Violeta Popescu

TiO2 thin films prepared by sol ? gel method

There is a growing awareness that titania (TiO2) and TiO2-based oxide systems are the most promising candidates for the development of photoelectrodes for photoelectrochemical cell (PEC) for solar-hydrogen production [1]. The PEC is equipped with a single photoelectrode (photoanode) and cathode, both of which are immersed in an aqueous electrolyte. In this work we present a sol-gel method to prepare TiO2 thin films on ITO using tetraisopropoxides of titanium, acetylacetone, 1-butanol and Tween 80 as surfactant. The films were deposited on ITO coated glass slides by spray pyrolysis. UV-VIS spectra and fluorescence measurements were made for the solutions and films. X-ray diffraction was used for structural investigations and the morphology of the film was studied by Scanning Electron Microscopy.

Structural and morphological properties of HA-ZnO powders prepared for biomaterials

Abstract The purpose of this study was to investigate the structural and morphological properties of hydroxyapatite – zinc oxide (HA-ZnO) powders prepared to be used in an endodontic sealer formulation. The HA-ZnO was synthesized from hydroxyapatite (HA) in the presence of zinc oxide (ZnO) sol. The starting reagents were CaO, H3PO4 and a suspention of ZnO (25% in water). Following precipitation, the obtained sol was subjected to heat treatment at 110°C, 400°C, 850°C and 1050°C. The study focused on the influence of the thermal treatment on the cristallinity of precipitated powders. X-ray diffraction was used in order to study the structural properties of the obtained powder. Fourier Transform Infrared Spectroscopy (FT-IR) was used in order to evaluate the interactions between HA and ZnO. The morphology of the samples was studied by Scanning Electron Microscopy (SEM). Transmission Electron Microscopy and High Resolution Transmission Electron Microscopy (TEM, HRTEM) were used for the determination of particle size and fractal analysis. The fractal analysis of images using the standard box-counting method is presented and the results are discussed. It was demonstrated that the fractal dimension analysis is a useful method to quantitatively describe the complex microstructures and it can reveal the relation between fractal parameters. Graphical Abstract

Obtaining and Characterizing Alginate/k-Carrageenan Hydrogel Cross-Linked with Adipic Dihydrazide

The aim of this paper is obtaining and characterizing hydrogels based on different ratios of oxidized alginate (oA) and k-carrageenan (C), chemically cross-linked with adipic dihydrazide (adh). The alginate (A) was first oxidized with sodium metaperiodate in order to transform it into the dialdehyde derivative, a more reactive compound than alginate. A known procedure for oxidation of alginate with sodium metaperiodate in ethanol-water in order to improve alginate reactivity by transforming the hydroxyl end-groups into dialdehyde was used, preceded by a partially cleavage of the alginate chains. In the second stage, the mixture of dialdehydic derivative of oxidized alginate, k-carrageenan and glycerol subjected to reaction with adipic dihydrazide leads to a Semi-Interpenetrated Network covalently cross-linked alginate/k-carrageenan hydrogel (oACadh), based on the dihydrazone compound which is responsible for the chemical cross-linking. Pure alginate, k-carrageenan, oxidized alginate, adipic dihydrazide and the cross-linked hydrogel were characterized by: FTIR, XRD, and SEM.

Utilization of granular activated carbon adsorber for nitrates removal from groundwater of the Cluj region

The level of nitrates from groundwater from Cluj County and other areas from Romania have increased values, exceeding or getting close to the allowed limit values, putting in danger human and animal heath. In this study we used granular activated carbon adsorbent (GAC) for nitrate (NO − 3) removal for the production of drinking water from groundwater of the Cluj county. The influences of the contact time, nitrate initial concentration, and adsorbent concentration have been studied. We determined the equilibrium adsorption capacity of GAC, used for NO − 3 removal and we applied the Langmuir and Freundlich isotherm models. Ultraviolet-visible (UV-Vis) and Fourier transform infrared (FTIR) spectroscopy, X ray diffraction (XRD), Scanning Electron Microscopy (SEM) were used for process characterization. We also determined: pH, conductivity, Total Dissolved Solids and Total Hardness. The GAC adsorbents have excellent capacities of removing nitrate from groundwater from Cluj County areas.

TiO2 – based systems for photoelectrochemical generation of solar hydrogen

In the present work our attention was focused on the obtaining photoelectrodes for photoelectrochemical cell that incorporate two electrodes, one of which has been titania (TiO2) coated on a transparent conducting oxide (TCO), referred to as the primary electrode and the other, the counter electrode, a non-corrosive metal such as a thin layer of platinum. A thin layer of a nanoporous TiO2 semiconductor was deposited onto a sheet of ITO conducting glass (sheet resistance ~ 30 Ωcm−2). Several complementary investigation techniques like BET, SEM and XRD were used to follow the influence of the reactants molar ratio and thermal treatment on the TiO2 photoanode. The nanocrystalline TiO2/ITO conducting glass electrode seems to be a promising photoanode in a photoelectrochemical cell for hydrogen generation by water splitting.

Toxicity caused by para-substituted phenols on Tetrahymena pyriformis: The structure-activity relationships

The toxicity of thirty para-substituted phenols on Tetrahymena pyriformis was modelled using an original methodology that uses the complex structural information of the compounds. Two models were built. The methodology allows atomic properties to be assigned to toxicity based on the selection of pairs of descriptors from the entire family, which is called Molecular Descriptors Family (MDF). One model has two independent structural descriptors and the other has four. The model with four descriptors proved to have high estimated and predictive abilities (over 97% of toxicity could be explained by structural information). The partial charge distribution by bonds (molecular topology) and space (molecular geometry) interaction proved to be related with the toxicity of para-substituted phenols on Tetrahymena pyriformis . The predictive ability of the model was tested by using the following methods: the cross-validation leave-one-out and the training versus test experiments . The comparisons among the models were performed using the correlated correlations method. The embedding of the complex information from the structure using MDF methodology can lead to further investigations of the mechanism of chemicals toxicity on Tetrahymena pyriformis .

Synthesis and Characterization of an Experimental Zn-Hydroxyapatite Powders with Application in Dentistry

In the present study, Zn-hydroxyapatite (Zn-HA) was synthesized, the powder was thermally treated at different temperatures and then characterized. The Zn-HA powder was characterized mainly by FTIR and XRD, but have been performed investigations like SEM, BET and size distribution. The addition of ZnO in hydroxyapatite causes alleged interactions with the existing groups in HA, which amend the corresponding signals to these groups in the IR spectra. X-ray diffractograms for samples (untreated and heat-treated) have been recorded and microstructural parameters for the all samples have been calculated. The obtained average sizes of the crystallites and the network tensions support the idea that Zn-HA powders are nanostructured. The SEM images and size distributions for Zn-HA indicate a cluster of crystals with nanometer-scale of the population-base. Was determined the adsorption-desorption isotherms for Zn-HA powder at 100 o C and 800 o C. The dates obtained from the analysis of particle size distribution indicates for the Zn-HA powder an size distribution for granules in the range from 0.05 to 0.3μm

The characteristics of gold films deposited on ceramic substrate

A large quantity of gold (approximately 10 tonnes yearly) is consumed, all over the world, just to decorate ceramic and glassware. Due to their advanced chemical stability gold films are used for different high technology applications. The technologies for obtaining the best “liquid bright gold” were intensively studied, but the quality of the decor coatings (films) were empirically assessed. We proposed a scientific investigation of the characteristics of gold films, deposited on ceramic substrates, from “liquid bright golds”. The composition of the film has been determined by EDS (Energy Dispersive X-ray Spectrometry). The distribution of the elements was determined at the surface of the film and in cross-section. The surface distribution of the elements was uniform. The diffusion process of the film into substrate and the migration of the substrate elements at the interface region and into the film have been highlighted.The morphology of the film was studied by SEM microscopy. The grain size varied between 0.05 – 2 μm as a function of the film composition. The major phases from the film and interface were evidenced by X-ray diffraction. The film consisted of crystalline gold. At the interface region a solid solution of Au-ZrSiO4 was identified. Other phases were in amorphous state. The reflection spectra of the films were recorded from optical properties, using a mirror gold as standard, for comparison. The film with the smaller particle size reflected the UV — VIS wavelengths in the same way as a gold mirror. The adherence of the film on the substrate can be explained by the formation of an interfacial layer from solid solution Au−ZrSiO4 and by diffusion processes.

Research Aiming Simultaneously Recycling of Waste Polyolefins by Pyrolysis, in Order to Obtain Some Fuels for Compression Ignition Engines

This paper presents the undertaken research for the establishment of the compatibility of some polyolefin waste to be recycled by pyrolysis. Polyolefin are materials produced by a polymerization process of unsaturated aliphatic hydrocarbons and represents the most important group of plastic materials. It is important to mention that among polyolefin, polyethylene (PE) and polypropylene (PP) own the first places as quantity of produced waste. Due to the common origin of the two plastic materials (PE and PP) and the relatively close melting points, we chose them for the obtaining of some fuels which are compatible with compression ignition engines. Starting from 100 % PE, the weight concentration of PP was increased up to 100%, the results of the undertaken experiments and measurements allowed us, in the final, to draw the chart of the variation of the yield of solid-liquid conversion as a function of weight concentration of the two chosen materials subjected to the process of recycling by pyrolysis.

Study on the removal of nitrate in groundwater from Căpuş, Cluj county by natural zeolite of Mirşid and granular activated carbon

AbstractThis paper focuses on a comparative study regarding the performance of natural zeolite from Mirsid (NZM) and granular activated carbon (GAC), respectively, for treatment process of contaminated groundwater from Căpus, Cluj region for nitrate removal. The effect of pH, conductivity, contact time, and nitrate concentration have been studied. The Langmuir and Freundlich models were used to fit the experimental data and these showed good correlations with the Freundlich model, providing a better description of the equilibrium (higher R2 value). Textural analysis was employed in order to determine the specific surface area, and pore size distribution of the used activated carbon and natural zeolite. The adsorbents (GAC and NZM) were characterized by using Fourier transform infrared spectroscopy and x-ray powder diffraction.