Piezoelectricity in Structural Adhesives and Application for Monitoring Joint Integrity via Guided Ultrasonic Waves.

In an adhesively bonded structure, utilizing the adhesive itself for monitoring the joint integrity can be beneficial in reduction of labor, time, and potential human errors while avoiding problems associated with introduction of a foreign sensor component. This work started from the examination of effective piezoelectricity of commercial structural adhesives/sealants, and five of them were found to possess effective piezoelectric property, with effective piezoelectric coefficient d33 from -0.11 to -1.77 pm/V depending on frequency under substrate clamping condition. With stable piezoelectric response at least up to megahertz, an epoxy adhesive with inorganic filler was selected for structural health monitoring (SHM) feasibility demonstration via generating or sensing guided ultrasonic Lamb waves. The presence of disbond in the adhesive joint is detectable by comparing the Lamb waves signal with a reference baseline signal associated with an intact structure. The results show that the selected adhesive with piezoelectric response can perform the dual roles of structural bonding and ultrasonic joint integrity monitoring.

Facile solvothermal approach to pristine tetrahedrite nanostructures with unique multiply-voided morphology.

Tetrahedrite (Cu12Sb4S13) is a highly promising environmentally friendly material for energy conversion applications but its synthesis generally requires several days of heating at high temperature conditions. To fabricate tetrahedrite in a more rapid way and under milder conditions, solvothermal synthesis has been recently explored. However, a common problem faced when using this technique is the formation of significant amounts of other ternary Cu-Sb-S phases along with the desired tetrahedrite phase. Here, we present an optimized solvothermal procedure for synthesizing high-purity samples of tetrahedrite at moderate temperatures and reasonable heating times. The as-prepared samples are single-crystalline nanometer-sized structures having multiple voids or pores. By modifying certain experimental parameters such as the reaction temperature and heating time, we have shown that we can alter the nanocrystal architecture. The formation mechanism was investigated and it was found that these porous tetrahedrite nanostructures are a product of the non-classical oriented aggregation growth process. Porosity in nanomaterials is known to improve material properties and is desirable in many important applications so the construction of void-containing tetrahedrite nanostructures will potentially extend the utility of tetrahedrite to a wider range of applications. In this work, we explore its possible use as a photothermal-responsive drug delivery vehicle.

Alloyed ZnS-CuInS2 Semiconductor Nanorods and Their Nanoscale Heterostructures for Visible-Light-Driven Photocatalytic Hydrogen Generation.

A promising photocatalytic system in the form of heterostructured nanocrystals (HNCs) is presented wherein alloyed ZnS-CuInS2 (ZCIS) semiconductor nanorods are decorated with Pt and Pd4 S nanoparticles. This is apparently the first report on the colloidal preparation and photocatalytic behavior of ZCIS-Pt and ZCIS-Pd4 S nanoscale heterostructures. Incorporation of Pt and Pd4 S cocatalysts leads to considerable enhancement of the photocatalytic activity of ZCIS for visible-light-driven hydrogen production.

Colloidal nanocrystals of orthorhombic Cu2ZnGeS4: phase-controlled synthesis, formation mechanism and photocatalytic behavior.

The orthorhombic polymorph of Cu2ZnGeS4 (CZGS) is a metastable wurtzite-derived phase that can only be prepared in the bulk form by extensive heating at high temperatures (≥790 °C) when using the conventional solid-state reaction route. By employing a facile solution-based synthetic strategy, we were able to obtain phase-pure orthorhombic CZGS in nanocrystalline form at a much lower reaction temperature. Prior to this work, the colloidal synthesis of single-phase orthorhombic CZGS on the nanoscale has never been reported. We find that the use of an appropriate combination of coordinating solvents and precursors is crucial to the sole formation of this metastable phase in solution. A possible formation mechanism is proposed on the basis of our experimental results. Because CZGS consists of environmentally benign metal components, it is regarded as a promising alternative material to the technologically useful yet toxic cadmium-containing semiconductors. The orthorhombic CZGS nanocrystals display strong photon absorption in the visible spectrum and are photocatalytically active in dye degradation under visible-light illumination.

Dual-phase spinel MnCo2O4 and spinel MnCo2O4/nanocarbon hybrids for electrocatalytic oxygen reduction and evolution.

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential reactions for energy-storage and -conversion devices relying on oxygen electrochemistry. High-performance, nonprecious metal-based hybrid catalysts are developed from postsynthesis integration of dual-phase spinel MnCo2O4 (dp-MnCo2O4) nanocrystals with nanocarbon materials, e.g., carbon nanotube (CNT) and nitrogen-doped reduced graphene oxide (N-rGO). The synergic covalent coupling between dp-MnCo2O4 and nanocarbons effectively enhances both the bifunctional ORR and OER activities of the spinel/nanocarbon hybrid catalysts. The dp-MnCo2O4/N-rGO hybrid catalysts exhibited comparable ORR activity and superior OER activity compared to commercial 30 wt % platinum supported on carbon black (Pt/C). An electrically rechargeable zinc-air battery using dp-MnCo2O4/CNT hybrid catalysts on the cathode was successfully operated for 64 discharge-charge cycles (or 768 h equivalent), significantly outperforming the Pt/C counterpart, which could only survive up to 108 h under similar conditions.

Colloidal synthesis and photocatalytic properties of orthorhombic AgGaS2 nanocrystals.

AgGaS2 (AGS) nanocrystals that exist in the orthorhombic phase were successfully prepared for the first time through a one-pot colloidal synthetic strategy using suitable coordinating solvents. These orthorhombic AGS nanocrystals were found to display great potential in visible-light-driven photocatalysis.

Antimicrobial functionalization of silicone surfaces with engineered short peptides having broad spectrum antimicrobial and salt-resistant properties.

Catheter-associated urinary tract infections (CAUTIs) are often preceded by pathogen colonization on catheter surfaces and are a major health threat facing hospitals worldwide. Antimicrobial peptides (AMPs) are a class of new antibiotics that hold promise in curbing CAUTIs caused by antibiotic-resistant pathogens. This study aims to systematically evaluate the feasibility of immobilizing two newly engineered arginine/lysine/tryptophan-rich AMPs with broad antimicrobial spectra and salt-tolerant properties on silicone surfaces to address CAUTIs. The peptides were successfully immobilized on polydimethylsiloxane and urinary catheter surfaces via an allyl glycidyl ether (AGE) polymer brush interlayer, as confirmed by X-ray photoelectron spectroscopy and water contact angle analyses. The peptide-coated silicone surfaces exhibited excellent microbial killing activity towards bacteria and fungi in urine and in phosphate-buffered saline. Although both the soluble and immobilized peptides demonstrated membrane disruption capabilities, the latter showed a slower rate of kill, presumably due to reduced diffusivity and flexibility resulting from conjugation to the polymer brush. The synergistic effects of the AGE polymer brush and AMPs prevented biofilm formation by repelling cell adhesion. The peptide-coated surface showed no toxicity towards smooth muscle cells. The findings of this study clearly indicate the potential for the development of AMP-based coating platforms to prevent CAUTIs.

A stable solution-processed polymer semiconductor with record high-mobility for printed transistors.

Microelectronic circuits/arrays produced via high-speed printing instead of traditional photolithographic processes offer an appealing approach to creating the long-sought after, low-cost, large-area flexible electronics. Foremost among critical enablers to propel this paradigm shift in manufacturing is a stable, solution-processable, high-performance semiconductor for printing functionally capable thin-film transistors - fundamental building blocks of microelectronics. We report herein the processing and optimisation of solution-processable polymer semiconductors for thin-film transistors, demonstrating very high field-effect mobility, high on/off ratio, and excellent shelf-life and operating stabilities under ambient conditions. Exceptionally high-gain inverters and functional ring oscillator devices on flexible substrates have been demonstrated. This optimised polymer semiconductor represents a significant progress in semiconductor development, dispelling prevalent skepticism surrounding practical usability of organic semiconductors for high-performance microelectronic devices, opening up application opportunities hitherto functionally or economically inaccessible with silicon technologies, and providing an excellent structural framework for fundamental studies of charge transport in organic systems.

Alloyed (ZnS)x(CuInS2)(1-x) semiconductor nanorods: synthesis, bandgap tuning and photocatalytic properties.

Rod-like nanocrystals of the semiconductor alloy (ZnS)(x)(CuInS(2))(1-x) (ZCIS) have been colloidally prepared by using a one-pot non-injection-based synthetic strategy. The ZCIS nanorods crystallize in the hexagonal wurtzite structure and display preferential growth in the direction of the c axis. The bandgap of these quarternary alloyed nanorods can be conveniently tuned by varying the ratio of ZnS to CuInS(2). A non-linear relationship between the bandgap and the alloy composition is observed. The ZCIS nanorods are found to exhibit promising photocatalytic behaviour in visible-light-driven degradation of Rhodamine B.

Temperature and chemical bonding-directed self-assembly of cobalt phosphide nanowires in reaction solutions into vertical and horizontal alignments.

The preparation of vertically or horizontally aligned self-assemblies of CoP nanowires is demonstrated for the first time by aging them in the reaction solution for a sufficient time at 20 or 0 °C. This strategy opens up a way for exploring the controlled self-assembly of various highly anisotropic nanostructures into long-range ordered structures with collective properties.

Ternary cobalt-iron phosphide nanocrystals with controlled compositions, properties, and morphologies from nanorods and nanorice to split nanostructures.

Structural phase-controlled formation of binary Co(2)P and CoP nanocrystals is achieved by reacting cobalt(II) oleate with trioctylphosphine. In the absence of oleylamine, Co(2)P nanowires are formed at both 290 and 320 °C. In the presence of oleylamine, Co(2)P nanorods are formed at 290 °C, and CoP nanorods are formed at 320 °C. With the simultaneous reaction of iron(III) oleate and cobalt(II) oleate with trioctylphosphine in the presence of oleylamine, ternary Co(2)P-type cobalt-iron phosphide nanostructures are produced at both 290 and 320 °C, corresponding to rice-shaped Co(1.5)Fe(0.5)P nanorods and split Co(1.7)Fe(0.3)P nanostructures, respectively. The controlled incorporation of iron into cobalt phosphide can alter the magnetic properties from paramagnetic binary Co(2)P to ferromagnetic Co(2)P-type ternary cobalt-iron phosphide nanostructures. Meanwhile, the time-dependent morphological evolution from small nanodots/nanorods, through seeded growth to unique split nanostructures is demonstrated in one-pot reaction at 320 °C.

One-pot synthesis of Cu1.94S-CdS and Cu1.94S-Zn(x)Cd(1-x)S nanodisk heterostructures.

Nanodisk heterostructures consisting of monoclinic Cu(1.94)S and wurtzite CdS have been colloidally synthesized for the first time. Initially, hexagonal-shaped nanodisks of Cu(1.94)S were produced upon thermolysis of a copper complex in a solvent mixture of HDA and TOA at 250 °C. Rapid addition of Cd precursor to the reaction mixture resulted in the partial conversion of Cu(1.94)S into CdS, yielding Cu(1.94)S-CdS nanoheterostructures. The original morphology of the Cu(1.94)S nanodisks was conserved during the transformation. When Zn precursor was added together with the Cd precursor, Cu(1.94)S-Zn(x)Cd(1-x)S nanodisks were generated. These two-component nanostructures are potentially useful in the fabrication of heterojunction solar cells.

Morphological tuning, self-assembly and optical properties of indium oxide nanocrystals.

In this paper, weak acids, weak bases or their mixtures were used as reaction media/coordinating ligands to achieve systematic morphological control over amphoteric indium oxide nanostructures. Different indium/oleic acid molar ratios from 1 : 0, 1 : 1, 1 : 2, 1 : 3, 1 : 6 and 1 : 15 in non-coordinating, weakly coordinating, strongly coordinating and their mixed media were adopted to prepare irregular aggregated nanoparticles and uniform regular/truncated octahedra, etc. In addition to their strong size-dependent absorption, single-crystalline indium oxide octahedra also gave a strong band-edge emission while irregular indium oxide aggregated nanoparticles only exhibited a weak deep-trap emission. Meanwhile, the truncated octahedra were self-assembled into either zigzag lines or pentagram patterns, and the regular octahedra and truncated cubes were self-assembled into hexagonally packed nanocrystal arrays. In addition, the formation mechanism of the various nanostructures under different conditions was investigated in detail.

Graphitically encapsulated cobalt nanocrystal assemblies.

Graphitically encapsulated cobalt nanocrystal assemblies are chemically prepared by one-pot reaction at >380 degrees C followed by a reversed etching process to produce porous graphitic structure for revealing their self-assembling nature.

Robust gold-decorated silica-titania pebbles for low-temperature CO catalytic oxidation.

A deposition-precipitation (DP) process was used to prepare silica-titania core-shell pebbles decorated with nanocrystalline gold suitable for low-temperature catalytic oxidation of carbon monoxide (CO). The microstructure, phase content, crystallography, and catalytic activity were correlated with the pH (3-8), aging time (15, 30, 60 min), and heat treatment employed for gold crystallization (200-400 degrees C). A homogeneous metal distribution, high gold loading (3.7-4.4 wt %), and superior interfacial adhesion between gold and titania were obtained when the support pebbles were prepared at 600 degrees C, a temperature lower than that required for the anatase-to-rutile transformation. Nucleation and growth of {111} faceted gold was favored at mid-pH (6.4-8), while smaller crystals (<7.5 nm) were obtained at short aging times (

Simple route to monodispersed silica-titania core-shell photocatalysts.

A monodispersed silica-titania core-shell photocatalyst was synthesized via a sol-gel route without the need of pH adjustment, cationic polyelectrolytes, or surfactants in a process where silica spheres were impregnated with hydrolyzed titanium tetrabutoxide, incubated at room temperature, and then condensed using an ethanol/water (1:1) solvent. Four coating cycles in a 10% v/v titania sol produced homogeneous titania shells. The quality of catalysts was assessed quantitatively using Rietveld analysis of powder X-ray diffraction patterns combined with X-ray fluorescence spectrometry. During calcination, the anatase-to-rutile transformation was delayed to 1000 degrees C, which is approximately 300 degrees C higher than usually observed. The thermal stability and surface area of titania were enhanced through the slow crystal growth of anatase. The photocatalytic activity of the core-shell photocatalysts calcined at 400-600 degrees C was found to be proportional to the thickness of titania but did not directly correlate with the surface area.