Violeta Purcar

San copolymer membranes with ion exchangers for Cu(II) removal from synthetic wastewater by electrodialysis.

Heterogeneous membranes were obtained by using styrene-acrylonitrile copolymer (SAN) blends with low content of ion-exchanger particles (5wt.%). The membranes obtained by phase inversion were used for the removal of copper ions from synthetic wastewater solutions by electrodialytic separation. The electrodialysis was conducted in a three cell unit, without electrolyte recirculation. The process, under potentiostatic or galvanostatic control, was followed by pH and conductivity measurements in the solution. The electrodialytic performance, evaluated in terms of extraction removal degree (rd) of copper ions, was better under potentiostatic control then by the galvanostatic one and the highest (over 70%) was attained at 8V. The membrane efficiency at small ion-exchanger load was explained by the migration of resin particles toward the pores surface during the phase inversion. The prepared membranes were characterized by various techniques i.e. optical microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis and differential thermal analysis and contact angle measurements.

The Influence of New Hydrophobic Silica Nanoparticles on the Surface Properties of the Films Obtained from Bilayer Hybrids

Ultra-hydrophobic bilayer coatings on a glass surface were fabricated by sol–gel process using hexadecyltrimethoxysilane (C16TMS) and tetramethoxysilane (TMOS) (1:4 molar ratio) as precursors. After coating, silica nanoparticles (SiO2 NPs) functionalized with different mono-alkoxy derivatives (methoxytrimethylsilane, TMeMS; ethoxydimethylvinylsilane, DMeVES; ethoxydimethylphenylsilane, DMePhES; and methoxydimethyloctylsilane, DMeC8MS) were added, assuring the microscale roughness on the glass surface. Influences of the functionalized SiO2 NPs and surface morphology on the hydrophobicity of the hybrid films were discussed. The successful functionalization of SiO2 NPs with hydrophobic alkyl groups were confirmed by Fourier transform infrared spectroscopy (FTIR). The thermal stability of hydrophobic SiO2 NPs showed that the degradation of the alkyl groups takes place in the 200–400 °C range. Bilayer coating with C16TMS/TMOS and SiO2 NPs modified with alkoxysilane substituted with C8 alkyl chain (SiO2 NP-C8) has micro/nano structure. Hydrophobicity of functionalized SiO2 NPs-C8 and its higher degree of nanometer-scale roughness gave rise to ultra-hydrophobicity performance for bilayer coating C16TMS/TMOS + SiO2 NPs-C8 (145°), compared to other similar hybrid structures. Our synthesis method for the functionalization of SiO2 NPs is useful for the modification of surface polarity and roughness.

On the photocatalytic reduction of MTT tetrazolium salt on the surface of TiO2 nanoparticles: Formazan production kinetics and mechanism.

HYPOTHESIS The MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide] cell cytotoxicity indicator is photocatalytically reduced on the surface of TiO2 nanoparticles in phosphate-buffered-saline (PBS) environment. We hypothesize that specific phosphate adsorption may be used to modulate the efficiency of the TiO2-MTT reaction through colloidal and semiconductor-liquid interface processes. EXPERIMENTS The TiO2-MTT reaction kinetics was studied in PBS, with respect to photocatalyst and MTT concentrations and irradiation wavelength. The effects of PBS and electron scavengers (Fe(3+) ions) on reaction efficiency and the role of colloidal surface charge in the photocatalytic process were investigated. The structural and spectroscopic characteristics of relevant TiO2-formazan systems were studied by X-ray diffraction, transmission electron microscopy and IR-spectroscopy. FINDINGS The reaction was pseudo-first order with respect to photocatalyst and showed a negative and fractional partial order with respect to MTT. Formazan production rates were directly proportional to radiation wavelength and TiO2 concentration and inversely proportional to the MTT initial concentration. The addition of Fe(3+) ions, as well as the absence of PBS, induced strong reaction inhibition. Reaction efficiency and catalyst Zeta potential were enhanced by Na2HPO4 (PBS component) and showed a maximum around the phosphate concentration 0.005 M. Structural/spectroscopic characterization confirmed the formation of amorphous MTT-formazan on the surface of TiO2 and the TiO2-phosphate binding.

Polymer-clay nanocomposites obtained by solution polymerization of vinyl benzyl triammonium chloride in the presence of advanced functionalized clay

AbstractPolymer-clay nanocomposites were synthesized by solution polymerization method using advanced functionalized clay and vinyl benzyl trimethyl ammonium chloride as monomer. First stage consisted in the silylation of a commercial organo-modified clay-Cl 20A using alkoxysilanes with different chain lengths. In the second step, the synthesis and characterization of polymer-nanocomposites were followed. To evaluate the clay functionalization process as well as the final polymer-clay products, thermogravimetric, X-ray diffraction, dynamic light scattering, Fourier transform infrared spectroscopy and three test liquid contact angles analyses were used. The loss of ammonium ions from commercial clay, the grafting degree, the lengths and the nature of alkyl chain influence the dispersion of the advanced modified clay into the polymer solution and, furthermore, the properties of the final polymer-clay nanocomposite film. Graphical AbstractPolymer-clay nanocomposites were obtained by solution polymerization using advanced functionalized clay and a water soluble monomer. The loss of ammonium ions, the grafting degree, the lengths and the nature of alkyl chain influenced the dispersion of the modified clay into the polymer solution and the properties of the final hybrid film.

The Effect of Different Coupling Agents on Nano-ZnO Materials Obtained via the Sol–Gel Process

Hybrid nanomaterials based on zinc oxide were synthesized via the sol–gel method, using different silane coupling agents: (3-glycidyloxypropyl)trimethoxysilane (GPTMS), phenyltriethoxysilane (PhTES), octyltriethoxysilane (OTES), and octadecyltriethoxysilane (ODTES). Morphological properties and the silane precursor type effect on the particle size were investigated using dynamic light scattering (DLS), environmental scanning electron microscopy (ESEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). The bonding characteristics of modified ZnO materials were investigated using Fourier transform infrared spectroscopy (FTIR). The final solutions were deposited on metallic substrate (aluminum) in order to realize coatings with various wettability and roughness. The morphological studies, obtained by ESEM and TEM analysis, showed that the sizes of the ZnO nanoparticles are changed as function of silane precursor used in synthesis. The thermal stability of modified ZnO materials showed that the degradation of the alkyl groups takes place in the 300–500 °C range. Water wettability study revealed a contact angle of 142 ± 5° for the surface covered with ZnO material modified with ODTES and showed that the water contact angle increases as the alkyl chain from the silica precursor increases. These modified ZnO materials, therefore, can be easily incorporated in coatings for various applications such as anti-corrosion and anti-icing.

Synthesis of Non-Toxic Silica Particles Stabilized by Molecular Complex Oleic-Acid/Sodium Oleate

The present work is focused on the preparation of biocompatible silica particles from sodium silicate, stabilized by a vesicular system containing oleic acid (OLA) and its alkaline salt (OLANa). Silica nanoparticles were generated by the partial neutralization of oleic acid (OLA), with the sodium cation present in the aqueous solutions of sodium silicate. At the molar ratio OLA/Na+ = 2:1, the molar ratio (OLA/OLANa = 1:1) required to form vesicles, in which the carboxyl and carboxylate groups have equal concentrations, was achieved. In order to obtain hydrophobically modified silica particles, octadecyltriethoxysilane (ODTES) was added in a sodium silicate sol–gel mixture at different molar ratios. The interactions between the octadecyl groups from the modified silica and the oleyl chains from the OLA/OLANa stabilizing system were investigated via simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC) (TG-DSC) analyses.A significant decrease in vaporization enthalpy and an increase in amount of ODTES were observed. Additionally, that the hydrophobic interaction between OLA and ODTES has a strong impact on the hybrids’ final morphology and on their textural characteristics was revealed. The highest hydrodynamic average diameter and the most negative ζ potential were recorded for the hybrid in which the ODTES/sodium silicate molar ratio was 1:5. The obtained mesoporous silica particles, stabilized by the OLA/OLANa vesicular system, may find application as carriers for hydrophobic bioactive molecules.

Silver-Polymer Nanohybrids Prepared by Microemulsion Polymerization

This work presents the preparation of some Ag°-polymer nanoparticles by emulsion polymerization of styrene (St), butyl acrylate (BuA) or methyl methacrylate (MMA), followed by the metal particles engendering. In order to increase the polymer-Ag° interaction, acrylic acid (AcrA), hydroxyethylmethacrylate (HEMA), sodium styrenesulfonate (StSO3Na) and vinyltriethoxysilane (VTES) coupled with tiopropyltrimethoxysilane (HSTMS) were subsequently used as comonomers when the polymeric latexes were prepared. Comparing the two surfactants used in this study – nonylphenol ethoxylated with 25 moles of ethylene oxide (NPEO25) and sodiumdodecylsulfate (SDS) - one can notice that particle size was larger and zeta potential value decreased when, instead of the ionic surfactant SDS, the nonionic surfactant NPEO25 was added to the formulation. The latexes UV-Vis spectra shows absorptions at ~400 nm due to plasmon resonance adsorption assigned to Ag° nanoparticles. The value of λ caused by this phenomenon decreases in the following order: PSt>PBuA>PMMA, because of the increase of polarity. The reactive comonomers, mentioned above, cause the decrease of the maximum value, due to the increase of the polymer-metal interaction. Thermal stability of PSt is higher when silver nanoparticles are present and is lower after copolymerization. For HEMA and StSO3Na copolymers, the XRD studies point out the existence of a cubic crystalline phase, generated because of the maximum (high) concentration of Ag°. The UV-Vis reflexion spectra show maximum values of reflectance for the same two copolymers, proving that the crystalline phase of Ag° has a mirror effect.

Facile Preparation of Impurity Doped CdS Nanoparticles in New Polymeric Templates

Cadmium sulfide nanocrystals (quantum dots) have been prepared using polymer solution as template. The new polymer is a vinyl acetate- maleic anhydride (VAcMA) copolymer obtained by using an original procedure developed in our laboratory. The influence of composition and concentration of the polymer on the size and the optical properties of the semiconductor nanoparticles has been studied. The influence of the reaction parameter was also investigated in order to obtain a versatile procedure to prepare nanocrystals with tunable optical properties. The reaction in polymeric matrix could lead to the formation of wide range of particle size (3–8 nm). In addition to modify the emission properties by controlling the particle size, CdS nanocrystals were doped with Zn, Cu and Mn ions. Both blue and red shifts of the maximum emission wavelength were recorded. QD-polymer composites obtained from CdS nanoparticles prepared in VAcMA matrix have been investigated by UV-VIS, fluorescence and IR spectroscopy, TEM and DLS. The photophysical properties of the semiconductor nanoparticles obtained in polymer matrix was compared for different QD-polymer composites, according to the obtaining procedure.

Nanostructured Hybrid Systems with Rhodamine 6G

We synthesized hybrid materials by sol-gel process, using: methyltriethoxysilane, tetraetylorthosilicate and vinyltriethoxysilane, in the presence of Rhodamine 6G. It was synthesized as well organic-inorganic hybrids with addition of tetraisopropyl orthotitanate and maleic anhydride UV-VIS spectra of dye show two absorption peaks at 499 nm (dimer) and 530 nm (monomer). Evaluating FTIR spectra of hybrid films, it was observed a band at 1077 cm−1, characteristic of the asymmetric Si-O-Si stretching vibration in oligomer. Fluorescence spectra show that tetraisopropyl orthotitanate presence in the composites modifies the nature of the inorganic matrix and affects the interaction with the added dye.

Polymer-silica hybrids latexes dyed with Rhodamine B

Abstract Synthesis of latexes based on polystyrene (PSt) and polybutylacrylate (PBuA) dyed with Rhodamine B (RhB), by polymerization in ternary microemulsions, is discussed in this paper. Silica was generated through the solgel process of methacryloxypropyl-trimethoxysilane (MPTS) and glycidyloxypropyltrimethoxysilane (GMPS). MPTS copolymerizes, through its double bounds, with St or BuA. GMPS can form covalent bonds with RhB by opening of the oxyranic cycle. The smallest average diameter of the particles was obtained for latexes prepared with MPTS+GMPS couple. Latexes with RhB prepared in the presence of an organophilic layered silicate (Cloisite 20 A) were used for comparing the influence of the inorganic fillers on microemulsion properties. By St and BuA copolymerization with MPTS hybrids which can react by sol-gel process with GMPS, a coupling agent for RhB, were prepared. By using RhB as molecular sample, polarity modifications for polymer-inorganic latexes were put in evidence.