Materials Today Nano最新文献

Phthalocyanine (PC) has a unique N₄-coordinated structure that offers an inherent advantage with respect to the accommodation of metal ions. This feature can help overcome the limitations of many single-atom electrocatalysts, i.e. low loading and poor stability. Here, we detail the development of a universal electrochemical template and a cationic substitution synthesis protocol for preparing various single-atom catalysts with high-loading (≌ 8.6 wt%) from commercial copper phthalocyanine (CuPC). Commercial CuPC is transformed into Cu NPs and vacant N₄-sites are created during applied potential cycling. The generated vacant N₄-sites, with strong negative charges, can take-up Pd²⁺ ions from a precursor solution to create single-atom catalysts with Pd high-loadings. The material’s structural transformation and cationic substitution mechanism were investigated by in situ X-ray absorption spectroscopy (XAS). We also demonstrate the viability of extending the proposed electrochemical template synthesis method to the development of other high-loading transition metal single-atom catalysts, e.g., Ni, Co, and Fe.

Cost-efficient and readily scalable platinum-free electrocatalysts are crucial for a smooth transition to future renewable energy systems. Top-down activation of MoS₂ promises the production of sustainable hydrogen evolution electrocatalysts from the Earth-abundant molybdenite ore. Here, the deterministic nanopatterning of multilayer MoS₂ with numerous zigzag edges is explored as a pathway to enhance hydrogen evolution reaction (HER). Nanopatterned single-nanosheet MoS₂ electrodes are assessed by two highly localized electrochemical techniques: selected area voltammetry (with lithography-defined regions of electrode-electrolyte contact) and Scanning ElectroChemical Microscopy (SECM). The nanopatterning effect is the most pronounced after prolonged electrochemical cycling in an acidic electrolyte. The electrocatalytic hydrogen evolution activity of edge-enriched electrodes is dramatically enhanced: the maximum electrochemical current density (j${}_{max}$) achieved at -510 mV vs. reversible hydrogen electrode (mV${}_{RHE}$) is increased by two orders of magnitude, reaching >300 mA⋅cm⁻². Both the ${\eta }_{10}$ and ${\eta }_{100}$ overpotentials are significantly reduced as well. Meanwhile, pristine MoS₂ shows just ≈6 times j${}_{max}$ increase (≈30 mA⋅cm⁻²) after the very same cycling. The increased electrocatalytic activity comes with electrode morphology degradation, evidenced by ex-situ scanning electron microscopy. SECM directly visualizes stronger HER activity in the regions with densely located zigzag edges. Intense white light illumination significantly boosts HER on MoS₂ electrodes due to the photo-enhanced MoS₂ conductivity. These results improve the understanding and reveal the limitations of MoS₂-based electrocatalytic water splitting.

The growth mechanism of star-shaped Au–Ag nanoparticles, which is important for improving the absorption efficiency of nanoparticles in the near-infrared region, remains to be clarified. In this study, the growth mechanism by stabilizing certain facets of Au in spines by underpotential deposition of Ag was investigated. The nanoparticles were analyzed primarily by scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy. Analysis of spines on nanoparticles synthesized with an Au/Ag ratio of 18/4 revealed that approximately 1 nm of Ag was deposited on the topmost surface of Au, and the growth direction of spines was <200>. Underpotential deposition of Ag nanolayers on specific facets of the spines on nanoparticles was observed for the first time by elemental mapping and high-angle annular dark-field STEM tomography. These findings are expected to contribute to the morphology control of plasmonic nanoparticles.

The surface modification of three-dimensional (3D) materials is an efficient method for adjusting their interfacial defect concentration, electronic conductivity and content of functional groups with extensive applications in catalysis, electrode materials and bioengineering. In this work, a multiphase iron nanocrystals consisting of Fe₃C, Fe and FeN nanoparticles encapsulated in hierarchical structure of graphite carbon (denoted as Fe/Fe₃C/FeN@GC) is synthesized for the first time by a novel high temperature plasma method. Meanwhile, more defects and functional groups are introduced by surface modification of graphite carbon layer of Fe/Fe₃C/FeN@GC with controllable CO₂ (low temperature) plasma. Benefiting from the advantages of multiple heterogenous interface and the abundant interfacial polarization relaxation that represent strong electromagnetic (EM) wave dissipation as well as an applicable impedance matching, the optimized Fe/Fe₃C/FeN@GC demonstrate superior microwave absorption (MA) properties. The minimum reflection loss (RL) achieves −54.4 dB (more than 99.9% MA) at 17.6 GHz with a thin thickness of 1.8 mm, and the maximum effective absorption bandwidth (EAB, RL < −10 dB) is up to 6.2 GHz (11.8–18.0 GHz) at 2.0 mm. The above results reveal that the optimized Fe/Fe₃C/FeN@GC composites with strong absorption, broad EAB, light mass (only filling content of 30 wt%) and ultrathin thickness are prospective candidate for high performance EM wave absorbers.

Carbon nanotubes (CNTs) have been regarded as ideal functional fillers for enhancing superior mechanical properties of polymer composites. However, the performances of CNTs-based composites are well below the theoretical values, due to the poor dispersion of inert CNTs and weak interfacial interaction with the polymer matrix. Herein, “hydrothermal and in-situ growth” approach is induced to synthesize multiscale TiO₂@CNTs functional fillers. Such the TiO₂@CNTs show excellent dispersibility and strong interfacial bonding with matrix. The biobased TiO₂@CNTs/poly (ethylene furandicarboxylate) (TCP) composite films are prepared via loading a small amount (0.05–0.2 wt%) of TiO₂@CNTs. When the mass content of fillers is 0.2 wt%, TCP composite film exhibits the optimal of strength (80 MPa), Young's modulus (4.12 GPa), and toughness (1.2 MJ/m³). Moreover, the presence of TiO₂ nanoparticles endow the films with excellent oxygen barrier and UV-shielding properties. We believe these composite films promise a spread application potential in high-performance food packing materials.

Multi-layer Ti₃C₂T_x coatings have demonstrated an outstanding wear performance with excellent durability due to beneficial tribo-layers formed. However, the involved formation processes dependent on the tribological conditions and coating thickness are yet to be fully explored. Therefore, we spray-coated Ti₃C₂T_x multi-layer particles onto stainless steel substrates to create coatings with two different thicknesses and tested their solid lubrication performance with different normal loads (100 and 200 mN) and sliding frequencies (1 and 2.4 Hz) using linear-reciprocating ball-on-disk tribometry. We demonstrate that MXenes’ tribological performance depends on their initial state (delaminated few-layer vs. multi-layer particles), coating thickness, applied load and sliding frequency. Specifically, the best behavior is observed for thinner multi-layer coatings tested at the lower frequency. In contrast, coatings made of delaminated few-layer MXene are not as effective as their multi-layer counterparts. Our high-resolution interface characterization by transmission electron microscopy revealed unambiguous differences regarding the uniformity and chemistry of the formed tribo-layers as well as the degree of tribo-induced MXenes’ exfoliation. Atomistic insights into the exfoliation process and molecular dynamic simulations quantitatively backed up our experimental results regarding coating thickness and velocity dependency. This ultimately demonstrates that MXenes’ tribological performance is governed by the underlying tribo-chemistry and their exfoliation ability during rubbing.

Gold-based bimetallic nanostructures exhibit unique optical and catalytic properties that are strongly dependent on their composition and nanoscale geometry. Here we show the nano-structural transformation of mesoporous-silica-coated Au-M (Ag, Pd, Pt) core-shell nanoplatelets (NPLs) with a triangular shape to alloyed platelets at temperatures at least 300 °C below the lowest melting point of the metals while still retaining the out-of-equilibrium triangular shape and intact mesoporous shell. Before the alloying started the rough core-shell morphology of the Au–Pd and Au–Pt NPL systems were first observed to relax into a much smoother core-shell morphology. The alloying temperature was found to be related to the melting points and atom fractions of the shell metals; the higher the melting point and atomic fraction of the shell metal, the higher the temperature required for alloying. The highest alloying temperature was found for the Au–Pt system (650 °C), which is still hundreds of degrees below the bulk melting points. Surprisingly, a phase separation of Au and Pt, and of Au and Pd, was observed at 1100 °C while both systems still had an anisotropic plate-like shape, which resulted in Janus-like morphologies where the pure Pt and pure Pd ended up on the tips of the NPLs as revealed via in-situ heating in the scanning transmission electron microscope (STEM). The Janus-type morphologies obtained at elevated temperatures for the NPLs composed of combinations of Au–Pt and Au–Pd, and the smooth core-shell morphologies before alloying, are very interesting for investigating how differences in the bi-metallic morphology affect plasmonic, catalytic and other properties.

Neuromorphic sensory system plays a critical role for human being to perceive, interact and even deduce with the external environment. Multimodal plasticity implementation of neuromorphic sensory system that can learn with diversified information empowers the development of environment-interactive artificial intelligence. In this work, we demonstrated a multimodal neuromorphic sensory system based on Ag loaded porous SiO_x based memristor. The humidity-mediated synaptic plasticity behaviors were detailedly analyzed in the range of 10–90% relative humidity (RH). The humidity-mediated silver ion migration in porous SiO_x memristors was studied by theoretical and experimental methods, and the mechanism of synergistic effect between porous micro-structure and ambient humidity was elucidated. A multimodal neuromorphic sensory system was finally constructed and the adaptive behavior of the human eye was also successfully simulated by taking advantage of this well-designed Au/Ag-SiO_x/ITO memristor. The biomimetic intelligence demonstrated in our multimodal neuromorphic sensory devices and systems shows its potential in promoting the advancement in brain-like artificial intelligence.

To date, the high cost of organic linkers and the energy-consuming synthesis processes remain two of the main challenges for the commercialization of metal-organic frameworks (MOFs). Herein, we demonstrate that polyethylene terephthalate (PET)-derived bis(2-hydroxyethyl) terephthalate (BHET) is a new linker source that enables the facile solvent-free and hydrothermal synthesis of BDC-based MOFs. Using BHET as a linker source, UiO-66(Zr) was rapidly synthesized via a solvent-free “grind and bake” technique, while Ca-BDC and Ba-BDC were easily obtained by using hydrothermal synthesis. We found that the hydrolysis of BHET to terephthalate anion (BDC²⁻) over proton produced from the hydrolysis/clustering of Zr precursor and hydroxyl anion produced from the dissolution of M(OH)₂ (M = Ca or Ba) was the key to the crystal growth of solvent-free synthesized UiO-66(Zr) and hydrothermally synthesized M-BDC (M = Ca or Ba), respectively. While the as-synthesized UiO-66(Zr) was highly active for the esterification of lactic acid (LA) with ethanol (EtOH), Ca-BDC and Ba-BDC exhibited remarkable electrochemical performance for lithium storage. Our strategy provides a major step towards realizing the idea of a more facile, green, and low-cost synthesis of PET-derived MOFs compared to prior arts applicable for catalysis and energy applications.

Ultrathin gold (Au) films are a critical component in plasmonics, metal optics, and nano-electronics devices. However, fabricating ultrathin Au films faces a great challenge due to the dewetting behavior of Au when being deposited onto an oxide (such as SiO₂/Si or Al₂O₃) substrate. This problem is often relieved by introducing a metal or an organic adhesion layer to bind the Au film with the substrate. While the interdiffusion and thermal instability of the adhesion layers often negatively affect the physical properties of the films. Besides, this kind of Au film is usually untransferable due to the strong chemical bonding at the interfaces. Herein, we demonstrate a new strategy of utilizing a nanocrystalline MoS₂ layer as the adhesion interlayer to stabilize the Au film. The atomically thin nanocrystalline MoS₂ with abundant fresh edges enhances the wetting of Au films and allows for the ultra-smoothness and a few nanometers in thickness of the Au films without interdiffusion. The resulting ultrathin Au films possess superior electrical conductivity, high optical transmittance, and eminent thermal stability, which are much better than those utilizing Cu or Ti as the adhesion layers. Moreover, these Au films can be easily transferred to arbitrary substrates. Our method provides a new benchmark in the fabrication of transferable ultrathin and thermally stable Au films.