Daniel Sibera

Equilibrium and kinetic studies on acid dye Acid Red 88 adsorption by magnetic ZnFe2O4 spinel ferrite nanoparticles.

A magnetic ZnFe2O4 (MNZnFe) was synthesized by microwave assisted hydrothermal method and was used as an adsorbent for the removal of acid dye Acid Red 88 (AR88) from aqueous solution. The effects of various parameters such as initial AR88 concentration (10-56 mg L(-1)), pH solution (3.2-10.7), and temperature (20-60°C) were investigated. Prepared magnetic ZnFe2O4 was characterized by XRD, SEM, HRTEM, ICP-AES, BET, FTIR, and measurements of the magnetic susceptibility. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption. Equilibrium data fitted well with the Langmuir model. Pseudo-first-order and pseudo-second-order kinetic models and intraparticle diffusion model were used to examine the adsorption kinetic data. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. Thermodynamics parameters, ΔG°, ΔH° and ΔS°, indicate that the adsorption of AR88 onto MNZnFe was spontaneous and exothermic in nature.

Magnetic properties of ZnFe2O4 nanoparticles

Fine particles of ZnFe2O4 were synthesized by a wet chemical method in the (80 wt.% Fe2O3 + 20 wt.% ZnO) system. The morphological and structural properties of the mixed system were investigated by scanning electron microscopy, X-ray diffraction, inductively coupled plasma atomic emission, and X-ray photoelectron spectroscopy. The major phase was determined to be the ZnFe2O4 spinel with particle size of 11 nm. The magnetic properties of the material were investigated by ferromagnetic resonance (FMR) in the temperature range from liquid helium to room temperature. A very intense, asymmetric FMR signal from ZnFe2O4 nanoparticles was recorded, which has been analyzed in terms of two Callen-lineshape lines. Temperature dependence of the FMR parameters was obtained from fitting the experimental lines with two component lines. Analysis of the FMR spectra in terms of two separate components indicates the presence of strongly anisotropic magnetic interactions.

Preparation of aluminium ammonium calcium phosphates using microwave radiation

Microwave radiation was used in the acquisition of aluminium ammonium calcium phosphates. The substrates such as CaCO3, H3PO4, aqueous ammonia were reagent grade, whereas Al(OH)3 was prepared afresh. The influence of process parameters (pH 6 ± 2, molar ratios of Al3+: Ca2+: PO43− in the substrates, respectively 0.31: 0.62: 1; 0.5: 0.5: 1; 0.72: 0.36: 1) on the phase composition and the product properties was determined. Statistical software STATISTICA 10 was used for planning and evaluation of the experiments. The process parameters making it possible to acquire the material with the anticipated physicochemical properties were determined based on statistical evaluation of the planned research by the plan fractional factorial design at three levels 3(k−p). The phase composition of the samples was studied using XRD analysis. The specific surface area was calculated using the BET method and the particle size was determined by LSM. Materials with a molar ratio of Al3+: Ca2+ and Al3+: NH4+ in the range of 0.07–0.76 and 0.75–3.4, respectively, with an absorption oil number of 36–56 g per 100 g, SBET within 8.2–73 m2 g−1, and particle size in the range of 156–252 nm were obtained.

FMR and Magnetization Study of ZnFe 2 O 4 Nanoparticles in 0.40Fe 2 O 3 /0.60ZnO Nanocomposite

Zinc oxide (ZnO) nanocrystals containing Fe2O3 have been synthesized by the calcination method. Ferromagnetic resonance (FMR) and dc magnetization measurements of 0.40(Fe2O3)/0.60(ZnO) nanocomposite have been carried out in the 4-300 K range to study the magnetic properties of agglomerated magnetic zinc ferrite ZnFe2O4 (ZFO) nanoparticles with an average crystallite size of 12 nm. Temperature dependence of the resonance field, linewidth, and the integrated intensity calculated from FMR spectra have been determined to obtain the value of the uniaxial anisotropy field and to establish the ranges of different relaxation types. Magnetization measurements in ZFC and FC modes as well as the study of hysteresis loops allowed calculating different magnetic characteristics - blocking/freezing temperature, magnetic moment, anisotropy constant, and anisotropy field. The observed magnetic properties of 0.40(Fe2O3)/0.60(ZnO) nanocomposite were explained based on the core-shell model of ZFO nanoparticles. From comparison of FMR and dc magnetization measurements, the temperature ranges of magnetic phases existing in ZFO nanoparticles in 0.40Fe2O3/0.60ZnO nanocomposite are proposed.

Adsorptive removal of cationic dye from aqueous solutions by ZnO/ZnMn2O4 nanocomposite

ABSTRACT The ZnO/ZnMn2O4 nanocomposite (ZnMn) was used as adsorbent for the removal of cationic dye Basic Yellow 28 (BY28) from aqueous solutions. The adsorbent was characterized by X-ray diffraction, scanning electron microscope, TEM, Fourier transform infrared ray, BET, particle size distribution and zeta potential measurements. The adsorption parameters, such as temperature, pH and initial dye concentration, were studied. Kinetic adsorption data were analyzed using the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models. The Langmuir and Freundlich isotherm models were applied to fit the equilibrium data. The maximum adsorption capacity of BY28 was 48.8 mg g−1. Various thermodynamic parameters, such as ΔG°, ΔH° and ΔS°, were calculated.

Magnetic Properties of n CoO/(1- n )ZnO Nanocomposites Obtained by Calcination

Magnetic properties of the nCoO/(1-n)ZnO (n = 0.4, 0.50, 0.60 and 0.70) nanocomposites obtained by using traditional wet chemical synthesis method followed by calcination at 600∘C were investigated by dc magnetometry and magnetic resonance spectroscopy. XRD measurements revealed the presence of only two phases: ZnO (hexagonal nanocrystals with sizes in 64–300 nm range) and spinel phase Co3O4 (spheroidal nanocrystals with sizes in 14–21 nm range). Magnetic dc susceptibility measurements in 2–300 K range revealed dominating paramagnetic behavior in the whole temperature range and the presence of a strong temperature-independent component. With exception of n = 0.70 sample, no behavior connected with the expected phase transition to antiferromagnetic phase in Co3O4 and superparamagnetism was registered. Experimental results could be consistently explained by assuming that the most of high-spin Co2+ ions are involved in formation of antiferromagnetic pairs or clusters. Low intensity electron paramagnetic resonance spectra registered at RT were attributed to two different magnetic components – one involving paramagnetic Co2+ ions at Zn2+ sites in ZnO and the other due to Co2+ in Co3O4 phase or more probably the superparamagnetic resonance of Co3O4 nanoparticles. The former component dominates in nanocomposites with small concentration of cobalt, the latter in highly Co concentrated samples.

Surface characteristics of KOH-treated commercial carbons applied for CO2 adsorption:

The effect of an alkali treatment (potassium hydroxide) on the properties of a commercial activated carbon has been studied. The aim of the treatment was to improve the adsorption properties of the material toward carbon dioxide. In the result of the treatment, silica contained in the raw carbon was removed and the density of the material increased. The changes in the surface chemistry were observed as well. The treatment of the activated carbon with KOH resulted in a complete removal of carboxy and lactone groups and a decrease of the general content of the acidic groups (more significant than that of basic groups). Simultaneously, the surface concentration of hydroxyl groups increased. The alkali treatment of activated carbon resulted in an increase of carbon dioxide uptake of 14% (measured using a volumetric method at 0℃). The adsorption of carbon dioxide on activated carbon has a mixed (physicochemical) character and that two types of adsorption sites are present at the surface. The adsorption energy varies roughly from 25 to 60 kJ/mol.

Magnetic resonance study of nanocrystalline 0.10MnO/0.90ZnO

Magnetic properties of nanosize ZnO powders doped with MnO magnetic dopand have been studied. Sample designated as 0.10MnO/0.90ZnO was characterized by XRD that revealed the presence of ZnO and ZnMnO3 phases. An average size of magnetic ZnMnO3 nanocrystallites was 9 nm. Magnetic resonance study has been carried out in the 4-290 K temperature range. The spectrum at each temperature was analyzed in terms of three components. The temperature dependences of resonance field, linewidth and integrated intensity of these components have been determined. Magnetic centers responsible for producing the observed spectra have been proposed.