UV-vis Absorption Spectroscopy Studies Research Articles

UV–vis absorption spectroscopic study for on-line monitoring of uranium concentration in LiCl–KCl eutectic salt

UV–vis absorption spectroscopy of uranium in LiCl–KCl eutectic salt at 773K was studied for the on-site use in pyrochemical process. Uranium(III) chloride was electrochemically prepared from uranium metal in LiCl–KCl eutectic salt at 773K by using chronopotentiometry. Three absorption peak positions were selected and calibrated for the quantitative analysis of uranium in the molten salt medium. The molar absorptivity and minimum detectable concentration for the selected wavelength were obtained with a confidence level of 99%.

Facile synthesis of near-monodisperse Ag@Ni core–shell nanoparticles and their applicationfor catalytic generation of hydrogen

Magnetically recyclable Ag–Ni core–shell nanoparticles have been fabricatedvia a simple one-pot synthetic route using oleylamine both as solvent andreducing agent and triphenylphosphine as a surfactant. As characterized bytransmission electron microscopy (TEM), the as-synthesized Ag–Ni core–shellnanoparticles exhibit a very narrow size distribution with a typical size of14.9 ± 1.2 nm and a tunable shell thickness. UV–vis absorption spectroscopy study shows thatthe formation of a Ni shell on Ag core can damp the surface plasmon resonance(SPR) of the Ag core and lead to a red-shifted SPR absorption peak. Magneticmeasurement indicates that all the as-synthesized Ag–Ni core–shell nanoparticlesare superparamagnetic at room temperature, and their blocking temperaturescan be controlled by modulating the shell thickness. The as-synthesized Ag–Nicore–shell nanoparticles exhibit excellent catalytic properties for the generation ofH2 from dehydrogenation of sodium borohydride in aqueous solutions. The hydrogengeneration rate of Ag–Ni core–shell nanoparticles is found to be much higher than that ofAg and Ni nanoparticles of a similar size, and the calculated activation energyfor hydrogen generation is lower than that of many bimetallic catalysts. Thestrategy employed here can also be extended to other noble-magnetic metal systems.

Effect of thermal annealing on the formation of silicon nanoclusters in SiO X films grown by PLD

Silicon nanoclusters formation in pulsed laser deposited (PLD) silicon suboxide (SiO X ) films by thermal annealing is reported. The SiO X films are prepared by ablation of silicon target at different oxygen partial pressures. The different deposition conditions are employed to study the effect of oxygen concentration on the size of the nanoclusters. Post deposition thermal annealing of the films leads to the phase separation in silicon suboxide films. Fourier transform infrared spectroscopy, micro-Raman spectroscopy and UV–vis absorption spectroscopy studies were carried out to characterize the formation of silicon nanoclusters in SiO X films.

Donor-π-Acceptor Double-Cable Polythiophenes Bearing Fullerene Pendant with Tunable Donor/Acceptor Ratio: A Facile Postpolymerization

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ChemInform Abstract: Spectroscopic and Kinetic Studies of the Aldehyde-Lactol Tautomerization of Gossypol in Solution

1 H NMR spectra of gossypol in C2H5OD solution show that an equilibrium between aldehyde 1 and lactol 2 tautomers is formed and that the aldehyde tautomer is predominant, whereas in C2H5OD–DCl solution (pH ⩽ 1) only the lactol form is observed. UV–VIS absorption spectroscopy studies demonstrate that in ethanol and ethanol–HCl solutions gossypol shows different spectra which can be attributed to both tautomers 1 and 2. The influence of various solvents on the 1⇌2 equilibrium is studied by means of UV–VIS absorption spectroscopy and the results are compared with those of 1H NMR studies. Furthermore, the decrease of the absorbance at the long wavelength band in the spectrum of 1 is used to determine the kinetic parameters of aldehyde–lactol tautomerization in ethanol–HCl solution (pH ⩽ 3): k298=(2.14 ± 0.03) 10–2 dm3 mol–1 s–1; ΔH≠= 64.0 ± 3.4 kJ mol–1; ΔS≠=–63 ± 11 J mol–1 K–1; and the value of kinetic isotope effects, kH/kD= 5.6 at 55 °C. A mechanism for aldehyde–lactol tautomerization of gossypol is proposed.

Donor-π-acceptor double-cable polythiophenes bearing fullerene pendant with tunable donor/acceptor ratio: A facile postpolymerization

A novel type of donor-π-acceptor double cable poly(3-hexylthiophene) (P3HT) derivative bearing a fullerene pendant and a phenyl group as the linking bridge between the P3HT donor and C60 acceptor (C60-Ph-P3HT-1,2,3,4) with tunable donor/acceptor ratio was synthesized via a facile postpolymerization functionalization. The molecular structure, electronic property and molecular arrangement, as well as the surface morphology of the synthesized C60-Ph-P3HT-1,2,3,4 were characterized by FTIR, 1H NMR, UV-Vis and fluorescence emission spectroscopies, XRD and AFM. FTIR and 1H NMR spectroscopic studies confirm the polymeric structures of C60-Ph-P3HT-1,2,3,4 with the successful grafting of the C60 moiety with tunable donor/acceptor ratio (wt.% ∼1 : 1; 1 : 0.9; 1 : 0.8; 1 : 0.6). UV-Vis absorption spectroscopic study confirms the nature of C60-Ph-P3HT as the mono-adduct of C60, and indicates a very weak perturbation of the molecular arrangement of the P3HT backbone upon the grafting of the C60 pendant. The fluorescence intensity of C60-Ph-P3HT-1,2,3,4 is found to be dramatically quenched compared to that of the P3HT and P3HT/C60 (1 : 1) blend, and notably, C60-Ph-P3HT-1 approaches 98% quenching. The molecular arrangement of C60-Ph-P3HT is investigated by XRD analysis, suggesting that the grafted C60 moieties in the side chain slightly interferes with the lamellar stacking of the polythiophene main chain of P3HT. The AFM measurements on the surface film morphology of C60-Ph-P3HT-1,2,3,4 reveal that the rms roughness of C60-Ph-P3HT-1,2,3,4 is larger than that of P3HT.

Direct electrochemistry of catalase at multiwalled carbon nanotubes-nafion in presence of needle shaped DDAB for H 2O 2 sensor

The direct electrochemistry of catalase (CAT) at didodecyldimethylammonium bromide (DDAB) present on nafion dispersed multiwalled carbon nanotubes (MWCNTs-NF) modified glassy carbon electrode (GCE) has been reported. The presence of DDAB in MWCNTs-NF-CAT film enhances the surface coverage concentration of CAT (Fe III/II) to 48%. Similarly, in presence of DDAB, there is a 57% enhancement in electron transfer rate ( k s) with 66% increase in CAT stability. (Fe III/II) redox couple exhibits linear dependence with the pH variation (−51 mV pH −1). The UV–vis absorption spectroscopy study reveals the entrapped CAT in DDAB film retains its native structure at MWCNTs-NF modified electrodes. Similarly, electrochemical impedance spectroscopy results confirm the co-existence of CAT and DDAB in the modified film. Further, scanning electron microscopy results reveal the structural morphological difference between various components in MWCNTs-NF-(DDAB/CAT) film. The cyclic voltammetry (CV) and amperometry ( i– t curve) have been used for the measurement of electroanalytical properties of H 2O 2 by means of various film modified GCEs. The sensitivity values of MWCNTs-NF-(DDAB/CAT) film for H 2O 2 using CV (35.62 μA mM −1 cm 2) are higher than the values which are obtained for MWCNTs-NF-CAT film (2.74 μA mM −1 cm 2). Similarly, the sensitivity values using i– t curve are 101.74 μA mM −1 cm 2 for MWCNTs-NF-(DDAB/CAT) and 74.69 μA mM −1 cm 2 for MWCNTs-NF-CAT film. Finally, the diffusion coefficient of H 2O 2 at MWCNTs-NF-(DDAB/CAT) film (3.4 × 10 −10 cm 2 s −1) has been calculated using rotating disc electrode studies.

AGGREGATION OF P-TERPHENYL ALONG WITH PMMA/SA AT THE LANGMUIR AND LANGMUIR–BLODGETT FILMS

Molecular aggregation and monolayer characteristics of non-amphiphilic p-terphenyl (TP) mixed with either polymethyl methacrylate (PMMA) or stearic acid (SA) at the air–water interface were investigated. The miscibility of the two components was evaluated by measuring and analyzing surface pressure versus area per molecule (π–A) isotherm. Both attractive and repulsive interactions between the sample (TP) and the matrix (PMMA or SA) were observed depending on the composition and microenvironment. TP and PMMA/SA were not completely miscible in the mixed monolayer. Aggregation and phase separation between sample TP and matrix molecule were revealed by UV–Vis absorption spectroscopic studies and confirmed by scanning electron micrograph of Langmuir–Blodgett films.

X-ray radiolysis induced formation of silver nano-particles: A SAXS and UV–visible absorption spectroscopy study

We show that X-ray irradiation of metal salt aqueous solutions in the absence of any stabilizer leads to the synthesis of metal nano-particles, similarly to γ-ray irradiation. The chemical route is the reduction of silver metal ions induced by radiolysis of water. Moreover, X-rays used for the synthesis allow following in situ the formation of silver nano-particles by Small Angle X-ray Scattering associated with UV–visible absorption spectroscopy. The synthesized nano-objects appear spherical with a radius of about 14 nm.

Role of various LB parameters on the optical characteristics of mixed Langmuir–Blodgett films

This communication reports the spectroscopic characterizations of mixed Langmuir–Blodgett (LB) films of non-amphiphilic N, N-bis (2,5-di-tert-butylphenyl)- 3,4,9-perylenedicarboximide (DBPI) molecules, mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). J- aggregates of DBPI molecules in the mixed LB films have been confirmed by UV–Vis absorption spectroscopic study. Formation of organized structure of molecular stacking in the mixed LB films gives rise to the strong excimeric emission, which is manifested by a broad structureless band in the longer wavelength region of the fluorescence spectra and is confirmed by excitation spectroscopic study. A weak hump at around 576 nm due to monomeric emission is observed in the fluorescence spectra of 0.1 M of DBPI-PMMA mixed LB films of lower number of layers. The intensity of the 0–0 band at 530 nm in the fluorescence spectra is observed to be a function of the molefraction, number of layers, surface pressure of lifting and the matrix materials.

Langmuir and Langmuir-Blodgett film preparation and study of a metalloporphyrin dimer molecule

Two iron complexes of a porphyrin dimer molecule were synthesized and studied at the air-water interface and in Langumir-Blodgett (LB) films. Surface pressure-area isotherm and UV-vis absorption spectroscopic studies revealed an interesting molecular switching behavior between the two iron porphyrin complexes under basic or acidic conditions. Such a reversible structural transition does not only occur in solution phase, but readily takes place in the deposited Langmuir-Blodgett films. Domains with strip or disk-like shapes were formed in the Langmuir films of the metalloporphyrin complexes when barbituric acid was added into the subphase, an indication of supramolecular network formation between the metalloporphyrin dimer and barbituric acid molecules. Magnetic property studies of the Langmuir-Blodgett films of the iron porphyrin complexes by magnetic force microscopy provide further insights into relationships between the magnetic response and molecular structures of the metalloporphyrin LB films.

Spectroscopic characterizations of non-amphiphilic 2-(4-biphenylyl)-6-phenyl benzoxazole molecules at the air–water interface and in Langmuir–Blodgett films

This communication reports about the successful incorporation of a well-known non-amphiphilic derivative of oxazole chromophore 2-(4-biphenylyl)-6-phenyl benzoxazole abbreviated as PBBO, in Langmuir–Blodgett films when mixed with stearic acid (SA) as well as also an inert polymer matrix polymethylmethacrylate (PMMA). The surface pressure versus area per molecule isotherms of the Langmuir films of PBBO mixed with PMMA or SA at different mole fractions reveal that the area per molecule decreases consistently with increasing mole fractions of PBBO. Area per molecule versus mole fraction curve shows that the experimental data points coincide with the ideality curve predicted by the additivity rule, which leads to the conclusion of either ideal mixing or complete demixing of the binary components. The UV-vis absorption and fluorescence spectroscopic studies of mixed LB films of PBBO reveal the nature of complete demixing of the binary components of the sample molecules (PBBO) and PMMA or SA molecules. This complete demixing leads to the formation of clusters and aggregates of PBBO molecules in Langmuir and Langmuir–Blodgett films. J-type aggregates of PBBO molecules in LB films have been confirmed by UV-vis absorption spectroscopic study. Aggregation of PBBO molecules in LB films giving rise to excimeric emission has been demonstrated by fluorescence spectroscopic study. Excitation spectroscopic study clearly confirmed the presence of excimeric sites.

Langmuir–Blodgett films of 9-phenyl anthracene molecules incorporated into different matrices

This communication reports the surface pressure ( π) versus area per molecule (A) isotherm characteristics of the mixed films of 9-phenyl anthracene (PA) in stearic acid (SA) and polymethyl methacrylate (PMMA) matrices, at the air–water interface. The mixed Langmuir films at the air–water interface have been observed to be easily transferred onto solid substrates to form uniform Langmuir–Blodgett films. By changing various parameters, namely molefraction, surface pressure of lifting and number of layers, the mixed Langmuir–Blodgett (LB) films of various types have been fabricated successfully and their spectroscopic characteristics have been reported. From the isotherm characteristics and the area per molecule versus molefraction plot, it is evident that the PA molecules are successfully incorporated into mixed Langmuir–Blodgett films. UV–vis absorption spectroscopic study of the mixed LB films at various molefractions of PA in two different matrices reveal that formation of I-type aggregate in PMMA matrix whereas both I- and H-type aggregates are playing their dominant role in SA matrix. Moreover, fluorescence spectroscopic study reveals reabsorption effect. Molecular movement persists in the freshly prepared LB films, as is evident from the time dependent changes in both UV–vis absorption and fluorescence spectra of the mixed LB films in both matrices. From our observation it is evident that about 200 h is required to get the LB films in a stable condition. Dimers and higher order n-mers are formed at a higher surface pressure of 30 mN m −1.

Synthesis and Supramolecular Self-Assembly Study of a Novel Porphyrin Molecule in Langmuir and Langmuir−Blodgett Films

The self-assembly and supramolecular engineering of porphyrins into ordered arrays have recently attracted much interest because of their promising application potential in molecular and electronic devices, spintronics, energy harvesting and storage, catalysis, and sensor development. We herein report the synthesis and supramolecular self-assembly study of a novel porphyrin molecule, 2Por-TAZ, in Langmuir and Langmuir-Blodgett films. The 2Por-TAZ molecule contains two porphyrin macrocycles attached to a triaminotriazine headgroup. Triaminotriazines are known to form a highly ordered linear supramolecular self-assembly through complementary hydrogen bonding with barbituric acid molecules at the air-water interface. Surface pressure-area isotherm measurements and polarized UV-vis absorption spectroscopic studies indicate that the 2Por-TAZ molecules adopted an edge-on orientation at the air-water interface. Polarized UV-vis absorption study also revealed that the 2Por-TAZ molecules formed linear supramolecular networks on pure water and barbituric acid subphase with porphyrin flat planes facing toward the compression direction. The binding of barbituric acid with 2Por-TAZ molecules was observed from the expansion of the Langmuir monolayer film. Compared to the transferred LB film from pure water subphase, both the UV-vis absorbance and fluorescence emission intensity of the LB film transferred from barbituric acid subphase increased significantly.

A cell for combined UV-visible and x-ray absorption spectroscopy studies under low-temperature and air exclusion conditions

A measuring system that integrates a low-temperature optical cell UV-visible (UV-Vis) for air exclusion experiments with a liquid x-ray absorption spectroscopy (XAS) cell (x-ray absorption near-edge spectroscopy and extended x-ray absorption fine structure) is reported here together with its application in studies of organometallic complexes. UV-Vis measurements are performed in a three-compartment glass vessel, fitted with an external fiber optics probe. This UV-Vis cell is suitable for the measurement of oxygen- and air-sensitive compounds at variable temperatures (RT to −78 °C). The liquid XAS cell is filled with the UV-Vis solution at low temperature and can be used in both fluorescence- or transmission-mode measurements with (frozen) solutions. The complete measuring system is reusable and easy to clean and handle. To test the performance of these cells the oxygenation behavior of a dinuclear organometallic copper(I) complex was studied in acetone by UV-Vis and XAS. It is shown that direct correlation of low-temperature UV-Vis and XAS data is possible in organic solvents.

Characterization of mixed Ti/Al oxide thin films prepared by ion-beam-induced CVD

The ion-beam-induced chemical vapor deposition (IBICVD) method has been used for the preparation of TiO 2, Al 2O 3 and mixed oxide Al n Ti m O x amorphous films on silica substrates. Also, a double-layer Al 2O 3/TiO 2 film has been prepared. The reflectivity (low angle X-ray diffraction) technique, together with transmission electron microscopy (TEM) and UV–Vis absorption spectroscopy, have been used to get information about thickness, roughness and electronic density of the films. It has been found that the films are homogeneous and flat being the Al 2O 3 layers less dense than the TiO 2 layers. In particular, Al n Ti m O x films can be prepared with variable composition and refraction index. The values obtained for electronic density by X-ray reflectivity have been correlated with the compaction degree of the films as stated from TEM and UV–Vis absorption spectroscopy studies.

Oxidative polymerization of some monomers with pyrrole moieties—an UV–vis absorption spectroscopy study

Using UV–vis absorption spectroscopy, a study on the electrochemical polymerization of some Schiff’s base—type monomers containing pyrrole moieties was performed. Similar data were obtained for pyrrole polymerization too. Some 1H-NMR spectra are reported and discussed. The spectral changes of the polymerization solutions point out distinctly stages of the electrooxidative polymerization process. The chemical structure of the monomers influences the electronic absorption spectra of the polymers.

Application of Chemometric Methods in UV-Vis Absorption Spectroscopic Studies of Uranyl Ion Dimerization Reaction in Aqueous Solutions

Article Application of Chemometric Methods in UV-Vis Absorption Spectroscopic Studies of Uranyl Ion Dimerization Reaction in Aqueous Solutions was published on August 1, 1998 in the journal Radiochimica Acta (volume 81, issue 4).

UV-Vis absorption spectroscopic studies of plasma-polymerized m-xylene thin films

Plasma-polymerized m-xylene (PPm-X) thin films have been prepared using a dry and flawless process. Films were smooth and of light-tea colour. UV-Vis spectroscopic investigations have been carried out on unannealed, annealed and aged PPm-X thin films to ascertain the effect of annealing temperature and aging on the optical properties of PPm-X. The bandgap, allowed direct transition energy gap and indirect transition energy gap have been determined. The results are discussed in the light of possible structural modification in PPm-X thin film on annealing and aging.

Spectroscopic and kinetic studies of the aldehyde–lactol tautomerization of gossypol in solution

1 H NMR spectra of gossypol in C2H5OD solution show that an equilibrium between aldehyde 1 and lactol 2 tautomers is formed and that the aldehyde tautomer is predominant, whereas in C2H5OD–DCl solution (pH ⩽ 1) only the lactol form is observed. UV–VIS absorption spectroscopy studies demonstrate that in ethanol and ethanol–HCl solutions gossypol shows different spectra which can be attributed to both tautomers 1 and 2. The influence of various solvents on the 1⇌2 equilibrium is studied by means of UV–VIS absorption spectroscopy and the results are compared with those of 1H NMR studies. Furthermore, the decrease of the absorbance at the long wavelength band in the spectrum of 1 is used to determine the kinetic parameters of aldehyde–lactol tautomerization in ethanol–HCl solution (pH ⩽ 3): k298=(2.14 ± 0.03) 10–2 dm3 mol–1 s–1; ΔH≠= 64.0 ± 3.4 kJ mol–1; ΔS≠=–63 ± 11 J mol–1 K–1; and the value of kinetic isotope effects, kH/kD= 5.6 at 55 °C. A mechanism for aldehyde–lactol tautomerization of gossypol is proposed.