The study of the speciation of uranyl–sulphate complexes by UV–Vis absorption spectra decomposition

Uranyl–sulphate complexes are the predominant U(VI) species present in acid solutions resulting either from underground uranium ore leaching or from the remediation of leaching sites. Thus, the study of U(VI) speciation in these solutions is of practical significance. The spectra of UO₂(NO₃)₂ + Na₂SO₄ solutions of different Φ _S = [SO₄²⁻]/[U(VI)] ratio at pH = 2 were recorded for this purpose. As the presence of uranyl-nitrate complexes should be expected under these experimental conditions, the spectra of UO₂(NO₃)₂ + NaNO₃ solutions with different Φ _N = [NO₃⁻]/[U(VI)] ratio at pH = 2 were also measured. The effects of Φ _S and Φ _N ratios value were most pronounced in wavelength interval 380–500 nm. Therefore, these parts of experimental overall spectra were used for deconvolution into the spectra of individual species by the method proposed. It enabled to calculate stability constants of anticipated species at zero ionic strength. The Specific Ion Interaction Theory (SIT) was used for this purpose. Stability constants of UO₂SO₄, UO₂(SO₄)₂²⁻, UO₂NO₃ ⁺ and UO₂(NO₃)₂ coincided well with published data, but those for UO₂(SO₄)₃⁴⁻ and UO₂(NO₃)₃⁻ were significantly lower.     

Novel PEI–AuNPs–MnIIIPPIX nanocomposite with enhanced peroxidase-like catalytic activity in aqueous media

Mn porphyrin provides a possibility to constitute the novel mimic catalyst with peroxidase-like activity. A simple method for preparing a novel catalyst PEI–AuNPs–Mn^IIIPPIX, used in aqueous media, was presented in this paper. The covalent anchoring of Mn^IIIPPIX and PEI were verified, meanwhile gold nanoparticles with the diameter less than 10 nm were dispersed uniformly and stably. The remarkable peroxidase-like catalytic activity of PEI–AuNPs–Mn^IIIPPIX was displayed in the oxidative degradation of azo dye acid orange 7 (AO7) as the model reaction in the presence of trace of H₂O₂. The synergistic effects of PEI–AuNPs and Mn^IIIPPIX on the enhancement of catalytic activity were observed at pH 2.0. Possible pathways involving in the formation of active radicals are proposed. The construction of PEI–AuNPs–Mn^IIIPPIX nanocomposite offers a new insight into the application of Mn porphyrin upon activation of H₂O₂, which have potential applications in many fields.     

Highly efficient UV–visible absorption of TiO2/Y2O3 nanocomposite prepared by nanosecond pulsed laser ablation technique

Nanostructured TiO₂-based composites are promising materials because of their superior optical, structural, and electronic properties relative to pristine nanostructured TiO₂. The enhanced properties of TiO₂-based composites have been used in several important applications such as gas sensors, solar cells, and photocatalytic applications. In the past, numerous materials have been coupled with TiO₂ to enhance their optical properties. In this work, full-spectrum (UV and Visible) responsive TiO₂ /Y₂O₃ nanocomposite has been synthesized via pulsed laser ablation in liquid (PLA) to study the impact of Y₂O₃ on the structural, morphology, and optical property of the TiO₂. The nanostructured composites prepared were characterized by XRD, Raman spectroscopy, Field-Emission Scanning Electron Microscope (FESEM) attached with Energy-Dispersive X-ray spectroscopy (EDX), Photoluminescence, XPS, and UV–Vis absorbance spectra. The result demonstrates that the coupling Y₂O₃ with TiO₂ not only changes the structural, optical, and morphology of the TiO₂ but also significantly amplified the light absorption characteristics of the TiO₂ within the UV and visible region. The synthesized TiO₂ /Y₂O₃ nanocomposite could potentially be useful for visible-light responsive applications.     

Gold nanorod separation and characterization by asymmetric-flow field flow fractionation with UV–Vis detection

The application of asymmetric-flow field flow fractionation (A4F) for low aspect ratio gold nanorod (GNR) fractionation and characterization was comprehensively investigated. We report on two novel aspects of this application. The first addresses the analytical challenge involved in the fractionation of positively charged nanoparticles by A4F, due to the interaction that exists between the negatively charged native membrane and the analyte. We show that the mobile phase composition is a critical parameter for controlling fractionation and mitigating the membrane-analyte interaction. A mixture of ammonium nitrate and cetyl trimethyl ammonium bromide at different molar ratios enables separation of GNRs with high recovery. The second aspect is the demonstration of shape-based separation of GNRs in A4F normal mode elution (i.e., Brownian mode). We show that the elution of GNRs is due both to aspect ratio and a steric-entropic contribution for GNRs with the same diameter. This latter effect can be explained by their orientation vector inside the A4F channel. Our experimental results demonstrate the relevance of the theory described by Beckett and Giddings for non-spherical fractionation (Beckett and Giddings, J Colloid and Interface Sci 186(1):53–59, 1997). However, it is shown that this theory has its limit in the case of complex GNR mixtures, and that shape (i.e., aspect ratio) is the principal material parameter controlling elution of GNRs in A4F; the apparent translational diffusion coefficient of GNRs increases with aspect ratio. Finally, the performance of the methodology developed in this work is evaluated by the fractionation and characterization of individual components from a mixture of GNR aspect ratios.     

Characterisation of Ni carbonate-bearing minerals by UV–Vis–NIR spectroscopy

Four nickel carbonate-bearing minerals from Australia have been investigated to study the effect of Ni for Mg substitution. The spectra of nullaginite, zaratite, widgiemoolthalite and takovite show three main features in the range of 26,720–25,855 cm⁻¹ (ν₁-band), 15,230–14,740 cm⁻¹ (ν₂-band) and 9,200–9,145 cm⁻¹ (ν₃-band) which are characteristic of divalent nickel in six-fold coordination. The Crystal Field Stabilization Energy (CFSE) of Ni²⁺ in the four carbonates is calculated from the observed ³A_2g(³F) → ³T_2g(³F) transition. CFSE is dependent on mineralogy, crystallinity and chemical composition (Al/Mg-content). The splitting of the ν₁- and ν₃-bands and non-Gaussian shape of ν₃-band in the minerals are the effects of Ni-site distortion from regular octahedral. The effect of structural cation substitutions (Mg²⁺, Ni²⁺, Fe²⁺ and trivalent cations, Al³⁺, Fe³⁺) in the carbonate minerals is noticed on band shifts. Thus, electronic bands in the UV–Vis–NIR spectra and the overtones and combination bands of OH and carbonate ion in NIR show shifts to higher wavenumbers, particularly for widgiemoolthalite and takovite.     

Constructing holey γ-Fe2O3 nanosheets with enhanced capability for microwave absorption

Iron-based nanostructured materials are desirable for various applications owing to their high magnetization. Herein, we presented a facile fabrication of free-standing γ-Fe₂O₃ nanosheets by a molten salt method for microwave absorption. Furthermore, Al component was incorporated to serve as the template for hole production. The designed holey γ-Fe₂O₃ nanosheets were effective to maximize the usage of nanomaterials, thereby providing larger surface area, richer defects, and more polarization centers. Both experimental measurements and electric field simulation showed an enhanced capability for microwave absorption using holey γ-Fe₂O₃ when compared with its intact counterpart. Oxygen vacancy was generated during the hole evolution, which significantly improved the electrical conductivity and thus promoted the conductive loss mechanism. In addition, the holey configuration may extend the transmission path of microwave and confer it with multiple reflection and scattering within the absorbent matrix. Meantime, the polarization loss was strengthened owing to Al modulation associated with the induced defect sites. With the improvement in conductive loss, polarization, impedance matching, and attenuation constant, the as-synthesized holey γ-Fe₂O₃ exhibited promising microwave absorbability, with a maximum reflection loss of 52.4 dB and an effective bandwidth of 5.12 GHz at a thickness of 2.2 mm, overperforming most pure Fe-based materials.     

Chlorine Dioxide–Iodine–Ethyl 2-Chloroacetoacetate Oscillation Reaction Investigated by UV–Vis and Online FTIR Spectrophotometric Methods

In order to study the chemical oscillatory behavior and mechanism of a new chlorine dioxide–iodine–ethyl 2-chloroacetoacetate reaction system, a series of experiments were carried out by using UV–Vis and online FTIR spectrophotometric methods. The initial concentrations of ethyl 2-chloroacetoacetate, chlorine dioxide, iodine, sulfuric acid, and the pH value have great influence on the oscillations observed at wavelength of 585 nm for the starch–triiodide complex ( \( \text{QI}_{3}^{ - } \) ). There is a pre-oscillatory or induction stage, the amplitude and the number of oscillations are associated with the initial concentration of reactants. Equations were obtained for the starch–triiodide complex reaction rate change with reaction time and the initial concentrations in the oscillation stage. The intermediates were detected by the online FTIR analysis. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.     

UV–Vis spectroscopy with chemometric data treatment: an option for on-line control in nuclear industry

Chemometrics can be very useful for the classical field of UV–Vis determination of metals in aqueous solutions. A conventional approach consisting of using selective bands in a univariate mode is often not applicable to the real-world samples from e.g. hydrometallurgical processes, because of overlapping signals, light scattering on foreign particles, gas bubble formation, etc. And this is where chemometrics can do a good job. This paper overviews certain contributions to the field of multivariate data processing of UV–Vis spectra for seemingly simple case of metal detection in aqueous solutions. Special attention is given to applications in nuclear technology field.     

Photoluminescence and enhanced visible light driven photocatalysis studies of MoO3·CuO·ZnO nanocomposite

Research on Chemical Intermediates - A trimetallic, MoO3·CuO·ZnO nanocomposite was synthesized by co-precipitation method. The nanocomposite was characterized by X-ray...     

Bicarbazole-based oxalates as photoinitiating systems for photopolymerization under UV–Vis LEDs

Photoinitiators are critical to initiate chain reactions in photopolymerization. For such applications, the absorption of photoinitiator must be compatible with the emission of light sources and enables the fast manufacturing of three-dimensional network or structures. Light-emitting diode (LED) is a new kind of energy-saving and environmental protection light source, exhibiting a substantial response in the near UV and visible range to replace the traditional mercury lamp and other light sources in photopolymerization. Here, we introduce methyl oxalate into bicarbazole chromophore ( BiCz ). By variation of the single or double substituents in the BiCz , we demonstrate that the absorption spectra can be adjusted and redshift to visible range and show good absorption in the near UV and visible range (365–475 nm). We explore their photochemistry based on experimental results and theoretical calculations and the mechanism of photoreactions have been verified. The super photostability by themselves and good hydrogen abstraction ability from amine co-initiator make them as excellent near UV and visible light active photoinitiators. Critically, the photoinitiation of the free-radical polymerization of acrylate monomers with low content (0.1% concentration) upon LED irradiation at 365–475 nm, exhibits excellent application potential in light curing and other fields.     

Preparation,magnetic properties and microwave absorption of Zr–Zn–Co substituted strontium hexaferrite and its nanocomposite with polyaniline

Russian Journal of Applied Chemistry - M-type strontium hexaferrite substituted by Zr4+, Zn2+, and Co2+ was firstly synthesized by a sol-gel auto combustion method. Then the polyaniline/hexaferrite...     

Chlorine Dioxide–Iodine–Sodium Thiosulfate Oscillating Reaction Investigated by the UV–Vis Spectrophotometric Method

A new chlorine dioxide–iodine–sodium thiosulfate chemical oscillatory reaction was studied by the UV–Vis spectrophotometric method. The initial concentrations of sodium thiosulfate, chlorine dioxide, iodine, sulfuric acid, and pH have great influences on the oscillations observed at wavelength 238 nm. The oscillations occur as long as the reactants are mixed. The amplitude and the number of oscillations are associated with the initial concentrations of reactants. The equations for the triiodide ion reaction rate changes with reaction time and the initial concentrations in the oscillation stage are an attenuation sine function. Based upon the experimental data in this work and in the literature, a plausible reaction mechanism was proposed for the oscillation reaction.     

UV–Vis spectra and structure of acid-base forms of dimethylamino- and aminoazobenzene

The changes in the UV–Vis absorption spectra of dimethylaminoazobenzene (DAB) in the cellulose triacetate (CTA) matrix during the absorption of gaseous hydrogen chloride and protonation of DAB in weakly and strongly acid solutions of hydrochloric and sulfuric acids were studied. The yellow-orange color of DAB and its analog aminoazobenzene (AAB) was shown to be due to the dimers, whose structure involves phenylaminyl type cations formed due to the promotion of the sp ² electrons of the azo groups to the Rydberg R _3s orbitals of the azo groups and possessing Vis bands at 400–417 nm. The cations exist immanently as the dimers due to the Rydberg intermonomer bonds; the Vis bands of the dimers shifted toward 500–520 nm under the action of HCl (in CTA) and weakly acid media as a result of the formation of phenyl aminyl type pair cations, whose π* levels are split by Simpson’s mechanism, during the protonation of interrelated monomers. In the concentrated sulfuric acid, the Vis bands at 500–520 nm vanished because of the decomposition of the dimers into diprotonated monomers possessing Vis bands at 400–417 nm. The mechanism of transformations of chromogens responsible for the spectral transformation was given.     

Zn2+ doped ormosil–phosphotungstate hybrid films with enhanced photochromic response

Owing to the wide use of photochromic materials in UV sensors and dosimeters, considerable efforts have been made to increase the UV-response and sensitivity of the existing classes of photochromic materials. In this study, we report a simple sol–gel route for the preparation of highly photochromic transparent films based on ormosil–phosphotungstate hybrid materials. The effect of addition of Zn²⁺ ions on the photochromic response of these hybrid films and the possible mechanism involved is discussed. Compared to the undoped samples, the photochromic response of the Zn²⁺-doped hybrid films increases by 59–237 % depending on the concentration of Zn²⁺ ions added to the sol formulation. No structural or electronic change in the phosphotungstate dye was observed by vibrational spectroscopy or UV spectroscopy, though micro X-ray fluorescence (μ-XRF) analysis showed that the addition of Zn²⁺ in the sol–gel preparations leads to an increase in the amount of phosphotungstate (HPW) incorporated in the dip-coated films. Furthermore, TEM and nano-energy-dispersive X-ray showed formation of nano-agglomerates consisting of Zn and HPW in the Zn²⁺-doped samples. Zn K-edge X-ray absorption near edge structure analysis also confirmed the formation of the salt H_x[Zn(OH₂)₆] _2?xPW₁₂O₄₀. It is suggested that these Zn-phosphotungstate nano-agglomerates get trapped into the ormosil network during films preparation leading to increased concentration of the phosphotungstate anions in the films, in accordance with results from μ-XRF analysis. Raman spectroscopy confirmed that the Keggin structure of HPW is preserved in the hybrid films. FTIR spectra of the matrix part of the samples are identical before and after UV-irradiation, which suggests that the photochromic process does not involve oxidation of the organic functionalities. These highly photochromic hybrid films are promising candidates for the design of practical UV-sensing devices and dosimeters.     

CeO2 nanofibers-CdS nanostructures n–n junction with enhanced visible-light photocatalytic activity

In the present work, the n-cerium (IV) oxide (CeO₂)/n-cadmium sulfide (CdS) composite nanofibers were successfully synthesized via a facile electrospinning and hydrothermal synthesis strategy. The physicochemical properties of the synthesized composite nanofibers were investigated by using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy Dispersive X-Ray Spectroscopy (EDS), diffuse Reflectance Spectroscopy (DRS), Fourier-transform infrared (FTIR), photoluminescence (PL), Brunauer–Emmett–Teller (BET) and Raman spectroscopy analysis. The activities of the CeO₂/CdS were evaluated through the photocatalytic degradation of Rose Bengal (RB) in an aqueous solution under blue LED light radiation. CeO₂/CdS composites exhibit higher photocurrent density in photocurrent response experiment and smaller charge-transfer resistance in electrochemical impedance spectroscopy (EIS). Overall, the results confirmed higher charge separation efficiency in CeO₂/CdS composites compared to pristine CeO₂ nanofibers, and CdS, which is related to intimately contact among the CeO₂, and CdS. The present work provides a new approach to construct n-n heterojunction photocatalysts based on electrospinning and a deeper insight for the photocatalytic degradation activity. In addition, possible degradation mechanism and pathways were proposed according to the identified intermediates.