Valentin Nica

Imino-chitosan biopolymeric films. Obtaining, self-assembling, surface and antimicrobial properties

The paper reports the preparation of twelve imino-chitosan biopolymer films by acid condensation of the amino groups of chitosan with various aldehydes, in aqueous medium, followed by slow water removal. FTIR spectroscopy has shown drastic conformation changes of chitosan macromolecular chains—from a stiff coil to a straight one, while wide angle X-ray diffraction evidenced a layered morphology of the biopolymer films. Contact angle and surface free energy determination indicated a higher biocompatibility of the new biopolymers as compared to the chitosan parent, while the microbiological screening demonstrated their self-defense properties against common and virulent pathogen agents. It was concluded that the reversibility of imine forming promotes the self-assembling of imino-chitosan biopolymer films into a lamellar morphology and, on the other hand, the slow release of the antimicrobial aldehyde in the microbiological culture. The obtained results demonstrate that chitosan polyamine is a challenging workbench to functional biodynamic materials.

Nanosized spinel ferrites synthesized by sol-gel autocombustion for optimized removal of azo dye from aqueous solution

Nanosized spinel ferrites MFe2O4 (M = Ni, Co, and Zn) have been prepared by sol-gel autocombustion method using citric acid as a fuel agent. The materials are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The spinel ferrites have been applied for Congo-Red (CR) dye adsorption using batch technique. Different kinetic and equilibrium models have been fitted by nonlinear regression to analyze the adsorption data. In accordance with Langmuir isotherm, the maximum adsorption capacity at 293 K is 14.06mg/g for CoFe2O4 and 17.13 mg/g for NiFe2O4. The values of mean free energy determined from Dubinin-Radushkevich isotherm are higher than 8 (kJ mol-1), indicating a chemisorption mechanism. Based on the calculated thermodynamic parameters (free energy, enthalpy, and entropy) the adsorption of CR onto ferrites is a spontaneous and endothermic process. Response surface methodology has been applied to construct the multiple regression models for prediction of the adsorption capacity and removal efficiency. The model-based optimization has been performed using genetic algorithms and desirability function approach. The single-objective optimization has yielded a maximum value of color removal efficiency of 98.995%, using NiFe2O4 adsorbent. The multiobjective optimization has resulted in the improvement of both removal efficiency and adsorption capacity.

The influence of the chelating/combustion agents on the structure and magnetic properties of zinc ferrite

AbstractThe present study is reporting the influence of the chelating/combustion agents on the magnetic properties of Zn ferrite. Six chelating/combustion agents, citric acid, egg white, tartaric acid, glycine, glucose and urea, were used to obtain monophase zinc nanoferrite via a sol-gel auto-combustion method. The samples were subjected to a comparative study of structural features and magnetic properties by means of infrared spectroscopy, X-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Significant influence of fuel and combustion mode was observed in the magnetic behavior of as-obtained samples. Values of the structural parameters were discovered to vary as a function of fuel choice, and to obtain crystallite size between 38 and 62 nm, inversion degree between 0.239 and 0.807, lattice parameter between 8.4125 and 8.4432 Å. The optimization of sol-gel method synthesis of zinc ferrite nanoparticles by chosing the appropriate fuel is providing structural and magnetic properties of zinc nanoferrite as potential materials to be used in biomedical applications.

Optimization of synthesis conditions and the study of magnetic and dielectric properties for MgFe2O4 ferrite

AbstractNano-sized magnesium ferrites were synthesized by the sol-gel auto-combustion method using a variety of chelating/combustion agents: tartaric acid, citric acid, cellulose, glycine, urea and hexamethylenetetramine. The original purpose of this work was the synthesis of nano-sized magnesium ferrite by using, for the first time, cellulose and hexamethylenetetramine as chelating/combustion agents. Synthesized samples were subjected to different heat treatments at 773 K, 973 K and, respectively 1173 K in air. The disappearance of the organic phase and nitrate phase with the spinel structure formation was monitored by infrared absorption spectroscopy. Spinel structure, crystallite size and cation distribution were evaluated by X-ray diffraction data. The morphology of as-prepared powders was studied using scanning electron microscopy. The magnetic and dielectric properties were studied for the obtained samples.

Polyurethane-extracellular matrix/silver bionanocomposites for urinary catheters

Polyurethane–extracellular matrix membranes with bionanocomposites or coatings containing a small amount of biocompatible polymers such as hydrolyzed collagen, elastin, hyaluronic acid or chondroitin sulfate, and silver were obtained by solvent casting or electrospinning/electrospraying of the polyurethane–extracellular matrix–Ag formulations onto pure polyurethane membrane in order to achieve improved antibacterial biomaterials for urinary catheters. Using Fourier transform infrared spectroscopy, the interaction of the incorporated silver nanoparticles with polyurethane–extracellular matrix was found, while X-ray photoelectron spectroscopy and X-ray diffraction analyses ws used to determine the presence of metallic Ag for polyurethane membrane and Ag only in oxidized state for polyurethane–extracellular matrix membranes due to the stabilizing effect of polymeric components. The in vitro antimicrobial tests against Escherichia coli, Salmonella typhymurium, and Listeria monocytogenes were used for the evaluation of the antimicrobial efficiency.

Investigations on nanoconfinement of low-molecular antineoplastic agents into biocompatible magnetic matrices for drug targeting

Magnetic mesoporous silica nanoparticles are employed as biocompatible matrices to host low-molecular antineoplastic drugs. 5-Fluorouracil is a well-known antimetabolite drug used to treat many malignancies: colon, rectal, breast, head and neck, pancreatic, gastric, esophageal, liver and G-U (bladder, penile, vulva, prostate), skin cancers (basal cell and keratosis). Unfortunately severe gastrointestinal, hematological, neural, cardiac and dermatological toxic effects are often registered due to its cytotoxicity. Thus, this work focuses on development of a magnetic silica nanosystem, capable of hosting high amounts of 5-fluorouracil and delivers it in a targeted manner, under the influence of external magnetic field. There are few reports on nanoconfinement of this particular small molecule antimetabolite on mesoporous silica hosts. Therefore we have investigated different ways to confine high amounts of 5-FU within amino-modified and non-modified mesopores of the silica shell, from water and ethanol, under magnetic stirring and ultrasound irradiation. Also, we have studied the adsorption process from water as a function of pH in order to rationalize drug-support interactions. It is shown that nature of the solvent has great influence on diffusion of small molecules into mesopores, which is slower from alcoholic solutions. More importantly, sonication is proven as an excellent alternative to long adsorption tests, since the time necessary to reach equilibrium is drastically reduced to 1h and higher amounts of drug may be immobilized within the mesopores of amino-modified magnetic silica nanoparticles. These results are highly important for optimization of drug immobilization process in order to attain desired release profile.

Synthesis and Characterization of Co-Substituted Ferrite Nanocomposites

We report the synthesis of CoxNi1-xFe2O4 (where x is 0, 0.25, 0.50, 0.75, 1) nanoparticles (NPs) by a wet chemical method using carboxymethyl cellulose (CMC) solution as surfactant. Their structure and magnetic properties were evaluated by X-ray diffraction (XRD), Fourier-Transform Infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The gas and humidity sensing properties of the samples were also investigated. Powder X-ray diffraction analysis demonstrated the formation of face-centered cubic structure for all the samples. The average crystallite size and lattice parameters have been calculated by Rietveld refinement. The FTIR spectra of NPs confirm the presence of CMC functional groups and stretching bands attributed to the intrinsic vibrations of tetrahedral and octahedral sites of spinel ferrite. The magnetization curves of the nanocomposites at room temperature demonstrated saturation magnetizations from 21 emu/g to 58 emu/g and coercivity values between 130 Oe and 835 Oe. As not many studies have been published on this topic, the gas sensing properties of Ni-substituted Co ferrites have been evaluated. The measurements revealed that Co0.25Ni0.75Fe2O4 is the most sensitive to acetone vapors.

Synthesis and Characterization of Co-Ni and Fe

Co-Ni needle-like and Fe3O4-Pd spherical nanoparticles were prepared by water-in-oil microemulsion (W/O). The as-synthesized nanoparticles have been encapsulated by silica (SiO2) and polyvinyl alcohol (PVA) in N2 atmosphere. Their structure and magnetic properties were evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The influence of structural modifications to the magnetic properties of nanocomposites has been investigated. Powder X-ray diffraction analysis indicated the formation of face-centered cubic phase for both Co-Ni and Fe3O4-Pd systems. The average crystallite size for the studied samples has been calculated in the range of 7-26 nm. TEM images revealed the morphology of the particles as needle-like nanoparticles for Co-Ni alloy and spherical for Fe3O4-Pd system. The magnetization curves of nanocomposites at room temperature demonstrated coercivity values between 8.2 and 15.5 kA/m for Co-Ni nanocomposites and superparamagnetic behavior of Fe3O4-Pd nanocomposites due to the small-size effect of nanoparticles.

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In this study, we analyze the unexplored field of combined effects of active surface area and p–n heterojunctions of a composite material dedicated to gas sensing applications. The used materials are thin films of mixtures of copper and zinc oxides. Individually, both copper oxide and zinc oxide shows interesting sensing performances toward a broad category of gases. The investigated films are obtained by thermal oxidation of Cu/Zn metallic multilayers. Cu/Zn metallic multilayers were obtained by using physical vapor deposition technique. The sensitivity of the composite materials, at ethanol, LPG and CO respectively, was investigated and it was observed that the highest sensitivity is obtained for ethanol. Complementary investigations (X-ray Diffraction, X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy respectively) were conducted in order to understand, explain and confirm the relationship between the oxidation conditions, structure, surface morphology and the exhibit sensing properties. The experimental results indicate that the sensitivity depend on the oxidation duration.

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Abstract Two cationic ester-bonded cleavable gemini surfactants of different hydrophobic chain length ethane-1,2-diyl bis(N,N-dimethyl-N-alkylammoniumacetoxy)dichloride, CnH2n+1(CH3)2N+(CH2COOCH2)2N+(CH3)2CnH2n+1. 2Cl- (n-E2-n, n=12, 16), having ester linkage in the spacer, were synthesized adopting the reported procedure. Physicochemical properties of the single and binary gemini-conventional mixed micelles of different mole fractions were studied by conductivity measurements at 30 ºC. The conventional surfactants used were: DTAC (dodecyltrimethylammonium chloride), CTAC (hexadecyltrimethylammonium chloride), CPC (cetylpyridinium chloride), SDS (sodium dodecyl sulfate), SDBS (sodium dodecylbenzene sulfonate), TX-100 (t-octylphenoxypolyethoxyethanol) and Brij 58 (polyoxyethylene (20) cetyl ether). Whereas the critical micelle concentration (cmc) values for the dicationic geminis (12-E2-12 and 16-E2-16) were found to be very low as compared to the respective monomeric surfactant with the same number of carbon atoms in the hydrophobic chain per hydrophilic head group, those for all the binary systems were found to be less than the ideal cmc values studied at different mole fractions of the geminis. This synergistic interaction between the surfactants has been analyzed in the light of various theoretical models such as Clint, Rubingh, Motomura and Maeda.