Maria Zaharescu

TiO2(Fe3+) nanostructured thin films with antibacterial properties

TiO2-based nanostructured Fe3+-doped coatings have been prepared by the sol–gel method on glass substrates. The coatings were characterized by X-ray diffraction and spectroellipsometry methods. The influence of Fe3+ dopant concentration, number of coatings, and calcination temperature on the films structure was established. The antibacterial activity against E. coli, has been studied applying the so-called antibacterial-drop test. The bactericidal activity for the above bacteria cells was estimated by relative number of bacteria survived calculated from the number of viable cells which form colonies on the nutrient agar plates. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the temperature of thermal treatment and formation of anatase crystalline structure. The long thermal treatment results in rutile crystalline structure formation followed by the decrease in the antibacterial activity of the coating.

Influence of the silica based matrix on the formation of iron oxide nanoparticles in the Fe2O3–SiO2 system, obtained by sol–gel method

Composite iron oxide–SiO2 materials were prepared by a sol–gel method starting with two types of precursors, tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS), as the SiO2 source. As the iron source a soluble Fe2+ salt, mainly Fe(SO4)2·7H2O, was used, the iron oxides were generated during the sol–gel process. The amorphous gels obtained were thermally treated up to 1000 °C in order to obtain iron oxides with different structures and grain size. The initial gels and the thermally treated samples were characterised by DTA/TGA analysis, DR-UV–VIS and IR-spectroscopy, EPR measurements, transmission electron microscopy (TEM) and BET surface area methods. The matrices obtained from the precursors play a major role in the evolution of the process. In both cases the initial gels are amorphous. In the non-porous matrix obtained by thermal treatment using methyltriethoxysilane (MTEOS), the tendency for crystallisation increases, and the iron oxide particle size is increased.

Comparative study of the sol–gel processes starting with different substituted Si-alkoxides

Abstract In the present work a comparative study of the hydrolysis–polycondensation processes of different Si-substituted alkoxides, leading to hybrid materials with covalent –Si–C– bonds, was carried out. The following alkoxides were used: tetraethoxysilane (TEOS), methyltriethoxysilane (MTEOS) and vinyltriethoxysilane (VTEOS). Using gas chromatography coupled with mass spectrometry (CG-MS), nuclear magnetic resonance (29Si-NMR) and infrared spectrometry (IR), information about the sol–gel process in the mentioned systems were obtained. The differences in the reactivity of the studied alkoxides are connected with the steric effect of the organic substituents. The reactivity of the alkoxides in the early stages of the hydrolysis-polycondensation process increased in the order TEOS

Thermal behaviour of hydrotalcite-like compounds: study of the resulting oxidic forms

Abstract Hydrotalcite (HT)-like compounds of general formula [Ni 1− x Al x (OH) 2 ](CO 3 ) x /2 · m H 2 O, where 0.25≤ x ≤0.66, have been synthesised 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 450–500°C, 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 450°C calcination temperatures of HT-like precursors, whereas the corresponding spinel, NiAl 2 O 4 , was formed by interaction between NiO and Al 2 O 3 , at 900°C. New information was evidenced by combining isothermal pre-reduction of oxidic systems obtained at 450 and 900°C with temperature-programmed reduction (TPR) experiments; a NiO–Al 2 O 3 structure with a spinel-type local order and NiO were found in all samples at 450°C, oxidic forms that were thermally stable up to 900°C. 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.

Tin dioxide sol-gel derived thin films deposited on porous silicon

SnO/sub 2/ and SnO/sub 2/:Sb sol-gel derived thin films have been prepared from tin (II) ethylhexanoate and tin (IV) ethoxide precursors (the later not reported before) in order to be used for gas sensing applications where porous silicon is used as a substrate. Transparent, crack-free and adherent layers were obtained on different types of substrates (Si, SiO/sub 2//Si). By energy dispersive X-ray spectroscopy (EDXS) performed on the cross section of the porosified silicon (PS) coupled with XTEM analysis, the penetration of the SnO/sub 2/ sol-phase in the nanometric pores followed by the SnO/sub 2/ consolidation film in the pores of the PS, during subsequent annealing at 500/spl deg/C has been experimentally proved.

Al2TiO5 preparation starting with reactive powders obtained by sol-gel method

Abstract Individual Al 2 O 3 , TiO 2 and SiO 2 , as well as binary Al 2 O 3 -TiO 2 powders have been obtained by sol-gel method, polymeric route. The obtained powders have been characterized by X-ray diffraction (XRD), IR-spectrometry and transmission electron microscopy (TEM) methods. In the used experimental conditions amorphous, submicronic, monodisperse powders have been obtained. The preparation of Al 2 TiO 5 and of some compositions situated in the Al 2 TiO 5 -Al 6 Si 2 O 13 pseudobinary system has been realized by solid-state reaction starting with the mentioned above powders. The thermal treatment schedule of the pressed powder mixtures has been established according to the results of differential thermal and thermogravimetric analysis (DTA/TGA). The formation of the compound has been followed by XRD, dimensional variation of the samples and apparent density measurements. The results obtained starting with reactive powders have been compared with those obtained starting with commercial powders. The samples have shown a high reactivity and the formation of tialite was enhanced. However the sintering tendency was not essentially increased.

New SnO2 Nano-Clusters Obtained by Sol-Gel Route, Structural Characterization and Their Gas Sensing Applications

SnO2 is a well known and widely studied sensor material for the detection of CO and flammable gases like H2. Here we discuss the use of porous networks of SnO2 nanoparticles for an optical detection of the reducing gas CO. Nano-sized SnO2 clusters were prepared by the sol-gel method using an organically modified Sn precursor. After thermal treatment at 550°C the mean diameters of the primary SnO2 nanoparticles constructing the network were estimated to ∼25 nm and ∼15 nm, respectively, for particles obtained in acid and basic catalysis. The reversible redox behavior of SnO2 nano-clusters in reducing and oxidizing atmospheres (CO, O2) was studied optically by in-situ DR-UV/VIS spectroscopy.

Atomic Force Microscopy Study of TiO2 Films Obtained by the Sol-Gel Method

Atomic Force Microscopy (AFM) was used to study the influence of thermal treatments on the structural and textural properties of the sol-gel TiO2 films obtained from Ti(OC3H7i)4. X-ray diffraction (XRD), ellipsometric and porosity measurements have also been made.The TiO2 sol-gel films were homogeneous, transparent and amorphous. Heat treatments in the 400–600°C range indicate that the films have a strong tendency to crystallization. The high initial homogeneity of the TiO2 films was preserved during the crystallization process. AFM shows that the thermally treated films exhibit uniform, monodispersed crystals.

Contribution to the study of SnO2-based ceramics

Sintered SnO2-based ceramics are considered to be promising construction materials for manufacturing stable electrodes for various technological applications. The high-temperature interactions of components, important with respect to the sintering capacity and consequently the densification, have been investigated in the binary systems SnO2-Sb2O3 and SnO2-CuO, and the ternary system SnO2-Sb2O3-CuO. In contrast to the Sno2-Sb2O3 mixtures with a poor sintering ability, the binary SnO2-CuO and ternary SnO2-Sb2O3-CuO mixtures exhibit significantly improved sintering properties owing to the formation of liquid phase (eutectic melt) in the presence of copper(II)oxide.

SnO2 electroceramics with various additives

Abstract The electrical properties of SnO 2 based ceramics are enhanced by the addition of different substituents into the SnO 2 lattice. For the composition containing 2.5 mol% Sb 2 O 3 the highest value of the electrical conductivity was obtained. The mentioned composition has a SnO 2 solid solution structure and presents semiconducting properties. In the present work, the influence of Sb 2 O 3 , CuSb 2 O 6 , CuO+Sb 2 O 3 , In 2 O 3 , CeO 2 used in the same concentration as additives, on the structure and electrical properties of the SnO 2 was studied. The phase composition analyzed by XRD, pointed out the formation of the SnO 2 solid solution. When using In 2 O 3 , a mixture of phases is formed. The XRD results are confirmed by IR spectroscopy. The formation of rutile type structure is evidenced by the decreasing, up to disappearance, of SnO 2 bands. The Seebeck coefficient values and the resistivity measurements results showed a semiconductive behavior, with a n -type electrical conductivity for all the samples.