Matching Low Viscosity with Enhanced Conductivity in Vat Photopolymerization 3D Printing: Disparity in the Electric and Rheological Percolation Thresholds of Carbon-Based Nanofillers Is Controlled by the Matrix Type and Filler Dispersion.

This study investigated the impact of carbonaceous fillers (carbon black, multiwalled carbon nanotubes, graphene, and highly defective graphene) on aromatic and nonaromatic photopolymer resins' properties, such as viscosity, long-term stability, complex permittivity, curing efficiency, final conversion, storage modulus, heat deflection and glass transition temperatures, network density, and DC resistivity. The presented results also highlight challenges that must be addressed in designing and processing carbonaceous filler-based 3D-printed photopolymer resins. The improved dielectric and electrical properties were closely tied to the dispersion quality and filler-matrix affinity. It favored the enhanced dispersion of anisotropic fillers (nanotubes) in a compatible matrix above their percolation threshold. On the other hand, the dispersed filler worsens printability due to the elevated viscosity and deteriorated penetration depth. Nonetheless, electrical and rheological percolation was found at different filler concentrations. This window of despaired percolation combines highly enhanced conductivity with only mildly increased viscosity and good printability.

Gigahertz-Based Visible Light Detection Enabled via CdS-Coated TiO2 Nanotube Layers.

Detection of visible light is a key component in material characterization techniques and often a key component of quality or purity control analyses for health and safety applications. Here in this work, to enable visible light detection at gigahertz frequencies, a planar microwave resonator is integrated with high aspect ratio TiO2 nanotube (TNT) layer-sensitized CdS coating using the atomic layer deposition (ALD) technique. This unique method of visible light detection with microwave-based sensing improves integration of the light detection devices with digital technology. The designed planar microwave resonator sensor was implemented and tested with resonant frequency between 8.2 and 8.4 GHz and a resonant amplitude between -15 and -25 dB, depending on the wavelength of the illuminated light illumination on the nanotubes. The ALD CdS coating sensitized the nanotubes in visible light up to ∼650 nm wavelengths, as characterized by visible spectroscopy. Furthermore, CdS-coated TNT layer integration with the planar resonator sensor allowed for development of a robust microwave sensing platform with improved sensitivity to green and red light (60 and 1300%, respectively) compared to the blank TNT layers. Moreover, the CdS coating of the TNT layer enhanced the sensor's response to light exposure and resulted in shorter recovery times once the light source was removed. Despite having a CdS coating, the sensor was capable of detecting blue and UV light; however, refining the sensitizing layer could potentially enhance its sensitivity to specific wavelengths of light in certain applications.

2D FeSx Nanosheets by Atomic Layer Deposition: Electrocatalytic Properties for the Hydrogen Evolution Reaction.

2-dimensional FeSx nanosheets of different sizes are synthesized by applying different numbers of atomic layer deposition (ALD) cycles on TiO2 nanotube layers and graphite sheets as supporting materials and used as an electrocatalyst for the hydrogen evolution reaction (HER). The electrochemical results confirm electrocatalytic activity in alkaline media with outstanding long-term stability (>65 h) and enhanced catalytic activity, reflected by a notable drop in the initial HER overpotential value (up to 26 %). By using a range of characterization techniques, the origin of the enhanced catalytic activity was found to be caused by the synergistic interplay between in situ morphological and compositional changes in the 2D FeSx nanosheets during HER. Under the application of a cathodic potential in alkaline media, the as-synthesized 2D FeSx nanosheets transformed into iron oxyhydroxide-iron oxysulfide core-shell nanoparticles, which exhibited a higher active catalytic surface and newly created Fe-based HER catalytic sites.

Multifunctional Electrospun Nanofibers Based on Biopolymer Blends and Magnetic Tubular Halloysite for Medical Applications.

Tubular halloysite (HNT) is a naturally occurring aluminosilicate clay with a unique combination of natural availability, good biocompatibility, high mechanical strength, and functionality. This study explored the effects of magnetically responsive halloysite (MHNT) on the structure, morphology, chemical composition, and magnetic and mechanical properties of electrospun nanofibers based on polycaprolactone (PCL) and gelatine (Gel) blends. MHNT was prepared via a simple modification of HNT with a perchloric-acid-stabilized magnetic fluid-methanol mixture. PCL/Gel nanofibers containing 6, 9, and 12 wt.% HNT and MHNT were prepared via an electrospinning process, respecting the essential rules for medical applications. The structure and properties of the prepared nanofibers were studied using infrared spectroscopy (ATR-FTIR) and electron microscopy (SEM, STEM) along with energy-dispersive X-ray spectroscopy (EDX), magnetometry, and mechanical analysis. It was found that the incorporation of the studied concentrations of MHNT into PCL/Gel nanofibers led to soft magnetic biocompatible materials with a saturation magnetization of 0.67 emu/g and coercivity of 15 Oe for nanofibers with 12 wt.% MHNT. Moreover, by applying both HNT and MHNT, an improvement of the nanofibers structure was observed, together with strong reinforcing effects. The greatest improvement was observed for nanofibers containing 9 wt.% MHNT when increases in tensile strength reached more than two-fold and the elongation at break reached a five-fold improvement.

Microwave plasma-based high temperature dehydrogenation of hydrocarbons and alcohols as a single route to highly efficient gas phase synthesis of freestanding graphene.

Understanding underlying processes behind the simple and easily scalable graphene synthesis methods enables their large-scale deployment in the emerging energy storage and printable device applications. Microwave plasma decomposition of organic precursors forms a high-temperature environment, above 3000 K, where the process of catalyst-free dehydrogenation and consequent formation of C2molecules leads to nucleation and growth of high-quality few-layer graphene (FLG). In this work, we show experimental evidence that a high-temperature environment with a gas mixture of H2and acetylene, C2H2, leads to a transition from amorphous to highly crystalline material proving the suggested dehydrogenation mechanism. The overall conversion efficiency of carbon to FLG reached up to 47%, three times as much as for methane or ethanol, and increased with increasing microwave power (i.e. with the size of the high-temperature zone) and hydrocarbon flow rate. The yield decreased with decreasing C:H ratio while the best quality FLG (low D/G-0.5 and high 2D/G-1.5 Raman band ratio) was achieved for C:H ratio of 1:3. The structures contained less than 1 at% of oxygen. No additional hydrogen was necessary for the synthesis of FLG from higher alcohols having the same stoichiometry, 1-propanol and isopropanol, but the yield was lower, 15%, and dependent on the atom arrangement of the precursor. The prepared FLG nanopowder was analyzed by scanning electron microscopy, Raman, x-ray photoelectron spectroscopy, and thermogravimetry. Microwave plasma was monitored by optical emission spectroscopy.

Deposition of MoSe2 flakes using cyclic selenides.

The currently limited portfolio of volatile organoselenium compounds used for atomic layer deposition (ALD) has been extended by designing and preparing a series of four-, five- and six-membered cyclic silylselenides. Their fundamental properties were tailored by alternating the ring size, the number of embedded Se atoms and the used peripheral alkyl chains. In contrast to former preparations based on formation of sodium or lithium selenides, the newly developed synthetic method utilizes a direct and easy reaction of elemental selenium with chlorosilanes. Novel 2,2,4,4-tetraisopropyl-1,3,2,4-diselenadisiletane, which features good trade-off between chemical/thermal stability and reactivity, has been successfully used for gas-to-solid phase reaction with MoCl5 affording MoSe2. A thorough characterization of the as-deposited 2D MoSe2 flakes revealed its out-of-plane orientation and high purity. Hence, the developed four-membered cyclic silylselenide turned out to be well-suited Se-precursor for ALD of MoSe2.

Influence of sample surface topography on laser ablation process.

In this work we discuss how sample surface topography can significantly influence the laser ablation (LA) process and, in turn, the analytical response of the LA Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) method. Six different surface topographies were prepared on a certified aluminium alloy sample BAM 311 and SRM NIST 610 to investigate the phenomenon. All the samples were repetitively measured by LA-ICP-MS using a spot by spot analysis. The effect of laser fluence in the range of 1-13 J/cm2 was studied. For majority of measured isotopes, the ICP-MS signal was amplified with roughening of the sample surface. A stronger effect was observed on the Al alloy sample, where the more than sixty-time enhancement was achieved in comparison to the polished surface of the sample. Since the effect of surface topography is different for each analyte, it can be stated that surface properties affect not only the ICP-MS response, but also elemental fractionation in LA. The presented results show that different surface topographies may lead to misleading data interpretation because even when applying ablation preshots, the signal of individual elements changes. The utmost care must be taken when preparing the surface for single shot analysis or chemical mapping. On the other hand, by roughening the sample surface, it is possible to significantly increase the sensitivity of the method for individual analytes and supress a matrix effect.

Cyclic Silylselenides: Convenient Selenium Precursors for Atomic Layer Deposition.

Three cyclic silylselenides were prepared in a straightforward manner. Property tuning has been achieved by varying the ring size and the number of embedded selenium atoms. All silylselenides possess improved resistance towards moisture and oxidation as well as high thermal robustness and sufficient volatility with almost zero residues. The six-membered diselenide proved to be particularly superior Se precursors for atomic layer deposition and allowed facile preparation of MoSe2 layers. Their structure and composition have been investigated by Raman and X-ray photoelectron spectroscopy as well as scanning electron microscopy revealing vertically aligned flaky shaped nanosheets.

Laser-induced crystallization of anodic TiO2 nanotube layers.

In this study, crystallization of amorphous TiO2 nanotube (TNT) layers upon optimized laser annealing is shown. The resulting anatase TNT layers do not show any signs of deformation or melting. The crystallinity of the laser annealed TNT layers was investigated using X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The study of the (photo-)electrochemical properties showed that the laser annealed TNT layers were more defective than conventional TNT layers annealed in a muffle oven at 400 °C, resulting in a higher charge recombination rate and lower photocurrent response. However, a lower overpotential for hydrogen evolution reaction was observed for the laser annealed TNT layer compared to the oven annealed TNT layer.

2D MoS2 nanosheets on 1D anodic TiO2 nanotube layers: an efficient co-catalyst for liquid and gas phase photocatalysis.

One-dimensional TiO2 nanotube layers with different dimensions were homogeneously decorated with 2D MoS2 nanosheets via atomic layer deposition and employed for liquid and gas phase photocatalysis. The 2D MoS2 nanosheets revealed a high amount of exposed active edge sites and strongly enhanced the photocatalytic performance of TiO2 nanotube layers.

Effect of halloysite nanotube structure on physical, chemical, structural and biological properties of elastic polycaprolactone/gelatin nanofibers for wound healing applications.

Nanofibrous elastic material based on the blend of hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic gelatin (Gel) reinforced with halloysite nanotubes (HNTs) was prepared by electrospinning process by respecting principles of "green chemistry" required for tissue engineering and drug delivery carriers. Three different kinds of HNTs with similar aspect ratio, but different length and inner diameter were examined to explain the effect of HNT concentration and geometry on a structure, morphology, chemical composition, mechanical properties and biocompatibility of nanostructured materials. Reinforcing effect of each type of HNTs has been confirmed up to 6 wt%. However, the highest improvement of mechanical properties was exhibited by addition just 0.5 wt% of HNTs. All HNT modified nanofibers have been confirmed as non-cytotoxic based on the interaction with mouse fibroblasts NIH-3T3 cells and therefore suitable for biomedical applications, e.g. as wound healing coverings with controlled drug delivery.

Laser Desorption Ionization Quadrupole Ion Trap Time-of-Flight Mass Spectrometry of Au m Fe n+/- Clusters Generated from Gold-Iron Nanoparticles and their Giant Nanoflowers. Electrochemical and/or Plasma Assisted Synthesis.

Gold nanoparticles (NP) with average diameter ~100 nm synthesized from tetrachloroauric acid solution using stainless steel as a reducing agent were found to contain iron. Applying simultaneously high frequency (HF) plasma discharge in solution during the electrochemical reduction, giant gold-iron nanoflowers with average size ~1000-5000 nm were formed. Scanning electron microscopy (SEM) shows the morphology of the nanopowders produced as polygonal yet nearly spherical, whereas iron content in both products determined by energy dispersive X-ray analysis (EDX) was found to be at ~2.5 at. %. Laser desorption ionization (LDI) of both nanomaterials and mass spectrometric analysis show the formation of Au m Fe n+/- (m = 1-35; n = 1-3) clusters. Structure of few selected clusters in neutral or monocharged forms were computed by density functional theory (DFT) calculations and it was found that typical distances of an iron nucleus from adjacent gold nuclei lie in the interval 2.5 to 2.7 Å. Synthetized Au-Fe nanoparticles were found stable for at least 2 mo at room temperature (even in aqueous solution) without any stabilizing agent. Produced Au-Fe nanoparticles in combination with standard MALDI matrices enhance ionization of peptides and might find use in nanomedicine. Graphical Abstract ᅟ.

Novel electrospun gelatin/oxycellulose nanofibers as a suitable platform for lung disease modeling.

Novel hydrolytically stable gelatin nanofibers modified with sodium or calcium salt of oxycellulose were prepared by electrospinning method. The unique inhibitory effect of these nanofibers against Escherichia coli bacteria was examined by luminometric method. Biocompatibility of these gelatin/oxycellulose nanofibers with eukaryotic cells was tested using human lung adenocarcinoma cell line NCI-H441. Cells firmly adhered to nanofiber surface, as determined by scanning electron microscopy, and no signs of cell dying were detected by fluorescent live/dead assay. We propose that the newly developed gelatin/oxycellulose nanofibers could be used as promising scaffold for lung disease modeling and anti-cancer drug testing.