Boron Nitride Nanosheet-Magnetic Nanoparticle Composites for Water Remediation Applications.

The combination of 0D nanoparticles with 2D nanomaterials has attracted a lot of attention over the last years due to the unique multimodal properties of resulting 0D-2D nanocomposites. In this work, we developed boron nitride nanosheets (BNNS) functionalized with manganese ferrite magnetic nanoparticles (MNPs). The functionalization process involved attachment of MNPs to exfoliated BNNS by refluxing the precursor materials in a polyol medium. Characterization of the produced BNNS-MNP composites was carried out using powder X-ray diffraction, transmission electron microscopy, vibrating sample magnetometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The adhesion of MnFe2O4 magnetic nanoparticles onto the BNNS remained unaffected by repeated sonication and heating in a furnace at 400 °C, underscoring the robust nature of the formed bond. FTIR spectra and XPS deconvolution confirmed the presence of strong bonding between BNNS and the MNPs. Membranes were fabricated from the BNNS and the BNNS-MnFe2O4 nanocomposites for evaluating their efficiency in removing the methylene blue dye pollutant. The membranes have been characterized by scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, and mercury intrusion porosimetry. The effectiveness of dye removal was monitored using ultraviolet-visible spectroscopy. The BNNS-MnFe2O4 nanocomposite membranes exhibited enhanced MB capture compared to membranes made from pure BNNS alone. The recyclability assessment of BNNS-MnFe2O4 demonstrated exceptional performance, retaining 92% efficiency even after eight cycles. These results clearly demonstrate the high potential of these magnetic nanocomposites as reusable materials for water filtration membranes. Furthermore, the introduction of magnetic functionality as part of the membrane brings an exciting opportunity for in situ magnetic heating of the membrane, which shall be explored in future work.

A Retrofittable Photoelectron Gun for Low-Voltage Imaging Applications in the Scanning Electron Microscope.

Low-voltage scanning electron microscopy is a powerful tool for examining surface features and imaging beam-sensitive materials. Improving resolution during low-voltage imaging is then an important area of development. Decreasing the effect of chromatic aberration is one solution to improving the resolution and can be achieved by reducing the energy spread of the electron source. Our approach involves retrofitting a light source onto a thermionic lanthanum hexaboride (LaB6) electron gun as a cost-effective low energy-spread photoelectron emitter. The energy spread of the emitter's photoelectrons is theorized to be between 0.11 and 0.38 eV, depending on the photon energy of the ultraviolet (UV) light source. Proof-of-principle images have been recorded using this retrofitted photoelectron gun, and an analysis of its performance is presented.

Boron Nitride Nanosheets Functionalized with Fe3O4 and CoFe2O4 Magnetic Nanoparticles for Nanofiltration Applications.

Nanofiltration (NF) is one of the emerging technologies that is very promising for water purification among many other applications. 2D boron nitride (BN) based nanomaterials are excellent building blocks for NF membranes. In our work, BN nanosheets (BNNS) have been functionalized with magnetic nanoparticles (MNPs) to form BNNS-MNP nanocomposites. It was found that the nanocomposites are stable with the MNPs giving very good coverage with both magnetite and cobalt ferrite MNPs and showing good attachment and stability to sonication. These nanocomposites have been tested for removal of methylene blue (MB) dye and MNPs from water. BNNS-magnetite nanocomposites showed higher removal efficiency of the MB from water than the corresponding pure BNNS, while the BNNS-cobalt ferrite removal efficiency was slightly less than the pure BNNS. The BNNS-cobalt ferrite material was regenerated by burning off the MB and recycled to show the recyclability of this material. The BNNS membranes were tested for filtration of 14 ± 4 nm magnetite MNPs and were found to capture 100% of the nanoparticles with no MNPs left in the filtrate. Thus, we have developed magnetic nanocomposite membranes, which have demonstrated great potential for water remediation. We believe that this research opens up promising ways for production of 2D nanocomposite materials with multiple applications.

Demonstrating the source of inherent instability in NiFe LDH-based OER electrocatalysts.

Nickel-iron layered double hydroxides are known to be one of the most highly active catalysts for the oxygen evolution reaction in alkaline conditions. The high electrocatalytic activity of the material however cannot be sustained within the active voltage window on timescales consistent with commercial requirements. The goal of this work is to identify and prove the source of inherent catalyst instability by tracking changes in the material during OER activity. By combining in situ and ex situ Raman analyses we elucidate long-term effects on the catalyst performance from a changing crystallographic phase. In particular, we attribute electrochemically stimulated compositional degradation at active sites as the principal cause of the sharp loss of activity from NiFe LDHs shortly after the alkaline cell is turned on. EDX, XPS, and EELS analyses performed after OER also reveal noticeable leaching of Fe metals compared to Ni, principally from highly active edge sites. In addition, post-cycle analysis identified a ferrihydrite by-product formed from the leached Fe. Density functional theory calculations shed light on the thermodynamic driving force for the leaching of Fe metals and propose a dissolution pathway which involves [FeO4]2- removal at relevant OER potentials.

Understanding the effect of MXene in a TMO/MXene hybrid catalyst for the oxygen evolution reaction.

Very recently, it has been reported that mixed transition metal oxide (TMO)/MXene catalysts show improved performance over TMO only catalysts for the oxygen evolution reaction (OER). However, the reasoning behind this observation is unknown. In this work mixed Co(OH)2/Ti3C2Tx were prepared and characterized for the OER using ex situ and operando spectroscopy techniques in order to initiate the understanding of why mixed TMO/MXene materials show better performances compared to TMO only catalysts. This work shows that the improved electrocatalysis for the composite material compared to the TMO only catalyst is due to the presence of higher Co oxide oxidation states at lower OER overpotentials for the mixed TMO/MXene catalysts. Furthermore, the presence of the MXene allows for a more mechanically robust film during OER, making the film more stable. Finally, our results show that small amounts of MXene are more advantageous for the OER during long-term stability measurements, which is linked to the formation of TiO2. The sensitivity of MXene oxidation ultimately limits TMO/MXene composites under alkaline OER conditions, meaning mass fractions must be carefully considered when designing such a catalyst to minimize the residual TiO2 formed during its lifetime.

Tuning the Photo-electrochemical Performance of RuII -Sensitized Two-Dimensional MoS2.

Covalently tethering photosensitizers to catalytically active 1T-MoS2 surfaces holds great promise for the solar-driven hydrogen evolution reaction (HER). Herein, we report the preparation of two new RuII -complex-functionalized MoS2 hybrids [RuII (bpy)2 (phen)]-MoS2 and [RuII (bpy)2 (py)Cl]-MoS2 . The influence of covalent functionalization of chemically exfoliated 1T-MoS2 with coordinating ligands and RuII complexes on the HER activity and photo-electrochemical performance of this dye-sensitized system was studied systematically. We find that the photo-electrochemical performance of this RuII -complex-sensitized MoS2 system is highly dependent on the surface extent of photosensitizers and the catalytic activity of functionalized MoS2 . The latter was strongly affected by the number and the kind of functional groups. Our results underline the tunability of the photovoltage generation in this dye-sensitized MoS2 system by manipulation of the surface functionalities, which provides a practical guidance for smart design of future dye-sensitized MoS2 hydrogen production devices towards improved the photofuel conversion efficiency.

Comparison of Metal Adhesion Layers for Au Films in Thermoplasmonic Applications.

If thermoplasmonic applications such as heat-assisted magnetic recording are to be commercially viable, it is necessary to optimize both thermal stability and plasmonic performance of the devices involved. In this work, a variety of different adhesion layers were investigated for their ability to reduce dewetting of sputtered 50 nm Au films on SiO2 substrates. Traditional adhesion layer metals Ti and Cr were compared with alternative materials of Al, Ta, and W. Film dewetting was shown to increase when the adhesion material diffuses through the Au layer. An adhesion layer thickness of 0.5 nm resulted in superior thermomechanical stability for all adhesion metals, with an enhancement factor of up to 200× over 5 nm thick analogues. The metals were ranked by their effectiveness in inhibiting dewetting, starting with the most effective, in the order Ta > Ti > W > Cr > Al. Finally, the Au surface-plasmon polariton response was compared for each adhesion layer, and it was found that 0.5 nm adhesion layers produced the best response, with W being the optimal adhesion layer material for plasmonic performance.

Adverse effects of nanosilver on human health and the environment.

Silver and silver nanoparticles (AgNPs) exhibit antimicrobial properties against some bacteria, fungi and viruses, however, the ever-increasing application of nanosilver in consumer products, water disinfection and healthcare settings, have raised concerns over the public health/environmental safety of this nanomaterial. The current ubiquity of nanosilver may result in repeated exposure through various routes (skin, inhalation, or ingestion) which may lead to health complications. While there are a number of review articles and case studies published to date on the subject, an updated coherent review that clearly delineates thresholds and safe doses is lacking. Thus, it is plausible to have an overview of the most recent findings on the threshold limits, safe doses of silver and its related nanoscale forms, and the needed actions to ensure the safety and health of human, terrestrial and aquatic lives. This review provides an account of the effects of nanosilver in our daily lives. STATEMENT OF SIGNIFICANCE: This manuscripts is a review of the toxicity of nanosized silver. With respect to the existing literature, it goes beyond stating that there is a knowledge gap, drawing the attention of a wider readership to the ever-growing evidence of nanosilver toxicity to human and nature, and outlining the dose thresholds based on comprehensive data mining and visualisation. There are nearly 500 consumer products that claim to contain nanosilver. Thus, we trust a review of recent conclusive findings is timely. This manuscript is in line with the scope of the Journal, enabling a better understanding of the biological response to a widely-used bionanomaterial. Moreover, it provides a bigger picture of the link between surface properties and biocompatibility of nanosilver in different forms.

Less is More: Improved Thermal Stability and Plasmonic Response in Au Films via the Use of SubNanometer Ti Adhesion Layers.

The use of a metallic adhesion layer is known to increase the thermo-mechanical stability of Au thin films against solid-state dewetting, but in turn results in damping of the plasmonic response, reducing their utility in applications such as heat-assisted magnetic recording (HAMR). In this work, 50 nm Au films with Ti adhesion layers ranging in thickness from 0 to 5 nm were fabricated, and their thermal stability, electrical resistivity, and plasmonic response were measured. Subnanometer adhesion layers are demonstrated to significantly increase the stability of the thin films against dewetting at elevated temperatures (>200 °C), compared to more commonly used adhesion layer thicknesses that are in the range of 2-5 nm. For adhesion layers thicker than 1 nm, the diffusion of excess Ti through Au grain boundaries and subsequent oxidation was determined to result in degradation of the film. This mechanism was confirmed using transmission electron microscopy and X-ray photoelectron spectroscopy on annealed 0.5 and 5 nm adhesion layer samples. The superiority of subnanometer adhesion layers was further demonstrated through measurements of the surface-plasmon polariton resonance; those with thinner adhesion layers possessed both a stronger and spectrally sharper resonance. These results have relevance beyond HAMR to all Ti/Au systems operating at elevated temperatures.

Oxide-mediated recovery of field-effect mobility in plasma-treated MoS2.

Precise tunability of electronic properties of two-dimensional (2D) nanomaterials is a key goal of current research in this field of materials science. Chemical modification of layered transition metal dichalcogenides leads to the creation of heterostructures of low-dimensional variants of these materials. In particular, the effect of oxygen-containing plasma treatment on molybdenum disulfide (MoS2) has long been thought to be detrimental to the electrical performance of the material. We show that the mobility and conductivity of MoS2 can be precisely controlled and improved by systematic exposure to oxygen/argon plasma and characterize the material using advanced spectroscopy and microscopy. Through complementary theoretical modeling, which confirms conductivity enhancement, we infer the role of a transient 2D substoichiometric phase of molybdenum trioxide (2D-MoO x ) in modulating the electronic behavior of the material. Deduction of the beneficial role of MoO x will serve to open the field to new approaches with regard to the tunability of 2D semiconductors by their low-dimensional oxides in nano-modified heterostructures.

RuII Photosensitizer-Functionalized Two-Dimensional MoS2 for Light-Driven Hydrogen Evolution.

Metallic-phase molybdenum disulfide (1T-MoS2 ) nanosheets have proven to be highly active in the hydrogen evolution reaction (HER). We describe construction of photosensitizer functionalized 1T-MoS2 by covalently tethering the molecular photosensitizer [RuII (bpy)3 ]2+ (bpy=2,2'-bipyridine) on 1T-MoS2 nanosheets. This was achieved by covalently tethering the bpy ligand to 1T-MoS2 nanosheets, and subsequent complexation with [RuII (bpy)2 Cl2 ] to yield [RuII (bpy)3 ]-MoS2 . The obtained [RuII (bpy)3 ]-MoS2 nanosheets were characterized using infra-red, electronic absorption, X-ray photoelectron, and Raman spectroscopies, X-ray powder diffraction and electron microscopy. The fabricated material exhibited a significant improvement of photocurrent and HER performance, demonstrating the potential of such two-dimensional [RuII (bpy)3 ]-MoS2 constructs in photosensitized HER.

The benefit of the European User Community from transnational access to national radiation facilities.

Transnational access (TNA) to national radiation sources is presently provided via programmes of the European Commission by BIOSTRUCT-X and CALIPSO with a major benefit for scientists from European countries. Entirely based on scientific merit, TNA allows all European scientists to realise synchrotron radiation experiments for addressing the Societal Challenges promoted in HORIZON2020. In addition, by TNA all European users directly take part in the development of the research infrastructure of facilities. The mutual interconnection of users and facilities is a strong prerequisite for future development of the research infrastructure of photon science. Taking into account the present programme structure of HORIZON2020, the European Synchrotron User Organization (ESUO) sees considerable dangers for the continuation of this successful collaboration in the future.

Nitrogen-doped pyrolytic carbon films as highly electrochemically active electrodes.

Nitrogen-doped Pyrolytic Carbon (N-PyC) films were employed as an electrode material in electrochemical applications. PyC was grown by via non-catalysed chemical vapour deposition and subsequently functionalised via exposure to ammonia-hydrogen plasma. The electrochemical properties of the N-PyC films were investigated using the ferri/ferro-cyanide and hexaamine ruthenium(III) chloride redox probes. Exceptional electron transfer properties were observed and quantified for the N-PyC compared to the as-grown films. X-ray photoelectron spectroscopy confirmed the presence of nitrogen in edge plane graphitic configurations and the surface of the N-PyC was investigated using scanning electron microscopy and atomic force microscopy. The excellent electrochemical performance of the N-PyC, in addition to its ease of preparation, renders this material ideal for applications in electrochemical sensing.

Solubility of Mo6S4.5I4.5 nanowires in common solvents: a sedimentation study.

Due to their ease of fabrication and monodisperse, metallic nature, molybdenum-sulfur-iodine nanowires are an interesting alternative to carbon nanotubes for some applications. However very little is known about the solubility of these materials. In this work we have investigated the solubility of Mo(6)S(4.5)I(4.5) nanowire soot in a range of common solvents by performing sedimentation studies and microscopic and spectroscopic characterization. A sedimentation equation was derived showing that the concentration of any insoluble dispersed phase decreases exponentially with time. We find that in all solvents, Mo(6)S(4.5)I(4.5) nanowire soot contains three phases, two of which are insoluble with one stable phase. Microscopy and spectroscopy show that the first insoluble phase is associated mainly with spherical impurities and sediments rapidly out of solution resulting in purification. The second phase appears to consist of insoluble nanowire bundles and sediments more slowly, eventually leaving a stable dispersion of nanowire bundles. The stably dispersed bundles tend to be smaller than their insoluble counterparts. The best solvents studied were 2-propanol and dimethylformamide. Microscopy studies showed that, in the case of 2-propanol, sonication significantly reduced the bundle size relative to the unsonicated bulk. However, during sedimentation, large quantities of bundles were observed to reaggregate to form larger bundles which subsequently sedimented out of solution. In general, the sedimentation properties of the various phases did not vary significantly with concentration indicating that the insoluble nanowires are intrinsically insoluble. However, the diameter of the stably dispersed bundles decreased with concentration, until very small bundles consisting of only two or three nanowires were observed at concentrations below 0.003 mg/mL. In addition, stable composite dispersions were produced by mixing the nanowires with poly(vinylpyrrolidone) in 2-propanol opening the way for the formation of polymer/inorganic nanowire composites.