Dissolution Behavior and Varied Mesoporosity of Zeolites by NH4 F Etching

The mesopores formation in zeolite crystals has long been considered to occur through the stochastic hydrolysis and removal of framework atoms. Here, we investigate the NH₄ F etching of representative small, medium, and large pore zeolites and show that the zeolite dissolution behavior, therefore the mesopore formation probability, is dominated by zeolite architecture at both nano- and sub-nano scales. At the nano-scale, the hidden mosaics of zeolite structure predetermine the spatio-temporal dissolution of the framework, hence the size, shape, location, and orientation of the mesopores. At the sub-nano scale, the intrinsic micropore size and connectivity jointly determine the diffusivity of reactant and dissolved products. As a result, the dissolution propensity varies from removing small framework fragments to consuming nanodomains and up to full digestion of the outmost part of zeolite crystals. The new knowledge will lead to new understanding of zeolite dissolution behavior and new adapted strategies for tailoring hierarchical zeolites.

Time-resolved dissolution elucidates the mechanism of zeolite MFI crystallization

Zeolite crystal growth mechanisms are not fully elucidated owing to their complexity wherein the formation of a particular zeolite can occur by more than one crystallization pathway. Here, we have conducted time-resolved dissolution experiments of MFI-type zeolite crystals in ammonium fluoride medium where detailed structural analysis allowed us to extrapolate and elucidate the possible mechanism of nucleation and crystal growth. A combination of electron and scanning probe microscopy shows that dissolution initiates preferentially at lattice defects and progressively removes defect zones to reveal a mosaic structure of crystalline domains within each zeolite crystal. This mosaic architecture evolves during the growth process, reflecting the changing conditions of zeolite formation that can be retroactively assessed during zeolite crystal dissolution. Moreover, a more general implication of this study is the establishment that dissolution can be used successfully as an ex situ technique to uncover details about crystal growth features inaccessible by other methods.

Design features and elemental/metal analysis of the atomizers in pod-style electronic cigarettes

BACKGROUND

The atomizers of electronic cigarettes (ECs) contain metals that transfer to the aerosol upon heating and may present health hazards. This study analyzed 4th-generation EC pod atomizer design features and characterized their elemental/metal composition.

METHODS

Eleven EC pods from six brands/manufacturers were purchased at local shops and online. Pods were dissected and imaged using a Canon EOS Rebel SL2 camera. Elemental analysis and mapping of atomizer components was done using a scanning electron microscope coupled with an energy dispersive x-ray spectrometer.

RESULTS

EC pods varied in size and design. The internal atomizer components were similar across brands except for variations occurring mainly in the wicks and filaments of some products. The filaments were either Elinvar (nickel, iron, and chromium) (36.4%), nichrome (36.4%), iron-chromium (18.2%), or nickel (9%). Thick wires present in 55% of the atomizers were mainly nickel and were joined to filaments by brazing. Wire-connector joints were Elinvar. Metal air tubes were made of Elinvar (50%), nickel, zinc, copper, and tin (37.5%), and nickel and copper (12.5%). Most of the wick components were silica, except for two pods (PHIX and Mico), which were mainly ceramic. Connectors contained gold-plated nickel, iron-chromium multiple alloys of nickel, zinc, gold, iron, and copper. Wick chambers were made of Elinvar. Outer casings were either nickel, copper-tin, or nickel-copper alloys. Magnets were nickel with minor iron, copper, and sulfur. Some frequently occurring elements were high in relative abundance in atomizer components.

CONCLUSIONS

The atomizers of pods are similar to previous generations, with the introduction of ceramic wicks and magnets in the newer generations. The elements in EC atomizers may transfer into aerosols and adversely affect health and accumulate in the environment.

A natural impact-resistant bicontinuous composite nanoparticle coating

Nature utilizes the available resources to construct lightweight, strong and tough materials under constrained environmental conditions. The impact surface of the fast-striking dactyl club from the mantis shrimp is an example of one such composite material; the shrimp has evolved the capability to localize damage and avoid catastrophic failure from high-speed collisions during its feeding activities. Here we report that the dactyl club of mantis shrimps contains an impact-resistant coating composed of densely packed (about 88 per cent by volume) ~65-nm bicontinuous nanoparticles of hydroxyapatite integrated within an organic matrix. These mesocrystalline hydroxyapatite nanoparticles are assembled from small, highly aligned nanocrystals. Under impacts of high strain rates (around 10⁴ s^-1), particles rotate and translate, whereas the nanocrystalline networks fracture at low-angle grain boundaries, form dislocations and undergo amorphization. The interpenetrating organic network provides additional toughening, as well as substantial damping, with a loss coefficient of around 0.02. An unusual combination of stiffness and damping is therefore achieved, outperforming many engineered materials.

Potential Penetration of CTAB- and MUDA-coated Gold Nanorods into Tooth Enamel

AIM

Gold nanorods (GNRs) have gained interest as a promising carrier for antibiotics. Gold nanorods may reduce the development of antimicrobial resistance in certain microbial species. Although applications of GNRs to mitigate oral biofilms are under development, their use in the oral cavity may have adverse effects. The aim of this study was to evaluate the potential penetration of GNRs into the tooth enamel structure using confocal laser scanning microscopy (CLSM) and scanning transmission electron microscopy (STEM).

MATERIALS AND METHODS

Our approach was to synthesize GNRs with cationic [cetyltrimethylammoniumbromide (CTAB)] and anionic [11-mercaptoundecanoic acid (MUDA)] surface coatings. We hypothesized that penetration would be surface coating dependent.

RESULTS

Regardless of the chemical modification of the GNRs of size ∼20 nm × 8 nm, exposure of these materials did not result in superficial penetration into the enamel.

CONCLUSION

Within the limitations of this study, it is concluded that the use of CLSM and STEM is a feasible approach to investigate the penetration of nanomaterials into the tooth structure.

CLINICAL SIGNIFICANCE

Exposure of the enamel with chemically modified GNRs of size ∼20 nm × 8 nm will not result in superficial penetration into the enamel.

Aerosol Synthesis of High Entropy Alloy Nanoparticles

Homogeneously mixing multiple metal elements within a single particle may offer new material property functionalities. High entropy alloys (HEAs), nominally defined as structures containing five or more well-mixed metal elements, are being explored at the nanoscale, but the scale-up to enable their industrial application is an extremely challenging problem. Here, we report an aerosol droplet-mediated technique toward scalable synthesis of HEA nanoparticles with atomic-level mixing of immiscible metal elements. An aqueous solution of metal salts is nebulized to generate ∼1 μm aerosol droplets, which when subjected to fast heating/quenching result in decomposition of the precursors and freezing-in of the zero-valent metal atoms. Atomic-level resolution scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis reveals that all metal elements in the nanoparticles are homogeneously mixed at the atomic level. We believe that this approach offers a facile and flexible aerosol droplet-mediated synthesis technique that will ultimately enable bulk processing starting from a particulate HEA.

Analysis of the elements and metals in multiple generations of electronic cigarette atomizers

BACKGROUND

Since their release in 2004, electronic cigarettes (ECs) and their atomizers have undergone significant evolution.

OBJECTIVE

The purpose of this study was to evaluate and compare the elemental/metal composition of atomizers in cartomizer and tank style ECs produced over a 5-year period.

METHODS

Popular cartomizer and tank models of ECs were dissected and photographed using a stereoscopic microscope, and elemental analysis of EC atomizers was done using scanning electron microscopy coupled with energy dispersive x-ray spectroscopy.

RESULTS

Eight elements/metals were found in most products across and within brands purchased at different times. These included chromium, nickel, copper, silver, tin, silicon, aluminum, and zinc. Iron and lead were found in some but not all products, while manganese, cobalt, molybdenum, titanium, and tungsten were only found in a few of the products. The metals used in various components were often similar in cartomizer and tank models. Filaments were usually chromium and nickel (nichrome), although in some newer products, the filament also contained iron, copper, and manganese. The thick wire in earlier products was usually copper coated with silver, while in some newer products, the thick wire was predominantly nickel. In all products, the wick was silica, and sheaths, when present, were fiberglass (silicon, oxygen, calcium, aluminum, magnesium). Wire-to-wire joints were either brazed or clamped with brass (copper and zinc), and air-tube-to-thick wire joints, when present, were usually soldered with tin. Tank style products generally lacked a thick wire and sheaths.

CONCLUSION

In general, atomizer components in ECs were remarkably similar over time and between brands. Certain elements/metals were consistently found in most models from all generations, and these should be studied carefully to determine if their transfer to aerosols affects user's health and if their accumulation in trash affects the environment.

Oriented epitaxial TiO2 nanowires for water splitting

Highly oriented epitaxial rutile titanium dioxide (TiO₂) nanowire arrays have been hydrothermally grown on polycrystalline TiO₂ templates with their orientation dependent on the underlying TiO₂ grain. Both the diameter and areal density of the nanowires were tuned by controlling the precursor concentration, and the template surface energy and roughness. Nanowire tip sharpness was influenced by precursor solubility and diffusivity. A new secondary ion mass spectrometer technique has been developed to install additional nucleation sites in single crystal TiO₂ templates and the effect on nanowire growth was probed. Using the acquired TiO₂ nanowire synthesis knowhow, an assortment of nanowire arrays were installed upon the surface of undoped TiO₂ photo-electrodes and assessed for their photo-electrochemical water splitting performance. The key result obtained was that the presence of short and dispersed nanowire arrays significantly improved the photocurrent when the illumination intensity was increased from 100 to 200 mW cm^-2. This is attributed to the alignment of the homoepitaxially grown nanowires to the [001] direction, which provides the fastest charge transport in TiO₂ and an improved pathway for photo-holes to find water molecules and undertake oxidation. This result lays a foundation for achieving efficient water splitting under conditions of concentrated solar illumination.

Breakdown current density in h-BN-capped quasi-1D TaSe3 metallic nanowires: prospects of interconnect applications

We report on the current-carrying capacity of the nanowires made from the quasi-1D van der Waals metal tantalum triselenide capped with quasi-2D boron nitride. The chemical vapor transport method followed by chemical and mechanical exfoliation were used to fabricate the mm-long TaSe3 wires with the lateral dimensions in the 20 to 70 nm range. Electrical measurements establish that the TaSe3/h-BN nanowire heterostructures have a breakdown current density exceeding 10 MA cm(-2)-an order-of-magnitude higher than that for copper. Some devices exhibited an intriguing step-like breakdown, which can be explained by the atomic thread bundle structure of the nanowires. The quasi-1D single crystal nature of TaSe3 results in a low surface roughness and in the absence of the grain boundaries. These features can potentially enable the downscaling of the nanowires to lateral dimensions in a few-nm range. Our results suggest that quasi-1D van der Waals metals have potential for applications in the ultimately downscaled local interconnects.

Solid state lithiation-delithiation of sulphur in sub-nano confinement: a new concept for designing lithium-sulphur batteries

We investigate the detailed effects and mechanisms of sub-nano confinement on lithium-sulfur (Li-S) electrochemical reactions in both ether-based and carbonate-based electrolytes. Our results demonstrate a clear correlation between the size of sulfur confinement and the resulting Li-S electrochemical mechanisms. In particular, when sulfur is confined within sub-nano pores, we observe identical lithium-sulfur electrochemical behavior, which is distinctly different from conventional Li-S reactions, in both ether and carbonate electrolytes. Taken together, our results highlight the critical importance of sub-nano confinement effects on controlling solid-state reactions in Li-S electrochemical systems.

Critical role of interfacial effects on the reactivity of semiconductor-cocatalyst junctions for photocatalytic oxygen evolution from water

Photocatalytic water splitting has the potential to provide a sustainable approach for storing the energy of solar photons in the form of chemical bonds.

3D Study of the Morphology and Dynamics of Zeolite Nucleation

The principle aspects and constraints of the dynamics and kinetics of zeolite nucleation in hydrogel systems are analyzed on the basis of a model Na-rich aluminosilicate system. A detailed time-series EMT-type zeolite crystallization study in the model hydrogel system was performed to elucidate the topological and temporal aspects of zeolite nucleation. A comprehensive set of analytical tools and methods was employed to analyze the gel evolution and complement the primary methods of transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR) spectroscopy. TEM tomography reveals that the initial gel particles exhibit a core-shell structure. Zeolite nucleation is topologically limited to this shell structure and the kinetics of nucleation is controlled by the shell integrity. The induction period extends to the moment when the shell is consumed and the bulk solution can react with the core of the gel particles. These new findings, in particular the importance of the gel particle shell in zeolite nucleation, can be used to control the growth process and properties of zeolites formed in hydrogels.

Intertwined nanocarbon and manganese oxide hybrid foam for high-energy supercapacitors

Rapid charging and discharging supercapacitors are promising alternative energy storage systems for applications such as portable electronics and electric vehicles. Integration of pseudocapacitive metal oxides with single-structured materials has received a lot of attention recently due to their superior electrochemical performance. In order to realize high energy-density supercapacitors, a simple and scalable method is developed to fabricate a graphene/MWNT/MnO2 nanowire (GMM) hybrid nanostructured foam, via a two-step process. The 3D few-layer graphene/MWNT (GM) architecture is grown on foamed metal foils (nickel foam) via ambient pressure chemical vapor deposition. Hydrothermally synthesized α-MnO2 nanowires are conformally coated onto the GM foam by a simple bath deposition. The as-prepared hierarchical GMM foam yields a monographical graphene foam conformally covered with an intertwined, densely packed CNT/MnO2 nanowire nanocomposite network. Symmetrical electrochemical capacitors (ECs) based on GMM foam electrodes show an extended operational voltage window of 1.6 V in aqueous electrolyte. A superior energy density of 391.7 Wh kg(-1) is obtained for the supercapacitor based on the GMM foam, which is much higher than ECs based on GM foam only (39.72 Wh kg(-1) ). A high specific capacitance (1108.79 F g(-1) ) and power density (799.84 kW kg(-1) ) are also achieved. Moreover, the great capacitance retention (97.94%) after 13 000 charge-discharge cycles and high current handability demonstrate the high stability of the electrodes of the supercapacitor. These excellent performances enable the innovative 3D hierarchical GMM foam to serve as EC electrodes, resulting in energy-storage devices with high stability and power density in neutral aqueous electrolyte.

Phage-directed synthesis of copper sulfide: structural and optical characterization

The growth of crystalline copper sulfide using a viral template was investigated using sequential incubation in CuCl2 and Na2S precursors. Non-specific electrostatic attraction between a genetically-modified M13 bacteriophage and copper cations in the CuCl2 precursor caused phage agglomeration and bundle formation. Following the addition of Na2S, polydisperse nanocrystals 2-7 nm in size were found along the length of the viral scaffold. The structure of the copper sulfide material was identified as cubic anti-fluorite type Cu1.8S, space group Fm3[overline]m. Strong interband absorption was observed within the ultraviolet to visible range with an onset near 800 nm. Furthermore, free carrier absorption, associated with the localized surface plasmon resonance of the copper sulfide nanocrystals, was seen in the near infrared with absorbance maxima at 1060 nm and 3000 nm, respectively.

The production of oxygenated polycrystalline graphene by one-step ethanol-chemical vapor deposition

Large-area mono- and bilayer graphene films were synthesized on Cu foil (~ 1 inch(2)) in about 1 min by a simple ethanol-chemical vapor deposition (CVD) technique. Raman spectroscopy and high resolution transmission electron microscopy revealed the synthesized graphene films to have polycrystalline structures with 2-5 nm individual crystallite size which is a function of temperature up to 1000°C. X-ray photoelectron spectroscopy investigations showed about 3 atomic% carboxylic (COOH) functional groups were formed during growth. The field-effect transistor devices fabricated using polycrystalline graphene as conducting channel (L(c)=10 μm; W(c)=50 μm) demonstrated a p-type semiconducting behavior with high drive current and Dirac point at ~35 V. This simple one-step method of growing large area polycrystalline graphene films with semiconductor properties and easily functionalizable groups should assist in the realization of potential of polycrystalline graphene for nanoelectronics, sensors and energy storage devices.

Peptide-mediated shape- and size-tunable synthesis of gold nanostructures

While several biological processes have been shown to be useful for the production of well-designed, inorganic nanostructures, the mechanism(s) controlling the size and shape of nano and micron size particles remains elusive. Here we report on the controlled size- and shape-specific production of gold nanostructures under ambient reaction conditions using a dodecapeptide, Midas-2, originally selected from a phage-displayed combinatorial peptide library. Single amino acid changes in Midas-2 greatly influence the size (a few nanometers to approximately 100 microm) and shape (nanoparticles, nanoribbons, nanowires and nanoplatelets) of the gold nanostructures produced, and these are controllable by adjusting the solution pH and gold ion concentration. The ability to control the shape and size of the gold nanostructures by changing the peptide structure and reaction conditions will lead to many potential applications, including nanoelectronics, sensors and optoelectronics, because of their unique size- and shape-dependent optical and electrical properties.

Study of a single InSb nanowire fabricated via DC electrodeposition in porous templates

InSb nanowire arrays have been fabricated by direct current electrodeposition inside the nanochannels of anodic alumina membranes without subsequent annealing. After Au contacts were patterned to the nanowires using electron beam lithography, photoresponse studies were conducted. Absorbance peaks were also recorded from free suspending nanowires. A significant response was observed when the wires were exposed to visible light and infrared absorption peaks were observed during absorption experiment. Comparisons were also made between single and multiple nanowires' responses. The nanowires also conduct almost no current in the dark, but when hit with light, they conduct 10,000 times more current. This photoconducting property could lead to a variety of tiny optoelectronic devices potentially useful in future generations of nanoelectronics and chemical sensors.

Synthesis and characterization of cadmium telluride nanowire

CdTe nanowires with controlled composition were cathodically electrodeposited using track-etched polycarbonate membrane as scaffolds and their material and electrical properties were systematically investigated. As-deposited CdTe nanowires show nanocrystalline cubic phase structures with grain sizes of up to 60 nm. The dark-field images of nanowires reveal that the crystallinity of nanowires was greatly improved from nanocrystalline to a few single crystals within nanowires upon annealing at 200 °C for 6 h in a reducing environment (5% H(2)+95% N(2)). For electrical characterization, a single CdTe nanowire was assembled across microfabricated gold electrodes using the drop-casting method. In addition to an increase in grain size, the electrical resistivity of an annealed single nanowire (a few 10(5) Ω cm) was one order of magnitude greater than in an as-deposited nanowire, indicating that crystallinity of nanowires improved and defects within nanowires were reduced during annealing. By controlling the dopants levels (e.g. Te content of nanowires), the resistivity of nanowires was varied from 10(4) to 10(0) Ω cm. Current-voltage (I-V) characteristics of nanowires indicated the presence of Schottky barriers at both ends of the Au/CdTe interface. Temperature-dependent I-V measurements show that the electron transport mode was determined by a thermally activated component at T>-50 °C and a temperature-independent component below -50 °C. Under optical illumination, the single CdTe nanowire exhibited enhanced conductance.

Synthesis of zeolite nanocrystals at room temperature

Zeolite A nanoparticles were synthesized under room-temperature conditions from a very reactive organic-template-free gel system. The optimization of the syntheses parameters, namely, the composition of the initial system and the careful choice of the reactants, allowed the crystallization to be accomplished within 3 days. At this stage the individual zeolite crystals were in the range of 100-300 nm without well-developed crystal faces. The prolongation of the synthesis time up to 10 days led to formation of larger well-faceted cubic crystals averaging about 400-500 nm in size. The high-resolution transmission electron microscopy (HRTEM) study revealed that a thin layer of amorphous material covers the zeolite particles acting as a binder between individual zeolite crystals. The postsynthesis treatment of the product in NH(3) media under ultrasonic radiation disintegrated the loosely attached zeolite particles and decreased the fraction of zeolite A particles with low colloidal stability. The employed approach, however, did not result in complete disintegration of aggregated crystals. The zeolite crystals obtained under ambient conditions were characterized by XRD, SEM, dynamic light scattering, and N(2) adsorption measurements.

Evidences for Zeolite Nucleation at the Solid−Liquid Interface of Gel Cavities

The entire sequence of crystallization events, starting with formation of the initial organic-cation-free gel, proceeding through the zeolite nucleation stage, and finishing with complete transformation into LTA-type zeolite crystals, has been monitored by means of high-resolution transmission electron microscopy. Formation and development of voids, containing highly hydrated material transformed later into negative crystals, has been discovered in the solid part of the system. The evolution of these areas has been found to be an integral and noteworthy part of the chemical transformation of the gel that preceded the nucleation in the system. These void structures and, in particular, their solid-liquid interfaces have been identified as the specific locations where the formation of protozeolite nuclei took place. Further development of the system followed the classical for zeolite-yielding systems of crystallization that could be described by the autocatalytic model.

TEM Investigation of Formation Mechanism of Monocrystal-Thick b-Oriented Pure Silica Zeolite MFI Film

The first direct transmission electron microscopic (TEM) observation has been carried out on the continuous monocrystal-thick b-oriented pure silica zeolite MFI films produced by in situ crystallization. The self-supporting film samples for TEM study were fabricated by dissolving the steel substrate with acid. This TEM study is free of those artifacts that are typically associated with TEM sample preparations, and allows us to investigate the "true" structure and texture of a very large area of the film and at the same time to focus at will on each individual zeolite crystal in the film. Abundant TEM information including crystallographic orientation relationships among crystals in the film (both out-of-plane and in-plane), grain boundaries, and each crystal grain was obtained. This TEM investigation provides direct unambiguous new evidence to support the homogeneous nucleation mechanism, by which the films form through homogeneous nucleation and crystal growth in the bulk to form equal-sized disk-shape crystals, followed by self-assembly of these crystals onto the substrate to produce a two-dimensional close-packed structure. The last stage of the film formation involves simultaneous space-limited growth and rotation of the individual crystals to realize the in-plane crystallographic control within the film.

Clinoenstatite in alpe arami peridotite: additional evidence of very high pressure

Observations by transmission electron microscopy show that lamellae of clinoenstatite are present in diopside grains of the Alpe Arami garnet lherzolite of the Swiss Alps. The simplest interpretation of the orientation, crystallography, and microstructures of the lamellae and the phase relationships in this system is that the lamellae originally exsolved as the high-pressure C-centered form of clinoenstatite. These results imply that the rocks were exhumed from a minimum depth of 250 kilometers before or during continental collision.