Maria Zaharescu | Institute of Physical Chemistry "Ilie Murgulescu" (original) (raw)

Papers by Maria Zaharescu

Book Publisher International (a part of SCIENCEDOMAIN International), Jul 14, 2020

Nanomaterials

This work presents the synthesis of nanostructured TiO2 modified with noble metal nanoparticles (... more This work presents the synthesis of nanostructured TiO2 modified with noble metal nanoparticles (Au, Ag) and lysozyme and coated on titanium foil. Moreover, the specific structural and functional properties of the resulting inorganic and hybrid materials were explored. The purpose of this study was to identify the key parameters for developing engineered coatings on titanium foil appropriate for efficient dental implants with intrinsic antibacterial activity. TiO2 nanoparticles obtained using the sol–gel method were deposited on Ti foil and modified with Au/Ag nanoparticles. Morphological and structural investigations (scanning electron and atomic force microscopies, X-ray diffraction, photoluminescence, and UV–Vis spectroscopies) were carried out for the characterization of the resulting inorganic coatings. In order to modify their antibacterial activity, which is essential for safe dental implants, the following aspects were investigated: (a) singlet oxygen (1O2) generation by ino...

Journal of Environmental Protection, 2010

Pesticides are widely used in agriculture, although they may create hazards both to humans and to... more Pesticides are widely used in agriculture, although they may create hazards both to humans and to the environment. In order to reduce the harmful effects of their administration, there has been made a great effort to find solutions. The porous sol-gel silica materials which are able to entrap different organic molecules represent new studied controlled release carriers. The aim of the present work was to prepare and characterize sol-gel composites based on trichlorfon as organophosphorous pesticide embedded in silica matrices generated from three different SiO 2 sources: tetraethylorthosilicate (TEOS), colloidal silica (CS), and sodium silicate (SS). Similar samples to those containing only trichlorfon have also been synthesised, in which α-, β-, and γ-cyclodextrin have been included in order to study the possibility of improving the release of the pesticide from the silica matrices. The porous sol-gel silica materials generated from TEOS and CS are able to entrap the trichlorfon and ensure an efficient delivery of the pesticide. In the absence of cyclodextrins, better results are obtained in the case of TEOS precursor, compared to colloidal silica. The addition of cyclodextrins in order to improve the release of the pesticide from the silica matrices was successful only in the case of CS as SiO 2 precursor. The best release of the pesticide was obtained with β-CD.

Key Engineering Materials, 1997

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any fo... more All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 66.249.72.140-02/09/11,18:44:08) ... Euro Ceramics V doi:10.4028/www.scientific.net/ ...

Journal of the European Ceramic Society, 2007

Journal of the European Ceramic Society, 2000

We present the formation mechanism and structure of the superconducting phases in the BiSrCaCu... more We present the formation mechanism and structure of the superconducting phases in the BiSrCaCuO system by TEM and SEM observations. Oxalate coprecipitation was used as preparation method. The average particle size, distribution and the presence of different ...

Key Engineering Materials, 2004

Bismuth oxide system exhibit high oxide ionic conductivity and have been proposed as good electro... more Bismuth oxide system exhibit high oxide ionic conductivity and have been proposed as good electrolyte materials for application such as solid oxide fuel cell (SOFC) and oxygen sensor. A preliminary investigation for depositing thin and dense antimony doped Bi2O3 films based on wet chemical routes was realized. Antimony doped Bi2O3 films were deposited onto glass substrate from bismuth nitrate and antimony precursor solutions. As chelating agent polyethyleneglycol (PEG) was used and the above-mentioned precursor solutions were sufficiently viscous. Crystallization behavior and microstructure evolutions of the obtained films were investigated using spectroscopic ellipsometry (SE), polarized microscope observation, X-ray diffractometry (XRD), and infrared spectrometry (IR). The thickness and the porosity of the films were evaluated. The preparation techniques differ mainly in precursor materials and method of deposition, leading to different quality of the resulting films.

Key Engineering Materials, Sep 9, 2001

Journal of Materials Science: Materials in Electronics, 2007

Journal of the European Ceramic Society, 1998

Bi-based ceramic materials with superconducting properties were prepared using the solid state re... more Bi-based ceramic materials with superconducting properties were prepared using the solid state reaction technique, starting with reactive powders obtained via oxalate coprecipitation, as well as by the traditional powders route. The powder characteristics were evaluated using BET method and transmission electron microscopy (TEM). The stages of the high Tc supeconducting phases formation process were investigated by TG, DTA, XRD and

Journal of Nanomaterials, 2019

Nowadays, multifunctional materials are of high interest due to their ability to be used in diffe... more Nowadays, multifunctional materials are of high interest due to their ability to be used in different applications by controlling one or two parameters (e.g., morphology and/or dopant). Zinc oxide is an intensive-studied material because of its large usability. Recently, we have shown that the conduction, transparency, and charge carrier concentration of ZnO can be controlled by changing the dopants, leading to promising materials as transparent conductive oxide films. In this work, sol-gel (SG) and hydrothermal (HT) methods were used separately or in combination in order to obtain ZnO films doped with Mn (1, 2, and 5%) for possible application in transparent optoelectronics or as piezoelectric materials. The manganese (Mn) dopant in the form of anhydrous manganese acetate was used to obtain Mn-doped ZnO films. ZnO hydrothermal (HT) growth was made on a previously ZnO seed layer, formed by sol-gel method. The Mn-doped ZnO films were deposited on microscope glass and on Pt/Ti/SiO2/Si...

Revue Roumaine de Chimie

The formation mechanism of ZnO nanopowders was investigated by appropriate experimental methods. ... more The formation mechanism of ZnO nanopowders was investigated by appropriate experimental methods. The studied samples have been obtained using a wet chemical route based on Zn(NO3)2·nH2O (ZAH) - (CH2)6N4 (HMTA) system in which the molar ratio of the components was 4:1 and 2:1. From the same solution, depending on the experimental conditions used, gels, precipitates or hydrothermally grown powders were obtained. Thermal decomposition of the as-prepared powders was analysed by simultaneous thermogravimetric and differentialthermal analysis (TG/DTA) and differential scanning calorimetry (DSC) methods. X-ray diffraction method (XRD), FT-IR Spectroscopy and Scanning Electron Microscopy (SEM) were used to study the structure and morphology of the obtained samples and their evolution with thermal treatment. The correlation between the preparation parameters and the properties of the resulted ZnO powders was established.

Journal of Thermal Analysis and Calorimetry, 2015

ZnO, Li doped and Li,Ni co-doped ZnO powders to be later used as transparent conductive oxide (TC... more ZnO, Li doped and Li,Ni co-doped ZnO powders to be later used as transparent conductive oxide (TCO) thin film were prepared by heat treatment of gels obtained from alcoholic Zn(CH 3 COO) 2 •2H 2 O, LiNO 3 •nH 2 O and NiSO 4 •6H 2 O solutions with (CH 3 CH 2 OH) 3 N as chelating agent. The properties of the powders and their thermal treatment were studied by thermogravimetric and termodifferential anlysis (TG/DTA), differential scanning calorimetry (DSC), evolved gas analysis coupled with mass spectroscopy (EGA-MS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray (SEM/ EDX). The as-prepared gels consisted of submicron platelet-like particles and contained zinc acetate dihydrate and hydrozincite in different amount and with different preferred orientations. During annealing the gels, zinc-acetate decomposed between 110-350 °C with the release of CH 3 COOH, acetone and CO 2. The N content of the chelating agent was responsible for NH 3 and NO evolution. The thermal behavior of the doped gels was similar, but there were also differences in the mass losses, amount of released gases. Based on TG/DTA data, ZnO powders were obtained from the gels by annealing both at 275 and 500 °C. After heating at 275 °C, the obtained powders consisted of spherical 1-2 micron grains of wurtzite. The inclusion of the dopants was successful according to EDX and cell parameter data. Thermal study of the powder annealed at 275 °C confirmed that they still contain some zinc acetate. In the case of the doped samples the mass loss was smaller, since the Li and Ni dopants catalized the composition of zinc acetate during the previous annealing at 275 °C. After annealing the gels at 500 °C, stable un-doped ZnO or doped ZnO particles were obtained.

Journal of Thermal Analysis, 1979

A new differential therml analysis method has been developed wich allows fast and accurate determ... more A new differential therml analysis method has been developed wich allows fast and accurate determination of phase equilibria in condensed system between 400 and 1100o. in this method the temperature is increased stepwise, heat effects being determined by analysis of transient thermoelectric effects afer each step. Beetwen steps the temperature is kept constant until equilibrium is attained. The method has tested in measurements of displasive solid-state transformation and meltin points.

Molecules (Basel, Switzerland), Jan 5, 2018

A wide range of hybrid biomaterials has been designed in order to sustain bioremediation processe... more A wide range of hybrid biomaterials has been designed in order to sustain bioremediation processes by associating sol-gel SiO₂ matrices with various biologically active compounds (enzymes, antibodies). SiO₂ is a widespread, chemically stable and non-toxic material; thus, the immobilization of enzymes on silica may lead to improving the efficiency of biocatalysts in terms of endurance and economic costs. Our present work explores the potential of different hybrid morphologies, based on hollow tubes and solid spheres of amorphous SiO₂, for enzyme immobilization and the development of competitive biocatalysts. The synthesis protocol and structural characterization of spherical and tubular SiO₂ obtained by the sol gel method were fully investigated in connection with the subsequent immobilization of lipase from . The immobilization is conducted at pH 6, lower than the isoelectric point of lipase and higher than the isoelectric point of silica, which is meant to sustain the physical inte...

International Journal of Inorganic Materials, Jun 1, 2000

Hydrotalcite (HT)-like compounds of general formula [Ni Al (OH) ](CO) ?mH O, where 0.25#x#0.66, h... more Hydrotalcite (HT)-like compounds of general formula [Ni Al (OH) ](CO) ?mH O, where 0.25#x#0.66, have been synthesised 12x x 2 3 x / 2 2 by coprecipitation at constant pH and were hydrothermally treated. The thermal decomposition of the compounds was followed by DTA and TGA and the resulting products at different temperatures were studied by X-ray and IR spectroscopy techniques. In every case, there was a loss of interlayer water in a first stage, followed by the complete decomposition of the product at around 450-5008C, depending on the hydrotalcite composition. A slightly different decomposition behaviour was found for compounds with 0.4#x#0.66. Only NiO was identified at 4508C calcination temperatures of HT-like precursors, whereas the corresponding spinel, NiAl O , was formed by interaction 2 4 between NiO and Al O , at 9008C. New information was evidenced by combining isothermal pre-reduction of oxidic systems obtained at 2 3 450 and 9008C with temperature-programmed reduction (TPR) experiments; a NiO-Al O structure with a spinel-type local order and 2 3 NiO were found in all samples at 4508C, oxidic forms that were thermally stable up to 9008C. These results on the sample reducibility were found to be in agreement with some models proposed in the literature for the oxidic forms derived from HT-like structures and also with our own IR and UV-Vis spectroscopic structural data.

Springer eBooks, 1999

Sintered SnO2-based ceramics were considered to be promising materials for manufacturing the stab... more Sintered SnO2-based ceramics were considered to be promising materials for manufacturing the stable electrodes for the various technological applications, as aluminium electrolysis 1 (inert anodes) or glass industry 2,3. For such applications, a high electrical conductivity and high sintering ability ensuring a high density and, consequently low porosity of the final product are necessary.

Journal of thermal analysis, Aug 1, 1997

The scientific interest for the Bi203-PbO system has increased due to the importance of the PbO i... more The scientific interest for the Bi203-PbO system has increased due to the importance of the PbO in the high-T e superconducting phase formation in the Bi203-SrO-CaO-CuO system. Also Bi203-PbO system contains compounds with some specific semiconductor and dielectric properties and Bi2Oa-based solid solutions are well known as high oxygen ion conductors. Previously, several low melting defined compounds have been identified in the system: 6Bi203.PbO; 3Bi203.2PbO; 4Bi2Oy5PbO; 4Bi203.6PbO and Bi2Oy3PbO. This work deals with the phase formation and thermal stability of these compounds. Under non-isothermal conditions, in all mixtures regardless of the Bi203/PbO ratio, the compound 6Bi2OyPbO is preferentially formed, followed by the compound 4Bi2Oy5PbO. The formation of the compound 4Bi2Oy6PbO was not confirmed while the formation of the compound Bi2Oy 3PbO occurs through a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isothermal conditions in the same temperature range the tendency to form the stoichiometric compounds increases. All compounds form, decompose and melt at temperatures between 530-780~