Showing papers by "Ganesan Ravi published in 2017"

Ni-CeO2 spherical nanostructures for magnetic and electrochemical supercapacitor applications.

Abstract: The synthesis of nanoparticles has great control over the structural and functional characteristics of materials. In this study, CeO2 and Ni–CeO2 spherical nanoparticles were prepared using a microwave-assisted method. The prepared nanoparticles were characterized via thermogravimetry, X-ray diffraction (XRD), Raman, FTIR, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometry (VSM) and cyclic voltammetry (CV). The pure CeO2 sample exhibited a flake-like morphology, whereas Ni-doped CeO2 showed spherical morphology with uniform shapes. Spherical morphologies for the Ni-doped samples were further confirmed via TEM micrographs. Thermogravimetric analyses revealed that decomposition varies with Ni-doping in CeO2. XRD revealed that the peak shifts towards lower angles for the Ni-doped samples. Furthermore, a diamagnetic to ferromagnetic transition was observed in Ni-doped CeO2. The ferromagnetic property was attributed to the introduction of oxygen vacancies in the CeO2 lattice upon doping with Ni, which were confirmed by Raman and XPS. The pseudo-capacitive properties of pure and Ni-doped CeO2 samples were evaluated via cyclic voltammetry and galvanostatic charge–discharge studies, wherein 1 M KOH was used as the electrolyte. The specific capacitances were 235, 351, 382, 577 and 417 F g−1 corresponding to the pure 1%, 3%, 5% and 7% of Ni doped samples at the current density of 2 A g−1, respectively. The 5% Ni-doped sample showed an excellent cyclic stability and maintained 94% of its maximum specific capacitance after 1000 cycles.

Hydrothermal synthesis of spherical NiCO 2 O 4 nanoparticles as a positive electrode for pseudocapacitor applications

Abstract: Hydrothermal method was adapted to synthesis NiCo2O4 nanoparticles by varying nickel and cobalt precursor concentration as 1:1, 1:2, and 1:3 ratios. X-ray diffraction (XRD) results revealed the spinel NiCo2O4 structure belongs to $${\rm{Fd}}\overline {\rm{3}} {\rm{m}}$$ space group system with face-centered cubic crystal structure. Raman characteristic peaks observed at 495 and 654 cm−1 explored Eg and A2g modes of spinel NiCo2O4 product. Photoluminescence (PL) results revealed the hole recombination of Ni2+/Co2+ ions from 3d-Eg and 3d-Tg electronic state of spinel NiCo2O4 material. The characteristic Fourier transform infrared spectroscopy (FTIR) metal–oxygen bands appeared at 658 and 558 cm−1 revealed the spinel-type crystal structure. SEM image revealed the NiCo2O4 spherical nanoparticles formation with an average particle size of around 500 nm. The cyclic voltammetry studies revealed the estimated average specific capacitance value of NC3 (NiCo2O4 spherical nanoparticles) as 542 F g−1 relatively higher than NC1 and NC2. The electro impendence spectroscopy results explored the small arc formation in high frequency range and very low charge transfer resistance (R ct), which resulted high conductive active materials. The estimated specific capacitance for NC3 exhibited superior galvanstatic charging and discharging (GCD) characteristics with high specific capacitance of 294 F g−1 at high current density of 1 A g−1 and revealed that the obtained electrode is suitable for supercapacitor applications. Hydrothermal synthesis using an excess of Co source leads to smaller and more uniform particle size. This particle size and the slightly larger crystallite size formed in the materials leads to the improved electrochemical performance of the particles.

Influence of reducing agent concentration on the structure, morphology and ferromagnetic properties of hematite (α-Fe 2 O 3 ) nanoparticles

Abstract: Hematite (α-Fe2O3) nanoparticles are successfully synthesized by using the chemical reduction synthesis method. The obtained XRD results revealed the formation of rhombohedral crystal structure of hematite α-Fe2O3with R3c space group. Raman-forbidden LO Eu mode and E1g mode observed at 657, 409 and 285 are clearly revealed hematite α-Fe2O3 formation. The prominent PL peak observed at 576 nm is attributed to stronger 3d–4sp hybridization due to the impact of size and morphology effect on synthesized hematite (α-Fe2O3) nanoparticles. SEM analysis revealed that the estimated average hematite nanoparticle size is reduced to be about 600–300 nm with an increase in the concentration of the reducing agent. The investigation of the magnetic properties of hematite nanoparticles showed that the product synthesized at low NaBH4 concentration exhibited an extremely small hysteresis loop and low coercivity when compared to higher concentrations. The influence of reducing agent concentration on the structure, morphology and ferromagnetic properties of hematite (α-Fe2O3) nanoparticles are discussed comprehensively.

Physico-chemical properties of pure and zinc incorporated cobalt nickel mixed ferrite (Zn x Co 0.005−x Ni 0.005 Fe 2 O 4, where x = 0, 0.002, 0.004 M) nanoparticles

Abstract: Pure and zinc substituted Co–Ni mixed ferrites (ZnxCo0.005−xNi0.005Fe2O4, where x = 0, 0.002, 0.004 M) were effectively prepared by employing co-precipitation method and their physico-chemical properties were investigated. XRD results confirmed face centered cubic cobalt nickel spinel ferrite formation. The noticeable variations were found in peaks corresponding to planes (220) and (440) as well as in crystallite size with Zn2+ ion incorporation. SEM images revealed rock like ferrite particles with agglomerated nature. Raman spectra revealed typical phonon vibration modes T2g(1), T2g(2) and Eg of cubic ferrite system. The Raman stoke shift and line broadening effect was revealed with foreign cation substitution in Co–Ni mixed ferrite system. Transition mechanism of spinel ferrites as 3A2(3F) → 1T2(1D) and 3d5 → 3d4 4 s observed at 493 and 521 nm was confirmed by photoluminescence studies. The emission and luminescent property of prepared ferrite was strongly depending on substituted cations into the spinel structure. FTIR bands in finger print region located at 584 (υ1) and 432 (υ2) cm−1 could be attributed to the cationic vibration preferred in tetrahedral A site and octahedral B site. The electrochemical behavior strongly reflected the cationic incorporation by means of possessing specific capacitance value of about 183 F/g for the sample Zn0.002Co0.003Ni0.005Fe2O4 at the scan rate of 5 mV/s. The substitution of foreign cations into the spinel lattice is one of the effective processes for tailoring the physico-chemical properties of nanoferrites.

Design, Fabrication, and Characterization of Hematite (α-Fe 2 O 3 ) Nanostructures

Abstract: The influence of processing parameters on the physicochemical properties of hematite α-Fe2O3 nanostructures was investigated. X-ray diffraction results revealed the hematite phase rhombohedral structure. Scanning electron microscope results explored nanospheres, nanohexagonal platelets, nanoellipsoids, distorted nanocubes, and interconnected platelets nanostructures. Rhombohedral single-phase hematite was confirmed through five Raman active modes. 2P 3/2 (1) → 2P 1/2 transition in photoluminescence spectra and Fourier-transform infrared spectroscopy band observed at ~ 555 cm−1 revealed the hematite formation. The highest specific capacitance value of 151.09 F/g for scan rate of 10 mV/s was obtained for the hydrothermal-assisted product using an Fe(NO3)2·9H2O precursor in KOH electrolyte solutions.

Properties of SILAR deposited magnetite (Fe3O4) thin films: effect of bath temperatures

Abstract: Magnetite thin films were deposited by varying the temperature of the bath in the SILAR deposition process. Structural, morphological and optical properties of the deposited films were analyzed using X-ray diffraction, Raman spectroscopy, Field emission scanning electron microscopy, UV–Visible spectroscopy. With the increase in bath temperature of the deposition process, crystallite size decreases and dislocation density and microstrain increases. Raman spectra confirm the formation of magnetite phase for all the deposited films. FESEM images reveal the bath temperature’s influence on the surface morphology. Considerable variations in the optical properties were observed for the films and were discussed in detail.

Hexamine, PEG-400 effect on α-MoO3 nanoparticle synthesis for pseudo capacitance applications

Abstract: Effect of different capping agents such as hexamine and PEG-400 on the synthesis of α-MoO3 nanoparticles was investigated employing a simple chemical reduction method by adopting NaBH4 as reducing agent. Owing to the general fact that the two capping agents are unique in chemical properties, different physico-chemical properties on the synthesized samples were expected. The impact of capping agents on crystallite size, structural, morphological and optical properties of the obtained product has been studied employing standard characterization techniques. X-ray diffraction analysis typically shows the formation of orthorhombic α-MoO3 nanoparticles with high crystalline nature. Raman studies also confirm the formation of α-MoO3 by exhibiting the characteristic Mo–O stretching and bending modes in the regions of 900–600 and 400–200 cm−1. PL and IR studies further ensured the formation of α-MoO3 nanoparticles. SEM image clearly revealed the nanoscale spherical morphology of synthesized α-MoO3 nanoparticles with and without capping agent. PEG-400 assisted α-MoO3 nanoparticles have demonstrated a good specific capacitance with 121 F/g as a suitable candidate for pseudo capacitance applications.

Growth and characterization of pure, chloroacetamide and 4-dimethylaminobenzaldehyde doped triglycine sulphophosphate (TGSP) crystals

Abstract: Triglycine sulphophosphate (TGSP), chloroacetamide (AC) and 4-dimethylaminobenzaldehyde (DB) doped TGSP crystals were successfully grown from their respective aqueous solutions by slow cooling method. X-ray powder diffraction patterns were collected for pure, AC and DB doped TGSP crystals in order to determine their lattice parameter values. Fourier Transform Infra-Red (FTIR) spectroscopic analysis was carried out to confirm the molecular vibrations of TGSP and the presence of AC and DB in TGSP qualitatively. From the UV–Vis spectroscopic analysis, the absorption range was observed for the grown crystals. From the microhardness test, the Vickers’s hardness of the AC and DB doped TGSP crystals measured on (001) face was found to be higher than that of pure TGSP crystals. The dielectric studies showed the variation of dielectric constant as a function of frequency at room temperature. The thermal behavior of the pure and doped TGSP samples was studied from their thermogravimetric and differential thermal curves.