Spectroscopical splitting of Cu ion energy levels in magnesium lead fluoro silicate glasses

Homogeneous 40.0 MgO-(10-x) PbF₂-50.0 SiO₂: x CuO glasses were prepared using melt-quenching technique under controlled conditions. Spectroscopic studies (UV-vis absorption, ESR, FT-IR) are carried out for these glasses. One broad characteristic visible absorption band is observed around 700-850 nm in these glasses, the optical band gap decreases as the content of the CuO increases in the glass network up to 0.7 mol % then reversal trend is observed. ESR spectra of all these glasses show resonance peaks characteristic of Cu²⁺ ions and hyperfine splitting is resolved with increasing the CuO content in the glass network. From the observed ESR spectra, the spin-Hamiltonian parameters have been evaluated and indicate that Cu²⁺ ions have octahedral coordination with a strong tetragonal distortion in these glasses. By correlating ESR and optical absorption data, the molecular orbital coefficients have been evaluated. FT-IR spectra give important information about the nature of bonds in the glass matrix. The density of the glasses is also measured and is found to decrease with the increase CuO contents in the glass matrix. The physical parameters along with spectroscopic parameters are measured.     

Effect of Ag nanoparticle addition and ultrasonic treatment on a stable TiO2 nanofluid

Nanoparticles, when homogeneously dispersed in a base fluid, e.g. water, ethylene glycol etc. are commonly known as nanofluids. Nanofluids have gained attention in the scientific community for their enhanced thermal properties. One of the major problems in using nanofluids as a heat transfer medium for commercial applications is that, in most of the closed circuit industrial cooling processes, the cooling fluid has to be replaced after several cycles of cooling operation because of an increased presence of contaminants. If nanofluids were used as a coolant, it would be very hard to separate the nanoparticles from the waste fluid. The present work is aimed at the separation and recycling of nanoparticles from fluid waste by means of quick settling of titanium dioxide nanoparticles using silver nanoparticles along with ultrasonic treatment. It is observed that with increasing silver concentration and time of ultrasonication, the stability of the dispersion decreases. There is a value for both the silver concentration and ultrasonication time above which the settling time decreases drastically.     

Effect of Cr doping on the ac electrical properties of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Magnesium aluminate nanoparticles with different chromium concentration (0–12%) have been synthesized by a citrate–nitrate sol–gel route. X-ray diffraction studies confirmed the formation of single-phase cubic spinel structure excluding the presence of any secondary phase. Crystallite size of the synthesized nanoparticles was found to increase from 8.5 to 19.8 nm with the increase in Cr concentration. Fourier transformed infrared spectroscopic studies confirmed the presence of AlO₆ group which led to the formation of MgAl₂O₄ spinel structure. Surface morphology of the sintered pellets was investigated with the help of a field emission scanning electron microscope which revealed the existence of both grain and grain boundary along with their aggregates. The dielectric constant, dielectric loss and ac conductivity were studied as a function of frequency of the applied electric field for different composition and their nature of variation with frequency has been elucidated on the basis of Maxwell–Wagner interfacial model. Impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of this spinel oxide. All the electrical parameters showed strong dependence on the nanostructural properties and were found to vary consistently with the increase of doping concentration.     

Photophysical characterization of 1,8 naphthalimide in micelle-diblock copolymer nano-composite: a case of morphological transformation and vesicle formation

This paper reports a morphological transition of the spherical colloidal structures of the sodium dodecyl sulfate-polyethylene-b-polyethylene glycol (SDS-PE-b-PEG) complex and anionic micelle (SDS) to "rod-shaped" colloidal structures induced by a charge transfer dye, 1,8-naphthalimide (NAPMD) (forms anions in aqueous solution by intermolecular charge transfer). The distinct steady-state results of NAPMD in the above two media point toward the formation of a new microenvironment. SDS and SDS-PE-b-PEG form unilamellar (ULV) and multilamellar vesicles (MLV), respectively, along with the rod-shaped colloidal structures as observed from transmission electron microscopy (TEM) images. This dye causes a variation in the hydrophilic/hydrophobic ratio and forms a hydrogen bond with the copolymer in the SDS-PE-b-PEG complex and subjected to electrostatic interaction with the SDS micelle in aqueous solution, which causes this morphological transformation. These vesicles show complete encapsulation of a hydrophobic dye in its interior as evident from the TEM images. ULV get ruptured at low pH, pointing toward their lower stability over MLV at low pH value. The formation of these vesicles with complete idea of its mechanism, encapsulation of bioactive molecules and its rupture at lower pH raise hope as a potential nanoscale vehicle for biologically relevant compounds and their release at low pH medium.     

Metal ions as cofactors for aggregation of therapeutic peptide salmon calcitonin

The effects of multivalent metal ions (Cu(2+)/Zn(2+)/Al(3+)) on the aggregation of salmon calcitonin (sCT)--a therapeutic peptide used worldwide in the treatment of osteoporosis and Paget's disease--have been studied in vitro using NMR (both solution state and solid state), TEM, ThT-fluorescence, and FT-IR spectroscopy. Overall, the various results indicated that the metal-ions-induced conformational transitions in the peptide--mostly toward the β-sheet--facilitate the aggregation of sCT in solution. First, the solution NMR has been used to check the interaction between the peptide and the metal ions. Following this, the formation and characterization of calcitonin aggregates has been performed using TEM, solid state NMR, and FT-IR spectroscopy. The TEM and ThT-fluorescence results revealed that the sCT peptide incubated with Cu(2+) and Zn(2+) metal ions (in aqueous environment) forms globular aggregates, while that with Al(3+) ions forms fibrils. The solid state NMR and FT-IR studies revealed the presence of a substantial amount of β-sheet content in sCT aggregates (formed in the presence of these metal ions) compared to the monomeric sCT, indicating that the metal binding is concomitant with conformational changes. The present study becomes crucial while prescribing this drug peptide under physio-pathological conditions associated with an abnormal accumulation of metal ions (Cu(2+)/Zn(2+)/Al(3+)) in the body (i.e., abnormal metal ion homeostasis).     

Fluorination suppresses thermal quenching in perovskite QLEDs

正Perovskite nanocrystals and quantum dots(QDs) have attracted great attention due to their potential in optical and optoelectronic applications, especially in ultra-high definition displays because of their high purity of photo/electroluminescence(PL/EL) [1,2]. Although the external quantum efficiency(EQE) of light-emitting diodes(LEDs) based on perovskite quantum dots(PeQDs) has been over 20% [3,4],another key problem, the PL/EL stability, still remains open.The thermal PL/EL quenching phenomenon, which is ubiquitously observed, has not aroused enough attention in this     

Kinetics of oxidation of methanol and mono-deutero-methanol by chromium(VI) in perchloric acid medium

Kinetics of the oxidation of methanol and mono-deutero-methanol by Cr(VI) over a wide range of temperature (25–40°) have been studied in perchloric acid medium at constant ionic strength (μ = 1.0 M) adjusted with sodium perchlorate. Each reaction is first order with respect to the substrate and dichromate concentrations but the order with respect to [H⁺] is nearly 3 in each case. Both these reactions take place at almost the same rate under identical experimental conditions. The activation parameters of the reactions are not widely different and the values of ΔH3 and ΔS3 for the oxidation of methanol are 79.5 kJ mole ^-1 and - 38.1 J deg^-1 mole^-1 respectively, whereas the corresponding values for the deuterated compound are 83.8 kJ mole^-1 and -23.9 J deg^-1 mole^-1. The probable mechanism of the reactions is discussed.     

Kinetics of the oxidation of sulphite by tetrachloroaurate(III)

Summary The reaction between sulphite and gold(III) in hydrochloric acid medium has been studied; an initial complex is formed prior to electron transfer. The reaction rate is inversely proportional to the hydrogen ion concentration and the reaction appears to proceed through the intermediate formation of a free radical which reacts with gold(III) to give the products. Evidence for the formation of dithionate together with sulphate is presented.