Two-dimensional Nanostructures Research Articles

Uracil derivative-assisted universal synthesis of defective 2-dimensional porous flaky carbon nitride for efficient photocatalytic CO2 reduction

In this paper, three novel defective two-dimensional lamellar carbon nitride were successfully synthesized by molecular self-assembly using melamine and cyanuric acid as supramolecular aggregates and introducing three different uracil derivatives (5-formyluracil, 5-acetyluracil, uracil-5-carboxylic acid). In our previous work, we found that the introduction of thymine into supramolecular precursors has good photocatalytic oxidation ability for NO. On this basis, we discovered that by introducing uracil derivatives as ligands for supramolecular aggregates, not only two-dimensional porous sheet nanostructures can be constructed, but also abundant nitrogen and oxygen defects can be introduced, which is supported by various characterizations. These defects can effectively modulate the electronic structure of carbon nitride and thus improve the separation of photogenerated carriers. In addition, the introduction of uracil derivatives affects the energy band structure of the catalyst, and these are important factors affecting the catalytic activity. Compared with bulk carbon nitride, the synthesized materials exhibited significantly enhanced photocatalytic CO2 reduction activity under mild conditions, with CO yields of 10.34, 28.65, 32.28, and 36.48 μmol g−1h−1 for BCN, CNU2.5, CNF2.5, and CNY2.5, respectively. More importantly, with the support of in situ DRIFTS, we proposed the reaction mechanism of photocatalytic reduction of CO.

MoS2-TiO2 Nanocomposites for Enhanced Photo-electrocatalytic Hydrogen Evolution

The investigation on the designing and fabrication of highly efficient electrocatalysts for hydrogen evolution reaction (HER) is critical for future applications in renewable sustainable energy. The present work reports the hydrothermal synthesis of two-dimensional MoS2 and MoS2-TiO2 nanostructures. The as-prepared nanostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman analysis, UV–vis-NIR, and photoluminescence spectrophotometry and vibrating sample magnetometer (VSM). Systematic electrochemical measurements for HER were performed and MoS2-TiO2 nanocomposites demonstrated the lowest onset potential in comparison with MoS2. The results suggest that the nanofusion interface between MoS2 nanoflakes and TiO2 nanoparticles induced an efficient charge transfer from the conduction band of MoS2 to TiO2 and favored the reduction of H+ at active sites. We believe the present work can open up new possibilities that would provide deep insights for the rational design of 2D materials-based catalysts for energy storage and conversion applications.

Engineering Two-Dimensional Multilevel Supramolecular Assemblies from a Bifunctional Ligand on Au(111).

Herein, we demonstrate the supramolecular assemblies from a bifunctional ligand on Au(111), towards engineering two-dimensional (metal-) organic multilevel nanostructures. The bifunctional ligand employed, including two Br atoms and one carboxylic terminal, offers multiple bonding motifs with different configurations and binding energies. These bonding motifs are highly self-selective and self-recognizable, and thus afford the formation of subunits that contribute to engineering multilevel self-assemblies. Our scanning tunneling microscopy experiments, in combination with the density functional theory calculations, revealed various hydrogen, halogen and alkali-carboxylate bonding motifs dictating the different levels of the assemblies. The multilevel assembly protocol based on a judicious choice of multiple bonding motifs guarantees a deliberate control of surface-confined (metal-) organic nanostructures. Our findings may present new opportunities for the fabrication of complex two-dimensional (metal-) organic nanostructures with potential in applications of functionally diverse nanomaterials.

Robust Ti3C2Tx MXene foam modified with natural antioxidants for long-term effective electromagnetic interference shielding

MXenes have been proven to be outstanding lossy phase of advanced electromagnetic interference (EMI) shielding materials. However, their poor tolerance to oxygen and water results in fast degradation of the pristine two-dimensional (2D) nanostructure and fading of the functional performance. Herein, in this research, natural antioxidants (e.g., melatonin, tea polyphenols, and phytic acid) were employed to protect the Ti3C2Tx MXene from its degradation in order to achieve a long-term stability of the EMI shielding performance. The results showed that the synthesized composites comprised of antioxidants and Ti3C2Tx exhibited a decelerating degradation rate resulting in an improved EMI shielding effective (SE) stability. The antioxidation mechanism of the applied antioxidants is discussed with respect to the nanostructure evolution of the Ti3C2Tx MXene. This work contributes to the basic foundations for the further development of advanced MXenes for stable applications in the EM field.

Dislocation-Assisted Quasi-Two-Dimensional Semiconducting Nanochannels Embedded in Perovskite Thin Films.

Defect engineering in perovskite thin films has attracted extensive attention recently due to the films' atomic-scale modification, allowing for remarkable flexibility to design novel nanostructures for next generation nanodevices. However, the defect-assisted three-dimensional nanostructures in thin film matrices usually has large misfit strain and thus causes unstable thin film structures. In contrast, defect-assisted one- or two-dimensional nanostructures embedded in thin films can sustain large misfit strains without relaxation, which make them suitable for defect engineering in perovskite thin films. Here, we reported the fabrication and characterization of edge-type misfit dislocation-assisted two-dimensional BiMnOx nanochannels embedded in SrTiO3/La0.7Sr0.3MnO3/TbScO3 perovskite thin films. The nanochannels are epitaxially grown from the surrounding films without noticeable misfit strain. Diode-like current rectification was spatially observed at nanochannels due to the formation of Schottky junctions between BiMnOx nanochannels and conducting La0.7Sr0.3MnO3 thin films. Such atomically scaled heterostructures constitute more flexible ultimate functional units for nanoscale electronic devices.

Sonochemistry of Liquid-Metal Galinstan toward the Synthesis of Two-Dimensional and Multilayered Gallium-Based Metal-Oxide Photonic Semiconductors.

The scientific field of two-dimensional (2D) nanostructures has witnessed tremendous development during the last decade. To date, different synthesis approaches have been developed; therefore, various exceptional properties of this family of advanced materials have been discovered. It has recently been found that the natural surface oxide films of room-temperature liquid metals is an emerging platform for the synthesis of novel types of 2D nanostructures with numerous functional applications. However, most of the developed synthesis techniques for these materials are based on the direct mechanical exfoliation of 2D materials as research targets. This paper reports a facile and functional sonochemical-assisted approach for the synthesis of 2D hybrid and complex multilayered nanostructures with tunable characteristics. In this method, the intense interaction of acoustic waves with microfluidic gallium-based room-temperature liquid galinstan alloy provides the activation energy for synthesis of hybrid 2D nanostructures. The microstructural characterizations reveal the impact of sonochemical synthesis parameters, including the processing time and composition of the ionic synthesis environment, on the growth of GaxOy/Se 2D hybrid structures and InGaxOy/Se multilayered crystalline structures with tunable photonic characteristics. This technique shows promising potential for synthesis of various types of 2D and layered semiconductor nanostructures with tunable photonic characteristics.

Atomic Layer Deposition of Ultra-Thin Crystalline Electron Channels for Heterointerface Polarization at Two-Dimensional Metal-Semiconductor Heterojunctions

Atomic layer deposition (ALD) has emerged as a promising technology for the development of the next generation of low-power semiconductor electronics. The wafer-scaled growth of two-dimensional (2D) crystalline nanostructures is a fundamental step toward the development of advanced nanofabrication technologies. Ga2O3 is an ultra-wide bandgap metal oxide semiconductor for application in electronic devices. The polymorphous Ga2O3 with its unique electronic characteristics and doping capabilities is a functional option for heterointerface engineering at metal-semiconductor 2D heterojunctions for application in nanofabrication technology. Plasma-enhanced atomic layer deposition (PE-ALD) enabled the deposition of ultra-thin nanostructures at low-growth temperatures. The present study used the PE-ALD process for the deposition of atomically thin crystalline ß-Ga2O3 films for heterointerface engineering at 2D metal-semiconductor heterojunctions. Via the control of plasma gas composition and ALD temperature, the wafer-scaled deposition of ~5.0 nm thick crystalline ß-Ga2O3 at Au/Ga2O3-TiO2 heterointerfaces was achieved. Material characterization techniques showed the effects of plasma composition and ALD temperature on the properties and structure of Ga2O3 films. The following study on the electronic characteristics of Au/Ga2O3-TiO2 2D heterojunctions confirmed the tunability of this metal/semiconductor polarized junction, which works as functional electron channel layer developed based on tunable p-n junctions at 2D metal/semiconductor interfaces.

Titanium (IV) oxide composite hollow nanofibres with silver oxide outgrowth by combined sol–gel and electrospinning techniques and their potential applications in energy and environment

A two-dimensional nanostructure composed of Ag2O nanobranches attached to TiO2 hollow nanofibres (denoted as 2D Ag2O/TiO2) was successfully prepared via sol–gel and coaxial electrospinning techniques. The Ag/TiO2 hollow nanofibres were fabricated and calcined in ambient air at 500 °C. By calcination, the removal of organic materials and the formation of anatase TiO2 were achieved with a well-retained hollow structure. The embedded Ag nanoparticles functioned as seeds for the Ag2O outgrowth on the TiO2 surface using a hydrothermal treatment at different times and temperatures, which caused the change in physical appearance, surface area, and electrical conductivity of 2D Ag2O/TiO2. A high quantity of Ag2O nanobranches on TiO2 nanofibres were obtained with increasing the temperature from 110 to 115 °C and the reaction time to 60 min. Consequently, the electrochemical active surface area (EASA) value was maximised to 65.25 cm2 per cm2 with an enhanced electrical conductivity of 91.3 ± 3.9 × 10−2 S cm−1. Further studies on the depth-profiles of Ag, Ti, and O revealed the presence of Ag2O attached to the core structure of TiO2. The photoelectrochemical and photocatalytic tests confirmed the excellent physical and electrochemical properties of 2D Ag2O/TiO2 (@115 °C, 60 min) for use in energy and environmental applications.Graphical

Hydrophobic MXene with enhanced electrical conductivity

Two-dimensional nanostructured (2D) layers of transition metal nitrides, carbides, or carbonitrides, known as MXenes, are inherently hydrophilic mainly due to the presence of surface terminating groups like –O, -OH, etc. In this work, hydrophilic MXenes have been converted to hydrophobic ones by low-energy N+ ion irradiation at different fluences. The removal of surface functional groups after irradiation is supported by various characterizations. DFT simulations confirm the strong influence of -OH and -O-OH on the hydrophilic nature of pristine MXene. Adsorption energy data reveals that the adsorption of water molecules on surface terminal group-free MXenes is energetically unfavorable, pointing towards hydrophobic character. Ion irradiation is exploited as a tool to partially remove the surface-terminating functional groups to make MXenes hydrophobic. Additionally, a remarkable enhancement in electrical conductivity has been noticed with increase in ion fluence, which can also be attributed to preferential sputtering of the functional groups and the structural change of MXene.

Interactions between Layered Double Hydroxide Nanoparticles and Egg Yolk Lecithin Liposome Membranes.

The burgeoning need to study the applications of nanoparticles (NPs) in biomedical and pharmaceutical fields requires an understanding of their interactions with lipid membranes for further in vivo studies. In this paper, negatively charged egg yolk lecithin liposome (EYL) has been prepared and used as model lipid membranes. Positively charged Mg3Al-layered double hydroxides (LDHs) are viewed as models of clay particles. The ability of the LDH NPs, a two-dimensional nanostructure with an average diameter of 100 nm (LDHs-100) or 500 nm (LDHs-500) to cross the membranes, has been thoroughly investigated via (high-resolution) transmission electron microscopy (TEM), optical microscopy (OM), scanning electron microscopy (SEM), confocal fluorescence microscopy (CLSM), and dynamic light scattering (DLS). The liposomes with an average diameter of 1.5 μm were prepared by the thin-film rehydration method followed by an extrusion technique. A calcein leakage assay and steady-state fluorescence measurement displayed the variation of membrane integrity and polarity of the pyrene-located microenvironment during the interaction between EYL and calcein-interacted LDH NPs (CE-LDHs) or LDH NPs, respectively. These results imply that not only spherical particles but also even more sophisticated nanostructured materials are able to effectively cross the lipid bilayers, thereby engineering new compounds that may be encapsulated for safe and potential use in biomedical applications.

Structural coloration with two-dimensional nanostructures fabricated by elliptical vibration nanoindentation

Structural color stemming from the two-dimensional (2D) nanostructures that induced light interference attracts more attention than 1D grating due to its higher design flexibility. However, the fast and cost-effective fabrication of pixel-by-pixel 2D nanostructures is challenging. This study prompts nanoindentation as a promising technique for fabricating 2D nanostructure on metallic surfaces by adding an ultrafast elliptical vibration on the nanoindenter. First, the elliptical vibration nanoindentation (EVN) process principle is analyzed. Next, an ultrafast elliptical vibration nanoindentation tool (UEVNT) with a maximum working frequency of 2 kHz is developed. Then, machining experiments were conducted on aluminum to evaluate the performance of EVN, whose results demonstrate the successful fabrication of pyramid-type nanostructures with a depth of hundreds of nanometers and a spacing of 1–3 μm. Based on the unique spatial diffraction characteristic of 2D nanostructures, a high-decoupling optical variable device has also been fabricated on the aluminum surface by rendering two images into two orthogonal observation directions. Finally, the 2D nanostructures on a metallic surface were transferred to the flexible polymer to fabricate a structural color-based bidirectional strain sensor. Stretching tests have been performed with results verifying the potential application of 2D nanostructures-induced structural color in the wireless measurement of mechanical deformation.

Advances in two-dimensional engineered nanomaterials applications for the agro- and food-industries.

Two-dimensional nanomaterials, such as graphene, transition metal dichalcogenides, MXenes, and other layered compounds, are the subject of intense theoretical and experimental research for applications in a wide range of advanced technological solutions, given their outstanding physical, chemical, and mechanical properties. In the context of food science and technology, their contributions are starting to appear, based on the advantages that two-dimensional nanostructures offer to agricultural- and food-related key topics, such as sustainable water use, nano-agrochemicals, novel nanosensing devices, and smart packaging technologies. These application categories facilitate the grasping of the current and potential uses of such advanced nanomaterials in the field, backed by their advantageous physical, chemical, and structural properties. Developments for water cleaning and reuse, efficient nanofertilizers and pesticides, ultrasensitive sensors for food contamination, and intelligent nanoelectronic disposable food packages are among the most promising application examples reviewed here and demonstrate the tremendous impact that further developments would have in the area as the fundamental and applied research of two-dimensional nanostructures continues. We expect this work will contribute to a better understanding of the promising characteristics of two-dimensional nanomaterials that could be used for the design of novel and feasible solutions in the agriculture and food areas. © 2023 Society of Chemical Industry.

2D Nanostructures for Optoelectronic and Green Energy Devices

Two-dimensional (2D) materials and nanostructures have gathered significant attention due to their excellent mechanical properties [...].

High power aqueous hybrid asymmetric supercapacitor based on zero-dimensional ZnS nanoparticles with two-dimensional nanoflakes CuSe2 nanostructures

Energy storage materials, particularly chalcogenides, are fascinating electrode materials for supercapacitors (SCs) because of their high capacitance, remarkable electrical conductivity, and multiple oxidation states contributed by numerous metal cations. Herein, a novel nanocomposite based on zinc sulfide and copper diselenide, denoted as (ZnS–CuSe2), was prepared via a sonochemical-assisted method. The structural analysis revealed the cubic structure for pure ZnS, orthorhombic for CuSe2, and co-existing cubic and orthorhombic phases for ZnS–CuSe2 nanocomposites with high purity and crystallinity. The ZnS–CuSe2 nanocomposite offered exceptional electrochemical performance with redox peaks from the CV analysis, and coupled with plateaus in the charge/discharge profile, confirming the faradaic energy storage properties with functional reversibility. Similarly, a high conductive feature of the ZnS–CuSe2 composite was revealed by impedance study, with a minor charge transfer resistance than their bulk materials. A hybrid asymmetric supercapacitor (HASCs) composed of ZnS–CuSe2//AC was constructed, which manifested an enlarged voltage window up to 1.7 V with capacitance of 95 F g−1 and a maximum specific energy of 38 Wh kg−1. Also, high power delivery was attained at 3927 Wkg-1 when specific energy goes down to 12 Wh kg− at 5 A g−1. Interestingly, only 81.8% retention was left beneath when cycled to 8000 cycles, specifying decent stability of the ZnS–CuSe2//AC HASCs.

Facile synthesis of Mn/RuO2 nanosheets for high-performance acidic oxygen evolution reaction

Due to the dimensional confinement, two-dimensional (2D) nanostructures have exposed more active atoms, allowing faster electron transport; Furthermore, Doping is widely used to modulate the local electronic structure within the material. In this work, we proposed a strategy for the facile synthesis of ultrathin transition metal-doped nanosheets. The 2D Mn/RuO2 nanosheets prepared by rapid thermal annealing (RTA), required an overpotential of only 185 mV to reach a current density of 10 mA cm−2 under acidic solution, which was much lower than that of commercial IrO2. This finding provides a promising strategy for the reduction of precious metal content and the preparation of ultrathin nanosheet, and brings inspiration for the design and fabrication of other advanced nano-catalysts.

Graphene Nanocomposites in Space Sector—Fundamentals and Advancements

Graphene is one of the most significant carbon nanomaterials, with a one-atom-thick two-dimensional nanostructure. Like other nanocarbons, graphene has been used as a polymer reinforcement. This review explores the impact of graphene and graphene-based nanocomposites on aerospace applications. The fabrication and indispensable features of graphene-derived nanocomposites have been considered. Numerous polymers and nanocomposites have been employed for aerospace systems such as reinforced thermosetting/thermoplastic polymers and epoxy/graphene nanocomposites. Moreover, graphene-modified carbon-fiber-based composites have been discussed for the space sector. Aerospace nanocomposites with graphene have been investigated for superior processability, structural features, morphology, heat stability, mechanical properties, flame resistance, electrical/thermal conductivity, radiation protection, and adhesion applications. Subsequently, epoxy and graphene-derived nanocomposites have been explored for heat/mechanically stable aerospace engineering structures, radiation-shielding materials, adhesives, coatings, etc.

Formation controllable two-dimensional surface optical lattices

The evanescent light field created by total internal reflection at a dielectric-vacuum interface has tight spatial confinement and high local intensity. These properties become more robust when a dual layer of dielectric thin films with different thicknesses is deposited on a planar dielectric surface. Optical construction is promising in nanoscale trapping of absorbed atoms congregating at extreme light field intensity distribution regions on the dielectric surface. Here, we theoretically demonstrate the controllable two-dimensional surface optical lattices based on the evanescent electric field generated by the Hermite-Gaussian light beam. By considering the coupling of lattice to quadrupole-active atomic transitions, we show that the topologies cannot just have high stability, but also the optical potential deep, and thus the dynamic trapping can be governed by changing the design parameters of the optical construction. We expect that this study may contribute to providing another unique method for fabricating spatially complicated two-dimensional nanostructures.

LUMINESCENCE OF TWO-DIMENSIONAL ZnO NANOSTRUCTURES: NANOWALLS, NANOSHEETS, NANOCOMBS

Preliminary comparative studies of the photoluminescent properties of two-dimensional ZnO nanostructures with morphology of nanowalls, nanosheets, and nanocombs, fabricated by gas-transport synthesis, have been performed. All structures exhibited near-band-edge (NBE) UV emission of the same order of intensity. Unlike nanocombs, whose spectrum contains a comparatively strong green luminescence band, nanowalls and nanosheets are characterized by a large ratio of the UV and visible components. This distinction is presumably due to the difference in the mechanisms of structure formation: nanowalls and nanosheets are formed according to the vapor–liquid–solid mechanism, whereas nanocombs grow according to the vapor–solid mechanism

Atomism of the Force-Field Influence on the Durability of Carbyne–Graphene Nanoelements and Similar Two-Dimensional Nanostructures

Atomism of the Force-Field Influence on the Durability of Carbyne–Graphene Nanoelements and Similar Two-Dimensional Nanostructures

Mesoscopic 2D molecular self-assembly on an insulator

Two-dimensional (2D) nanostructures and nanomaterials offer potential for a wide range of technological applications in electronics, optoelectronics, data storage, sensing and catalysis. On-surface molecular self-assembly—where organic molecules act as building blocks and where surfaces play the role of supporting templates—allows for the bottom-up synthesis of such 2D systems with tuneable atomically precise morphologies and tailored electronic properties. These self-assembly protocols are well established on metal surfaces, but remain limited on electronically gapped substrates (insulators, semiconductors). The latter are useful for preventing electronic coupling (that is, hybridization between molecular assembly and underlying surface) and for avoiding quenching of optical processes, necessary for prospective electronic and optoelectronic applications. In particular, molecular self-assembly on surfaces other than weakly interacting metals can be challenging due to substrate reactivity, defects and inhomogeneities, resulting in intricate energy landscapes that limit the growth kinetically and hampers the synthesis of large-area defect-free 2D systems. Here, we demonstrate the self-assembly of a 2D, atomically thin organic molecular film on a model wide bandgap 2D insulator, single-layer hexagonal boron nitride (hBN) on Cu(111). The molecular film consists of flat, aromatic 9,10-di-cyano-anthracene (DCA) molecules. Our low-temperature scanning tunnelling microscopy and spectroscopy measurements revealed mesoscopic (>100 × 100 nm2), topographically homogeneous crystalline molecular domains resulting from flat molecular adsorption and noncovalent in-plane cyano-ring bonding, with electronically decoupled molecular orbitals (MOs) lying within the hBN electronic gap. These MOs exhibit an energy level spatial modulation (∼300 meV) that follows the moiré work function variation of hBN on Cu(111). These findings pave the way for large-area, atomically precise, highly crystalline 2D organic (and metal-organic) nanomaterials on electronically functional wide bandgap insulators.