Synthesis and ESR Study of Transition from Ferromagnetism to Superparamagnetism in La_0.8Sr_0.2MnO₃ Nanomanganite

Electron spin resonance (ESR) spectroscopy was used to determine the magnetic state transitions of nanocrystalline La0.8Sr0.2MnO3 at room temperature, as a function of crystallite size. Ferromagnetic nanoparticles having an average crystallite size ranging from 9 to 57 nm are prepared by adopting the autocombustion method with two-step synthesis process. Significant changes of the ESR spectra parameters, such as the line shape, resonance field (Hr), g-factor, linewidth (∆Hpp), and the low-field microwave absorption (LFMA) signal, are indicative of the change in magnetic domain structures from superparamagnetism to single-domain and multi-domain ferromagnetism by increase in the crystallite size. Samples with crystallite sizes less than 24.5 nm are in a superparamagnetic state. Between 24.5 and 32 nm, they are formed by a single-domain ferromagnetic. The multi-domain state arises for higher sizes. In superparamagnetic region, the value of g-factor is practically constant suggesting that the magnetic core size is invariant with decreasing crystallite size. This contradictory observation with the core-shell model was explained by the phenomenon of phase separation that leads to the formation of a new magnetic state that we called multicore superparamagnetic state

Structural and Calorimetric Studies of Zinc, Magnesium and Manganese Based Phosphate and Phosphate-Silicate Glasses

Glasses of the (50-x/2)Na2O-xMO-(50-x/2)P2O5 (M = Zn, Mg or Mn) (0 ≤ x ≤ 33 mol%), (50-x)Na2O-xMO-50P2O5 (M = Zn, Mn) (0 ≤ x ≤ 33 mol%), and (0.9-x)NaPO3-xSiO2-0.1ZnO (0 ≤ x ≤ 0.1 mol) were prepared by the melt quenching technique. Samples were investigated by means of X-ray diffraction, Archimede’s method, ellipsometry, Fourier-transformed infrared (FTIR), Raman, 31P solid state magic angle spinning nuclear magnetic resonance (MAS-NMR), UV-visible spectroscopy and calorimetry. For zinc, manganese and magnesium phosphate glasses, the increase in density with the addition of MO oxide suggests the compactness of the vitreous network. For zinc phosphate silicate glasses, the variations of density and refractive index were attributed to the structural changes when SiO2 oxide is progressively introduced. The increase in the glass transition temperature (Tg) reflects an increase in the cross-link strength of the structure as MO and SiO2 oxides are gradually incorporated. For all glass composition, spectroscopic investigations revealed the depolymerization of metaphosphate chains (Q2) allowing the formation of phosphate dimers (Q1). Calorimetric dissolution shows that the dissolution is endothermic for lower MO content and become exothermic when x rises. For (50-x/2)Na2O-xZnO-(50-x/2)P2O5 (0 ≤ x ≤ 33 mol%) glasses, the formation enthalpy increases with the incorporation of ZnO oxide

Electrochemical Degradation of Phenol in Aqueous Solutions Using Activated Carbon-ZnO Composite

Olive mill wastewater (OMWW) has high added-value compounds namely phenolic alcohols, phenolic acid, flavonoids, and lignans. OMWW causes a certain amount of toxicity/phytotoxicity because of its phenolic compounds, which demands removal to acceptable levels before being discharged into water bodies. Therefore, the treatment of phenolic compounds of OMWW is very much needed. Actually, electrochemistry method is becoming a substitute method for wastewater treatment using modified carbon as an electrode. The modification of granular activated carbon with zinc oxide (ZnO) nanoparticles was done based on the deep-coating procedure. Electrochemistry degradation of phenol, with a molecular formula C6H5OH, was studied using an activated carbon modified by ZnO as an electrode. The composite activated carbon-ZnO was characterized by Scanning Electron Microscope, X-ray Diffraction, Transformer Fourier Infrared Spectroscopy, and the measure of pHPZC. The techniques used in this work confirmed that ZnO was immobilized onto activated carbon surface. The morphology and the chemical composition of activated carbon have been changed after the ZnO grafting. Electrochemical performances of the electrochemical process were determined under different conditions, like pH, nature, and concentration of the supporting electrolyte. In this work, NaCl is used as a supporting electrolyte; phenol groups were oxidized by indirect electrochemical oxidation. The degradation of 95% of phenol was achieved after 30 min at the optimal operating conditions (pH = 2 in 3% NaCl). It was concluded that electrochemical oxidation using activated carbon-ZnO is a promising process for the destruction of all phenolic compounds present in OMWW. This opens new perspectives in the field of adsorbent materials, to prepare very efficient carbon for environmental phenol remediation

Effect of gamma rays absorbed doses and heat treatment on the optical absorption spectra of silver ion-exchanged silicate glass

International audienceSamples of a commercial silicate glass have been subjected to ion exchange at 320 °C in a molten mixture of AgNO 3 and NaNO 3 with molar ratio of 1:99 and 5:95 for 60 min. The ion exchange process was followed by gamma irradiation in the dose range of 1–250 kGy and heating at the temperature of 550 °C for different time periods ranging from 10 to 582 min. The spectral absorption in UV–Vis range of the Ag–Na ion exchanged glass was measured and used to determine the states of silver prevailing in the glass during the ion exchange, the gamma irradiation and the heat treatment. The gamma irradiation induced holes and electrons in the glass structure leading to the creation of a brown colour, and silver ions trapped electrons to form silver atoms. We observed the first stage of aggregation after irradiation, as well as after heating. The silver atoms diffused and then aggregated to form nanoclusters after heating at 550 °C. A characteristic band at about 430 nm was induced. The surface Plasmon absorption of silver nanoclusters in the glass indicated that the nanoclusters radius grew between 0.9 and 1.43 nm with increasing of annealing time from 10 to 242 min and then saturated. We also found that the size of aggregates depends on the value of gamma radiation absorbed dose. Contrary to what was expected, we found that 20 kGy is the optimal absorbed dose corresponding to the larger size of the aggregates which decreases for absorbed doses above 20 kGy

Treatment of aqueous solutions of oxytetracycline by different electrochemical approaches: anodic oxidation, pressurized electro-Fenton and oxidation by electrogenerated active chlorine

The tetracycline group (TCs) includes the most common antibiotics for treatment of both human and animal infections. TCs are resistant to biological degradation; hence, conventional wastewater treatments are unable to remove these contaminants. Here, the utilization of different electrochemical processes, such as electro-Fenton (EF), direct anodic oxidation (AO) and indirect oxidation by electrogenerated active chlorine (EAC), for the treatment of aqueous solutions of oxytetracycline (OTC), which is one of the TCs, was studied. The effect of various operating conditions was evaluated to optimize the selected processes. EAC gave the fastest abatement of OTC, but the lowest removal of TOC and formation of chlorate. However, the utilization of carbon felt cathodes allowed the formation of chlorate to be reduced. AO gave the highest TOC removals, but it required the use of an expensive anode, as BDD, and high cell potentials. EF performed with pressurized-air (5–10 bar) presented intermediate removals of OTC and TOC with respect to AO and EAC and consumed the least energy

Synthesis Methods in Solid-State Chemistry

The synthesis of single crystal is an area of intense activity in the materials science. The obtaining of the single crystal with sufficient dimension for X-ray diffraction depends on several factors including the chemical composition, crystal structure of the reagents, and physical parameters (temperature and pressure). In this context, this chapter is dedicated to the description of the most common synthesis methods of single crystal in the solid-state chemistry: solid-state method, hydrothermal, and slow evaporation at room temperature. Same other materials can be obtained at high pressure. There are also some physical techniques to grow single crystal, each technique is specific for specific materials

Insights into Ionizing-Radiation-Resistant Bacteria S-Layer Proteins and Nanobiotechnology for Bioremediation of Hazardous and Radioactive Waste

S-layers are crystalline arrays formed by proteinaceous subunits that cover the outer surface of many different kinds of microorganisms. This “proteinaceous cover” is particularly important in the case of ionizing-radiation-resistant bacteria (IRRB) that might be used in bioremediating hazardous and radioactive wastes (HRW). Despite the exponential growth in the number of comparative studies and solved proteic crystal structures, the proteic networks, diversity, and bioremediation-useful structural properties of IRRB S-layers remain unknown. Here, aided by literature, a tentative model of Deinococcus radiodurans R1 S-layer proteins (SLPs) and the network of its main constituents were proposed. The domain analysis of this network was performed. Moreover, to show the diversity of IRRB S-layers, comparative genomics and computer modeling experiments were carried out. In addition, using in silico modeling, assisted by previously published data, the outermost exposed segments of D. radiodurans SlpA (surface layer protein A) that were predicted to interact with uranium were mapped. The combination of data and results pointed to various prospective applications of IRRB S-layers in nanobiotechnology for bioremediation of radioactive waste

Dielectric properties and electrical conductivity of MgO synthesized by chemical precipitation and sol-gel method

MgO Powders were synthesized via simple chemical precipitation (SPC) and sol-gel process (SG). The electrical behavior of these powders was determined by complex impedance spectroscopy using an alternative current conductivity at various temperatures and frequencies. For MgO elaborated by SG, the activation energy is 1.49 eV while MgO prepared by SPC, this energy is equal to 0.39 and 4.13 eV. The structural properties of MgO powders were analyzed by X-ray diffraction and FT-IR spectroscopy. The results show that the cristallites size was 28.4 nm for MgO SPC and 42.5 nm for MgO SG. Others methods such DTA, TGA, BET and SEM were used to characterized MgO materials