Search

Ytterbium (Yb) doped NiCr 0.1 Yb x Fe 1.9−x O 4 (x = 0.00, 0.002, 0.04, 0.06, 0.08) spinel ferrites with different crystallite sizes have been prepared by co-precipitation technique and their magnetic and dielectric properties were investigated. X-ray diffraction data suggested that, after doping, all the samples possess a main spinel phase along with few traces of YbFeO 3 (secondary phase). The addition of Yb 3+ resulted in a decrease of crystallite size and an increase in X-ray density. The magnetic measurements indicated that saturation magnetization (M s ), coercivity (H c ) and remanence (M r ) of all the samples decreased by increasing dopant (Yb) concentration. Dielectric constant, dielectric loss and tan loss were also minimized with the increase in frequency as well as increase in the concentration of Yb 3+ ions in the nickel chromium based spinel ferrites. AC conductivity was directly proportional to frequency and inversely proportional to concentration of Yb 3+ ions. These ytterbium doped nickel ferrites may be potential candidates for the fabrication and development of high frequency switching devices.

Synthesis of 2D MOFs is often sensitive to the reaction conditions like temperature and solvent etc. Cu(II)-5-azidoisophthalate MOF (Cu(II)–5N3IP) has been synthesized at room temperature as well as under solvothermal conditions. The azide functional group remained stable during solvothermal synthesis at 85 °C. Cu(II)–5N3IP crystallized in a Kagome-type structure. Typical Cu2 paddle-wheels are connected to each other by 5N3IP ligands in infinite 2D sheets in the (001) plane, featuring 1D infinite channels within each layer. This MOF is used for the adsorption of methylene blue (MB), rhodamine B (RhB), methyl orange (MO), and Congo red (CR). The adsorption is selective to the dimensions, shapes and ionic strengths of the dyes. Cu(II)–5N3IP exhibited adsorption rates in the order MB > CR > RhB > MO. Cu(II)–5N3IP is used as a catalyst for aerobic oxidation and Knoevenagel condensation. 3–10 mol% of Cu–5N3IP selectively catalyzes the oxidation of benzyl alcohol to benzaldehyde in 9–20 h at 60 °C. In Knoevenagel condensation, the reaction of both unsubstituted and substituted benzaldehydes at room temperature was observed at a very low catalyst loading of 3 mol% of MOF within a short time of 3–60 min. This 2D MOF has proved to be more efficient for dye adsorption and the catalytic applications under investigation (such as alcohol oxidation and Knoevenagel condensation) than its analogous 3D or 0D materials.

Methacrylamide-acrylic acid-N-isopropylacrylamide terpolymeric hydrogels have been prepared via free radical polymerization using diammonium-peroxo-disulphate initiator system and ethylene glycol-di-methacrylate as a cross-linker. The hydrogels were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. Molar mass was determined by viscometric method. Rheological profiling of the hydrogels was carried out by rheological measurements at various temperatures and methacrylamide contents in hydrogels. Thermogravimetric data were analyzed to assess the kinetic triplet by iso-conversional method. The values of apparent activation energy (E a) figured out from TG data were measured for each step by Kissinger–Akahira–Sunose method. On the findings of results, the decomposition reaction of terpolymeric hydrogels has been analyzed as a slow reaction, which is evident from the low-frequency factor values (A), i.e., 3 × 106, 2 × 1010, and 4 × 1015 s−1, respectively. The master plot method was used to predict the mechanism for degradation of MANIPAM-7. Flow curve and frequency sweep tests at different temperatures showed temperature dependency with shear rate indicating the pseudo-plastic nature of the synthesized samples. The rheological parameters were analyzed using various models. Out of these methods, the Ostwald, modified Bingham, and Herschel–Bulkley models were established to provide better fit to experimental data. Dynamic moduli measured as a function of angular frequency showed viscoelastic nature of all the samples. Frequency sweep studies indicated that storage (G′) and loss modulus (G″) showed an increase with increasing concentration of methacrylamide. Composition dependency of crossover frequency directed an increase in relaxation time with methacrylamide contents in the hydrogel.

Europium (Eu) doped spinel cobalt ferrites having composition CoEuxFe2−xO4 where x = 0.00, 0.03, 0.06, 0.09, 0.12 were fabricated by co-precipitation route. In order to observe the phase development of the ferrite samples, thermo-gravimetric analysis was carried out. The synthesized samples were subjected to X-ray diffraction analysis for structural investigation. All the samples were found to constitute face centered cubic (FCC) spinel structure belonging to Fd3m space group. Scanning electron microscopy revealed the formation of nanocrystalline grains with spherical shape. Energy dispersive X-ray spectra confirmed the presence of Co, Eu, Fe and O elements with no existence of any impurity. The magnetic hysteresis curves measured at room temperature exhibited ferrimagnetic behavior with maximum saturation magnetization (Ms) of 65 emu/g and coercivity (Hc) of 966 Oe. The origin of ferrimagnetism in Eu doped cobalt ferrites was discussed in detail with reverence to the allocation of Co2+ and Fe3+ ions within the spinel lattice. The overall coercivity was increased (944–966 Oe) and magnetization was decreased (65–46 emu/g) with the substitution of Eu3+. The enhancement of former is ascribed to the transition from multi domain to single domain state and reduction in lateral is attributed to the incorporation of nonmagnetic Eu ions for Fe, resulting in weak superexchange interactions. Keywords: Europium doped cobalt ferrites, Co-precipitation, X-ray diffraction, Scanning electron microscopy, Magnetic properties

Craving to search sources of energy is constantly compelling the mankind to find a source that is renewable or has enormous reservoirs and at the same time it poses no hazardous effect to mankind. Today’s energy deficient world has been seeking for an electrocatalyst which has a simple and facile synthesis strategy with marvellous catalytic performance and has outstandingly sustained stability for the highly lethargic Oxygen Evolution Reaction (OER). Here, a Ni-based mixed linker Metal Organic Framework (MOF) was synthesized using 1,3,5-benzenetricarboxylic acid (BTC) and 4,4`-bipyridine (bpy) as organic linkers. Carbon Dots (CDs) were incorporated into MOF during synthesis to impart synergistic effect to the as-synthesized composite. All the synthesized samples i.e CDs, MOF and CDs@MOF were characterized by various techniques to confirm the structural, compositional, morphological and textural analysis. The synthesized composite possessed rods like morphology with uniform distribution of CDs which offered superb stability for almost 40 hrs, large electrochemical active surface area (ECSA), least charge transfer resistance (Rct), high turnover frequency (TOF), reasonably low onset potential, low overpotential and a comparably low Tafel slope. The electrocatalyst owed its great catalytic efficiency and substantial stability due to the synergistic effect between CDs and MOF. This work is an effort to exploit the fabulous potential of MOF based nano-composite towards water splitting.

Dy–Ni substituted Mn1-xNixFe2-yDyyO4 (x = 0.0–0.1 and y = 0.0–0.2) soft magnetic oxides were synthesized using a size controlled micro-emulsion method. X-ray diffraction (XRD) analysis was employed to confirm the spinel structure of synthesized ferrites. Crystallite size was found to decrease (33-22 nm) while lattice constant was increased (8.58–8.63 A) by increasing dopants content. FTIR bands observed in the range 500–600 cm−1 is the evidence to form the spinel structure of these ferrites. Dielectric constant (e′) and dielectric loss (e") were observed to decrease with the increase of frequency due to hopping mechanism. Hysteresis curves exhibited soft nature of synthesized nanoferrites. Remanence (MR) and saturation magnetization (MS) were increased with the incorporation of Dy and Ni ions. The decreased in dielectric losses and increased in magnetic parameters suggested that these ferrites are potential candidates for magnetic recording heads.

A series of nanostructured ferrites having chemical composition Mg0.7Co0.3YbxFe2−xO4 (x=0.0–0.08) was prepared by the chemical co-precipitation route. The synthesized samples were characterized by X-ray diffraction (XRD), Thermo-gravimetric analysis (TGA), differential thermal analysis (DTA), vibrating sample magnetometer (VSM) and impedance analyzer. The analysis of XRD patterns confirmed the spinel structure and the crystallite size calculated by Scherer's formula was found in the range of 18–43 nm. The crystallite size was small enough to obtain considerable signal to noise ratio in the recording media. The lattice constant was increased from 8.362 Ǻ to 8.383 Ǻ as the Yb contents were increased in the magnesium-cobalt ferrites. The TGA and DTA were carried out for prepared sample to investigate the thermal decomposition process. Magnetization results obtained from VSM measurements elucidate that the substitution of rare earth ytterbium decreased the saturation magnetization and retentivity. The dielectric properties of the samples were studied at room temperature in the frequency range of 1 MHz to 3 GHz and the samples exhibited the dispersion in high frequency region. The dielectric constant (e) and dielectric loss (tan δ) were decreased with the increased frequency and ytterbium doping. The dielectric parameters were explained on the basis of space charge distribution. The dielectric and magnetic parameters suggested that these nano-materials are potential candidates for switching and recording media applications.

SummaryThe coordination networking of discrete metal-organic polyhedra (MOPs) involving different ligands as well as metals is a challenging task due to the features of limited solubility and chemical stability of these polyhedra. An unusual approach, ligand-oriented polyhedral networking via click chemistry and further metal coordination is reported here. An alkyne decorated Cu(II)-MOP self-catalyzes the regioselective click reaction (1,3-dipolar cycloaddition) using azide-functionalized ligands under unconventional reaction conditions. Introducing new metal ions, M(II), interlinks the carboxylic groups on the MOP surfaces creating coordination networks. On the other hand, exposure of the respective individual ligand components in the presence of Cu(II) promotes an in-situ click reaction along with metal coordination generating a new 3D-framework. These materials demonstrated a high drug hosting potential exhibiting a controlled progressive release of anticancer (5-flourouracil) and stimulant (caffeine) drugs in physiological saline at 37 °C. These innovative and unconventional MOP networks provide a significant conceptual advance in understanding.