Nicoleta Cornei

Studies on adsorption capacity of cationic dyes on several magnetic nanoparticles

Abstract In this study the dyes used are Basic fuchsin and Methylene blue. The adsorption was studied in relation to the metal in the ferrite, time of exposure and dye concentration. The highest adsorbtion capacity was observed for MgFe2O4 at a dye concentration of 0.06 mM, adsorption percent of 88% in 3 hours. Desorption was also studied by redispersion in ethanol. The main adsorption mechanism is thought to be through electrostatic interaction, mainly due to surfactant groups present on the nanoparticles. The nanoparticles have ferromagnetic behavior under magnetic field which allows for effective separation.

Synthesis and hydrophilic properties of Mo doped TiO2 thin films

Amorphous undoped TiO2 and Mo-doped TiO2 thin films were obtained by spray pyrolysis. By heat treatment, they became polycrystalline consisting in anatase, or mixed anatase/rutile phases, if deposited on glass or silicon, respectively. Mo enters in the TiO2 matrix as Mo5+, determining a slight red shift of the absorption edge. Based on Fourier transmission infrared analysis, performed on the studied films, before and after irradiation, providing information on the relationship between hydrophilicity and the amount of the adsorbed hydroxyl groups, we certify once again that the anatase phase (present in proportion of 100% in the films deposited on glass) is superior concerning the hydrophilic properties. Mo enhances wettability for the films deposited on silicon, compared to the undoped one, even if determines a rise in the rutile weight percentage, as a combined effect with the substrate nature. The decomposition of the oleic acid confirms that titania films with higher hydrophilic performances are also g...

Heterobimetallic Ba–Co aminopolycarboxylate complexes as precursors for BaCoO3-δ oxides; towards a one-stage-deposition of cobaltite films

Aminopolycarboxylate (APC) ligands have been selected to prepare seven new heterobimetallic barium-cobalt complexes as molecular precursors for BaCoO3-δ oxide materials. The use of APC = nitrilotriacetate (nta3−), ethylenediaminetetraacetate (edta4−), cyclohexane-1,2-diaminetetraacetate (cdta4−) and diethylenetriaminepentaacetate (dtpa5−) polydentate chelating agents enables the possible incorporation of Ba and CoII or CoIII in a 1 : 1 ratio. The crystal structure of the new BaCoII(nta)CH3COO·2H2O and BaCo(cdta)·5H2O have been refined from single crystal X-ray diffraction data. Our choice for the barium-cobalt system is based on the existence of a number of distinct BaCoO3-δ hexagonal perovskite polytypes, depending on the oxygen stoichiometry. It yields an easy probing of the cobalt oxidation state after thermal treatments. Temperature controlled X-ray diffraction (TCXRD) technique has been used to characterize the phases in competition upon thermal cycles of the precursors. The influences of the nature of ligands, initial cobalt oxidation state, temperature and working atmosphere on the process of formation of the mixed-oxide have been investigated. All the APC-precursors show appearance of a mixture of crystallized barium carbonate and Co3O4 in various ratio during the degradation process under air or flowing oxygen at 350–450 °C. Further thermal treatment under flowing oxygen leads to pure submicronic 2H-BaCoO3-δ above 650 °C in the case of cdta complexes, i.e. in softer conditions compared to the solid state route performed under high oxygen pressure. No essential influence of the cobalt valence in the precuror complexes was observed regarding the target BaCoO3-δ oxygen non stoichiometry. Finally, with a view to access porous electrodes for SOFCs, we demonstrated the possibility of one-stage-deposition of BaCoO3-δ layers on dense YSZ substrates, with a relatively good adherence, via the high temperature degradation of these complexes.

Platinum role in hydrophilicity enhancement of Cr-doped TiO2 thin films

Abstract In this paper, we have investigated the hydrophilic properties of the titania films doped with increasing chromium percentages (from 2.1 at.% till 4.0 at.%). Cr-doping induces an increase in the rutile weight %, a more compact structure, and a significant red shift of the TiO2 absorption edge, the last property being very important in the self cleaning applications. For the chosen Cr concentrations, the films did not show promising hydrophilic properties. To improve them, we have applied a novel surface modification method, reported in literature mainly for powders, namely, surface metallisation. We have observed that, by depositing Pt islands on the film with the highest Cr content, its hydrophilic properties improve for a certain metal coverage area. The explanation was based on FT-IR and X-ray photoelectron spectroscopy analysis, performed on the UV irradiated and non-irradiated films, which gives information on the relationship between hydrophilicity and the amount of the adsorbed hydroxyl groups.

Correlation Between Size of CoFe 2 O 4 Nanoparticles Determined from Experimental and Calculated Data by Different Mathematical Models

This study reports the synthesis of CoFe2O4 nanoparticles by coprecipitation method in the presence of Linseed Oil as surfactant. The capping agent was used to stabilize the particles and prevent their agglomeration. The characteriza- tion studies were conducted by in situ X-ray diffraction, transmission electron microscopy, thermal analysis (TG-DTA) and FTIR spectroscopy. The average particle sizes obtained by XRD data were used to obtain a correlation with size of CoFe2O4 nanoparticles determined, using mathematical equations based on different models. The statistical studies show that the cubic model gives a good correlation within the whole temperature range (100 - 850 °C). The result of these in- vestigations was very useful for establishing the optimal calcination temperature. FT-IR spectroscopy and thermogra- vimetric analysis (TG) showed that the core-shell structure type of CoFe2O4 nanoparticles is stable below this annealing temperature. TEM analysis indicates that the CoFe2O4 samples during the calcinations treatment were spherical in shape and uniform in morphology and particles size.

Influence of type of precursors on the sol-gel synthesis of the LaCoO3 nanoparticles

Abstract Perovskite-type LaCoO3 was prepared by sol-gel method using nitrates / chlorides as precursors and citric acid as chelating agent. Chemical composition was obtained by means of EDX method. The structures of sintered samples were investigated by scanning electron microscopy (SEM), IR and XRD analysis. The results of X-ray diffraction indicated that the LaCoO3nanopowders obtained using nitrate as precursors had a rhombohedral perovskite-type crystal structure (S. G: R-3c), while that obtained using chloride as precursors had a mixture of LaCoO3, LaOCl and Co3O4. The all lanthanum cobaltites exhibit catalytic activity on the decomposition of hydrogen peroxide, ascribed to their higher surface and Co3+ concentration