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The poverty-stricken population cannot withstand the shocks of global warming and can hardly pay the soaring expenditure of fossil fuels whose reservoirs are already approaching the threshold limit. These adventures guided the researchers towards water oxidation as a source of energy. In this study, a metal-organic framework (MOF)-based material was fabricated and catalyzed the lethargic oxygen evolution reaction (OER). The synthesized material is characterized with different analytical techniques to confirm structural, morphological and textural properties. Its huge surface area (87 m2/g) rendered it a promising material to carry the OER. It exhibited shallow onset potential that is, 1.40 V vs. RHE and displayed an exceptionally low overpotential of 1.42 V vs. RHE to reach the benchmark current density (10 mA/cm2) with remarkably small Tafel slope that is, 34 mV/dec. It surpassed the state of the art electrocatalyst for OER, that is, IrO2 and RuO2 in efficiency as well as in stability.

In recent decades, electrochemical water splitting has caught researcher’s attention for cost effective and green way to meet world’s energy requirement. In present work, rod structured hierarchical cerium oxide/C derived from metal organic framework (MOF) electrocatalyst was synthesized via hydrothermal route directly grown on nickel foam (NF) for oxygen evolution reaction (OER) in 1 M KOH solution. The fabricated electrocatalysts were characterized via different analytical techniques to analyze the morphology, crystallinity and oxidation states. The electrochemical performances of the synthesized materials were investigated exhibiting outstanding OER performances, with low over potential of 297 mV to achieve a current density of 10 mA/cm2. The electrocatalyst also attains low Tafel slope (46 mV/dec) provides the way of electron transfer with long term stability (1000 cyclic voltammetry cycles and 15 h) chronoamperometry. These all results suggest that cerium oxide derived from MOF could be used as substitution for noble metal catalysts to develop promising, new and active electrocatalyst.

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.

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.

Ca–Ni co-substituted samples of nanocrystalline spinel ferrites with chemical formula Mg 1− x Ca x Ni y Fe 2− y O 4 ( x =0.0–0.6, y =0.0–1.2) were synthesized by the micro-emulsion method and were annealed at 700 °C for 7 h. The synthesized samples were characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometry (VSM) and dielectric measurements. The XRD and FTIR analysis reveals that single phase samples can be achieved by substituting Ca and Ni ions at Mg and Fe sites respectively in cubic spinel nano-ferrites. The crystallite size of the synthesized samples was found in the range 29–45 nm. The saturation magnetization ( M s ) increases from 9.84 to 24.99 emu/g up to x =0.2, y =0.4 and then decreases, while the coercivity ( H c ) increases continuously from 94 to 153 Oe with the increase in dopants concentration. The dielectric properties of these nano materials were also studied at room temperature in the frequency range 100 MHz to 3 GHz. The dielectric parameters were found to decrease with the increased Ca–Ni concentration. Further the peaking behavior was observed beyond 1.5 GHz. The frequency dependent dielectric properties of all the samples have been explained qualitatively on the basis of the Maxwell–Wagner two-layer model according to Koop's phenomenological theory. The enhanced magnetic parameters and reduced dielectric properties make the synthesized materials suitable for switching and high frequency applications, respectively.

Magnesium ferrite (MgFe2O4) nano-structures doped with Ni–Co at magnesium and iron sites respectively were fabricated by the micro-emulsion method and characterized by the X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and dielectric measurements. The analysis of XRD patterns confirm the single phase spinel structure and the crystallite size calculated by Scherer’s formula lies in the range of 15–26 nm. The spectral studies elucidate the characteristic feature of spinel phase. The real and imaginary parts of dielectric constant and dielectric loss exhibit peaking behavior. The dielectric properties have been explained on the basis of Debye-type relaxation phenomenon in accordance with Koop’s phenomenological theory. The increase in the tendency of saturation magnetization is consistent with the enhancement of crystallinity. The crystallite size is small enough to obtain considerable signal to noise ratio in the recording media. The optimized dielectric and magnetic parameters suggest that the material with composition Mg0.6 Ni0.4 Co0.4 Fe1.6O4 may be used for applications in recording media and microwave devices.