Petrisor Samoila

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.

Novel Synthesis Route for Chitosan-Coated Zinc Ferrite Nanoparticles as Potential Sorbents for Wastewater Treatment

Magnetic chitosan–zinc ferrite (ChZnF) composites were proposed as potential adsorbents due to their appropriate physical characteristics and facile separation under external magnetic fields. The magnetic component (ZnFe2O4) was prepared by the sol–gel autocombustion method that yields nanometric spinel compounds with narrow size distribution and with low energy consumption. A certain amount of magnetic powder was dispersed consecutively by ultrasonication in a chitosan-PEG (polyethylene glycol) mixture, in order to obtain the desired nanocomposite. The as-obtained materials were characterized by FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), TEM (transmission electron microscopy), small-angle X-ray scattering, and Brunauer–Emmett–Teller test measurements. Finally, the chitosan-ferrite nanomaterial was successfully tested in simulated wastewater treatments. Different kinetic and equilibrium models have been fitted by nonlinear regression to analyze the adsorption data.

Influence of the B-site cation nature on dielectric properties of Ca2XBiO6 (X = Dy, Fe, Al) double perovskite

For the synthesis of Ca2XBiO6 (X = Dy, Fe, Al) metal oxides with ordered double-perovskite structure, the sol-gel auto-combustion method has been used for the first time. The synthesis progress was followed by the Fourier transform infrared spectroscopy and the samples structure was investigated by X-ray diffraction. The samples morphology was studied by means of scanning electron microscopy. The influence of the nature of the trivalent B-site cation on the dielectric properties was evaluated by resistivity measurements in vacuum at frequencies between 102–105 Hz. The best dielectric behavior was obtained for Ca2AlBiO6 and Ca2DyBiO6, while the best semiconductor behavior was found for Ca2FeBiO6.

Influence of A-site Cation on Structure and Dielectric Properties in A2DyBiO6 (A=Mg, Ca, Sr, Ba) Double Perovskites

Double perovskite metal oxides with formula A2DyBiO6 (A = Mg, Ca, Sr, Ba) were synthesised by a sol–gel auto-combustion method, using citric acid as the combustion agent. The effects of A-site cation on the structure, morphology, and dielectric properties were examined. The synthesis was monitored using Fourier transform infrared spectroscopy (FTIR) to indicate the absence of organic phase. X-ray diffraction (XRD) analysis showed that the compounds have three different perovskite structures. Structural characterisation of the samples was evaluated using XRD patterns. Scanning electron microscopy showed that all samples are formed by agglomerated particles. Dielectric properties were evaluated using dielectric permittivity and dielectric losses. Cole–Cole plots show a single semicircle for all materials, indicating that the double perovskites obtained are composed of well conducting grain boundaries and poorly conducting grains.

Ferromagnetic iron oxide–cellulose nanocomposites prepared by ultrasonication

This paper highlights the efficiency of ultrasonication, as a clean and energy-saving method for the preparation of cellulose–iron oxide ferromagnetic composites in two steps. Hydroxyl-functionalized maghemite–goethite nanoparticles (MG) having a saturation magnetization of 56.9 emu g−1 at room temperature were first synthesized by a one-pot procedure involving ultrasonication of an aqueous alkaline Fe2+ salt solution. Organic–inorganic nanocomposites were obtained by a second ultrasonication step of an aqueous suspension of micronized cellulose and MG nanoparticles. The cumulative effect of ultrasonication and MG nano-projectiles was found to strongly decrease the degree of crystallinity of cellulose. The microstructural characterisation of the resulting composite evidenced its size polydispersity, with small nanoparticles uniformly attached on the surface of cellulose microfibrils. Vibrating sample magnetic measurement indicated a hysteresis curve specific to ferromagnetic materials and the appearance of a superparamagnetic phenomenon at low temperature (a blocking temperature of 62 K). Cellulose/iron oxide clusters with an average size around 7 nm and characterized by high decomposition temperatures (around 645 °C) were proven to be responsible for the observed superparamagnetic phenomenon. The superiority of the ultrasonication process versus a procedure involving simple mechanical stirring, in terms of composite yield, dispersion uniformity of MG nanoparticles and magnetic properties is discussed.