2D Nanoplatelets Research Articles

Green synthesis of ultrathin 2D nanoplatelets, hematene and magnetene, from mineral ores in water, with strong optical limiting performance

Hematene and magnetene nanoplatelets have been produced by liquid phase exfoliation of natural mineral ores, in a water solution of melamine under mild sonication.

Expanding the color palette of bicolor-emitting nanocrystals.

Owing to their bright and tunable luminescence spectra, nanocrystals appear as a unique playground for light source design. Displays and lighting require white light sources that combine several narrow lines. As Kasha's rule prevents the emission of hot carriers, blends of multiple nanocrystal populations are currently the obvious strategy for broad-band source design. However, a few reports suggest that bicolor emission can also be obtained from a single particle even under weak excitation if a careful design of the exciton scattering mechanism sufficiently slows down its relaxation pathways. A key challenge remains to maintain quantum confinement for color tunability in the same structure, while simultaneously achieving a large size to leverage the critical, slower exciton diffusion or relaxation down to the ground state. Herein, we demonstrate that 2D nanoplatelets offer an original opportunity for the design of confined and large heterostructures. We demonstrate that bicolor emission is not limited to green-red pair and show that blue-yellow and purple-green emissions can be obtained from CdSe/CdTe/CdSe core/crown/crown and CdSe/CdS core/crown heterostructures, respectively.

Synergistic enhancement in mechanical, thermal, and dielectric properties of PANI@BT/PVDF composites by adding 2D nanoplatelets

AbstractPolymer‐based dielectric composites with simultaneously improved dielectric constant and breakdown strength have great potential applications in energy storage. In this paper, polyaniline@BaTiO3 (PANI@BT) nanoparticles with core‐shell structure are first fabricated by in‐situ chemical oxidative polymerization, and deposited on the surface of two‐dimensional nanoplatelets (graphene oxide [GO] and hexagonal boron nitride nanosheets [BNNS]), which are then utilized to prepare poly(vinylidene fluoride) (PVDF)‐based composites. The presence of 2D nanoplatelets is found to significantly ameliorate the dispersion of PANI@BT particles in the PVDF matrix, and thus endowing the resultant PVDF composites with improved comprehensive performance. The dielectric constant of PANI@BT‐GO/PVDF and PANI@BT‐BNNS/PVDF composites with 50 wt% fillers increase to 124.9 and 169.5 at 100 Hz, accompanied with relatively low dielectric loss. When the filler content is 10 wt%, the breakdown strength of PANI@BT‐BNNS/PVDF achieves 133.5 kV/mm, which is 9.7% and 71.8% higher than that of the pristine PVDF and PANI@BT/PVDF composites. Meanwhile, the tensile stress also reaches the highest value of 43.38 MPa. In addition, the PANI@BT‐GO/PVDF and PANI@BT‐BNNS/PVDF composites present higher thermal decomposition temperature in comparison with PANI@BT/PVDF composites.

Transparent, Stretchable, and Self‐Healable Gas Barrier Films with 2D Nanoplatelets for Flexible Electronic Device Packaging Applications

AbstractSelf‐healable elastomeric materials (PUAxPU10–x‐PDMS, x = 4, 6, or 8) have been synthesized and utilized as substrates or encapsulation films on the top of barrier films (deposited on polyethylene terephthalate (PET) substrates) to improve their gas barrier properties for packaging applications. Hexa‐layer (HL) assembly consisting of two inorganic 2D nanoplatelets, including Mg‐Al layered double hydroxide (LDH) and hexagonal boron nitride (hBN), and two oppositely charged polyelectrolytes, that is, polyethyleneimine (PEI) and poly(sodium styrene‐4‐sulfonate) (PSS), have been developed by alternative depositions of HL (i.e., PSS/LDH/PSS/PEI/hBN/PEI) sequentially. Then, a layer‐by‐layer technique is applied to produce multiple assemblies of hexa‐layer (HL)n and reduce water vapor transmission rate (WVTR) values of elastomeric PUA8PU2‐PDMS and PET substrates. The optimum WVTR values of 7.1 × 10−3 and 8.0 × 10−3 g m−2 day−1 are achieved using barrier PET/(HL)8/PUA8PU2‐PDMS (125/3/1 µm) and PUA8PU2‐PDMS/(HL)8 (125/3 µm) films, respectively. The self‐healable barrier PUA8PU2‐PDMS and PUA8PU2‐PDMS/(HL)8 films recover their initial WVTR values after self‐healing of mechanically damaged films. Organic light‐emitting diodes (OLEDs) encapsulated with PET/(HL)8/PUA8PU2‐PDMS and PUA8PU2‐PDMS/(HL)8 have 9–10 times longer half‐lifetime values than bare OLEDs. Accordingly, this report develops transparent, stretchable, and self‐healable gas barrier films for next‐generation flexible electronic device packaging applications.

Theoretical Investigation of the Electronic Spectra of Cadmium Chalcogenide 2D Nanoplatelets.

Although colloidal cadmium chalcogenide 2D nanoplatelets (NPLs) have recently demonstrated strongly enhanced one- and two-photon absorption (OPA, TPA) spectra, an understanding of the effects of quantum confinement in the lateral and vertical (thickness) dimensions is mostly lacking. In this work, we investigate theoretically CdS and CdSe NPLs passivated with formate and acetate ligands with thicknesses of two and three monolayers (MLs) and different lateral dimensions. Initial structures for CdS nanoplatelets were obtained using our recently developed deep neural network potential, and the low-energy geometries were subsequently optimized using density functional theory (DFT). Linear- and nonlinear-response calculations using time-dependent DFT (TDDFT) and the simplified Tamm-Dancoff approximation (sTDA) demonstrated good agreement between measured spectra and calculated TDDFT and sTDA spectra for 2 and 3 ML NPLs. The OPA red-shifts from 2 to 3 ML NPLs can be attributed to the electron delocalization in the lateral and vertical directions. TPA responses for CdS and CdSe NPLs were found to be dominated by weakly absorbing and forbidden OPA states.

AIE-Active, Stimuli-Responsive Fluorescent 2D Block Copolymer Nanoplatelets Based on Corona Chain Compression.

Aggregation-induced emission (AIE) represents a powerful tool in nanoscience as a result of enhanced luminescence in the condensed state. Although AIEgenic materials have been utilized in a wide range of applications, well-defined self-assembled nanoparticles with tailorable and uniform dimensions and morphology remain challenging to access. Herein, we use the seeded growth, living crystallization-driven self-assembly (CDSA) method to prepare size-tunable and uniform AIE-active 2D nanoplatelets from amphiphilic block copolymer (BCP) precursors with a crystallizable core-forming block and a corona-forming block to which tetraphenylethene (TPE) groups were covalently grafted as AIE-active pendants. The nanoplatelets were formed as a result of a solvophobicity-induced 1D to 2D morphology preference change, which accompanied the seeded growth of a BCP with a quaternized corona-forming block bearing the TPE luminogen. The 2D nanoplatelets exhibited a solvent-responsive fluorescent emission, and examples with coronas containing homogeneously distributed AIE-active TPE groups and Hg(II)-capturing thymine units exhibited excellent performance as proof-of-concept "turn-on" sensors for Hg(II) detection with a rapid response, high selectivity, and a low detection limit (5-125 × 10-9 M, i.e., 1-25 ppb). The fluorescence intensity was found to be nonlinear with respect to analyte concentration and to increase with the area of the nanoplatelet. This behavior is consistent with a cooperative mechanism based on changes in the steric compression of the corona chains, which gives rise to a restriction of the intramolecular motion (RIM) effect.

Double-crowned 2D semiconductor nanoplatelets with bicolor power-tunable emission

Nanocrystals (NCs) are now established building blocks for optoelectronics and their use as down converters for large gamut displays has been their first mass market. NC integration relies on a combination of green and red NCs into a blend, which rises post-growth formulation issues. A careful engineering of the NCs may enable dual emissions from a single NC population which violates Kasha’s rule, which stipulates that emission should occur at the band edge. Thus, in addition to an attentive control of band alignment to obtain green and red signals, non-radiative decay paths also have to be carefully slowed down to enable emission away from the ground state. Here, we demonstrate that core/crown/crown 2D nanoplatelets (NPLs), made of CdSe/CdTe/CdSe, can combine a large volume and a type-II band alignment enabling simultaneously red and narrow green emissions. Moreover, we demonstrate that the ratio of the two emissions can be tuned by the incident power, which results in a saturation of the red emission due to non-radiative Auger recombination that affects this emission much stronger than the green one. Finally, we also show that dual-color, power tunable, emission can be obtained through an electrical excitation.

Sensitivity improvement of hybrid active layer containing 2D nanoplatelets for indirect x-ray detector

In this paper, we attempted to improve the detection sensitivity of an indirect x-ray detector through using a hybrid active layer composed of a poly [N-90-heptadecanyl–2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) organic semiconductor and cadmium selenide nanoplatelets (CdSe NPLs) colloidal inorganic semiconductors. First, different blending ratio in the active layer (i.e. 2:1, 1:1, 1:2 and 1:3) of PCDTBT:CdSe NPL were examined, a sensitivity of 89.5 μC·Gyair −1·cm−2 was achieved using a 1:1 ratio due to the low series resistance (RS ) and defect density in this configuration. Then, the oleic acid (OA) that was initially applied in the CdSe NPL surface was replaced with pyridine ligands, this was done because the pyridine ligand is a short-chain ligand that can help charge transfer by reducing the distance between NPLs in the active layer. In addition, an experiment was conducted to determine the optimal ligand exchange time. A detector with an PCDTBT:CdSe NPL active layer fabricated using pyridine ligand exchange achieved a sensitivity of 219.8 μC·Gyair −1·cm−2 after an exchange time of 12 h, this is an improvement of 155% compared to the detector using a PCDTBT:CdSe NPL with the original OA ligands. Lastly, the optimal thickness for the PCDTBT:CdSe NPL active layer was investigated. The highest mobility of 7.60 × 10− 6 cm2/V·s was recorded after fabricating the layer using spin-coating at 1900 rpm, the highest sensitivity of 314.0 μC·Gyair −1·cm−2 was also achieved under these conditions. Compared to the initial state of the detector, our modifications improved the sensitivity of the PCDTBT:CdSe NPL detector by 251%.

Ultralow Threshold Room Temperature Polariton Condensation in Colloidal CdSe/CdS Core/Shell Nanoplatelets.

Room‐temperature exciton‐polariton Bose‐Einstein condensation (BEC), a phase transition to single quantum state with strong nonlinearity, provides a new strategy for coherent light sources and ultralow threshold optic switches. In this work, colloidal CdSe/CdS 2D nanoplatelets are embedded into a microcavity, and exciton‐polariton BEC is realized with an ultralow threshold of 0.5 µJ cm–2 at room temperature. The superlinear power‐dependent emission, macroscopic occupation of the ground state, strong blueshift and broadening of the emission peak, and long‐range coherence strongly confirm the realization of the polariton laser. This work suggests considerable prospects for colloidal nanoplatelets in low‐cost, high‐performance polariton devices, and coherent light sources.

Preparation of Polyethylene Nanocomposites Based on Polyethylene Grafted Exfoliated α-Zirconium Phosphate

Polymer nanocomposites containing well-exfoliated nanoplatelets have been shown to possess greatly enhanced physical and mechanical properties. However, it is still a significant challenge to achieve adequate exfoliation of 2D nanoplatelets in polyolefin matrices due to poor compatibility and associated entropic penalty between 2D inorganic filler and nonpolar polyolefin matrices. Grafting polyolefin chains onto the surfaces of an already exfoliated nanoplatelet is a simple, yet effective solution to this problem. The grafted polyolefin chains on the nanoplatelets can entangle and cocrystallize with the polyolefin matrix, preventing agglomeration. In this study, polyethylene (PE) grafted α-zirconium phosphate (ZrP), ZrP-g-PE, was prepared and blended with the PE matrix. The graft density of ZrP-g-PE was designed to maintain ZrP exfoliation during subsequent blending with the PE matrix. It was found that PE confined crystallization formed in ZrP-g-PE, resulting in the formation of PE crystal orientation perpendicular to the ZrP nanoplatelets. The usefulness of this study for preparation of high-performance polyolefin nanocomposites is discussed.

Engineering CsPbBr3 perovskite from 2D nanoplatelets to 0D quantum dots via polar solvent post-treatment

Cesium lead halide (CsPbX3 X = I, Br, Cl) perovskites have potential applications in the fields of X-ray fluorescence imaging, solar cells, light-emitting diodes (LEDs) and photocatalysis due to their excellent optical and electrical properties. In this work, we propose a novel method to tune the emission color of CsPbBr3 by polar solvent post-treatment. The blue emission color of the two-dimensional (2D) CsPbBr3 nanoplatelets (NPLs) prepared at room temperature is evidently changed to green under UV excitation via DMF post-treatment. We verify the DMF is used to decompose these NPLs into 0D quantum dots followed by the color variation. We further reveals the polarity of the employed solvent is the main parameter in the decomposition processes. This novel route might be suitable for other 2D perovskites and benefit the application of these colorful products in LEDs and information storage fields.

PMMA Nanocomposites Based on PMMA-Grafted α-Zirconium Phosphate Nanoplatelets

Dual-epoxide modification of α-zirconium phosphate (ZrP) nanoplatelets containing a bromine initiator was performed for surface-initiated activators regenerated by electron transfer atom transfer radical polymerization, resulting in poly(methyl methacrylate)-grafted ZrP (ZrP-g-PMMA) for dispersion in PMMA matrix. The morphology of the PMMA nanocomposites with variations in grafting density (σ) and grafted PMMA length (Ng) on ZrP-g-PMMA with a fixed PMMA matrix chain length (Nm) was investigated using transmission electron microscopy. Various types of polymer brush structures, including mushroom, semi-dilute polymer brush, and concentrated polymer brush structures, were prepared, which correspond to the wetting and dewetting phenomena of ZrP-g-PMMA in the PMMA matrices. The dual-epoxide functionalization helps decrease ZrP surface energy and improve the configurational entropy of grafted polymer chains, which results in the penetration of the matrix PMMA chains into the grafted brush layer at a low σ = 0.07 chain/nm2 even when Ng/Nm < 0.36. The rheological study in the melt state reveals that the flow properties of the PMMA nanocomposites can be tuned via changing the loading of nanoplatelets or varying the grafting characteristics at the interface between ZrP and PMMA matrix. Furthermore, the rheological behavior of PMMA/ZrP-g-PMMA which contains two-dimensional (2D) nanoplatelets was found to be significantly different from that of the PMMA/silica-g-PMMA which contains spherical nanoparticles. This drastic discrepancy in their rheological behaviors is likely caused by the anisotropic nature of the 2D nanoplatelets in PMMA. The implication of the present study on the preparation of thermoplastic nanocomposites containing 2D nanoplatelets is discussed.

Moisture-Assisted near-UV Emission Enhancement of Lead-Free Cs4CuIn2Cl12 Double Perovskite Nanocrystals.

Lead-based halide perovskite nanocrystals (NCs) are recognized as emerging emissive materials with superior photoluminescence (PL) properties. However, the toxicity of lead and the swift chemical decomposition under atmospheric moisture severely hinder their commercialization process. Herein, we report the first colloidal synthesis of lead-free Cs4CuIn2Cl12 layered double perovskite NCs via a facile moisture-assisted hot-injection method stemming from relatively nontoxic precursors. Although moisture is typically detrimental to NC synthesis, we demonstrate that the presence of water molecules in Cs4CuIn2Cl12 synthesis enhances the PL quantum yield (mainly in the near-UV range), induces a morphological transformation from 3D nanocubes to 2D nanoplatelets, and converts the dark transitions to radiative transitions for the observed self-trapped exciton relaxation. This work paves the way for further studies on the moisture-assisted synthesis of novel lead-free halide perovskite NCs for a wide range of applications.

Optimized Cation Exchange for Mercury Chalcogenide 2D Nanoplatelets and Its Application for Alloys

II–VI two-dimensional (2D) nanoplatelets (NPLs) exhibit the narrowest optical features among nanocrystals (NCs). This property remains true for Hg-based NPLs, despite a cation exchange procedure to...

Dimensionality Control of Inorganic and Hybrid Perovskite Nanocrystals by Reaction Temperature: From No-Confinement to 3D and 1D Quantum Confinement.

This work focuses on the systematic investigation of the shape, size, and composition‐controlled synthesis of perovskite nanocrystals (NCs) under inert gas‐free conditions and using pre‐synthesized precursor stock solutions. In the case of CsPbBr3 NCs, we find that the lowering of reaction temperature from ∼175 to 100 °C initially leads to a change of morphology from bulk‐like 3D nanocubes to 0D nanocubes with 3D‐quantum confinement, while at temperatures below 100 °C the reaction yields 2D nanoplatelets (NPls) with 1D‐quantum confinement. However, to our surprise, at higher temperatures (∼215 °C), the reaction yields CsPbBr3 hexapod NCs, which have been rarely reported. The synthesis is scalable, and their halide composition is tunable by simply using different combinations of precursor solutions. The versatility of the synthesis is demonstrated by applying it to relatively less explored shape‐controlled synthesis of FAPbBr3 NCs. Despite the synthesis carried out in the air, both the inorganic and hybrid perovskite NCs exhibit nearly‐narrow emission without applying any size‐selective separation, and it is precisely tunable by controlling the reaction temperature.

Dimensionality Control of Inorganic and Hybrid Perovskite Nanocrystals by Reaction Temperature: From No‐Confinement to 3D and 1D Quantum Confinement

AbstractThis work focuses on the systematic investigation of the shape, size, and composition‐controlled synthesis of perovskite nanocrystals (NCs) under inert gas‐free conditions and using pre‐synthesized precursor stock solutions. In the case of CsPbBr3 NCs, we find that the lowering of reaction temperature from ∼175 to 100 °C initially leads to a change of morphology from bulk‐like 3D nanocubes to 0D nanocubes with 3D‐quantum confinement, while at temperatures below 100 °C the reaction yields 2D nanoplatelets (NPls) with 1D‐quantum confinement. However, to our surprise, at higher temperatures (∼215 °C), the reaction yields CsPbBr3 hexapod NCs, which have been rarely reported. The synthesis is scalable, and their halide composition is tunable by simply using different combinations of precursor solutions. The versatility of the synthesis is demonstrated by applying it to relatively less explored shape‐controlled synthesis of FAPbBr3 NCs. Despite the synthesis carried out in the air, both the inorganic and hybrid perovskite NCs exhibit nearly‐narrow emission without applying any size‐selective separation, and it is precisely tunable by controlling the reaction temperature.

Morphological and Optical Tuning of Lead-Free Cs2SnX6 (X = I, Br) Perovskite Nanocrystals by Ligand Engineering

In order to overcome the toxicity of lead halide perovskites, in recent years the research has focused on replacing lead with more environmentally friendly metals like tin, germanium, bismuth or antimony. However, lead-free perovskites still present instability issues and low performances that do not make them competitive when compared to their lead-based counterparts. Here we report the synthesis of lead-free Cs2SnX6 (X = Br, I) nanostructures of different shapes by using various surface ligands. These compounds are a promising alternative to lead halide perovskites in which the replacement of divalent lead (Pb(II)) with tetravalent tin (Sn(IV)) causes a modification of the standard perovskite structure. We investigate the effects of different amines on the morphology and size of Cs2SnX6 (X = Br, I) nanocrystals, presenting a facile hot-infection method to directly synthesize three-dimensional (3D) nanoparticles as well as two-dimensional (2D) nanoplatelets. The amines not only modify the shape of the crystals, but also affect their optical properties: increasing the length of the amine carbon chain we observe a widening in the bandgap of the compounds and a blue-shift of their emission peak. Alongside the tuning of the chemical composition and the reduction of the crystal size, our study offers a new insight in controlling the physical properties of perovskite nanocrystals by means of the capping ligands, paving the way for future research on lead-free materials.

Characterization and adaptability of layered double hydroxides in cement paste

Layered double hydroxides (LDHs) improve the durability of concrete, whereas theirs characterization and adaptability in cement-based matrix has not been systematically investigated. Setting time, chemical shrinkage, rheology, compressive strength, hydration degree, pore structure as well as micro-mechanisms of high sulphate-resistant Portland cement (HSRPC) incorporating different LDHs, namely, CaFe-NO3 LDHs (LDHs-CF), CaAl-NO3 LDHs (LDHs-CA), and CaFeAl-NO3 LDHs (LDHs-CFA), were explored. At any types of LDHs, the trend of compressive strength of HSRPC pastes increased firstly and then decreased afterward with the addition of LDHs dosage, while the addition of LDHs increased the chemical shrinkage values of pastes during the early stage, but 28 d chemical shrinkage values were not particularly notable. Furthermore, radar map showed that the shortening of setting time, the increase of dynamic yield stress of samples presented great change with the increase of LDHs dosage, whereas the 28 d chemical shrinkage value changed little in all samples. LDHs, especially LDHs-CF and LDHs-CFA, reduced the volume fractions of harmful pores, refined on pore structure and increased tortuosity of samples since Fe-based LDHs have smaller nanoscale dimension and lower crystal transformation. The acceleration of cement hydration, decrease of workability and improvement of mechanical property at early stages were due to the interstitial filling and crystal seed effects, crystal transformation, or/and absorption of free water by LDHs 2D nano-platelets. In conclusion, LDHs shows good adaptability in cement paste, and as an effective hardening accelerator for HSRPC hydration.

Morphology-Dependent Ambient-Condition Growth of Perovskite Nanocrystals for Enhanced Stability in Photoconversion Device.

CsPbBr3 perovskite nanocrystals with two different dimensionalities were synthesized at different temperatures and then integrated as optoelectronic transducers into transistor-type photoconversion devices. Postsynthesis transformation was observed for two-dimensional (2D) nanoplatelets, while the transformation was rarely found in 3D nanocubes. At ambient temperature and pressure, neighboring nanoplatelets made facet-to-facet contact and then fused into larger 2D nanoplatelets (2-5 times) without defects. The coalescence of 2D nanoplatelets at the ambient condition lowered the density of defects at the surface of the nanocrystals and thus could facilitate effective and stable photoconversion behavior in the nanocrystal film integrated into the device. Consequently, the ambient-condition aging of 2D nanoplatelets on device substrate led to 3 times higher retention in photoconversion performance. Importantly, these results provide a new concept of how perovskite nanocrystals can be integrated into a device for enhanced stability in device performance.

Assessment of Physico-Chemical and Toxicological Properties of Commercial 2D Boron Nitride Nanopowder and Nanoplatelets.

Boron nitride (BN) nanomaterials have been increasingly explored for potential applications in chemistry and biology fields (e.g., biomedical, pharmaceutical, and energy industries) due to their unique physico-chemical properties. However, their safe utilization requires a profound knowledge on their potential toxicological and environmental impact. To date, BN nanoparticles have been considered to have a high biocompatibility degree, but in some cases, contradictory results on their potential toxicity have been reported. Therefore, in the present study, we assessed two commercial 2D BN samples, namely BN-nanopowder (BN-PW) and BN-nanoplatelet (BN-PL), with the objective to identify whether distinct physico-chemical features may have an influence on the biological responses of exposed cellular models. Morphological, structural, and composition analyses showed that the most remarkable difference between both commercial samples was the diameter of their disk-like shape, which was of 200–300 nm for BN-PL and 100–150 nm for BN-PW. Their potential toxicity was investigated using adenocarcinomic human alveolar basal epithelial cells (A549 cells) and the unicellular fungus Saccharomyces cerevisiae, as human and environmental eukaryotic models respectively, employing in vitro assays. In both cases, cellular viability assays and reactive oxygen species (ROS) determinations where performed. The impact of the selected nanomaterials in the viability of both unicellular models was very low, with only a slight reduction of S. cerevisiae colony forming units being observed after a long exposure period (24 h) to high concentrations (800 mg/L) of both nanomaterials. Similarly, BN-PW and BN-PL showed a low capacity to induce the formation of reactive oxygen species in the studied conditions. Even at the highest concentration and exposure times, no major cytotoxicity indicators were observed in human cells and yeast. The results obtained in the present study provide novel insights into the safety of 2D BN nanomaterials, indicating no significant differences in the toxicological potential of similar commercial products with a distinct lateral size, which showed to be safe products in the concentrations and exposure conditions tested.