Oxidized Carbon-Based Spacers for Pressure-Resistant Graphene Oxide Membranes.

In this study, we report the influence of carbon-based spacer-oxidized derivatives of fullerenes (fullerenols) C60(OH)26−32 and graphene oxide nanoribbons on the performance and pressure stability of graphene-oxide-based composite membranes. The impact of the intercalant shape and composition on the permeance of the selective layers for water vapors has been studied under pressure gradients. It is shown that the insertion of ball-shaped fullerenols between graphene oxide nanoflakes allows a suppression in irreversible permeance loss to 2−4.5% and reversible permeance loss to <25% (at 0.1 MPa), while retaining large H2O/N2 selectivities of up to ~30,000. The demonstrated approach opens avenues for the highly effective stabilization of GO membranes at elevated pressures for industrial-scale dehumidification.

Label-free silver triangular nanoplates for spectrophotometric determination of catecholamines and their metabolites.

A novel method towards spectrophotometric determination of catecholamines and their metabolites differing in their functional groups has been developed. This method is based on a change in morphology of silver triangular nanoplates upon the action of cateсholamines and their metabolites, which is manifested by the decrease of the nanoparticle local surface plasmon resonance (LSPR) band intensity or its shift to the short-wavelength region of the spectrum. The shift value of the LSPR band or the change of its intensity increases with increasing concentration of catecholamines or their metabolites, which is proposed for their spectrophotometric determination. The limits of detection of catecholamines and their metabolites under selected conditions increase in the series homovanillic acid < vanillylmandelic acid < L-epinephrine < L-norepinephrine < dopamine and are 0.25, 1.2, 3.0, 64, and 130 µmol L-1, respectively. The selectivity of the proposed method was assessed using vanillylmandelic acid as example. It was found that the determination of vanillylmandelic acid does is not interfered in the presence of 4000-fold excess of Na+, K+, CH3COO-, and 1000-fold excess of Mg2+, Ca2+, Al3+, NO3-. The method also allows for the selective determination of vanillylmandelic acid in the presence of a 1000-fold excess of structurally related substances that do not contain either a catechol fragment or an electron donor substituent. The proposed approach was successfully applied to the determination of catecholamines in pharmaceuticals and artificial urine. Graphical abstract.

Enhancement of Lewis Acidity of Cr-Doped Nanocrystalline SnO2 : Effect on Surface NH3 Oxidation and Sensory Detection Pattern.

Understanding ammonia oxidation over metal oxide surfaces is crucial for improving its detection with resistive type gas sensors. Formation of NOx during this process makes sensor response and calibration unstable. Cr-doping of nanocrystalline metal oxides has been reported to suppress NO2 sensitivity and improve response towards NH3 , however the exact mechanism of such chromium action remained unknown. Herein, by using EPR spectroscopy we demonstrate formation of Cr(VI) lattice defects on the surface of nanocrystalline Cr-doped SnO2 . Enhancement of Cr-doped SnO2 surface acidity and ammonia adsorption as a result has been revealed by using in situ IR spectroscopy. Moreover, a decrease in concentration of free electrons in the conduction band has been shown as a result of substitutional Cr(III) defects formation. Weaker NOx chemisorption during ammonia oxidation over SnO2 surface after Cr doping has been found with the use of mass-spectrometry assisted NH3 thermo-programmed desorption. The given example of surface acidity adjustment and electronic configuration by means of doping may find use in the design of new gas-sensing metal oxide materials.

Titanium Oxide Microspheres with Tunable Size and Phase Composition.

Due to their unique physical and chemical properties, monodisperse titanium oxide microspheres can be used in dye-sensitized solar cells, as cosmetic pigments, and for other applications. However, the synthesis of microspheres with narrow size distribution, desired phase composition, and porosity is still a challenge. In this work, spherical titania particles with controllable size, crystallinity, and pore size were obtained by Ti(OnBu)4 hydrolysis in ethanol. The influence of NaOH addition on the particles' size and morphology was investigated for the first time. Particle diameter can be tailored from 300 nm to 1.5 µm by changing water and NaOH concentrations. Particle size was analyzed by the statistical processing of scanning electron microscopy (SEM) images and differential centrifugal sedimentation (DCS) measurements. Optical properties of the microspheres were studied by diffuse reflectance UV-Vis spectroscopy. Thermal and hydrothermal treatment allowed transforming amorphous phase in as-prepared particles into nanocrystalline anatase and/or rutile. Transmission electron microscopy (TEM) study of the lamellae, cut out from spherical particles using focused ion beam (FIB), revealed that as-synthesized microspheres are non-hollow, homogeneous, and crystallize throughout the whole volume of the particle. The spherical particles possess photoprotective properties; the highest sun protection factor (SPF) was observed for amorphous microspheres.

Photochromic and Photocatalytic Properties of Ultra-Small PVP-Stabilized WO3 Nanoparticles.

Tungsten oxide-based bulk and nanocrystalline materials are widely used as photocatalytic and photo- and electrochromic materials, as well as materials for biomedical applications. In our work, we focused our attention on the effect of sodium cations on the structure and photochromic properties of the WO3@PVP aqueous sols. To establish the effect, the sols were synthesized by either simple pH adjusting of sodium or ammonium tungstates' solutions, or using an ion exchange technique to remove the cations from the materials to the greatest possible extent. We showed that the presence of sodium cations in WO3@PVP favors the formation of reduced tungsten species (W+5) upon UV irradiation of the materials, strongly affecting their photochromic and photocatalytic properties. The pronounced photoreductive properties of WO3@PVP sols in photocatalytic reactions were demonstrated. Due to photoreductive properties, photochromic sols of tungsten oxide can act as effective photoprotectors in photooxidation processes. We believe that our work provides a considerable contribution to the elucidation of photochromic and redox phenomena in WO3-based materials.

Towards highly selective detection using metal nanoparticles: A case of silver triangular nanoplates and chlorine.

The article describes a novel approach towards improving selectivity of volatile compounds detection using metal nanoparticles. It is based on combination of sensitive optical detection using convenient nanoparticle-modified paper test strips and dynamic gas extraction improving selectivity to volatile compounds. A simple and inexpensive setup allowing for realization of this combination is described. Analytical prospects of the approach are shown by the example of chlorine determination in highly salted aqueous solutions using silver triangular nanoplates and digital colorimetry. The limit of detection is equal to 0.03mgL-1 and the determination range is 0.1-2mgL-1. This determination can be successfully carried out in solutions containing at least 2·105 greater molar amounts of Na+, K+, Zn2+, Cl-, SO42-, and H2PO4- with no sample pretreatment. The approach seems to be compatible with different types of nanoparticles with respect to detection of various analytes, thus having good opportunities for further development.

Diffusion doping route to plasmonic Si/SiO x nanoparticles.

Semiconductor nanoparticles (SNPs) are a valuable building block for functional materials. Capabilities for engineering of electronic structure of SNPs can be further improved with development of techniques of doping by diffusion, as post-synthetic introduction of impurities does not affect the nucleation and growth of SNPs. Diffusion of dopants from an external source also potentially allows for temporal control of radial distribution of impurities. In this paper we report on the doping of Si/SiO x SNPs by annealing particles in gaseous phosphorus. The technique can provide efficient incorporation of impurities, controllable with precursor vapor pressure. HRTEM and X-ray diffraction studies confirmed that obtained particles retain their nanocrystallinity. Elemental analysis revealed doping levels up to 10%. Electrical activity of the impurity was confirmed through thermopower measurements and observation of localized surface plasmon resonance in IR spectra. The plasmonic behavior of etched particles and EDX elemental mapping suggest uniform distribution of phosphorus in the crystalline silicon cores. Impurity activation efficiencies up to 34% were achieved, which indicate high electrical activity of thermodynamically soluble phosphorus in oxide-terminated nanosilicon.

Key Roles of Size and Crystallinity of Nanosized Iron Hydr(oxides) Stabilized by Humic Substances in Iron Bioavailability to Plants.

Availability of Fe in soil to plants is closely related to the presence of humic substances (HS). Still, the systematic data on applicability of iron-based nanomaterials stabilized with HS as a source for plant nutrition are missing. The goal of our study was to establish a connection between properties of iron-based materials stabilized by HS and their bioavailability to plants. We have prepared two samples of leonardite HS-stabilized iron-based materials with substantially different properties using the reported protocols and studied their physical chemical state in relation to iron uptake and other biological effects. We used Mössbauer spectroscopy, XRD, SAXS, and TEM to conclude on iron speciation, size, and crystallinity. One material (Fe-HA) consisted of polynuclear iron(III) (hydr)oxide complexes, so-called ferric polymers, distributed in HS matrix. These complexes are composed of predominantly amorphous small-size components (<5 nm) with inclusions of larger crystalline particles (the mean size of (11 ± 4) nm). The other material was composed of well-crystalline feroxyhyte (δ'-FeOOH) NPs with mean transverse sizes of (35 ± 20) nm stabilized by small amounts of HS. Bioavailability studies were conducted on wheat plants under conditions of iron deficiency. The uptake studies have shown that small and amorphous ferric polymers were readily translocated into the leaves on the level of Fe-EDTA, whereas relatively large and crystalline feroxyhyte NPs were mostly sorbed on the roots. The obtained data are consistent with the size exclusion limits of cell wall pores (5-20 nm). Both samples demonstrated distinct beneficial effects with respect to photosynthetic activity and lipid biosynthesis. The obtained results might be of use for production of iron-based nanomaterials stabilized by HS with the tailored iron availability to plants. They can be applied as the only source for iron nutrition as well as in combination with the other elements, for example, for industrial production of "nanofortified" macrofertilizers (NPK).

Effect of nanostructured carbon coatings on the electrochemical performance of Li1.4Ni0.5Mn0.5O2+x -based cathode materials.

Nanocomposites of Li1.4Ni0.5Mn0.5O2+x and amorphous carbon were obtained by the pyrolysis of linear and cross-linked poly(vinyl alcohol) (PVA) in presence of Li1.4Ni0.5Mn0.5O2+x . In the case of linear PVA, the formation of nanostructured carbon coatings on Li1.4Ni0.5Mn0.5O2+x particles is observed, while for cross-linked PVA islands of mesoporous carbon are located on the boundaries of Li1.4Ni0.5Mn0.5O2+x particles. The presence of the carbon framework leads to a decrease of the polarization upon cycling and of the charge transfer resistance and to an increase in the apparent Li+ diffusion coefficient from 10-16 cm2·s-1 (pure Li1.4Ni0.5Mn0.5O2+x ) to 10-13 cm2·s-1. The nanosized carbon coatings also reduce the deep electrochemical degradation of Li1.4Ni0.5Mn0.5O2+x during electrochemical cycling. The nanocomposite obtained by the pyrolysis of linear PVA demonstrates higher values of the apparent lithium diffusion coefficient, a higher specific capacity and lower values of charge transfer resistance, which can be related to the more uniform carbon coatings and to the significant content of sp2-hybridized carbon detected by XPS and by Raman spectroscopy.