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Applied Nanoscience (v.2, #4)

Microstructural and electrochemical properties of rf-sputtered LiMn₂O₄ thin film cathodes by K. Jayanth Babu; P. Jeevan Kumar; O. M. Hussain (pp. 401-407).

Lithium transition metal oxides have received considerable attention in recent years as high voltage positive electrode materials in the fabrication of all solid state microbatteries. Among various lithium-based cathode materials, LiMn₂O₄ is one of the most promising cathode materials as it offers high energy density, high cell voltage, low cost, and low toxicity over the other electrode materials. Thin films of LiMn₂O₄ were prepared by radio frequency magnetron sputtering on gold-coated silicon substrates under various substrate temperatures ranging from 373 to 673 K in a partial pressure of 3 × 10⁻³ mbar with rf power 100 Watts. In the present investigation, the influence of substrate temperature on the growth and microstructural properties was studied. The films deposited at a substrate temperature less than 473 K was found to be X-ray amorphous. The initial crystallization has been observed at a substrate temperature of 523 K. The X-ray diffraction patterns of the films deposited in the substrate temperature range 523–673 K exhibited predominant (111) orientation representing cubic spinel structure with Fd3m symmetry. The grain size was found to be increased with the increase of substrate temperature as evidenced from SEM studies. However, additional impurity phases like Mn₃O₄ were observed for the films deposited at higher substrate temperatures (>673 K) because of re-evaporation of Li⁺ ions in the films. The electrochemical (EC) studies were carried for the films deposited at T _s = 673 K in aqueous media in the potential window of 0.0–1.2 V exhibited better electrochemical performance suggesting that the films are well suited as binder free thin film cathode material for commercially viable Li-ion secondary batteries.

Keywords: LiMn₂O₄ thin films; Sputtering; Microstructure; Electrochemical properties

Compositional variation of magnetic moment, magnetic anisotropy energy and coercivity in Fe(1−x₎M x (M = Co/Ni) nanowires: an ab initio study by S. Assa Aravindh; S. Mathi Jaya; M. C. Valsakumar; C. S. Sundar (pp. 409-415).

Ab initio simulations are used to investigate the magnetic and electronic properties of freestanding Fe(1−x₎M x (M = Co/Ni) nanowires. The stability of the nanowires increases with Co (Ni) addition, as seen from the increase in cohesive energy. With the addition of Co (Ni), the average magnetic moment shows a monotonic decrease, in contrast to the Slater–Pauling behavior observed in bulk Fe–Co/Ni alloys. The magnetic anisotropy energy of the nanowire is observed to change sign, from a parallel alignment of spins along the wire axis, to a perpendicular alignment with the increase of Co and Ni content. The magnetic anisotropy energy variation is seen to be correlated with the orbital moment anisotropy. The coercivity, as calculated using the Jacobs–Bean model is observed to decrease with Co (Ni) addition to the nanowire.

Keywords: Fe(1−x₎Co x and Fe(1−x₎Ni x nanowires; Magnetic moment; Magnetic anisotropy energy; Coercivity; Ab initio calculations

Deposition of a Ni₃P nano-scale layer on B₄C nanoparticles by simple electroless plating in an acidic bath by Mohsen Hajizamani; Ali Alizadeh; Naser Ehsani (pp. 417-421).

In this study, deposition of a Ni₃P nano-scale layer on B₄C nanoparticles via simple electroless plating in an acidic bath was investigated. B₄C nanoparticles were produced by mechanical milling with the average size of about 95 nm. Electroless nickel plating was carried out at temperature and pH of 85°C and 5.5, respectively. The uncoated and composite powders were characterized by transition electron microscope and the phases present were revealed by X-ray diffraction. Also, nickel and phosphorous contents of the coating were measured by inductively coupled plasma analysis. The results confirmed deposition of a Ni₃P layer with the average thickness of about 25 nm on B₄C nanoparticles.

Keywords: Electroless plating; B₄C nanoparticles; Ni₃P nano-scale layer; Acidic bath; TEM

Hydrothermal synthesis method of nickel phosphide nanoparticles by Bo Wang; Xiang Huang; Zhibin Zhu; He Huang; Jinhui Dai (pp. 423-427).

Nanometer nickel phosphide compounds (Ni₂P and Ni₁₂P₅) were synthesized via a mild hydrothermal method with red phosphor and nickel chloride as raw materials. XRD, EDS, TEM and SEM analysis were employed to characterize the obtained products. The results showed that the as-prepared products were well crystallized and particle sizes ranged from 10 to 40 nm. Effects of raw material ratios and initial pH of reaction system on the final products were investigated. The result showed that increased P/Ni ratio benefited the formation of Ni₂P but went against obtaining Ni₁₂P₅ and nanoparticles were obtained only in alkaline environment.

Keywords: Nanocrystalline materials; Nickel phosphides; Hydrothermal; Red phosphor

Synthesis and characterization of TiO₂/SiO₂ nano composites for solar cell applications by D. Arun Kumar; J. Merline Shyla; Francis P. Xavier (pp. 429-436).

The use of titania–silica in photocatalytic process has been proposed as an alternative to the conventional TiO₂ catalysts. Mesoporous materials have been of great interest as catalysts because of their unique textural and structural properties. Mesoporous TiO₂, SiO₂ nanoparticles and TiO₂/SiO₂ nanocomposites were successfully synthesized by sol–gel method using titanium (IV) isopropoxide, tetra-ethylorthosilicate as starting materials. The synthesized samples are characterized by X-ray diffraction, UV–Vis spectroscopy, Fourier transform infrared spectroscopy, Brunauett–Emmett–Teller and field-dependent photoconductivity. The UV–Vis spectrum of as-synthesized samples shows similar absorption in the visible range. The crystallite size of the as-synthesized samples was calculated by Scherrer’s formula. The BET surface area for TiO₂/SiO₂ nanocomposite is found to be 303 m²/g and pore size distribution has average pore diameter about 10 nm. It also confirms the absence of macropores and the presence of micro and mesopores. The field-dependent photoconductivity of TiO₂/SiO₂ nanocomposite shows nearly 300 folds more than that of TiO₂ nanoparticle for a field of 800 V/cm.

Keywords: Nano TiO₂ ; Nano SiO₂ ; Nanocomposites; Sol–gel; Photoconductivity

Synthesis and characterization of Ni-doped CdSe nanoparticles: magnetic studies in 300–100 K temperature range by Sunil Kumar; Nitu Kumari; Sanjeev Kumar; Sanyog Jain; N. K. Verma (pp. 437-443).

We are reporting the synthesis of surfactant wrapped Ni-doped dilute magnetic semiconductors (DMS) with their structural, optical and thermal studies with emphasis on magnetic studies in 300–100 K temperature range. The transmission electron microscopy (TEM) studies confirmed the round morphology of the nanoparticles. The wide peaks in X-ray diffraction (XRD) spectra depicted the very small granular size with zinc blend (cubic) structure of the nanoparticles. The energy dispersive spectroscopy (EDS) analysis confirmed the presence of Ni in the doped CdSe lattice. The magnetic studies showed that at 100 K the retentive magnetization is more than at 300 K. With the increased Ni doping concentration the magnetic behavior was shifted from diamagnetic to paramagnetic and then to ferromagnetic. From PL studies, the peaks were observed in at 485, 530 and 545 nm. The band gap of un-doped CdSe nanoparticles was found to be 1.78 nm and that of 5% Ni-doped CdSe nanoparticles was about 1.95 eV. The samples were found to thermally stable up to 450°C.

Keywords: Magnetization; Coercivity; Dilute magnetic semiconductors; Quantum confinement; Band gap

Examining microstructural composition of hardened cement paste cured under high temperature and pressure using nanoindentation and ²⁹Si MAS NMR by Jung J. Kim; Muhammad K. Rahman; Mahmoud M. Reda Taha (pp. 445-456).

Microstructural composition of the hardened cement pastes are analyzed using nanoindentation and ²⁹Si MAS NMR after curing time periods of 7 and 28 days. Two curing conditions, room condition (20°C with 0.1 MPa pressure) and an elevated condition (80°C with 10 MPa pressure) are prepared to hydrate cement pastes [water to cement (w/c) ratio of 0.45]. The degree of hydration of the cement paste quantified using nanoindentation was compared with that from ²⁹Si MAS NMR. From nanoindentation of the hardened cement pastes, microstructural hydration products are characterized with respect to the corresponding modulus of elasticity. A hydration product, which has a relatively high modulus of elasticity over other known hydration products, was found in the hardened cement paste cured in elevated temperature and pressure. The effect of high pressure on the composition of the hydration product is discussed and it is hypothesized that the packing density of calcium-silicate-hydrate (C-S-H) might increase when a cement paste is hydrated under high temperature and pressure.

Keywords: Nanoindentation; ²⁹Si MAS NMR; Cement; Microstructural phases

Carbon nanotubes and polyaniline supported Pt nanoparticles for methanol oxidation towards DMFC applications by A. Muneendra Prasad; C. Santhosh; A. Nirmala Grace (pp. 457-466).

A microwave reduction route was employed for the synthesis of Pt nanoparticles supported on multi-walled carbon nanotubes (MWCNT). The as-prepared Pt-MWCNT electrocatalysts were characterized by FT-IR, XRD and TEM analysis. Further, the as-prepared catalysts were probed for its electrocatalytic activity towards methanol oxidation by cyclic voltammetry (CV) in 0.5 M CH₃OH + 0.5 M H₂SO₄ solution. Two kinds of electrocatalysts viz. Pt-MWCNT and Pt-MWCNT/PANI were probed to study the effect of both carbon nanotubes and polyaniline (PANI) towards methanol oxidation. The effect of scan rate, concentration and long-term cycle stability analysis has been investigated in detail. Results show that the presence of MWCNT and PANI improves the electrocatalytic efficiency towards methanol oxidation. Pt-MWCNT/PANI shows high peak current density towards methanol oxidation and good long-term stability even after 600 cycles indicating that the catalyst could be used for practical applications.

Keywords: MWCNT; Polyaniline; Methanol oxidation; Fuel cells

Synthesis and characterization of nanocomposites based on polyaniline-gold/graphene nanosheets by Deepshikha Saini; T. Basu (pp. 467-479).

Polymer nanocomposites (NSPANI/AuNP/GR) based on nanostructured polyaniline, gold nanoparticles (AuNP) and graphene nanosheets (GR) have been synthesized using in situ polymerization. A series of nanocomposites have been synthesized by varying the concentration of GR and chloroauric acid to optimize the formulation with respect to the electrochemical activities. Out of these series of NSPANI/AuNP/GR nanocomposites, it has been found that only one particular nanocomposite has the best electrochemical properties, as analyzed by cyclic voltammetry (CV) and differential pulse voltammetry and conductivity. The best nanocomposite has been characterized by Fourier transform infrared Raman spectroscopy, UV–vis spectroscopy, X-ray diffraction studies, transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The CV of the best nanocomposites show the well-defined reversible redox peaks characteristic of polyaniline, confirming that the polymer maintains its electro activity in the nanocomposites. Another nanocomposite has been prepared with identical composition (as found with the best nanocomposite) by mixing of pre-synthesized nanostructured polyaniline with chloroauric acid and graphene dispersion in order to predict the mechanism of in situ polymerization. It is inferred that the nanocomposite prepared by blending technique loses its property within 48 h indicating phase separation whereas the nanocomposite prepared by in situ technique is highly stable.

Keywords: Polyaniline nanocomposite; Graphene nanosheet; Gold nanoparticles; Electrochemical properties

Hydrothermal synthesis of cobalt–nickel bimetallic phosphides by Bo Wang; Xiang Huang; Zhibin Zhu; He Huang; Jinhui Dai (pp. 481-485).

Ultrafine cobalt–nickel bimetallic phosphides were prepared by mild hydrothermal method and characterized by techniques, such as XRD, EDS, and TEM. The results showed that the as-prepared products were well crystallized and particle sizes ranged from 10 to 20 nm. With the increasing amount of Ni²⁺ in the suspensions, the crystallinity of obtained products was improved gradually and the crystallite sizes increased accordingly.

Keywords: Cobalt–nickel bimetallic phosphide; Hydrothermal; Nanoparticles

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Applied Nanoscience (v.2, #4)

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Applied Nanoscience (v.2, #4)