Ludvík Beneš

Green synthesis of hyaluronan fibers with silver nanoparticles

The application of green chemistry in the nano-science and technology is very important in the area of the preparation of various materials. In this work, an eco-friendly chemical method was successfully used for the preparation of hyaluronan fibers containing silver nanoparticles (AgNPs). Thus, hyaluronic acid (HA) was dissolved in an aqueous solution of sodium hydroxide to prepare a transparent solution, which was used for the preparation of fibers by a wet-spinning technique. Consequently, silver nanoparticles inside the fiber were prepared. Different parameters affecting the preparation of final product, such as concentration of silver nitrate, hyaluronan fiber concentration, time and temperature of the reaction, pH of the reaction mixture, were studied. AgNPs were confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD), two-dimensional X-ray scattering (2D SWAXS), UV/Vis spectroscopy, inductively coupled plasma optical emission spectrometry (ICP OES) and scan electron microscopy (SEM). Mechanical properties of prepared fibers were also measured.

Optical properties and phase change transition in Ge2Sb2Te5 flash evaporated thin films studied by temperature dependent spectroscopic ellipsometry

We studied the optical properties of as-prepared (amorphous) and thermally crystallized (fcc) flash evaporated Ge2Sb2Te5 thin films using variable angle spectroscopic ellipsometry in the photon energy range 0.54–4.13 eV. We employed Tauc–Lorentz (TL) model and Cody–Lorentz (CL) model for amorphous phase and TL model with one additional Gaussian oscillator for fcc phase data analysis. The amorphous phase has optical bandgap energy Egopt=0.65 eV (TL) or 0.63 eV (CL) slightly dependent on used model. The Urbach edge of amorphous thin film was found to be ∼70 meV. Both models behave very similarly and accurately fit to the experimental data at energies above 1 eV. The CL model is more accurate in describing dielectric function in the absorption onset region. The thickness decreases ∼7% toward fcc phase. The bandgap energy of fcc phase is significantly lower than amorphous phase, Egopt=0.53 eV. The temperature dependent ellipsometry revealed crystallization in the range 130–150 °C. The bandgap energy of amorph...

Raman scattering in GeS2 glass and its crystalline polymorphs compared

Abstract Raman spectrum of glassy GeS 2 and low-resolution ones of polycrystalline α- and β-GeS 2 were studied. It was shown that the medium range structure of glassy GeS 2 is similar to the three-dimensional structure of β-GeS 2 . Our conclusion of similarity of medium range order of glassy GeS 2 and β-GeS 2 was also confirmed by detection of β-GeS 2 microcrystals grown from glassy GeS 2 at annealing temperature sufficiently below glass transition temperature.

Preparation and some physical properties of Bi2−xInxSe3 single crystals

Bi2−xInxSe3 (x=0.00 to 0.66) single crystals were prepared using a modified Bridgmann method. Their homogeneity was studied by determining the indium content and the variations of Seebeck coefficient in the directions perpendicular and parallel to the crystal axis. X-ray structure analysis revealed that the volume of the unit cell of Bi2−xInxSe3 crystal lattice decreases with increasing value of x. Measurements of the electrical conductivity, Hall constant and Seebeck coefficient showed that incorporation of the indium atoms into the Bi2Se3 crystal lattice results in an increase of free electron concentration for low indium content, whereas the free electron concentration is suppressed in the range of the high indium content. This effect is explained qualitatively on the basis of our ideas on the nature of point defects in Bi2−xInxSe3 crystals.

Oxidation of intramolecularly coordinated distannyne by S8: from tin(I) to tin(IV) polysulfide via tin(II) sulfide.

The investigation of heavier Group 14 element analogues of alkynes of the type (RE)2 (where E=Si, Ge, Sn, or Pb) is of current interest. These studies showed that the presence of rather bulky substituents such as a variety of substituted aryl and silyl groups allowed the synthesis of RE ER, which possess multiple bonds. The studies dealing with the reactivity of the RE ER multiple bonds showed scission of the Si Si or Ge Ge triple bond by the addition of an olefin, and most recently, Power and coworkers nicely outlined the cleavage of the Sn Sn multiple bond in the distannyne [ArSnSnAr] (Ar=C6H3-2,6-(C6H32,6-iPr2)2) by complexation with two molecules of either ethylene or norbornadiene. Moreover, the latest study dealing with the reactivity of [ArSnSnAr] with cyclooctatetraene (cot) showed the powerful reducing character of the tin(I) compound towards neutral cot. The reactivity studies of [ArSnSnAr] towards N2O also showed the reducing character of the Sn species, yielding the organotin(II) oxide [ArSnOSnAr] as the final product. Recently, the single-bonded dimeric species [{SiACHTUNGTRENNUNG(NtBu)2CPh}2] and [({2,6-(Me2NCH2)2C6H3}Sn)2] (1), as the first example of an Sn N intramolecularly coordinated distannyne containing a built-in N,C,N-pincer-type ligand, were reported as well. The redox reaction of [{Si ACHTUNGTRENNUNG(NtBu)2CPh}2] with N2O showed the reducing character of the Si I species, and led to the production of the well-defined [R4Si4O6] compound (R= (NtBu)2CPh) with a double-decker structure. [8]

Layered compounds derived from vanadyl phosphate dihydrate

The layered crystalline solids stable in air with general formula [M(H{sub 2}O)]{sub x}(VO){sub 1{minus}x}PO{sub 4{sup {sm_bullet}}}2H{sub 2}O (M = Al, Cr, Fe, Ga; x = 0.15--0.20) were prepared by reaction of solid V{sub 2}O{sub 5} with a boiling aqueous solution of phosphoric acid and the corresponding metal salt. The elementary cells of these compounds are tetragonal (space symmetry group either P4/n or P4/nmm). The lattice parameters and densities were determined. The results of TG, DTA and magnetic susceptibility measurements are given.

Intercalation chemistry of layered vanadyl phosphate: a review

The intercalation chemistry of layered αI modification of vanadyl phosphate and vanadyl phosphate dihydrate is reviewed. The focus is on neutral molecular guests and on metal cations used as guest species. The basic condition for the ability of the neutral molecules to be intercalated into vanadyl phosphate is a presence of an electron donor atom in them. The most commonly used guest compounds are those containing oxygen, nitrogen or sulfur as electron donor atoms. Regarding the molecules containing oxygen, various compounds were used as molecular guests starting from water to alcohols, ethers, aldehydes, ketones, carboxylic acids, lactones, and esters. An arrangement of the guest molecules in the interlayer space is discussed in connection with the data obtained by powder X-ray diffraction, thermogravimetry, IR and Raman spectroscopies, and solid-state NMR. In some cases, the local structure was suggested on the basis of quantum chemical calculations. Besides of those O-donor guests, also N-donor guests such as amines, nitriles and nitrogenous heterocycles and S-donor guests such as tetrathiafulvalene were intercalated into VOPO4. Also intercalates of complexes like ferrocene were prepared. Intercalation of cations is accompanied by a reduction of vanadium(V) to vanadium(IV). In this kind of intercalation reactions, an iodide of the intercalated cation is often used as it serves both as a mild reduction agent and as a source of the intercalated species. Intercalates of alkali metals, hydronium and ammonium were prepared and characterized. In the case of lithium and sodium intercalates, a staging phenomenon was observed. These redox intercalated vanadyl phosphates undergo ion exchange reactions which are discussed from the point of the nature of cations involved in the exchange. Vanadyl phosphates in which a part of vanadium atom is replaced by other metals are also briefly reviewed.

Tg/dta, Xrd and NH3-TPD Characterization of Layered VOPO4·2H2O and its Fe3+-Substituted Compound

Iron(III)-substituted vanadyl phosphate, [Fe(H2O)]0.20VO0.80PO4·2.25H2O (FeVOP), has been prepared and characterized by XRD and TG/DTA analyses. The new compound is isomorphous with layered tetragonal VOPO4·2H2O (VOP), but it possesses a lower interlayer distance. Information on the reactivity and surface acidity of both VOP and FeVOP has been obtained by NH3-TPD experiments. The hydrated materials adsorb high amounts of NH3 (up to 2 mmol g-1). Different ammonia-containing phases are formed, characterized by lower interlayer distances in comparison with the NH3-free parent compounds. NH3 is intercalated between the layers without displacement of water. The materials dehydrated by heat treatment at 450°C retain the layered structure but adsorb NH3 only on the external surface. A wide variety of acid sites, from weak to strong, was observed. A mechanism is proposed for the NH3- acid sites interaction. SEM micrographs of VOP and FeVOP are shown.

Thermal, structural and acidic characterization of some vanadyl phosphate materials modified with trivalent metal cations

A set of new materials with general formula [M(H2O)]X(VO)1−XPO4·2H2O (M3+=Al, Cr, Ga, Mn), isomorphous with layered tetragonal VOPO4·2H2O and having potential catalytic properties, have been characterized by TG and DTA, X-ray diffraction and surface acid strength. During heating the compounds transform in the monohydrated and anhydrous phases, all maintaining a layered structure, with a proper interlayer spacing. Catalytic tests performed with 1-butene show that theM3+-vanadyl phosphates greatly improve the conversion of the olefine with respect to pure vanadyl phosphate.

Effect of intercalation and chromophore arrangement on the linear and nonlinear optical properties of model aminopyridine push–pull molecules

Three push–pull aminopyridine derivatives having D–π–A, D–(π–A)2, and D–(π–A)3 arrangements were examined as model organic chromophores capable of intercalation into inorganic layered materials (alpha modification of zirconium hydrogen phosphate, zirconium 4-sulfophenylphosphonate, and gamma modification of titanium hydrogen phosphate). The fundamental properties of these dyes, their methylated analogues as well as their intercalates were studied by X-ray analysis, electrochemistry, UV/Vis absorption spectra, TGA, IR spectra, SHG, and were completed by DFT calculations. The synthesis of tripodal tris(pyridin-4-yl)amine is given for the first time. The HOMO–LUMO gap, the position of the longest-wavelength absorption maxima, and the dipole moment of aminopyridines can easily be tuned by attaching/removing pyridin-4-yl electron withdrawing units and their quaternization (pyridine vs. pyridinium acceptors). Their intercalation proved to be feasible affording novel inorganic–organic hybrid materials. The intercalation is accompanied by protonation of the guest, which enhances its ICT and strongly anchors the aminopyridines into the confined space of the layered host. Moreover, this process results in ordering of the organic chromophores and also brings improved thermal and chemical robustness. As a result, the measured SHG efficiencies of the intercalates are larger than those observed for the pure organic push–pull chromophores. Hence, the methodology of intercalation turned out to be very useful strategy for property tuning of NLO-active organic molecules.