanosheets in aqueous media can be made to operate coherently to generate a propagating macroscopic wave under a non-equilibrium state. The nanosheets are initially forced to adopt a monodomain cofacial geometry with a large and uniform plane-to-plane distance of ~420 nm, where they are strongly correlated by competitive electrostatic repulsion and van der Waals attraction. When the electrostatic repulsion is progressively attenuated by the addition of ionic species, the nanosheets sequentially undergo coherent motions, generating a propagating wave. This elaborate wave in time and space can transport microparticles over a long distance in uniform direction and velocity. The present discovery may provide a general principle for the design of macroscopically movable devices from huge numbers of tiny components., Tiny movable components could generate macroscopic mechanical motion if precise coherent operation can be exerted simultaneously. Here, the authors demonstrate this by using 10^10 pieces of colloidally dispersed nanosheets to generate wave under non-equilibrium state.

This study reports a design of a variety of nanostructured films of 2D oxide nanosheets. We systematically examined the deposition of perovskite-type Ca2Nb3O10- nanosheets by spin-coating their dimethyl sulfoxide dispersion. Neat and homogeneous monolayer tiling was attained on various substrates by selecting an optimum rotation speed, which was dependent on the nanosheet concentration. Repeating the optimized spin-coating process allowed for layer-by-layer deposition of the nanosheets into multilayer films with a designed layer number. Vertical superlattice heterostructures could also be assembled by alternately spin-coating the suspensions of Ca2Nb3O10- and Ti0.87O20.52- nanosheets. Furthermore, spin-coating of a mixed suspension of Ca2Nb3O10- and Ti0.87O20.52- nanosheets led to a mixed mosaic-like monolayer of these two nanosheets. The present study thus demonstrated spin-coating as a facile and powerful route to construct various nanostructures based on 2D oxide nanosheets.

This paper presents a design of dual-polarized broad-beam reflective metasurface (MS) for 5G mmWave application at 28 GHz. Its broad-beam operation is simply realized by combining multiple MS sections with having different diffraction grating periods for different reflection angles. In the demonstration, the MS structure is designed by three sub-design sections that generate different reflection angles of 50°, 60°, and 70° under the identical normal incident angle. From the obtained results, the proposed MS can provide broad reflection beam from 45°-65° under both vertical- and horizontal-polarized incident waves.