Graphene oxide membranes for gas separation

Recently, the carbon based materials1 attracted attention of the scientific community for applications in membrane gas separation. Tremendous number of carbon based materials such as carbon nanotubes, chemically modified graphene, graphene oxide (GO) or graphite (nano)particles in mixed matrix membrane (MMM) composites was tested within past decade2. It was found that even small loading of graphene and (GO) additives, i.e. 0.05 to 1 wt.%3, led to considerable changes of composite materials properties (elastic modulus, tensile strength, electrical conductivity, and thermal stability) compared to neat polymers. Please click Additional Files below to see the full abstract

Mn DOPING OF GaN LAYERS GROWN BY MOVPE

In this contribution we present a growth of Ga1-xMnxN layers by MOVPE. Mn doped GaN layers were grown with and without undoped GaN templates on (0001) sapphire substrates in a quartz horizontal reactor. For the deposition of Ga1-xMnxN layers (MCp)2Mn was used as a Mn – precursor. The flow of the Mn precursor was 0.2-3.2 μmol.min-1. The deposition of Ga1-xMnxN layers was carried out under the pressure of 200 mbar, the temperature 1050 °C and the V/III ratio of 1360. For the growth of high quality GaN:Mn layers it was necessary to grow these layers on a minimally partially coalesced layer of pure GaN. The direct deposition of GaN:Mn layer on the low temperature GaN buffer layer led to a three-dimensional growth during the whole deposition process. Another investigated parameter was the influence of nitrogen on the layer’s properties. A nearly constant ferromagnetic moment persisting up to room temperature was observed on the synthesized thin films

Valley Polarization-Electric Dipole Interference and Nonlinear Chiral Selection Rules in Monolayer WSe2_2

In monolayer transition metal dichalcogenides time-reversal symmetry, combined with space-inversion symmetry, defines the spin-valley degree of freedom. As such, engineering and control of time-reversal symmetry by optical or magnetic fields constitutes the foundation of valleytronics. Here, we propose a new approach for the detection of broken time-reversal symmetry and valley polarization in monolayer WSe$_2$ based on second harmonic generation. Our method can selectively and simultaneously generate and detect a valley polarization at the $\pm K$ valleys of transition metal dichalcogenides at room temperature. Furthermore, it allows to measure the interference between the real and imaginary parts of the intrinsic (electric dipole) and valley terms of the second order nonlinear susceptibility. This work demonstrates the potential and unique capabilities of nonlinear optics as a probe of broken time-reversal symmetry and as a tool for ultrafast and non-destructive valleytronic operations.Comment: 27 pages 6 figure

Surface oxidation of Ti3C2Tx enhances the catalytic activity of supported platinum nanoparticles in ammonia borane hydrolysis

MXenes, first discovered in 2011, are two-dimensional transition metal carbides or nitrides. Because of their interesting electrical and optical properties, they are studied for applications in batteries, supercapacitors and electrocatalysis. However, MXenes are rarely used in heterogeneous catalysis and, to our knowledge, there are no reports on the use of oxidized MXenes in catalysis. Here we used Ti3C2Tx-derived materials as supports for platinum nanoparticles and studied their effectiveness for the hydrolysis of ammonia borane, which is a promising hydrogen carrier. Hydrogen can be released from ammonia borane through catalytic hydrolysis. Most heterogeneous catalysts reported for this purpose contain a noble metal supported on a metal oxide support. The interaction between the metal and the support is important in determining the catalytic performance. Our results show that the electronic environment of platinum can be modified by oxidising the surface of MXene, thus providing a new way of developing active catalysts. Oxidising agents such as water and ozone can be used for this purpose. This electronic modification enhances the catalytic activity of platinum for ammonia borane hydrolysis, which is relevant for other reactions related to energy production/storage.T K S was supported by NWO TOP-PUNT grant 718.015.004. Z S was supported by project LTAUSA19034 from Ministry of Education Youth and Sports (MEYS). E V R F and A S E would like to thanks financial support by MINECO (Spain) through the projects MAT2017-86992-R and MAT2016-80285-P

Enhanced voltammetric performance of sensors based on oxidized 2D layered black phosphorus

The exceptional properties of 2D layered black phosphorus (BP) make it a promising candidate for electrochemical sensing applications and, even though BP is considered unstable and tends to degrade by the presence of oxygen and moisture, its oxidation can be beneficial in some situations. In this work, we present an unequivocal demonstration that the exposition of BP-based working electrodes to normal ambient conditions can indeed be advantageous, leading to an enhancement of voltammetric sensing applications. This point was proved using a BP modified screen-printed carbon electrode (BP-SPCE) for the voltammetric determination of dopamine (DA) as a model target analyte. Oxidized BP-SPCE (up to 35% of PxOy at the surface) presented an enhanced analytical performance with a 5-fold and 2-fold increase in sensitivity, as compared to bare-SPCE and non-oxidized BP-SPCE stored in anhydrous atmosphere, respectively. Good detection limit, repeatability, reproducibility, stability, selectivity, and accuracy were also achieved. Overall, the results presented herein display the prominent possibilities of preparing and working with BP based-sensors in normal ambient settings and showcase their implementation under physiological conditions

Exploration of Charge Storage Behavior of Binder-Free EDL Capacitors in Aqueous Electrolytes

Charge storage in electrochemical double-layer capacitors (EDLCs) is via the adsorption of electrolyte counterions in their positive and negative electrodes under an applied potential. This study investigates the EDLC-type charge storage in carbon nanotubes (CNT) electrodes in aqueous acidic (NaHSO4), basic (NaOH), and neutral (Na2SO4) electrolytes of similar cations but different anions as well as similar anions but different cations (Na2SO4 and Li2SO4) in a two-electrode Swagelok-type cell configuration. The physicochemical properties of ions, such as mobility/diffusion and solvation, are correlated with the charge storage parameters. The neutral electrolytes offer superior charge storage over the acidic and basic counterparts. Among the studied ions, SO42– and Li+ showed the most significant capacitance owing to their larger solvated ion size. The charge stored by the anions and cations follows the order SO42– > HSO4– > OH– and Li+ > Na+, respectively. Consequently, the CNT//Li2SO4//CNT cell displayed outstanding charge storage indicators (operating voltage ∼0–2 V, specific capacitance ∼122 F·g–1, specific energy ∼67 W h·kg–1, and specific power ∼541 W·kg–1 at 0.5 A·g–1) than the other cells, which could light a red light-emitting diode (2.1 V) for several minutes. Besides, the CNT//Li2SO4//CNT device showed exceptional rate performance with a capacitance retention of ∼95% at various current densities (0.5–2.5 A·g–1) after 6500 cycles. The insights from this work could be used to design safer electrochemical capacitors of high energy density and power density

Heat-Up Colloidal Synthesis of Shape-Controlled Cu-Se-S Nanostructures-Role of Precursor and Surfactant Reactivity and Performance in N Electroreduction

Copper selenide-sulfide nanostructures were synthesized using metal-organic chemical routes in the presence of Cu- and Se-precursors as well as S-containing compounds. Our goal was first to examine if the initial Cu/Se 1:1 molar proportion in the starting reagents would always lead to equiatomic composition in the final product, depending on other synthesis parameters which affect the reagents reactivity. Such reaction conditions were the types of precursors, surfactants and other reagents, as well as the synthesis temperature. The use of 'hot-injection' processes was avoided, focusing on 'non-injection' ones; that is, only heat-up protocols were employed, which have the advantage of simple operation and scalability. All reagents were mixed at room temperature followed by further heating to a selected high temperature. It was found that for samples with particles of bigger size and anisotropic shape the CuSe composition was favored, whereas particles with smaller size and spherical shape possessed a CuSe phase, especially when no sulfur was present. Apart from elemental Se, AlSe was used as an efficient selenium source for the first time for the acquisition of copper selenide nanostructures. The use of dodecanethiol in the presence of trioctylphosphine and elemental Se promoted the incorporation of sulfur in the materials crystal lattice, leading to Cu-Se-S compositions. A variety of techniques were used to characterize the formed nanomaterials such as XRD, TEM, HRTEM, STEM-EDX, AFM and UV-Vis-NIR. Promising results, especially for thin anisotropic nanoplates for use as electrocatalysts in nitrogen reduction reaction (NRR), were obtained

Stabilization of black phosphorus by sonication-assisted simultaneous exfoliation and functionalization

Black phosphorus (BP) has extraordinary properties, but its ambient instability remains a critical challenge. Functionalization has been employed to overcome the sensitivity of BP to ambient conditions while preserving its properties. Herein, a simultaneous exfoliation–functionalization process is reported that functionalizes BP flakes during exfoliation and thus provides increased protection, which can be attributed to minimal exposure of the flakes to ambient oxygen and water. A tetrabutylammonium salt was employed for intercalation of BP, resulting in the formation of flakes with large lateral dimensions. The addition of an aryl iodide or an aryl iodonium salt to the exfoliation solvent creates a scalable strategy for the production of functionalized few‐layer BP flakes. The ambient stability of functionalized BP was prolonged to a period of one week, as revealed by STEM, AFM, and X‐ray photoelectron spectroscopy