Volume 232, Issue 1

The quenching of Rhodamine 6G in aqueous solution by citrate stabilized gold nanoparticles differing in their geometry (spheres, rods, prisms) was investigated. Static quenching was observed throughout. At constant surface area, the quenching rate diminished in the order spheres>rods>prisms. The effect is shown to be due to differing nanoparticle volumes rather than to variations in the surface area.

The present study evaluates the effect of Camellia sinensis leaves (CSL) extract on the corrosion inhibition of carbon steel in produced water using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and computational methods. The chromatographic investigation of the extract was performed by HPLC. It was found that CSL extract serves as a mixed-type corrosion inhibitor and its inhibitive performance increases with concentration. The corrosion inhibition was assumed to occur via adsorption of the primary constituents of CSL extract. Surface analysis (SEM and FTIR) was also carried out to establish the mechanism of corrosion inhibition. The outcomes obtained from the computational study were found to confirm experimental data.

In the present study, we have investigated the counter-ion effect on the thermodynamics of Cr(III) sorption by macroporous resin Amberlyst-15. The exchange reaction was studied as a function of concentration of Cr(III) and nature of counter-ions at different temperatures. It was observed that nature of counter-ions have a profound effect on the exchange of Cr(III) ions. The selectivity of Amberlyst-15 towards metal ion sorption follows the order univalent>divalent> trivalent forms. This trend can be associated to the electrostatic interaction of ions with the functional sites of the resin. The equilibrium pH values (pH eq ) were observed to decrease with Cr 3+ /H + exchange whereas an increase in pH eq was detected during the exchange of Cr 3+ /Li + , Cr 3+ /Na + , Cr 3+ /Ca 2+ and Cr 3+ /Al 3+ . Different adsorption models such as Dubinin–Radushkevich (D–R) and Langmuir were employed to analyze the sorption data. The maximum exchange capacities ( X m ) and binding energy constants ( K b ) values were determined by using the Langmuir model. The values of both ΔH o and ΔS o were found positive inferring that the exchange process is endothermic accompanied by the dehydration of Cr(III) ions. The thermodynamic parameters revealed that the mechanism of Cr(III) sorption for all the counter ions is entropy driven ion exchange.

Yb 3+ -doped silicate glasses (SiO 2 –Nb 2 O 5 –K 2 O–ZnF 2 ) were prepared by a conventional melt quenching technique and their spectroscopic properties were investigated. The emission cross-section was found to be 0.53×10 −20 cm 2 at 1006 nm from the reciprocity method described by McCumber from the measured absorption spectrum of 1.0 mol% Yb 2 O 3 -doped glass. The lifetime ( τ exp ) and figure of merit ( σ em × τ exp ) for the 2 F 5/2 → 2 F 7/2 transition of 1.0 mol% Yb 2 O 3 -doped silicate glass, were evaluated to be 0.50 ms and 0.26 cm 2 ms, respectively. The other spectroscopic parameters, β min , I sat and I min were found to be 0.17, 29.00 kW/cm 2 and 4.90 kW/cm 2 , respectively. The results indicate that the present Yb 3+ -doped silicate glasses could be useful as laser gain media at 1006 nm.

We studied the dependence between properties and synthesis method for PEGylated ZnS nanoparticles. Thus, we proposed the PEGylation of ZnS nanopowder, in non-aqueous medium, by a facile one-pot synthesis in very mild conditions, as an alternative for the chemical precipitation of PEGylated ZnS in an aqueous solution, and we compared the properties of zinc sulfide obtained by both methods. The structure and morphology of PEGylated ZnS nanopowders were investigated by X-ray diffraction and transmission electron microscopy, and the FTIR spectra confirmed the PEGylation of ZnS nanoparticles. The values for band gap energy are in good accordance with the quantum confinement effect for nanocrystals. The mean dimension of particles was calculated, on the basis of UV–Vis spectra, by using the Brus equation and it is in good agreement with the crystallites size, determined from X-ray diffraction. The photocatalytic properties of synthesized nanopowders were tested in the degradation of Congo red azo dye, demonstrating a faster bleaching of dye in the presence of PEGylated ZnS prepared in non-aqueous medium. The photoluminescence properties are also dependent on the synthesis method and can be correlated with the surface modifications by PEG.

Reactive wetting of quartz by silicon is an ideal model system for the understanding and control of reactive wetting effects. Very slow and well controlled reactive spreading of a small silicon droplet on quartz can be achieved and observed in a new type of chemical transport mini reactor equipped with a video microscope setup operating in the melting point vicinity of silicon at T m =1685 K. The spreading velocities are investigated in dependence of a very small temperature gradient that causes a slight chemical gradient and induces a slow oxygen transport through the system. The oxygen source is a SiO 2 substrate at the temperature T A . From here the oxygen is transported upwards through the liquid silicon droplet and is released to the gas phase in form of SiO-molecules. The SiO-molecules are transported towards a cooler SiO 2 substrate at T B where SiO 2 -nano whiskers are formed via a vapor–liquid–solid-growth mechanism. In this way the oxygen drain is located in the gas phase above the droplet. The source reaction drives the reactive spreading process. By reducing the temperature difference ΔT=T B −T A <0 a very small chemical potential difference Δμ O =μ OB −μ OA <0 of the oxygen between the sessile droplet at position A and the whiskers at position B can be created and adjusted. The velocity of the moving triple line is then measured in dependence of Δμ O and expressed by a power law. The results are explained in terms of an irreversible thermodynamic model that couples the dynamics of the triple line to an ongoing solid state reaction in the underlying substrate, where a thin solid silicon suboxide gradient layer forms between substrate and melt. By fitting the data to the model formula one can determine reactive contributions to the tensions at the triple line and investigate these quantities in the limit Δμ O →−0.

New organic single crystals of 2-amino-5-chloropyridinium-2,4-dinitrophenolate were successfully grown by the slow evaporation method at room temperature from methanol solution. Crystal structure and crystalline phases were confirmed from the single crystal XRD and powder XRD, respectively. 1 H NMR and 13 C NMR studies were conducted for the crystal. The functional groups have been confirmed using the Fourier transform infrared (FTIR) analysis. UV-visible studies show the absence of absorption in the visible region. To determine the thermal stability of the grown crystals it was subjected to thermo gravimetric analysis and differential thermal analysis. Dielectric studies were taken in the frequency range from 50 Hz to 5 MHz for various temperatures. Photo conductivity and photoluminescence studies were also carried out for the title crystal. The second harmonic generation (SHG) efficiency of the grown crystals was 11.37 times greater than that of the reference KDP. Particle size dependent phase matching studies were also investigated. The nonlinear refractive index ( n 2 ) and nonlinear absorption coefficient ( β ) were also measured by Z-Scan studies.

In this work, the experimental densities and viscosities have been determined for (propylene carbonate+acetonitrile, or dimethyl carbonate, or diethyl carbonate) binary mixtures over the whole concentration range at temperatures (293.15–333.15 K) and the atmospheric pressure. Excess molar volumes ( V E ), viscosity deviations (Δ η ), thermal expansion coefficients ( α ) and excess Gibbs free energy of activation of viscous flow (Δ G E *) were calculated. These excess functions and deviations were fit with the Redlich–Kister type polynomial equation. The sign and magnitude of these excess properties have been used to interpret the results in terms of intermolecular interactions and structural effects. The results obtained for viscosity of binary mixtures were also used to test the semi-empirical relations of Grunberg-Nissan and Katti-Chaudhri equations.