Search results for "Chemical engineering"
showing 10 items of 5892 documents
Influence of temperature on the synthesis of thiol-stabilized CdTe nanoparticles in aqueous solutions
2010
We have investigated the evolution of thiol-capped cadmium telluride nanocrystals prepared in aqueous solutions at low and room temperature followed by heating at 50–100 °C. The UV–visible absorption spectra, as well as transmission electron microscopy, atomic force microscopy, and dynamic light scattering observations made it possible to reveal differences in size and structure originating from different heating temperatures. It was shown that minimization of the nucleation process temperature provided formation of larger nanoparticles than at higher temperatures.
Interaction between nitroxyl radicals and CdTe quantum dots: Determination of fluorescence-quenching mechanisms in aqueous solution
2019
Abstract The present work characterizes the optical properties of CdTe quantum dots (CdTe QDs) after interaction with nitroxyl radicals based on steady-state and time-resolved fluorescence spectroscopy studies. QDs of different sizes were exposed to 2 different nitroxyl radicals, i.e., TEMPO and 4-amino-TEMPO radicals. A clear dependence of dynamic and static Stern-Volmer constants values, KD and KS, respectively, was observed as a function of the size of QDs used, with a change from a mostly static mechanism (for smaller QD sizes) to a dynamic mechanism predominating as the nanoparticles increase in size. All observed effects are dependent on both the concentration of the radical and the s…
New hydrogel matrices based on chemical crosslinked α,β -polyas parthydrazide: Synthesis, characterization and in vivo biocompatibility studies
1996
New swellable micromatrices of α,β-polyasparthydrazide (PAHy) crosslinked with glutaraldehyde were prepared. The effect of crosslinking agent concentration was evaluated. In particular, crosslinking density affected aqueous dynamic swelling and glass-transition temperature of the material. The structure of prepared networks was also studied by scanning electron microscopy and X-ray analysis. Finally, biocompatibility of PAHy derivatives was investigated in vivo by subcutaneous implantation and in oral administration to laboratory animals.
Conversion electron Mössbauer study of low carbon steel polarized in aqueous sulfate and sulfite containing sulfate solutions
1993
Abstract The passivation of low carbon steel was studied in aqueous solutions of 0.5 M Na 2 SO 4 (pH = 3.5 and 6.5) and of 0.5 M Na 2 SO 4 + 0.001 M NaHSO 3 (pH 3.5 and 6.5). The used conversion electron Mossbauer spectroscopy (CEMS) with the complementary electrochemical, microscopic and spectrophotometric investigations proved that the presence of sulfite ion induces pitting corrosion. The compositions and thichnesses of the passive films formed during the electrochemical treatments are determined from the conversion electron Mossbauer spectra. γ-FeOOH was found in each case as a major component. At pH = 3.5, the sextet belonging to Fe 3 C appears in the spectra in most cases, and also Fe…
In situ AFM study of proton-assisted electrochemical oxidation/reduction of microparticles of organic dyes
2008
In situ atomic force microscopy (AFM) images of crystals of organic dyes alizarin, indigo and morin have been monitored during the course of their solid-state electrochemical oxidation/reduction in contact with aqueous acetate buffer. Such images indicate that proton-assisted reduction and oxidation processes are localized in a shallow layer in the vicinity of the particle/electrolyte interface, in agreement with expectances from the Lovric and Scholz model with significantly restricted proton diffusion across the solids. Keywords: Voltammetry of nanoparticles, Atomic force microscopy, Organic dyes, Diffusion
Facile synthesis and characterization of functionalized, monocrystalline rutile TiO2 nanorods.
2006
Functionalized, monocrystalline rutile TiO2 nanorods were prepared from TiCl4 in aqueous solution under acidic conditions in the presence of dopamine, followed by aging and hydrothermal treatment at 150 degrees C. The surface-bound organic ligand controls the morphology as well as the crystallinity and the phase selection of TiO2. The presence of monocrystalline rutile TiO2 was confirmed by X-ray powder diffraction and HRTEM investigations. The as-prepared nanorods are soluble in water at pH3. The surface functionalization was analyzed by IR and 1H NMR, confirming the presence of dopamine on the surface. The surface amine groups can be tailored further with functional molecules such as dyes…
On the Creeping of Saturated Salt Solutions
2013
Creeping is a well-known but annoying phenomenon in the preparation of crystals from solution, where growing crystallites gradually extend up the walls of the growth vessel. In this process, solution is transported toward the tip of the creeping crystallites, where solvent evaporation takes place and solid material is deposited. In this study, the growth of crystal aggregates extending from evaporating droplets of saturated aqueous solutions of ionic salts, placed on different substrate materials, has been investigated using optical microscopy. It is shown that the rate determining step of the crystallization process is the evaporation of solution, following Fick’s laws. Fresh solution, nec…
Analysis of an impedance function of zinc anodic dissolution
2004
Zinc anodic dissolution has been studied by means of electrochemical impedance spectroscopy (EIS). The kinetic study of the oxidation mechanism has allowed us to propose a theoretical impedance function for this system in deaerated sulphate medium. Relevant information on the faradaic process is provided by analysis of the theoretical impedance function. Kinetic parameters of this system can be calculated from the fitting of experimental data to the faradaic impedance function deduced theoretically. The physical measurements of this function are analysed by means of the dependence of simulated EIS spectra on kinetic parameters.
Distribution potential in electrified microemulsions with potential determining salts
2018
Abstract The electrical polarization of lamellar and water-in-oil microemulsions composed of the aqueous solution of a potential determining salt (PDS), an organic solvent and a nonionic surfactant has been studied. The distribution of the PDS ions across the interface between two immiscible electrolyte solutions (ITIES) generates an electrical potential difference which can be used to control charge transfer processes. In macroscopic ITIES, this distribution potential is independent of the PDS concentration and can be determined from the electroneutrality condition far from the interface. In microemulsions, on the contrary, the distribution potential is smaller in magnitude and depends on …
The role of lithium, perchlorate and water during electrochemical processes in poly(3,4-ethylenedioxythiophene) films in LiClO4 aqueous solutions
2021
Abstract Thin films of poly(3,4-ethylendioxythiophene) (PEDOT) were electrochemically deposited on gold electrodes in aqueous media. The role of perchlorate, lithium, and water during the charge/discharge of PEDOT films was investigated by cyclic voltammetry together with EQCM, vis − NIR spectroscopy, and acoustic impedance, also by means of ac-electrogravimetry in a 0.1 M LiCl O 4 aqueous solutions. In this way, it has been possible to correlate the electrical, mass, color and electromechanical properties changes during the electrochemical reactions of this polymer. Both, hydrated lithium cations and perchlorate anions can act as counterions during the electrochemical reactions, however, a…