Adsorption and thermodynamics studies of U(VI) by composite adsorbent in a batch system

The adsorption of U(VI) from aqueous solutions onto composite adsorbent (algistar) has been studied using a batch adsorber. The parameters that affect the U(VI) sorption, such as contact time, solution pH, initial U(VI) concentration, and temperature, have been investigated and optimized conditions determined. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of composite adsorbent, and experimental results showed this to be 43.10 mg/g. The adsorption patterns of metal ions on composite adsorbent followed the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherms. The Freundlich, Langmuir, and D–R models have been applied, and the data correlate well with Langmuir model, and that the sorption is physical in nature (the sorption energy E _ads = 12.90 kJ/mol). Thermodynamic parameters (∆H _ads^o = −41.08 kJ/mol, ∆S _ads^o = −68.00 J/mol K, ∆G _ads (298.15 K) = −20.81 kJ/mol) showed the exothermic heat of adsorption and the feasibility of the process. The results suggested that the composite adsorbent is suitable as a sorbent material for recovery and biosorption/adsorption of uranium ions from aqueous solutions.     

Localized excitation effects in (E,E)-2,5-<Emphasis Type="Italic">bis</Emphasis>[2-(4-N,N-dipropylaminophenyl) ethylenyl]-3,6-dimethylpyrazine and generation of its different forms in solution

Dipole moments of (E,E)-2,5-bis[2-(4-N,N-dipropylaminophenyl)ethylenyl]-3,6-dimethylpyrazine (VS365) quadrupolar dye in 1,4-dioxane and cyclohexane in addition to its instantaneous fluorescence spectra and fluorescence lifetimes in dichloromethane (pure and with added trifluoroacetic acid) were measured. Quantumchemical calculations show that the π − π conjugated system is localized in the flattest part of the molecule due to disorder in the ground-state geometry of the dye molecule and that this part is the one responsible for light absorption. The effect of localized excitation of the dye causes a considerable change in its dipole moment Δ^aμ. Various fluorescent forms of the dye that feature considerably spaced emission spectra and different fluorescence lifetimes originate by adding trifluoroacetic acid to the solution of oligophenylenevinylene in dichloromethane.     

Spectroscopic characteristics of erbiumand ytterbium-activated laser media

Judd–Ofelt parameters (Ω₂ = 5.09∙10^–20, Ω₄ = 0.92∙10^–20, and Ω₆ = 0.63∙10^–20 cm²) and oscillator strengths of fundamental optical transitions involved in lasing at wavelength 1.54 μm have been calculated for borosilicophosphate glass co-activated with Er³⁺ and Tb³⁺ ions based on experimental luminescence and absorption spectra and refractive indices. The results were used to determine the emission (6∙10^–23 cm²) and absorption (5∙10^–21 cm²) cross sections for λ = 1.54 μm and the gain cross section as a function of inverse population levels.     

Assessment of the possibility of determination of the electrophysical characteristics of CdxHg1–xTe p+–n-structures using differential hall measurements

The process of reconstuction of the distribution profile of hole concentration in the p ⁺–n structure by the method of differential Hall measurements upon implantation of ions As⁺ (Е = 190 keV, D = 3.10¹⁴ cm^-2, j = 0.025 μA/cm²) into epitaxial films Cd _x Hg_1–x Te for x ~ 0.2, with the initial electron concentration and mobility n = 10¹⁴ cm^-3 and μ = 2∙10⁵ cm²∙V^–1∙s^–1 is numerically simulated. The dependences of degree of reconstruction of the hole-concentration distribution profile on the depth of a shunting n-layer and magnitude of the magnetic field, at which the electrophysical parameters of the p ⁺–n structure are measured, are calculated. The dependence of the limiting magnetic field determining the magnetic-field range for measurements on the n-layer depth is found. It is shown that in calculations one should use the conduction values measured at the same magnetic fields as the Hall coefficients for determination of the holeconcentration distribution profile using the Petritz model.     

The effects of lepton KK modes on the electric dipole moments of the leptons in the Randall–Sundrum scenario

We study the charged lepton electric dipole moments in the Randall–Sundrum model where the leptons and the gauge fields are accessible to the extra dimension. We observe that the electric dipole moment of the electron (muon; tau) reaches a value of the order of 10^-26 e cm (10^-20 e cm; 10^-20 e cm) with the inclusion of the lepton KK modes.     

Binding of Quercetin to Lysozyme as Probed by Spectroscopic Analysis and Molecular Simulation

The binding of quercetin to lysozyme (LYSO) in aqueous solution was investigated by fluorescence spectroscopy, UV-vis absorption spectroscopy and molecular simulation at pH 7.4. The fluorescence quenching of LYSO by addition of quercetin is due to static quenching, the binding constants, K _a , were 3.63 × 10⁴, 3.31 × 10⁴ and 2.85 × 10⁴ L·mol⁻¹ at 288, 298 and 308 K, respectively. The thermodynamic parameters, enthalpy change, ∆H, and entropy change, ∆S, were noted to be −7.56 kJ·mol⁻¹ and 61.07 J·mol⁻¹·K⁻¹. The results indicated that hydrophobic interaction may play a major role in the binding process. The distance r between the donor (LYSO) and acceptor (quercetin) was determined as 3.34 nm by the fluorescence resonance energy transfer. The synchronous fluorescence spectroscopy showed the polarity around the tryptophan residues increased and the hydrophobicity decreased. Furthermore, the study of molecular simulation indicated that quercetin could bind to the active site (a pocket made up of 24 amino-acid residues) of LYSO mainly via hydrophobic interactions and that there were hydrogen interactions between the residues (Gln 57, Ile 98) of LYSO and quercetin. The accessible surface area (ASA) calculation verified the important roles of tryptophan (Trp) residues during the binding process.     

Thermodynamics, Conformation and Active Sites of the Binding of Zn–Nd Hetero-bimetallic Schiff Base to Bovine Serum Albumin

The interactions between N,N′-di(2-hydroxy-3-methyoxy-phenyl-1-methylene)-o-phenyldiamine-mone Zn(II), Nd(III) nitrate (2LZnNd) and bovine serum albumin (BSA) was investigated by various spectroscopic techniques under physiological conditions. It was proved that the fluorescence quenching of BSA by 2LZnNb was a result of the formation of a non-fluorescent complex with the binding constants of 3.15 × 10⁵; 2.72 × 10⁵ and 2.44 × 10⁵ M^–1 at 298 K, 304 K and 310 K, respectively. A marked increase in the fluorescence anisotropy in the proteinous environments indicates that BSA introduces motional restriction on the drug molecule. The corresponding thermodynamics parameters ΔH and ΔS were calculated to be –16.36 kJ mol^–1 and 43.48 J mol^–1 K^–1 via van’t Hoff equation. Moreover, the competitive probes experiment revealed that the binding location of 2LZnNb to BSA is in the hydrophobic pocket of site II. The effect of 2LZnNb on the conformation of BSA has been analyzed by means of CD spectrum and three-dimensional fluorescence spectra. The results indicate that the conformation of BSA molecules was changed in the presence of 2LZnNb Schiff base.     

Development of Flow Injection Spectrofluorimetric Detection System for the Determination of Homocysteine

In this work, a new simple and sensitive flow injection method is developed for the determination of homocysteine with spectrofluorimetric detection technique. This method is based on the oxidation of homocysteine with Tl (III) in acidic media, producing fluorescence reagent, TlCl₃^2- (λ_ex = 237 nm, λ_em = 419 nm). The effects of chemical parameters (including pH of the solutions, the buffer, Tl (III) and potassium chloride concentrations), instrumental parameters (such as flow rate of the solutions, reaction coil length, and sample loop volume) and temperature on the fluorescence intensity as an analytical signal are studied and optimized. In the optimum conditions of the above variables, homocysteine can be determined in the range 4.0 × 10^-7–40.0 × 10^-6 M with the LDR from 4.0 × 10^-7 to 25.0 × 10^-6 M. The detection limit (with S/N = 3) is 6.0 × 10^-8 M of homocysteine and precision for the injection of 5.0, 10.0 and 15.0 μM of homocysteine are 0.8%, 1.5% and 2.5% (n = 10) respectively. The rate of analysis is 90 samples per hour. The influence of potential interfering substances, including amino acids and carbohydrates is also studied. The proposed method has been successfully used for the determination of homocysteine in the real sample (blood serum and tap water) matrix.     

Fluorescence Enhancement of the Silver Nanoparticales – Curcumin - Cetyltrimethylammonium Bromide-nucleic Acids System and its Analytical Application

It is found that silver nanoparticles (AgNPs) can further enhance the fluorescence intensity of curcumin (CU) - cetyltrimethylammonium bromide (CTAB) – nucleic acids and improve its anti-photobleaching activity. Under optimum conditions, the enhanced fluorescence intensity is proportion to the concentration of nucleic acids in the range of 2.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for fish sperm DNA (fsDNA), 2.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for calf thymus DNA (ctDNA), 1.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for yeast RNA (yRNA), and their detection limits (S/N = 3) are 8.0 ng mL⁻¹, 10.5 ng mL⁻¹ and 5.8 ng mL⁻¹, respectively. This method is used for determining the concentration of DNA in actual sample with satisfactory results. The interaction mechanism is also studied.     

Estimation of the deformation-potential constant for <Emphasis Type="Italic">p</Emphasis>-type isotropic polycrystalline silicon through the deformation potential of a <Emphasis Type="Italic">p</Emphasis>-type silicon single crystal

A method of calculating the effective deformation-potential constant E ₁ for holes and longitudinal acoustic phonons in isotropic polycrystalline silicon is suggested. The deformation-potential constant E ₁ is estimated through the deformation potentials a, b, and d of the silicon single crystal. The procedure of averaging of the squared modulus of the hole and acoustic phonon interaction Hamiltonian written in the plane wave basis over the polycrystal ensemble provides the basis for calculation of the constant E ₁ . It is demonstrated that for T = 200–600 K, hole concentration p = (5.0–10.0)∙10¹⁹ cm^–3, and crystallite size d = 300–3000 ?, the deformationpotential constant E ₁ is independent of the hole concentration p, temperature T, and crystallite size d.     

Absolute, high resolution water transpiration rate measurements on single plant leaves via tunable diode laser absorption spectroscopy (TDLAS) at 1.37 μm

A new sampling-free and calibration-free multi-channel hygrometer using near infrared (NIR) tunable diode laser absorption spectroscopy (TDLAS) at 1.37 μm was developed and used to determine absolute transpiration rates of single plant leafs. Four 8×6× 4 cm³, fiber-coupled absorption cells are used to simultaneously measure absolute water vapor concentrations with an absolute accuracy of about 5% and a temporal resolution of about 2 s. Two chambers (BOTTOM, TOP) are directly attached to the leaf surface, while two chambers (IN, OUT) analyze the purge gas supplied to the plant leaf and the total outflow of the leaf chambers. The BOTTOM–TOP comparison provided a direct, leaf-side resolved ratio of stomatal conductance and–by taking into account the purge gas flow and the leaf area exposed–leaf side resolved water transpiration rates. The OUT–IN-difference yielded the total leaf transpiration rate with 2 μmol/m²/s resolution. The new multi-point hygrometer was validated by monitoring of the transpiration dynamics of a plant of the species Epipremnum pinnatum (L.) Engl. during diurnal variation of the leaf irradiation. During these experiments the differential H₂O concentration resolution between two chambers was determined to be better than 3 ppm at Δt= 2 s (i.e. better than 711 ppb m Hz^1/2). This performance was verified by an Allan analysis over a 30 min time period using CH₄ as a surrogate absorber and yielded an average optimum optical resolution of 4.9×10^-6 for 83 s measurement time, i.e. a CH₄ resolution of 892 ppb, which corresponds to the optical resolution needed for a water sensitivity of 454 ppb m Hz^1/2. PACS  07.57.Ty; 42.62.Fi; 42.62.Be; 42.55.Px; 82.80.Gk     

Differential elastic cross-sections of excited exotic hydrogen atoms

Differential cross-sections for the elastic scattering of excited exotic hydrogen atoms by hydrogenic atoms are calculated for the first time. The calculations are performed for exotic atoms (μ a,π a; a=p,d,t) in the states with the principal quantum numbers n=2-10 at relative motion energies E=0.001-15 eV and at scattering angles ϑ =0–180^00B0;. This revised version was published online in August 2006 with corrections to the Cover Date.     

Online Monitoring of Bromate in Ozonized Water Without a Previous Separation Process

The use of ozonation for the purification of drinking water can lead to the formation of bromate. The US Environmental Protection Agency and the European Directive for human drinking water has lowered the regulatory level for bromate down to 10 μg l⁻¹, such that methods must be developed for monitoring the formation of bromate, particularly in on-site situations. In the present work we report a fluorometric method for the determination of bromate based on the reaction with carbostyril-124, a compound that shows florescence mainly at pH values above 4 and, when bromated, generates a non-fluorescent product. The reaction can thus be used as an indirect method for determination of the ion. The proposed method, which uses the flow injection (FI) technique, allows online application and kinetic control of the variables affecting the process, together with shorter reaction times, and it provides maximum sensitivity and selectivity. Under optimum conditions, it is possible to determine the analyte within the 4–200 μg l⁻¹ range, with a limit of detection of 0.9 μg l⁻¹ and a relative standard deviation (n = 12, [] = 5 and 30 μg l⁻¹) of 3.2% and 2.6% respectively. The determination rate was ten samples per hour.     

Study of resonance Raman cross section of aqueous <Emphasis Type="BoldItalic">β</Emphasis> -carotene at low concentrations

Applying Teflon-AF waveguide cell, we determined the absolute resonance Raman cross sections (RCS) for C=C and C-C stretching modes of β-carotene in aqueous solution at low concentrations (10^-6–10^-10 M) by measuring Raman intensity. It was unexpected that the RCS increased rapidly with the decrease of concentration at extremely low concentration range (10^-8–10^-10 M), and it reached the value of 1.22×10^-21 cm² molecule^-1Sr^-1 at 2.5×10^-10 M larger than general RCS (10^-30 cm² molecule^-1Sr^-1) for 10⁹ times. Additionally, we give the tentative theory exploration for the experimental results that the large RCSs at low concentrations attributed to both resonance Raman effect and dipole-induced dipole interactions between solute and solvent molecules. PACS 33.20.Fb; 87.64.Je; 42.81.Wg     

Application of Functionalized ZnSe Nanoparticles to Determinate Heavy Metal Ions

In this paper, ZnSe nanoparticles, which were modified with mercaptoacetic acid (MAA), worked as novel fluorescence sensors for the quantitative determination of copper(II) and nickel(II). Under the optimal conditions, the fluorescence intensities of functionalized ZnSe nanoparticles were quenched by the addtion of copper(II) or nickel(II) ions, there were linear relationships between the relative fluorescence intensity (logF₀/F) and the concentration in the range of 140–2,000 μg/L for copper(II) (R = 0.9973) and 30–1,000 μg/L for nickel(II) (R = 0.9992), the limits of detection were 50 μg/L and 5 μg/L, respectively.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

Study of optical properties and molecular structure of plasma polymerized diethylene glycol dimethyl ether

This paper deals with plasma polymerization processes of diethylene glycol dimethyl ether. Plasmas were produced at 150 mtorr in the range of 10 W to 40 W of RF power. Films were grown on silicon and quartz substrates. Molecular structure of plasma polymerized films and their optical properties were analyzed by Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy. The IR spectra show C–H stretching at 3000–2900 cm^-1, C=O stretching at 1730–1650 cm^-1, C–H bending at 1440–1380 cm^-1, C–O and C–O–C stretching at 1200–1000 cm^-1. The concentrations of C–H, C–O and C–O–C were investigated for different values of RF power. It can be seen that the C–H concentration increases from 0.55 to 1.0 au (arbitrary unit) with the increase of RF power from 10 to 40 W. The concentration of C–O and C–O–C decreases from 1.0 to 0.5 au in the same range of RF power. The refraction index increased from 1.47 to 1.61 with the increase of RF power. The optical gap calculated from absorption coefficient decreased from 5.15 to 3.35 eV with the increase of power. Due to its optical and hydrophilic characteristics these films can be applied, for instance, as glass lens coatings for ophthalmic applications.     

Gamma-ray irradiation effects on distributed-feedback laser diodes

Since laser diodes are increasingly used in harsh environments, the effect of irradiation on their performance attracts a lot of attention. We perform experiments for investigating the irradiation effects on laser diodes with distributed feedback operating at 1550 nm output wavelength with 2 mW output power. The radiation source is Co⁶⁰ gamma ray with a dose rate of 0.5 Gy/s and the dose range within 10² – 8 ∙ 10³ Gy. We study experimentally the threshold current, slope efficiency, and spectrum versus the variations in total dose. The results show that the threshold current increases exponentially and the slope efficiency decreases with increase in total dose. In addition, some sharp peaks appear in the spectrum at small driving current, and the spectrum broadens when the driving current increases and, meanwhile, the peak blue shift is observed. The spectrum can be recovered after annealing for 12 hours and when a greater driving current is applied.     

Fluorescence Enhancement Effect for the Determination of Polychlorinated Biphenyls with Bovine Serum Albumin

A sensitive and selective method for the trace determination of 3, 3’, 4, 4’-tetrachlorobiphenyl (PCB77) by using bovine serum albumin (BSA) as a fluorescence probe was introduced. Under optimum conditions, the enhanced fluorescence intensity was proportional to the concentration of polychlorinated biphenyls in the range of 8.9 × 10⁻⁸–5.0 × 10⁻⁶ mol L⁻¹ for PCB77, and 5.0 × 10⁻⁷–5.0 × 10⁻⁶ mol L⁻¹ for 2, 2’, 5, 5’-tetrachlorbiphenyl (PCB52). The detection limits (S/N = 3) of PCB77 and PCB52 were 2.6 × 10⁻⁸ mol L⁻¹ and 2.9 × 10⁻⁷ mol L⁻¹, respectively. Furthermore, the fluorescence enhancement mechanism was discussed in detail. Results indicated that fluorescence enhancement of the system originated from the formation of BSA-PCBs complexes. In addition, PCBs were mainly bound to the tyrosine residues in BSA molecules.     

Fabrication of a nanoparticle TiO<Subscript>2</Subscript> photoelectrochemical cell utilizing a solid polymeric electrolyte of PAN–PC–LiClO<Subscript>4</Subscript>

A nanoparticle TiO₂ solid-state photoelectrochemical cell utilizing as a solid electrolyte of poly(acrylonitrile)–propylene–carbonate–lithium perchlorate (PAN–PC–LiClO₄) has been fabricated. The performance of the device has been tested in the dark and under illumination of 100-mW cm⁻² light. A nanoparticle TiO₂ film was deposited onto indium tin oxide-covered glass substrate by controlled hydrolysis technique assisted with spin-coating technique. The average grain size for the TiO₂ film is 76 nm. LiClO₄ salt was used as a redox couple. The room temperature conductivity of the electrolyte is 4.2 × 10⁻⁴ S cm⁻¹. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows the rectification property in the dark and shows the photovoltaic effect under illumination. The best J _sc and V _oc of the device were 2.82 μA cm⁻² and V _oc of 0.58 V, respectively, obtained at the conductivity of 4.2 × 10⁻⁴ S cm⁻¹ and intensity of 100 mW cm⁻². The J _sc was improved by about three times by introducing nanoparticle TiO₂ and by using a solid electrolyte of PAN–PC–LiClO₄ replacing PVC–PC–LiClO₄ in the device. The current transport mechanism of the cell is also presented in this paper.