Nanoscale Faceting and Ligand Shell Structure Dominate the Self-Assembly of Nonpolar Nanoparticles into Superlattices.

Self-assembly of nanoscale structures at liquid-solid interfaces occurs in a broad range of industrial processes and is found in various phenomena in nature. Conventional theory assumes spherical particles and homogeneous surfaces, but that model is oversimplified, and nanoscale in situ observations are needed for a more complete understanding. Liquid-phase scanning transmission electron microscopy (LP-STEM) is used to examine the interactions that direct the self-assembly of superlattices formed by gold nanoparticles (AuNPs) in nonpolar liquids. Varying the molecular coating of the substrate modulates short-range attraction and leads to switching between a range of different geometric structures, including hexagonal close-packed (hcp), simple hexagonal (sh), dodecahedral quasi-crystal (dqc), and body-centered cubic (bcc) lattices, as well as random distributions. Langevin dynamics simulations explain the experimental results in terms of the interplay between nanoparticle faceting, ligand shell structure, and substrate-NP interactions.

High efficient arsenic removal by In-layer sulphur of layered double hydroxide.

High-risk arsenic contamination found in aqueous system is reported across the world and causing severe environmental issues. In this study, the Mg-Al Layered Double Hydroxide (LDH) modified by sulphur species (LDH-S) was found exhibiting high effectivity and selectivity in As(V) removal owing to the strong interaction between embedded HS- and AsO43-. The LDH-S with Mg to Al ratio 2-1 give the best performance with As(V) adsorption capacity 40.8 mg/g, which is 715% higher than that of pristine LDH (2-1). The adsorbent exhibits a high tolerance to concentrated competitive anions. In the continuous flow test, the adsorbent can reduce the As(V) concentration from 20 ppm to below-ppb-level indicating the potential in industry application. The adsorption mechanism is experimentally investigated and examined by Density Function Theory (DFT) calculation. The result illustrates that, differ from the traditional ion exchange mechanism of LDH, the enhanced removal capacity and selectivity of LDH-S for As(V) is attributed to the strong affinity between H atom from HS- ion (in the interlayer region of LDH) and the O atom from AsO43-.

Exceptional Deformability of Wurtzite Zinc Oxide Nanowires with Growth Axial Stacking Faults.

To ensure reliability and facilitate the strain engineering of zinc oxide (ZnO) nanowires (NWs), it is significant to understand their flexibility thoroughly. In this study, single-crystalline ZnO NWs with rich axial pyramidal I (π1) and prismatic stacking faults (SFs) are synthesized by a metal oxidation method. Bending properties of the as-synthesized ZnO NWs are investigated at the atomic scale using an in situ high-resolution transmission electron microscopy (HRTEM) technique. It is revealed that the SF-rich structures can foster multiple inelastic deformation mechanisms near room temperature, including active axial SFs' migration, deformation twinning and detwinning process in the NWs with growth π1 SFs, and prevalent nucleation and slip of perfect dislocations with a continuous increased bending strain, leading to tremendous bending strains up to 20% of the NWs. Our results record ultralarge bending deformations and provide insights into the deformation mechanisms of single-crystalline ZnO NWs with rich axial SFs.

Development of Mechanically Enhanced Polycaprolactone Composites by a Functionalized Titanate Nanofiller for Melt Electrowriting in 3D Printing.

Three-dimensional (3D) printing technologies are widely applied in various industries and research fields and are currently the subject of intensive investigation and development. However, high-performance materials that are suitable for 3D printing are still in short supply, which is a major limitation for 3D printing, particularly for biomedical applications. The physicochemical properties of single constituent materials may not be sufficient to meet the needs of modern biotechnology development and production. To enhance the materials' performance and broaden their applications, this work designed and tested a series of titanate nanofiller (nanowire and nanotube)-enhanced polycaprolactone (PCL) composites that were 3D-printable and provided superior mechanical properties. By grafting two different functional groups (phenyl- and thiol-terminated ligands), the nanofiller surface showed improved hydrophobicity, which significantly improved their dispersion in the PCL matrix. After characterizing the surface modification, we evaluated the significance of the homogeneity of the ceramic nanofiller in terms of printability, formability, and mechanical strength. Melt electrowriting additive manufacturing was used to fabricate microfibers of PCL and PCL/nanofiller composites. Improved nanofiller dispersion enabled intact and uniform sample morphology, and in contrast, nanofiller aggregation greatly varied the viscosity during the printing process, which could result in poorly printed structures. Importantly, the modified ceramic/PCL composite delivered enhanced and stable mechanical properties, where its Young's modulus was measured to be 1.67 GPa, which is more than 7 times higher compared to that of pristine PCL (0.22 GPa). Retaining the cell safety properties (comparable to PCL), the concept of enhancing biocompatible polymers with modified nanofillers shows great potential in the field of customized 3D printing for biomedicine.

Design tools for patient specific and highly controlled melt electrowritten scaffolds.

Melt electrowriting (MEW) has grown in popularity in biofabrication research due to its ability to fabricate complex, high-precision networks of fibres. These fibres can mimic the morphology of a natural extracellular matrix, enabling tissue analogues for transplantation or personalised drug screening. To date, MEW has employed two different collector-plate modalities for the fabrication of constructs. Flat collector plates, typical of traditional 3D printing methods, allow for the layer-by-layer fabrication of 2D structures into complex 3D structures. Alternatively, rotating mandrels can be used for the creation of tubular scaffolds. However, unlike other additive manufacturing techniques that can immediately start and stop the extrusion of material during printing, MEW instead requires a continuous flow of polymer. Consequently, conventional g-code control software packages are unsuitable. To overcome this challenge, a suite of customised pattern generation software tools have been developed to enable the design of MEW scaffolds with highly-controlled geometry, including crosshatch, gradient porosity, tubular, and patient-specific configurations. The high level of design control using this approach enables the production of scaffolds with highly adaptable mechanical properties, as well as the potential to influence biological properties for cell attachment and proliferation.

Simultaneous removal of cationic and anionic heavy metal contaminants from electroplating effluent by hydrotalcite adsorbent with disulfide (S2-) intercalation.

Hydrotalcite materials are generally utilized for anionic pollutants due to its interlayered anion exchange ability. Their potentiality for cationic contaminants is rarely explored. In this study, disulfide (S2-) intercalated LDH material demonstrated capability to remove both heavy metal cations and oxyanions simultaneously from water. The S2- intercalation of LDH significantly improved its adsorption capability towards both heavy metal cations (Co2+ and Ni2+) and oxyanion (CrO42-). The adsorption amount of S-LDH towards Co2+ and Ni2+ reached 88.6mg/g and 76.2mg/g, which are 405% and 281% higher than that of pristine LDH. For CrO42- removal, the adsorption amount reached 34.7mg/g, 402% higher than that of pristine LDH. The cations capture mechanism mainly depends on the novel layer sheet cation substitution mechanism based on irreversible precipitation and the generation of metal sulfide precipitates. Meanwhile, the interlayered S2- can be easily replaced by CrO42- to realize the simultaneous removal of both heavy metal cations and oxyanions. In the fixed-bed column experiments, 448 bed volume (BV) (672 mL) of simulating electroplating wastewater can be efficiently treated by yielding only 1 BV(15 mL) of chemical sludge, which is practically acceptable. This work provided a highly practical adsorption technology based on the S2- modification hydrotalcite material for the purification of heavy metal ions contaminated wastewater.

In Situ Atomic-Scale Study on the Ultralarge Bending Behaviors of TiO2-B/Anatase Dual-Phase Nanowires.

It is challenging but important to understand the mechanical properties of one-dimensional (1D) nanomaterials for their design and integration into nanodevices. Generally, brittle ceramic nanowires (NWs) cannot withstand a large bending strain. Herein, in situ bending deformation of titanium dioxide (TiO2) NWs with a bronze/anatase dual-phase was carried out inside a transmission electron microscopy (TEM) system. An ultralarge bending strain up to 20.3% was observed on individual NWs. Through an in situ atomic-scale study, the large bending behavior for a dual-phase TiO2 NW was found to be related to a continuous crystalline-structure evolution including phase transition, small deformation twinning, and dislocation nucleation and movements. Additionally, no amorphization or crack occurred in the dual-phase TiO2 NW even under an ultralarge bending strain. These results revealed that an individual ceramic NW can undergo a large bending strain with rich defect activities.

Atomic-scale investigation on the ultra-large bending behaviours of layered sodium titanate nanowires.

A study on the mechanical properties of one-dimensional layered titanate nanomaterials is crucial since they demonstrate important applications in various fields. Here, we conducted ex situ and in situ atomic-scale investigation on the bending properties of a kind of ceramic-layered titanate (Na2Ti2O4(OH)2) nanowire using transmission electron microscopy. The nanowires showed flexibility along the 100 direction and could obtain a maximum bending strain of nearly 37%. By analysing the defect behaviours, the unique bending properties of this ceramic material were found to correlate with a novel arrangement of dislocations, an active dislocation nucleation and movement along the axial direction resulting from the weak electrostatic interaction between the TiO6 layers and the low b/a ratio. These results provide a pioneering and key understanding on the bending behaviours of layered titanate nanowire families and potentially other one-dimensional nanomaterials with layered crystalline structures.

General existence of flexural mode doublets in nanowires targeting vectorial sensing applications.

Nanowires (NWs) are one of the fundamental building blocks for nanoscale devices, and have been frequently utilized as mechanical resonators. Earlier studies show that ultra-sensitive vectorial sensing toolkits can be fabricated by changing the flexural mode of NWs to oscillation doublets along two orthogonal directions. Based on in silico studies and the Timoshenko beam theory, this work finds that the dual orthogonal flexural mode of NWs can be effectively controlled through the proper selection of their growth direction. It is found that metallic NWs with a directional-independent shear modulus possess a single flexural mode. However, NWs with a directional-dependent shear modulus naturally exhibit flexural mode doublets, which do not disappear even with increasing slenderness ratio. Further studies show that such a feature generally exists in other NWs, such as Si NWs. Mimicking a pendulum configuration as used in NW-based scanning force microscopy, the cantilevered 110 Si NW demonstrates zeptogram mass resolution and a force sensitivity down to the order of 10-24 N Hz-1/2 (yN Hz-1/2) in both transverse directions. The findings in this work open up a new and facile avenue to fabricate 2D vectorial force sensors, which could enable ultra-sensitive and novel detection devices/systems for 2D effects, such as the anisotropy strength of atomic bonds.

Atypical Defect Motions in Brittle Layered Sodium Titanate Nanowires.

In situ tensile tests show atypical defect motions in the brittle Na2Ti3O7 (NTO) nanowire (NW) within the elastic deformation range. After brittle fracture, elastic recovery of the NTO NW is followed by reversible motion of the defects in a time-dependent manner. An in situ cyclic loading-unloading test shows that these mobile defects shift back and forth along the NW in accordance with the loading-unloading cycles and eventually restore their initial positions after the load is completely removed. The existence of the defects within the NTO NWs and their motions does not lead to plastic deformation of the NW. The atypical defect motion is speculated to be the result of the glidibility of the TiO6 layers, where weakly bonded cation layers are in between. Exploration of the above novel observation can establish new understandings of the deformation behavior of superlattice nanostructures.

In situ mechanical resonance behaviour of pristine and defective zinc blende GaAs nanowires.

The structural versatility of semiconducting gallium arsenide (GaAs) nanowires (NWs) provides an exciting direction for the engineering of their mechanical and dynamic properties. However, the dynamic behaviour of GaAs NWs remains unexplored. In this study, comprehensive in situ mechanical resonance tests were conducted to explore the dynamic behaviour of pristine and defective zinc blende GaAs NWs. The effects of stacking faults (SFs), amorphous shell, NW tapering and end-mass particles were investigated. The quality factors (QFs) of the GaAs NWs were found to be predominately governed by surface effects, which increased linearly with the volume to surface area ratio. Interestingly, SFs were found not to influence the QFs. To extract the mechanical properties, the Euler-Bernoulli beam theory was modified, to incorporate the core-shell model, NW tapering and end-mass particles. It was found that the core-shell model accurately predicts the mechanical properties of the pristine GaAs NWs, which exhibit significant stiffening at radii below 50 nm. Conversely, the mechanical properties of the defective NWs were influenced by the presence of SFs, causing a wide variance in the Young's modulus. Apart from establishing an understanding of the resonance behaviour of GaAs NWs, this research provides guidance for the design of NWs for their applications in dynamic nanomechanical devices with tailorable dynamic properties.

Nanojoint Formation between Ceramic Titanate Nanowires and Spot Melting of Metal Nanowires with Electron Beam.

Construction of nanoarchitectures requires techniques like joint formation and trimming. For ceramic materials, however, it is extremely difficult to form nanojoints by conventional methods like merging. In this work, we demonstrate that ceramic titanate nanowires (NWs) can be joined by spot melting under electron beam (e-beam) irradiation (EBI). The irradiation fuses the contacted spot of titanate NWs yielding an intact nanojoint. Nanojoints with different morphologies can be produced. The joint structures consist of titanium dioxide (TiO2) rutile, anatase, and titanate phases in the direction away from the e-beam melting spot. The titanate binds to anatase via a crystallographic matching coherent interface (the oxygen atoms at the interface are shared by the two phases) and the anatase solidly binds to the rutile joint. The resulting rutile joint is stable at high temperatures. Additionally, it is demonstrated that the heat production from EBI treated rutile can be utilized to break metal NWs (Ag, Cu, and Ni) apart by spot melting. The required e-beam intensity is considerably mild (75 pA/cm2) which allows visual access and control over the NW melting. Direct melting of Ag and Cu is not applicable under EBI due to their high thermal conductivity even with high current density (500 pA/cm2). Our findings reveal that ceramic nanojoint formation and spot melting at nanoscale are applicable if the properties of nanomaterials are understood and properly utilized.

Efficient Removal of Cationic and Anionic Radioactive Pollutants from Water Using Hydrotalcite-Based Getters.

Hydrotalcite (HT)-based materials are usually applied to capture anionic pollutants in aqueous solutions. Generally considered anion exchangers, their ability to capture radioactive cations is rarely exploited. In the present work, we explored the ability of pristine and calcined HT getters to effectively capture radioactive cations (Sr(2+) and Ba(2+)) which can be securely stabilized at the getter surface. It is found that calcined HT outperforms its pristine counterpart in cation removal ability. Meanwhile, a novel anion removal mechanism targeting radioactive I(-) is demonstrated. This approach involves HT surface modification with silver species, namely, Ag2CO3 nanoparticles, which can attach firmly on HT surface by forming coherent interface. This HT-based anion getter can be further used to capture I(-) in aqueous solution. The observed I(-) uptake mechanism is distinctly different from the widely reported ion exchange mechanism of HT and much more efficient. As a result of the high local concentrations of precipitants on the getters, radioactive ions in water can be readily immobilized onto the getter surface by forming precipitates. The secured ionic pollutants can be subsequently removed from water by filtration or sedimentation for safe disposal. Overall, these stable, inexpensive getters are the materials of choice for removal of trace ionic pollutants from bulk radioactive liquids, especially during episodic environmental crisis.

Catalytic transformation of aliphatic alcohols to corresponding esters in O2 under neutral conditions using visible-light irradiation.

Selective oxidation of aliphatic alcohols under mild and base-free conditions is a challenging process for organic synthesis. Herein, we report a one-pot process for the direct oxidative esterification of aliphatic alcohols that is significantly enhanced by visible-light irradiation at ambient temperatures. The new methodology uses heterogenerous photocatalysts of gold-palladium alloy nanoparticles on a phosphate-modified hydrotalcite support and molecular oxygen as a benign oxidant. The alloy photocatalysts can absorb incident light, and the light-excited metal electrons on the surface of metal nanoparticles can activate the adsorbed reactant molecules. Tuning the light intensity and wavelength of the irradiation can remarkably change the reaction activity. Shorter wavelength light (<550 nm) drives the reaction more efficiently than light of longer wavelength (e.g., 620 nm), especially at low temperatures. The phosphate-exchanged hydrotalcite support provides sufficient basicity (and buffer) for the catalytic reactions; thus, the addition of base is not required. The photocatalysts are efficient and readily recyclable. The findings reveal the first example of using "green" oxidants and light energy to drive direct oxidative esterification of aliphatic alcohols under base-free, mild conditions.

Removal of radioactive iodine from water using Ag2O grafted titanate nanolamina as efficient adsorbent.

Emergency treatment of radioactive material leakage and safety disposal of nuclear waste is a constant concern all along with the development of radioactive materials applications. To provide a solution, titanate with large surface area (143 m(2)g(-1)) and a lamina morphology (the thickness of the lamina is in range of tens of nanometers) was prepared from inorganic titanium compounds by hydrothermal reactions at 433 K. Ag(2)O nanocrystals (5-30 nm) were deposited onto the titanate lamina. The surface of the titanate lamina has crystallographic similarity to that of Ag(2)O nanocrystals. Hence, the deposited Ag(2)O nanocrystals and titanate substrate join together at these surfaces, forming a well-matched phase coherent interface between them. Such coherence between the two phases reduces the overall energy by minimizing surface energy and anchors the Ag(2)O nanocrystals firmly on the external surface of the titanate structure. The composite thus obtained was applied as efficient adsorbent to remove radioactive iodine from water (one gram adsorbent can capture up to 3.4 mmol of I(-) anions). The composite adsorbent can be recovered easily for safe disposal. The structure changes of the titanate lamina and the composite adsorbent were monitored by various techniques. The isotherm and kinetics of iodine adsorption, competitive adsorption and column adsorption using the adsorbent were studied to assess its iodine removal abilities. The adsorbent exhibited a capacity as high as 3.4 mmol of iodine per gram of adsorbent in 1h. Therefore, Ag(2)O deposited titanate lamina is an effective adsorbent for removing radioactive iodine from water.