What we have learned from studies on chemical properties of amorphous alloys?

Amorphous alloys have many attractive characteristics including extremely high corrosion resistance if the sufficient amounts of corrosion-resistant elements are added. The superiority of amorphous alloys is based on the homogeneous single phase nature without any chemical and physical heterogeneities. Although there are processing limitations to avoid the formation of heterogeneous crystalline structure in addition to no welding technology without crystallization, the application of corrosion-resistant amorphous alloys is expected particularly to the very aggressive environments, where any conventional crystalline metallic materials cannot be used. Some amorphous bulk alloys showed zero corrosion mass loss due to spontaneous passivation even in 12 M HCl. Production of amorphous bulk alloys became possible for selected compositions. The homogeneous single phase nature is also effective to form useful catalysts with unique composition and structure. An example of catalysts is for carbon dioxide methanation useful for supply of renewable energy in the form of methane.     

Rapid and efficient synthesis of colloidal gold nanoparticles by?arc discharge method

The microstructural (XRD and SEM) and dielectric behavior of Pb(Zr_0.54Ti_0.46)O₃ (PZT 54/46) ceramic system with donor (La, Nb and La+Nb) doping was studied. For all Nb-doped PZT samples, only one (tetragonal) phase was found, which confirms the compositional shifts near the morphotropic phase boundary. For La- and La+Nb-doped samples, there are two (rhombohedral and tetragonal) phases. Dielectric characteristic behavior (1/ε) for La- and La+Nb-doped PZT was associated with two-phase transitions: Ferro–Ferro at low temperature and Ferro–Para at Curie temperature. For Nb-doped samples, only one phase transition is observed, which indicates the presence of a single ferroelectric phase.     

Synthesis and characterization of binaphthalene-2,2′-diamine-functionalized gold nanoparticles

Gold nanoparticles 1.7 and 54 nm in diameters have been synthesized and functionalized successfully with their surfaces engineered using two atropisomeric capping ligands, 2,2′-bis(diphenylphosphino)-1,1′-binaphthalene (BINAP) and 1,1′-binaphthalene-2,2′-diamine (DABN), respectively. A systematic study to compare the two different gold nanoparticles is presented using multiple material characterization techniques. It was found that the two systems show different capping mechanism and hence differ in their intrinsic core and surface properties. The compound BINAP plays only surface capping agent and stabilizes the gold nanoparticles, resulting in small particle size and suppressed surface plasmon resonance absorption at 520 nm. The DABN capping ligand is different from BINAP and acts as both reducing and capping agent, causing the reduction of Au (III) to Au (0). The nucleation growth of the gold core occurs in accordance with the polymerization-passivation process by DABN, resulting in a big particle size of 20 nm. A strong surface plasmon resonance band shows a maximum peak at 564 nm, consistent with the Au core size. The simultaneous oxidative polymerization of DABN and the induced metal reduction process lead to the formation of gold nanoparticles encapsulated by a mixture of DABN oligomers or polymers.

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The preferential generation of anionic nanoparticles of mass around 30 kamu from thiol-derivatized gold nanoparticles and its significance

Thiol-derivatized gold nanoparticles have been prepared by the reduction of gold cations in an ethanol solvent in the presence of alkanethiols such as dodecanethiol and nonanethiol. Negative ion laser ablation time-of-flight mass spectra (LA-TOF-MS) of the as-prepared samples indicate the presence of a single predominant peak at around 30?kamu even for samples prepared using widely different gold to thiol molar ratios in the reactant mix. The preponderant observation of such nanoparticles in the mass spectra is attributed to a region of especially high thermodynamic stability existing in this mass range for negative ions derived from nanoparticles prepared from the Au–RSH material combine. These studies also support the assertion that the thiol-derivatized gold nanoparticles prepared by the method of Murthy et al. are qualitatively different than that prepared by the method of Brust et al.     

Biosynthesis of gold nanoparticles using diatoms—silica-gold and EPS-gold bionanocomposite formation

Novel synthesis of gold nanoparticles, EPS-gold, and silica-gold bionanocomposites by biologically driven processes employing two diatom strains (Navicula atomus, Diadesmis gallica) is described. Transmission electron microscopy (TEM) and electron diffraction analysis (SAED) revealed a presence of gold nanoparticles in the experimental solutions of the diatom culture mixed with tetrachloroaureate. Nature of the gold nanoparticles was confirmed by X-ray diffraction studies. Scanning electron microscopy (SEM) and TEM showed that the nanoparticles were associated with the diatom frustules and extracellular polysaccharides (EPS) excreted by the diatom cells. Due to its accessibility, simplicity, and effectiveness, this method of nanocomposites preparation has great importance for possible future applications.     

Interaction of albumin and γ-globulin molecules with gold nanoparticles in water solutions

The molecular mobility of scattering particles in water solutions of albumin and γ-globulin proteins with gold nanoparticles was investigated by the dynamic light scattering method. The dependences of translation diffusion coefficients of particles at various concentrations of the solution components have been obtained. It was revealed that in a wide range of concentrations of the solution components there is no interaction of gold nanoparticles with albumin, whereas gold nanoparticles form complexes with γ-globulin molecules.     

Detection of biotin–avidin affinity binding by exploiting a self-referenced system composed of upconverting luminescent nanoparticles and gold nanoparticles

We demonstrate an affinity system based on the interaction of two types of nanoparticles. The first consists of upconverting luminescent NaYF₄:Yb,Er nanoparticles (UCNPs) with a size of 40–100 nm, absorbing light in the infrared and showing luminescence at 521, 543 and at 657 nm. The second consists of (red) gold nanoparticles (Au-NPs) with a size of about 50 nm and capable of absorbing the green luminescence of the UCNPs. By labeling the UCNPs with avidin and the AuNPs with biotin we have established a model system for a self referenced affinity system applicable to sensing in biological samples. In the presence of avidin-modified UCNPs, the biotinylated Au-NPs can be detected in the range from 12 to 250 μg mL⁻¹ by ratioing the intensity of the red (analyte-independent) emission to that of the green (analyte-dependent) emission band. The nanoparticles were characterized in terms of size and composition using transmission electron microscopy, thermogravimetry, and FTIR spectroscopy.     

Sauna,sweat and science II – do we sweat what we drink?

ABSTRACT

Inspired by a previous ‘Sauna, sweat and science’ study [Zech et al. Isot Environ Health Stud. 2015;51(3):439–447] and out of curiosity and enthusiasm for stable isotope and sauna research we aimed at answering the question ‘do we sweat (isotopically) what we drink’? We, therefore, pulse-labelled five test persons in a sauna experiment with beverages that were ²H-enriched at about +25,600?‰. Sweat samples were collected during six sauna rounds and the hydrogen isotope composition δ²H_sweat was determined using an isotope ratio mass spectrometer. Before pulse labelling, δ²H_sweat – reflecting by approximation body water – ranged from –32 to –22?‰. This is ～35?‰ enriched compared to usual mid-European drinking water and can be explained with hydrogen-bearing food as well as with the respiratory loss of ²H-depleted vapour. The absence of a clearly detectable ²H pulse in sweat after pulse labelling and δ²H_sweat results of ≤+250?‰ due to a fast ²H equilibration with body water are moreover a clearly negative answer to our research question also in a short-term consideration. Given that the recovery of the tracer based on an isotope mass balance calculation is clearly below 100?%, we finally answer the question ‘where did the rest of the tracer go?’     

Enhanced spectroscopic properties and Judd–Ofelt parameters of Er-doped tellurite glass: Effect of gold nanoparticles

Glasses with composition 70TeO₂–20ZnO–10Na₂O–0.5Er₂O₃–(x)Au are synthesized by melt-quenching technique. Their spectroscopic and optical characterizations are made. The presence of gold nanoparticles (Au NPs) with average size ～9 nm is confirmed from TEM micrograph. The value of E_dir is found to lie between 3.082 and 3.073 eV, while E_indir lies within 2.765 to 2.724 eV. The observed visible up-conversion (UC) emission under 779 nm excitation wavelength exhibits two bands centered at 546 nm (green) and 637 nm (red) in all samples. The glass with 0.4 mol% Au NPs shows dominant enhancement in the UC emission intensity of the order of 3.5 times for the green band (⁴S_3/2 → ⁴I_15/2) and a weaker enhancement for the red (⁴F_9/2 → ⁴I_15/2) band. The optical properties of the system are affirmed to depend strongly on the Au concentration in the dielectric medium. The absorption spectra consist of six bands attributed to absorption from ground state (⁴I_15/2) to ⁴I_13/2, ⁴I_11/2, ⁴I_9/2, ⁴F_9/2, ²H_11/2, and ⁴F_7/2 excited states. The structural reveals that the types of bonding and difference in electro-negativity can be manipulated by the presence of metallic NPs in glass matrix. Judd–Ofelt analysis asserts the increase in Ω₂ and Ω₆ parameters with the addition of Au NPs and the enhancement of green and red emissions. The enhancement is mainly attributed to large plasmonic effect of Au NPs. The proposed glasses can be nominated as potential materials for solid state laser developments.     

Alloy formation of supported gold nanoparticles at their transition from clusters to solids: does size matter?

Gold nanoclusters of a size approaching the molecular limit (<3 nm) were prepared on Si substrates in order to study alloy formation on the nanometer scale. For this purpose, indium atoms are deposited on top of the gold particles at room temperature and the formation of AuIn(2) is studied by x-ray photoelectron spectroscopy in situ. It is observed that the alloy formation takes place independent of whether the particles electronically are in an insulating molecular or in a metallic state. Most important, however, closed packed full-shell clusters containing 55 Au atoms are found to exhibit an outstanding stability against alloying despite a large negative heat of formation of the bulk Au-In system. Thus, Au(55) clusters may play a significant role in the design of nanoscaled devices where chemical inertness is of crucial importance.     

Pure drug nanoparticles in tablets: what are the dissolution limitations?

There has been increasing interests for drug companies to incorporate drug nanoparticles into their existing formulations. However, technical knowledge in this area is still in its infancy and more study needs to be done to stimulate growth in this fledging field. There is a need to scrutinize the performance of pure drug nanoparticles in tablets, particularly relating formulation variables to their dissolution performance. Application of the pure form, synthesized without the use of surfactants or stabilizers, is often preferred to maximize drug loading and also to minimize toxicity. Cefuroxime axetil, a poorly water-soluble cephalosporin antibiotic, was used as the model drug in the formulation development. Drug release rate, tablet disintegration time, tensile strength and energy of failure were predominantly influenced by the amount of super-disintegrant, amount of surfactant, compression force and diluent species, respectively. The compression rate had minimal impact on the responses. The main hurdle confronting the effective use of pure drug nanoparticles in tablets is the difficulty in controlling aggregation in solution, which could potentially be aggravated by the tabletting process. Through the use of elevated levels of surfactants (8 w/w% sodium dodecyl sulphate), drug release from the nanoparticle preparation was enhanced from 58.0 ± 2.7% to 72.3 ± 0.7% in 10 min. Hence, it is recommended that physical formulations for pure drug nanoparticles be focused on the particle de-aggregation step in solution, if much higher rates are to be desired. In conclusion, even though pure drug nanoparticles could be easily synthesized, limitations from aggregation may need to be overcome, before successful application in tablets can be fully realized.     

Adsorption of carboxymethylester-azobenzene on copper and?gold?single crystal surfaces

The adsorption of 3,3′-di(methoxycarbonyl)azobenzene (CMA) on Au(111) and on Cu(001) substrates was studied by X-ray absorption spectroscopy measurements at the C, N, and O K edges. We find the molecules physisorbed in a planar conformation flat on the Au(111) surface. At higher coverages, a molecular crystal is formed wherein the molecules have the same flat geometry. On Cu(001), additional chemical bonds are formed between the molecules and the surface via the nitrogen atoms. Here the methyl benzoate moieties are tilted out of the surface plane.     

Stick-slip motion in spite of a slippery contact: do we get what we see in atomic friction?

Atomic force microscopy provides direct atomic-scale access to friction. In this paper, unexpected and potentially dramatic consequences of the tip elasticity are discussed. Under certain natural conditions an essentially new, nontrivial regime can be entered. Although the tip appears to perform typical stick-slip motion, the tip-surface contact is fully "lubricated" by fast thermal motion of the tip apex. The interpretation of the observations needs to be changed completely in this case.     

Apertureless SNOM imaging of the surface phonon polariton waves: what do we measure?

The apertureless scanning near-field microscope (ASNOM) mapping of surface phonon polariton (SPP) waves being excited at the surface of the SiC polar crystal at a frequency corresponding to the lattice resonance was investigated. The wave with well-defined direction and source position, as well as a well-known propagation law, was used to calibrate the signal of an ASNOM. An experimental proof is presented showing that the signal collected by the ASNOM in such a case is proportional (as a complex number) to the local field amplitude above the surface, regardless of the tip response model. It is shown that the expression describing an ASNOM response, which is, in general case, rather complicated nonlinear function of a surface/tip dielectric constants, wavelength, tip vibration amplitude, tip shape etc., can be dramatically simplified in the case of the SPP waves mapping in a mid-IR range, due to a lucky combination of the tip and surface parameters for the case being considered. A tip vibration amplitude is much less than a running SPP wave field decay height in a normal direction. At the same time, the tip amplitude is larger than a characteristic distance at which a tip–surface electromagnetic near-field interaction plays a significant role.     

Discrete quantum breathers: what do we know about them?

The knowledge about discrete quantum breathers, accumulated during the last two decades, is reviewed. "Prehistory" of the problem is described and some important properties differentiating localized and extended vibrational modes are outlined. The state of art of our understanding of the principal features of the quantum discrete breathers is presented.     

Fifty years of M?ssbauer spectroscopy: from alloys and oxides to glasses and nanoparticles

The M?ssbauer Effect was discovered in 1957. In 1960 M?ssbauer spectroscopy was born when two important papers appeared on (i) the magnetic hyperfine interaction and (ii) the electric monopole (isomer shift) and quadrupole interactions. These transformed an interesting phenomenon into a method for probing solids. Applications to magnetism, metals and alloys, chemical compounds, biological molecules, geology, archaeology and other sciences followed and are still of current interest. Two areas of research where M?ssbauer spectroscopy is making unique contributions are in determining oxidation states in (i) glasses and (ii) nanoparticles. Some recent measurements are described.     

Novel fabrication and catalytic application of poly(ethylenimine)-stabilized gold–silver alloy nanoparticles

Novel synthesis of amine-stabilized Au–Ag alloy nanoparticles with controlled composition has been devised using poly(ethylenimine) (PEI) as a reducing and a stabilizing agent simultaneously. The composition of Au–Ag alloy nanoparticles was readily controlled by varying the initial relative amount of HAuCl₄ and AgNO₃. Due to the presence of abundant amine functional groups in PEI, which could act as the dissolving ligand for AgCl, the precipitation problem of Ag⁺ in the presence of Cl⁻ from the gold salt was avoided. On this basis, the relatively high concentrations of HAuCl₄ and AgNO₃ salts were used for the fabrication of Au–Ag alloy nanoparticles. The PEI thus plays triple roles in this study that include the co-reducing agents for HAuCl₄ and AgNO₃, the stabilizing agents for Au–Ag alloy nanoparticles, and even the dissolving agents for AgCl. As a novel material for use in catalysis, the Au–Ag alloy nanoparticles including pure Au and Ag samples were exploited as catalysts for the reduction of 4-nitrophenol in the presence of NaBH₄. As the Au content was increased in the Au–Ag alloy nanoparticles, the rate constant of the reduction was exponentially increased from pure Ag to pure Au.