ABSTRACT
Ceramics of (Ba1-xSrx)2SmTi2Nb3O15, denoted as BSxSTN (x = 0, 0.25 and 0.5), were synthesized by the conventional solid-state reactions route. The impact of Sr-substitution in Ba2SmTi2Nb3O15 ceramics on their structural, optical, and dielectric properties are investigated. The Rietveld method was employed to confirm the formation of tetragonal tungsten bronze with the P4bm space group, using X-ray diffraction data. The substitution of Ba by Sr resulted in a decrease in cell parameters, density, and the average crystallite size as determined by Scherrer's formula ranged from 29.4 to 32 nm. The compounds frequency-dependent dielectric properties were studied using complex impedance spectroscopy over a temperature range of 50 to 420 °C at different frequencies. Dielectric measurements revealed a high dielectric constant, and the compounds exhibited characteristics of diffuse ferroelectric behavior. As the Sr content increased, optical gap energy increases from 3.29 to 3.59 eV, diffusivity increased from 1.19 to 1.52, Curie temperature (Tc) decreased from 269 to 213 °C, and the dielectric loss at room temperature and 1 kHz significantly decreased from 3 × 10-3 to 7 × 10-4. The correlation between (Tc) and the off-center cationic displacement of Ti/Nb in the octahedral Ti/NbO6 was analyzed. Cole-Cole plots for each sample displayed a single semicircular arc, indicating the presence of a single relaxation process.
ABSTRACT
The effects of Na+ substitution by Y3+ on the structural, microstructural, dielectric and electrical properties of Ba2Na(1-3x)YxNb5O15 compositions with (x = 0, 0.02 and 0.04) have been studied in detail. The solid solutions of different compositions were prepared by the solid state reaction route method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Complex Impedance Spectroscopy (CIS) techniques. The XRD study confirmed that all prepared compositions have a single-phase orthorhombic tungsten bronze structure with space group Cmm2 at room temperature. The microstructural studies revealed a grain shape and size change in response to increasing Y3+ concentration. The dielectric properties of the obtained compositions are evaluated over a temperature range of 40-600 °C. The dielectric properties were improved for the Y2O3-substituted Ba2NaNb5O15 compound compared to the undoped Ba2NaNb5O15 compound. The non-Debye type relaxation mechanism is confirmed by the -Zâ³ versus Z' traces. The grain contribution was studied using an equivalent electrical circuit with a Resistor R, a Capacitor C, and a Constant-Phase Element CPE in parallel, in the absence of the grain boundary response and the electrode effect in the frequency range 10 Hz-1MHz. The experimental AC conductivity data were evaluated by using Jonscher's power law. The activation energies obtained from the relaxation and conduction processes, present two different regions as a function of temperature related to the two electrical processes for the prepared ceramics.
ABSTRACT
In this paper, a benzyltriethylammonium/urea DES was investigated as a new green and eco-friendly medium for the progress of organic chemical reactions, particularly the dissolution and the functionalization of cellulose. In this regard, the viscosity-average molecular weight of cellulose (MÌw) during the dissolution/regeneration process was investigated, showing no significant degradation of the polymer chains. Moreover, X-ray diffraction patterns indicated that the cellulose dissolution process in the BTEAB/urea DES decreased the crystallinity index from 87% to 75%, and there was no effect on type I cellulose polymorphism. However, a drastic impact of the cosolvents (water and DMSO) on the melting point of the DES was observed. Besides, to understand the evolution of cellulose-DES interactions, the formation mechanism of the system was studied in terms of H-bond density and radial distribution function (RDF) using molecular dynamics modeling. Furthermore, density functional theory (DFT) was used to evaluate the topological characteristics of the polymeric system such as potential energy density (PED), laplacian electron density (LED), energy density, and kinetic energy density (KED) at bond critical points (BCPs) between the cellulose and the DES. The quantum theory of atoms in molecules (AIM), Bader's quantum theory (BQT), and reduced density gradient (RDG) scatter plots have been exploited to estimate and locate non-covalent interactions (NCIs). The results revealed that the dissolution process is attributed to the physical interactions, mainly the strong H-bond interactions.
ABSTRACT
This paper presents a systematic study of the substitution effect by lanthanides (Ln3+ = Sm3+ and La3+) in the A-site of perovskite Ba(1-x)Ln2x/3(Ti0.99Zr0.01)O3 with a substitution rate equal to 3.4%. All samples were synthesized by the classical solid-state reaction route and characterized by X-ray diffraction and a complex impedance spectroscopy technique. The synthesized compounds exhibit single-phase perovskite structures without detectable secondary phases. The P4mm space group was verified by the Rietveld method from the X-ray diffraction data, with the tetragonal distortion decreasing with the increasing ionic radius of the lanthanides. SEM micrographs of all ceramics revealed high densification, low porosity and homogeneous distribution of grains of different sizes over the entire surface. The dielectric properties of non-doped and Sm3+ and La3+ doped Ba(1-x)Ln2x/3(Ti0.99Zr0.01)O3 compound are studied in the temperature range of 40-250 °C. The dielectric permittivity ε' increases and the ferroelectric-paraelectric phase transition temperature decreases when the lanthanides are inserted into the A-site of Ba(1-x)Ln2x/3(Ti0.99Zr0.01)O3 perovskite. The Nyquist plots indicate a non-Debye type relaxation process. Conductivity and electrical modulus plots as a function of frequency (10 to 106 Hz) include two electrical responses corresponding to grain and grain boundary effects for all ceramics studied.
ABSTRACT
The aim of this study is to develop a new, efficient, and inexpensive natural-based adsorbent with high efficacy for the cationic dye methylene blue (MB). A natural-based nanocomposite based on hydroxyapatite (HAp) and hydroxypropyl methylcellulose (HPMC) was selected for this purpose. It was synthesized by the dissolution/reprecipitation method. A film with a homogeneous and smooth surface composed of nanoparticles was prepared from the nanocomposite. HPMC and HAp biopolymers were selected due to their compatibility, biodegradability, and non-toxicity. Total reflectance infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), and calorimetric/thermal gravimetric (DSC/TGA) analysis results revealed the existence of strong physical interaction between the composite components. Scanning electron microscopy (SEM) observations show a composite sheet with a homogenous and smooth surface, indicating excellent compatibility between HPMC and HAp in the composite. The nanocomposite was evaluated as an adsorbent for organic dyes in an aqueous solution. The effects of solution pH, initial MB concentration, composite concentration, and adsorption time on the adsorption efficiency were evaluated. The highest adsorption rate was seen as 52.0 mg of MB/g composite. The adsorption rate reached equilibrium in about 20 min. Fitting of the adsorption data to the Langmuir and Freundlich adsorption models was investigated. Results showed that the adsorption process follows the Langmuir isotherm model. The kinetic study results revealed that the adsorption process was pseudo-second-order. The herein composite is an excellent alternative for use as contemporary industrial-scale adsorbents.
ABSTRACT
Undoped Ba(Zr0.9Ti0.1)O3 and rare-earth-doped (Ba1-x RE2x/3)(Zr0.9Ti0.1)O3 (RE3+ = La3+, Sm3+) perovskite compounds were synthesized by the conventional solid-state reaction route. Both solubility of rare earth in Ba(Zr0.9Ti0.1)O3 and formation of perovskite structure with the Pm3Ìm space group were verified by the Rietveld method using X-ray diffraction data. SEM micrographs of all ceramics revealed high densification, low porosity, and even homogeneous grain distribution of various dimensions over the total surface. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of impedance, conductivity, modulus formalism, and charge carriers activation energy were used to explain the microstructure-electrical property relationships.
ABSTRACT
In this paper, a new deep eutectic solvent (DES) has been successfully synthesized that is based on benzyltriethylammonium bromide as a hydrogen bond acceptor (HBA) and urea as a hydrogen bond donor (HBD). However, its usability in modifying cellulose derivatives, especially acylating hydroxyethylcellulose (HEC) was investigated. The chemical modification (acetylation) of HEC was carried out in BTEAB/urea DES system without any additional conventional solvent or catalyst. However, the proposed structure of acetylated HEC (HECA) was confirmed according to the structural spectra analyses FTIR-ATR, 1H, 13C, and APT-NMR. The crystalline behavior of acetylated and unmodified HEC in the DES system has been evaluated using XRD patterns, where the thermal stability was evaluated basing on the TD-TGA thermograms. Hence, SEM images and EDX spectra were recorded to prove the changes that are expected at the morphological level and elemental profile. Yet, the nanometric sheets aspect was observed. The Functional Density Theory (DFT) was investigated as a useful computational tool to understand mechanism and donor-acceptor interactions. The topological parameters (electron density Laplacian, kinetic energy density, potential energy density, and energy density) at the bond critical points (BCP), between TBEAB and urea, are deducted according to Quantum Bader's theory, and Atoms-in-molecules (AIM). The non-covalent interactions and steric effect in the DES system were studied using the reduced density gradient isosurface (RDG). Theoretical and computational calculations revealed that the H-bonds and the electrostatic coexist, as predominant interactions in the BTEAB-based DES resulting chemical structure, and mechanism formation. The physical interactions between the component entities of DES lead to a new equilibrium that is more stable than that of HBA and HBD in their separate states.
ABSTRACT
In this work, Zn co-doped tungsten bronze having nominal formula Ba5CaTi1.94Zn0.06Nb8O30 has been synthesized and systematically studied for structure, dielectric and electrical properties. The formation of the phase of tetragonal tungsten bronze with space group P4bm and the occurrence of oxygen vacancies were verified by the Rietveld refinement using X-ray diffraction data. Scanning electron microscopy (SEM) of Ba5CaTi1.94Zn0.06Nb8O30 ceramic shows high densification, low porosity, and homogeneous distribution of grains of different sizes over the total surface. The sample shows a dielectric anomaly of ferroelectric paraelectric type at 262 °C, and has non-relaxor type of diffuse phase transition. The electrical property (complex impedance Z*, complex permittivity ε*, complex modulus M*) of Ba5CaTi1.94Zn0.06Nb8O30 ceramic has been investigated by non-destructive complex impedance spectroscopy (CIS) as a function of frequency at different temperatures. Grains and grain boundaries conduction is detected from a complex impedance spectrum by fitting the Nyquist plot with an appropriate electrical circuit. The Nyquist plot indicates the negative temperature coefficient of resistance (NTCR) character of Ba5CaTi1.94Zn0.06Nb8O30 ceramic. The variation of AC conductivity as a function of frequency reveals that the compound has an Arrhenius-type behavior of electrical conductivity. The DC electrical conductivities of grains and grain boundaries have been studied. The presence of non-Debye relaxations was verified by a complex modulus analysis.
ABSTRACT
In this paper, new quaternized cellulose derivative based on Ethylenediaminetetraacetic acid (EDTA) and hydroxyethyl cellulose (HEC) is successfully prepared in homogeneous medium. The resulted product is characterized using spectroscopy techniques (FTIR, 1H NMR and 13C NMR). At the supramolecular level, the x-ray patterns show that a high hydrogen bond density occurs by grafting EDTA on the HEC fibers. The new adsorbent (HEC-EDTA) shows a high adsorption capacity of heavy metals (Pb (II) and Cu (II)) from aqueous metals solutions. The adsorption of the both metal ions follows the pseudo-second-order kinetic model, while the adsorption isotherms are well described by the Langmuir model. The qm values are determined for Pb (II) and Cu (II), respectively. For each metal, the equilibrium adsorption time is found to be 30min. Moreover, the HEC-EDTA adsorption capacity is strongly dependent on the pH value; and the adsorption is favorable for pH values ââbetween 4 and 6. Moreover, the results show a high affinity toward Cu (II) than Pb (II).
