Infrared and infrared emission spectroscopy of gallium oxide α-GaO(OH) nanostructures

Infrared spectroscopy has been used to study nano- to micro-sized gallium oxyhydroxide α-GaO(OH), prepared using a low temperature hydrothermal route. Rod-like α-GaO(OH) crystals with average length of 2.5 μm and width of 1.5 μm were prepared when the initial molar ratio of Ga to OH was 1:3. β-Ga₂O₃ nano and micro-rods were prepared through the calcination of α-GaO(OH). The initial morphology of α-GaO(OH) is retained in the β-Ga₂O₃ nanorods.The combination of infrared and infrared emission spectroscopy complimented with dynamic thermal analysis were used to characterise the α-GaO(OH) nanotubes and the formation of β-Ga₂O₃ nanorods. Bands at around 2903 and 2836 cm⁻¹ are assigned to the –OH stretching vibration of α-GaO(OH) nanorods. Infrared bands at around 952 and 1026 cm⁻¹ are assigned to the Ga–OH deformation modes of α-GaO(OH). A significant number of bands are observed in the 620–725 cm⁻¹ region and are assigned to GaO stretching vibrations.     

Cathodic electrophoretic deposition of manganese dioxide films

Cathodic electrophoretic deposition (EPD) method has been developed for the deposition of manganese dioxide films. It was shown that phosphate ester (PE) is an effective charging additive, which provides stabilization of manganese dioxide nanoparticles in suspensions. The influence of PE concentration and deposition voltage on the deposition efficiency has been studied. EPD has been utilized for the fabrication of porous nanostructured films with thickness in the range of 0.5–20 μm for application in electrochemical supercapacitors (ES). Cyclic voltammetry and chronopotentiometry data for the films tested in the 0.1 M Na₂SO₄ solutions showed capacitive behavior in the voltage window of 1 V. The highest specific capacitance (SC) of 377 F g⁻¹ was obtained at a scan rate of 2 mV s⁻¹. The SC decreased with increasing film thickness and increasing scan rate in the range of 2–100 mV s⁻¹. The deposition mechanism, kinetics of deposition and charge storage properties of the films are discussed.     

Efficient hydrogen peroxide generation from organic matter in a bioelectrochemical system

Hydrogen peroxide (H₂O₂) is an important industrial chemical, but its current production methods are highly energy-intensive. This study presents a novel process for the production of H₂O₂ based on the bioelectrochemical oxidation of wastewater organics at an anode coupled to the cathodic reduction of oxygen to H₂O₂. At an applied voltage of 0.5 V, this system was capable of producing 1.9 ± 0.2 kg H₂O₂/m³/day from acetate at an overall efficiency of 83.1 ± 4.8%. As most of the required energy was derived from the acetate, the system had a low energy requirement of 0.93 kWh/kg H₂O₂.     

Molecular fine structure and transition dipole moment of NO2 using an external cavity quantum cascade laser

Rotational vibrational fine structure and transition dipole moment of NO₂ is measured using Doppler free saturation spectroscopy with an external grating cavity quantum cascade laser (QCL). The QCL wavelength is calibrated using a 310 cm long internally coupled Fabry–Perot interferometer. We obtain a frequency splitting of 139.68 ± 0.06 MHz (0.0047 cm⁻¹) between the spin doublets (17) of 000 → 001 transition of NO₂. The resolution of the QCL based saturation spectrometer is limited by the QCL linewidth of 3.99 MHz ( 0.00013 cm⁻¹) deduced from the half width of the Lamb dips. The Lamb dip spectroscopy is utilized to obtain a vibrational dipole moment of 0.37 Debye for the (17) transitions.     

Enhanced tungstate electrochromism via formation of transparent conductive networks

Indium tin oxide (ITO) nanopowder was added to a polymer film containing WO₃ · H₂O particles to enhance electron conductivity and complimentary Li ion kinetics in an electrochromic device. Film conductivity increased dramatically with ITO content, suggesting the formation of conductive ITO networks in the film. The improved electron conductivity leads to a substantial increase of the effective Li⁺ ion diffusion coefficient in the composite film, from 10⁻¹¹ to 10⁻⁹ cm²/s. Electrochromic contrast studies revealed that the presence of the ITO networks leads to enhanced blue/green color contrast.     

Interaction and photodynamic activity of cationic porphyrin derivatives bearing different patterns of charge distribution with GMP and DNA

The interaction of amphiphilic cationic porphyrins, containing different patterns of meso-substitution by 4-(3-N,N,N-trimethylammoniumpropoxy)phenyl (A) and 4-(trifluoromethyl)phenyl (B) groups, with guanosine 5′-monophosphate (GMP) and calf thymus DNA have been studied by optical methods in phosphate buffer solution. The properties of these synthetic porphyrins were compared with those of representative standard of anionic 5,10,15,20-tetra(4-sulphonatophenyl)porphyrin (TPPS₄⁴⁻) and cationic 5,10,15,20-tetra(4-N,N,N-trimethylammonium phenyl)porphyrin (TMAP⁴⁺). Stable complexes with GMP were found for cationic porphyrins, except for monocationic AB₃⁺. The binding constant (K_GMP  10⁴ M⁻¹) follows the order: A₃B³⁺  ABAB²⁺ > A₄⁴⁺  TMAP⁴⁺. Also, interaction with DNA was observed for all evaluated cationic porphyrins. For these related cationic porphyrins, the binding constant (K_DNA  10⁵ M⁻¹) increases with the number of cationic charges. On the other hand, the photodynamic activity of porphyrins was analyzed in solution of GMP and DNA. Monocationic AB₃⁺ is a less effective sensitizer to oxidize GMP in comparison with the other cationic porphyrins, in agreement with the lack of detected interaction with this nucleotide. The electrophoretic analysis of DNA indicates that photocleavage takes place when the samples are exposed to photoexcited tricationic and tetracationic porphyrins. In the presence of sodium azide the DNA decomposition was diminished. Also, reduction in the DNA photocleavage was observed under anoxic condition, indicating that oxygen is essential for DNA photocleavage sensitized by these cationic porphyrins. In addition, an increase in DNA degradation was not observed in deuteriated water. Therefore, an important contribution of type I photoreaction processes could be occurring in the DNA photodamage sensitized by these cationic porphyrins. These results provide a better understanding of the characteristics needed for sensitizers to produce efficient DNA photocleavage.     

Isoconversional kinetics of degradation of polyvinylpyrrolidone used as a matrix for ammonium nitrate stabilization

Thermogravimetric analyzer (TGA) has been applied to measure the kinetics of the thermal degradation of virgin polyvinylpyrrolidone (PVP) and a phase stabilized PVP–ammonium nitrate (AN) material. The PVP–AN samples have been prepared by using 20 wt.% of AN and PVP of three different molecular weights. Virgin PVP undergoes a major mass loss in the region 380–550 °C leaving a small amount of nonvolatile residue. The application of an advanced isoconversional method to the respective degradation process demonstrates that its effective activation energy increases from 70 kJ mol⁻¹ to a plateau value at 250–300 kJ mol⁻¹, which is independent of the molecular weight. The PVP–AN materials lose spontaneously 20% of their mass on heating above the glass transition temperature of the PVP matrix (160–180 °C). After the escape of AN, the remaining PVP matrix degrades in the same temperature region as virgin PVP, however, the effective activation energy of this degradation is 150–200 kJ mol⁻¹.     

Passivation layer–dependent catalysis of zinc oxide nanostructures

Electrochemical and photoelectrochemical catalysis of surface-passivated zinc oxide (ZnO) nanostructures with three different metal oxides were investigated. Initially, vertically aligned ZnO nanorods structures were developed over conductive substrates by a two-step approach and then passivated with an ultrathin zinc hydroxide, that is, Zn(OH)₂, cobalt oxide, that is, CoO, and Zn(OH)₂/CoO as bilayer, by electrochemical deposition. Compared with the pristine ZnO structures, the surface-passivated nanostructures possess slightly rough surfaces, whereas their crystal structure remains unchanged. From electrochemical catalysis studies under dark and illumination, it is noticed that vertically aligned ZnO nanostructures passivated with narrow band-gap CoO layers have a predominant water oxidation performance than that of the structures passivated with other oxide materials. It is mainly attributed to the eradication of surface states present on ZnO nanorods. Interestingly, the structures passivated with bilayers, that is, Zn(OH)₂/CoO, showed significant stability and durability (～103% retention in current density@60^th min) with a continuous oxygen evolution reaction process for long durations.     

Existence of clathrate-like structures in supercooled water: X-ray diffraction evidence

X-ray diffraction study of supercooled water has been performed using an imaging-plate X-ray detector down to −15 °C. The peak at 10.8 Å, which grows with decreasing temperature, in the radial distribution function {D(r) − 4πr²ρ₀} indicates the existence of clathrate-like structures in supercooled water. It is suggested that anomalous properties of water, which become more pronounced at low temperatures, are closely linked to the development of clathrate-like structures in water at low temperatures.     

Investigations of the local structures and spin Hamiltonian parameters for the trigonal Rh and Ir centers in rhombohedral BaTiO3

The local structures and spin Hamiltonian parameters (g factors and the hyperfine structure constants) of the Rh⁴⁺(4d⁵) and Ir⁴⁺(5d⁵) centers in rhombohedral BaTiO₃ are theoretically investigated from the formulas of these parameters for a nd⁵ (n = 4 and 5) ion with low spin (S = 1/2) in a trigonally distorted octahedron. From the calculations, the impurity ions are found not to occupy exactly the host Ti⁴⁺ site in BaTiO₃ but to suffer a slight inward shift (0.13 Å) towards the center of the oxygen octahedron along the C₃ axis, yielding much smaller trigonal distortion as compared with that of the host Ti⁴⁺ site. The theoretical spin Hamiltonian parameters based on the above impurity axial shifts are in good agreement with the observed values.     

Vibrational satellite of Na(3d ← 3s) dipole-forbidden transition in Na/CF4 mixture

Excitation spectra of Na fluorescence in mixtures with CF₄ display a new band shifted by the energy of one-vibrational quantum of the IR active ν₃-mode of CF₄ (1281 cm⁻¹) from Na 3d states. This band is attributed to a Na(3s)CF₄(ν₃ = 0) → Na(3d)CF₄(ν₃ = 1) transition and its intensity is explained by coupling with Na(4p)CF₄(v₃ = 0) resonance state which lies  180 cm⁻¹ below in energy. An analogous satellite of the Na 6p state combined with the same vibration and lying close to the Na 7p state is reported and discussed.     

Effect of small amount of poly(ethylene naphthalate) on isothermal crystallization and spherulitic morphology of poly(trimethylene terephthalate)

The effect of a small amount of poly(ethylene naphthalate) (PEN) in its blends with poly(trimethylene terephthalate) (PTT) on isothermal melt-crystallization kinetics and spherulitic morphology of the blends was thoroughly investigated. The maximum PEN content in the blends was 9 wt%. Due to the single composition-dependent glass transition temperature (T_g) that was observed for each blend, these blends appeared to be miscible in the amorphous state. After isothermal crystallization from the melt state, the neat PTT and its blends with PEN exhibited either double or triple melting endotherms. The triple endothermic peaks were observed in both the neat PTT and the blends when being crystallized at crystallization temperatures (T_c) of less than or equal to 195 °C. The equilibrium melting temperature () for the neat PTT was determined based on the linear Hoffman–Weeks extrapolative method to be 248 °C. Such values for the blends were found to decrease with the addition and increasing amount of PEN. Both the neat PTT and the blends were isothermally crystallized over the T_c range of 190–205 °C. At a given T_c, the 97PTT/3PEN blend exhibited a half-time of crystallization (t_0.5) value that was lower, while it exhibited reciprocal half-time (), Avrami rate constant (K_A), and spherulitic growth rate (G) values that were greater, than those of the neat PTT. With further increase in the PEN content, the t_0.5 value increased, while the , K_A, and G values decreased. Analysis of the G values based on the Lauritzen–Hoffman's (LH) secondary nucleation theory showed that the neat PTT and the 91PTT/9PEN blend exhibited a regime II→III transition at 194 °C (467.2 K), while no regime transition was observed for the other two blends. The lateral and the fold surface free energies (σ and σ_e) and the work of chain folding (q) for the neat PTT and the blends were 19.4, 30.2–46.3 erg cm⁻², and 2.4–3.6 kcal mol⁻¹, respectively. Lastly, the effect of both the T_c and the PEN content on morphology and texture of the PTT spherulites was also investigated and the results showed that the texture of the spherulites became coarser with increasing T_c and PEN content.     

A rapid approach for assessment of arsenic exposure by elemental analysis of single strand of hair using laser ablation-inductively coupled plasma-mass spectrometry

Application of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) as a method for identification of arsenic in a single hair strand was investigated. Using a single point ablation method detectability of ⁷⁵As and other two elements (²⁰⁸Pb and ⁶⁴Zn) were evaluated. Arsenic (⁷⁵As) signal is improved with enhanced laser ablation conditions. For the arsenic determination in hair single spots or single linear scans with enhanced laser ablation conditions described in the paper are satisfactory although  800 μm linear scans may be preferable. Arsenic levels in a single strand of hair from individuals who were chronically exposed to arsenic contaminated drinking water from a village in the Atacama Desert in northern Chile were determined by LA-ICP-MS. These results were satisfactorily correlated with total As concentration previously measured by hydride generation (HG)-ICP-MS. The sample throughput is high and it takes  3 min per each hair sample including mounting, focusing and analysis. LA-ICP-MS method can be used for the rapid identification and screening of toxic and nutritionally important elements in hair.     

Ultrafast dynamics of heat flow across molecules

An ultrafast flash thermal conductance apparatus is used to study heat flow through aliphatic and aromatic molecules arranged in self-assembled monolayers (SAMs). The apparatus consists of a thin metal film which can be flash-heated by many hundreds of degrees in 1 ps using a femtosecond pulse. Heat flow from the metal surface into the SAM molecules is detected using vibrational sum-frequency generation (SFG) spectroscopy. The SAMs studied were alkanethiolates (AT) ranging from C6 to C24, benzenethiolate (BT) and benzylmercaptide (BMT). SFG in the CH-stretch region selectively probes transitions of the terminal methyl groups of AT and the CH moiety at the 4-position of the phenyl ring of BT and BMT (opposite the thiolate-surface bond). The SFG signal is sensitive to temperature-jump induced thermal disorder of the SAM and also to vibrational frequency shifts induced by the changing intramolecular vibrational populations. The SFG probe functions as a thermometer, and this thermometer is 1.5 Å thick with a response time of 1 ps. In the AT chains, a study of the length dependence is used to determine the rate heat flows across the metal–SAM interface and the rate of heat flow through the AT chains. The interface thermal conductance is 220 GW m⁻² s⁻¹. The AT molecular conductance is 50 pW K⁻¹ or 0.3 eV s⁻¹ K⁻¹. Heat flow through the AT chains is ballistic with a velocity of 1 km/s. Heat flow into BMT is slower than in BT because BMT has one additional methylene linker group. The BT and BMT structures evidence a thermally-initiated surface rearrangement occurring in a few tens of picoseconds. These SAMs are strained and the phenyl rings cannot adopt the most stable staggered herringbone structure. After the T-jump, the SAM molecules have enough freedom to relax into more favorable configurations.     

Preparation and characterization of stable monodisperse silver nanoparticles via photoreduction

Silver nanoparticles were synthesized by UV irradiation of [Ag(NH₃)₂]⁺ aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) as both reducing and stabilizing agents. The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima around 420 nm. It was found that the formation rate of silver nanoparticles from Ag₂O was much quicker than that from AgNO₃, and the absorption intensity increased with PVP concentration as well as irradiation time. The maximum absorption wavelength (λ_max) was blue shift with increasing PVP content until 8 times concentration of [Ag(NH₃)₂]⁺ (wt%). The transmission electron microscopy (TEM) showed the resultant particles were 4–6 nm in size, monodisperse and uniform particle size distribution. X-ray diffraction (XRD) demonstrated that the colloidal nanoparticles were the pure silver. In addition, the silver nanoparticles prepared by the method were stable in aqueous solution over a period of 6 months at room temperature (25 °C).     

Dual electrochemical microsensor for simultaneous measurements of nitric oxide and oxygen: Fabrication and characterization

A planar-type amperometric dual microsensor was developed for the simultaneous measurement of the nitric oxide (NO) and oxygen (O₂) concentrations. The sensor (overall diameter = 500 μm) consisted of a dual working electrode (WE) containing two platinized platinum microdisks (25 μm diameter, WE1, WE2, distance between two disks > 330 μm) and a Ag/AgCl wire reference electrode covered with an expanded poly(tetrafluoroethylene) gas-permeable membrane. The differentiation and concurrent measurements of NO and O₂ were obtained successfully using two sensing WEs with different applied potentials (+0.75 V for WE1 and −0.4 V for WE2). Cross-talk between WE1 and WE2 was eliminated with an optimized internal solution composition. Linear dynamic range, selectivity, sensitivity, detection limit (<5 nM for NO; <500 nM for O₂), and stability (>50 h) were evaluated.     

Simultaneous determination of chloride, nitrate and sulphate in vegetable samples by single-column ion chromatography

A new ion chromatography method is described for the simultaneous determination of Cl⁻, NO₃⁻ and SO₄²⁻, using a selected eluent 1.3-mM sodium gluconate/1.3-mM borax (pH 8.5). The extraction methods of Cl⁻, NO₃⁻, SO₄²⁻ in vegetables are studied. The determination limits of Cl⁻, NO₃⁻, SO₄²⁻ are 0.17 μg/ml, 0.63 μg/ml and 0.81 μg/ml. The linear ranges are 060 μg/ml, 090 μg/ml and 090 μg/ml. The relative S.D. are <2.5%. The mean recoveries of Cl⁻, NO₃⁻, SO₄²⁻ in vegetables range from 97.0 to 104%.     

Solvent effect on the blue shifted weakly H-bound F3 CH…FCD3 complex

Solvent effect on the ν^c frequency of CH stretching vibration of the blue shifted F₃CH…FCD₃ complex has been studied in liquefied N₂, CO, Ar, Kr and Xe. In the case of Xe, the spectroscopic measurements have also been extended to the solid state. It was found that the ν^c position of the complex in the solutions studied lowers with respect to the value in the gas phase. In liquid Xe, characterized by the largest permittivity, this effect reaches its maximum value of −14.5 cm⁻¹. The ν^c frequency begins to grow again just below the freezing point of Xe, where a noticeable (15%) increase of the density of Xe occurs. The experimental results obtained for the liquid phase have been analyzed in the framework of the Onsager-like reaction field model and Polarizable Continuum Model (PCM) implemented into a standard Gaussian 98 Program.     

Electrochemical properties of polyaniline in p-toluene sulfonic acid solution

Polyaniline was deposited potentiodynamically on a stainless steel substrate in the presence of an inorganic acids (sulfuric acid). The electrochemical characterization of the electrode was carried out by means of cyclic voltammetry and electrochemical impedance spectroscopy in the organic acids (p-toluene sulfonic acid) solution. The results show that polyaniline has a high specific capacitance of 431.8 F g⁻¹ at 1 mV s⁻¹, high coulombic efficiency of 95.6% at 20 mV s⁻¹, and exhibits a high reversibility. This indicates the promising feasibility of the polyaniline used as an electrochemical capacitor material in the electrolyte of p-toluene sulfonic acid solution especially at high charge–discharge process.