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In 2008, one of the most costly materials on earth was graphene which was obtained by exfoliation method, having a model area of a human hair cross section costing more than $1000 as of April 2008 [2]. Since then, hunger for searching low-cost, non-hazardous alternative methods for scalable production of graphene continued. Graphene’s flexible chemistry with an atomic thickness makes it superlatives in material science, an ideal candidate for countless applications. Incredibly light weight and flexible, yet 200 times stronger than steel. Highly conductive but at the same time transparent, first 2D material existing but is one million times smaller than the diameter of a single human hair. Having all these amazing properties, graphene is creating an impact in wide range of industries including in fields of electronics, EMI shielding, composites, sensing devices as well as in energy storage, biomedical devices, and many more. Application of this wonder material is restricted to our imagination only. These engineering applications necessitate accessibility of graphene on the large scale, and methods used to synthesize this are facile, cost-effective, simple, quick, and single-step process, and thus appropriate processes are essential for synthesizing it down to a single-sheet level. The quality and quantity of graphene also plays an essential role, as the occurrence of defects, structural disorders, impurities, multiple domains, grain boundaries, and wrinkles in the graphene sheet can leave an unwanted effect on its electronic and optical properties. The present chapter will be aimed at the preparation of high quality few-layer graphene on a bulk scale from graphite in an affordable, nontoxic, and easy method. The methods which will be discussed in this chapter will be mostly on microwave-assisted synthesis of graphene and electrochemical exfoliation method used in our lab as well as reported by other workers, and how these methods are advantageous over conventional exfoliation methods. Last segment of this chapter will deal with applications of graphene particularly in EMI shielding.

This report underlines the systematic studies of crystalline structure, magnetic and ferroelectric properties of polycrystalline Bi 1− x − y La x Pr y FeO 3 ceramic samples, in which x changes continuously from 0 to 0.2 for y = 0 and y from 0 to 0.2 for x = 0.2. X-ray diffraction (XRD) patterns revealed that La and Pr substitution at Bi site in the ceramic eliminates the usual impurity phases completely. Rietveld refinement of the XRD patterns shows that the crystal structure changes gradually from Rhombohedral (R3c) to Orthorhombic (pbnm) with increasing La and Pr concentration. This transition has significant effects on the multiferroic properties of Bi 1− x − y La x Pr y FeO 3 ceramics. Substantial enhancement in magnetization of Bi 1− x − y La x Pr y FeO 3 has been observed and this is found to be correlated with the evolution of structural phase change with doping of Pr in samples having lanthanum concentration of x = 0.2. This leads to the suppression of helical spin order. However, the enhancement in magnetic behavior also takes place due to nanocrystallite nature of Bi 1− x − y La x Pr y FeO 3 ( x = 0.2, y = 0.05–0.2). For the nanocrystallites having sizes lower than 62 nm, which is the period of spin cycloid, this spin configuration will get destroyed resulting in the enhancement of magnetization. The studies of microstructures employing SEM and TEM revealed that Bi 1− x − y La x Pr y FeO 3 consists of nano size grained microstructures. It is also found that dielectric constant and dielectric loss get improved by La and Pr co-substitution. The dielectric constant for x = 0.0, y = 0.0 is 81 which changes to 354 for x = 0.2, y = 0.15 at 100 Hz. Dielectric losses are strongly diminished from 0.960 for x = 0.0, y = 0.0, 0.321 for x = 0.2, y = 0.0 and to 0.20 for x = 0.2, y = 0.05 at 100 Hz. This improvement in dielectric properties is likely due to the changes of lattice parameters and suppression of oxygen vacancies caused by La and Pr co substitution.

The structural and magnetic behavior of melt spun Cu 50 Mn 25 Al 25− x Ga x ( x =0, 2, 4, 8 and 10 at%) alloys synthesized in the form of ribbons have been investigated. Formation of Heusler single phase of the Cu 2 MnAl structure has been found only for the alloys with x ≤8. Further increase of Ga content gives rise to the formation of γ-Cu 9 Al 4 type phase together with Cu 2 MnAl Heusler phase. Long term annealing of the Cu 50 Mn 25 Al 25− x Ga x ( x =0 and 8) alloys at 903 K for 30 h leads to the formation of β-Mn and γ-Cu 9 Al 4 type phases. The alloys are ferromagnetically ordered and the saturation magnetization ( M s ) decreases slightly with increasing Ga concentration. Annealing of the ribbons significantly changes the magnetic properties of Cu 50 Mn 25 Al 25− x Ga x alloys. The decomposition of the Cu 2 MnAl Heusler phase into β-Mn and γ-Cu 9 Al 4 phases leads to the decrease in the magnitude of M s . The splitting in the zero field cooled (ZFC) and field cooled (FC) magnetization curves at low temperature has been observed for the Cu 50 Mn 25 Al 25− x Ga x ( x =0–10) alloys.

In the present study, we have investigated the combined effect of different transition metals such as Ti, Fe and Ni on the de/rehydrogenation characteristics of nano MgH 2 . Mechanical milling of MgH 2 with 5 wt% each of Ti, Fe and Ni for 24 h at 12 atm of H 2 pressure lead to the formation of nano MgH 2 -Ti5Fe5Ni5. The decomposition temperature of nano MgH 2 -Ti5Fe5Ni5 is lowered by 90 °C as compared to nano MgH 2 alone. It is also found that the nano MgH 2 -Ti5Fe5Ni5 absorbs 5.3 wt% within 15 min at 270 °C and 12 atm hydrogen pressures. However, nano MgH 2 reabsorbs only 4.2 wt% under identical condition. An interesting result of the present study is that mechanical milling of MgH 2 separately with Fe and Ni besides refinement in particle size also leads to the formation of alloys Mg 2 NiH 4 and Mg 2 FeH 6 respectively. On the other hand, when MgH 2 is mechanically milled together with Ti, Fe and Ni, the dominant result is the formation of nano particles of MgH 2 . Moreover the activation energy for dehydrogenation of nano MgH 2 co-catalyzed with Ti, Fe and Ni is 45.67 kJ/mol which is 35.71 kJ/mol lower as compared to activation energy of nano MgH 2 (81.34 kJ/mol). These results are one of the most significant in regard to improvement in de/rehydrogenation characteristics of known MgH 2 catalyzed through transition metal elements.

High performance carbonized bamboo fibers were synthesized for a wide range of temperature dependent energy storage applications. The structural and electrochemical properties of the carbonized bamboo fibers were studied for flexible supercapacitor applications. The galvanostatic charge-discharge studies on carbonized fibers exhibited specific capacity of ~510F/g at 0.4 A/g with energy density of 54 Wh/kg. Interestingly, the carbonized bamboo fibers displayed excellent charge storage stability without any appreciable degradation in charge storage capacity over 5,000 charge-discharge cycles. The symmetrical supercapacitor device fabricated using these carbonized bamboo fibers exhibited an areal capacitance of ~1.55 F/cm2 at room temperature. In addition to high charge storage capacity and cyclic stability, the device showed excellent flexibility without any degradation to charge storage capacity on bending the electrode. The performance of the supercapacitor device exhibited ~65% improvement at 70 °C compare to that at 10 °C. Our studies suggest that carbonized bamboo fibers are promising candidates for stable, high performance and flexible supercapacitor devices.

We have synthesized pure nanocrystalline CeO2 powders of nearly spherical shape using high-energy attritor ball mill. Milling parameters such as the milling speed of 400 rpm, ball to powder ratio (40:1), milling time (30 h) and water cooled media were determined to be suitable for synthesizing nanosize (∼10 nm) powders of CeO2. The powders after milling for various durations (up-to 50 h) were characterized by X-ray Diffraction, Scanning Electron Microscopy, Energy-dispersive X-ray Spectrometry and Transmission Electron Microscopy. An average particle size of 10 nm was obtained at 30 h milling, after which the particle agglomeration started, and a mixture of nanocrystalline and amorphous phase was observed after 50 h milling.

The growth of hexagonal wurzite one dimensional (1D) gallium nitride (GaN) nanostructures on sapphire substrates using hydride vapor phase epitaxy (HVPE) process was carried out at two different temperatures (973 K and 1023 K). The GaN nanoneedles were formed at 973 K and hexagonal nanorods get formed at 1023 K. The morphologies of these nanostructures were studied using high resolution scanning electron microscope. X-ray diffraction and micro-Raman spectroscopy measurements confirmed that the as grown GaN nanostructures are of hexagonal wurtzite structure without any oxide phase. The emission properties of these nanostructures have been investigated using photoluminescence.

The jatropha-derived biodiesel, a green precursor was found to be a new and promising precursor for the synthesis of carbon nanotubes (CNTs) and carbon–nitrogen (C–N) nanotubes. The CNTs and C–N nanotubes have been synthesised by spray pyrolysis of biodiesel with ferrocene and ferrocene–acetonitrile, respectively, at elevated temperature under an argon atmosphere. The typical length and diameter of as-grown CNTs are 20 µm and 20–50 nm, respectively. The C–N nanotubes are found in bundles with effective length of ∼30 µm and diameter ranging between 30 and 60 nm with bamboo-shaped morphology. The as-grown CNTs and C–N nanotubes were characterised through scanning and transmission electron microscopes, X-ray photoelectron, Raman and Fourier transform infrared spectroscopic techniques. These investigations revealed that the nanotubes synthesised by jatropha-derived biodiesel are clean from carbonaceous impurities and the bamboo compartment formations in C–N nanotubes are due to nitrogen incorporation. The nit...

Mesoporous silica (MS) and zinc loaded MS composites have been synthesized and characterized using high resolution transmission electron microscopy, X-ray diffraction, UV–visible spectroscopy, photoluminescence spectroscopy, N 2 adsorption–desorption isotherms, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Thermal treatment of the zinc loaded MS composite lead to the formation of ZnO–MS composite. The well ordered uniform pore structure of MS (pore size ∼3.4 nm) is found to remain stable even after 30% Zn loading albeit decrease in the pore size 1.2 nm indicates the formation of ZnO inside the pores.

In the present investigation, we have synthesized different morphologies of carbon nanofibres (CNFs) to investigate their catalytic effect on the hydrogenation characteristics of 25 h ball-milled MgH2 (nano MgH2). The TEM analysis reveals that 25 h of ball-milling leads to the formation of nanocrystalline particles with size ranging between 10 and 20 nm. Different morphologies of CNFs were synthesized by catalytic thermal decomposition of acetylene (C2H2) gas over LaNi5 alloy. Helical carbon nanofibers (HCNFs) were formed at a temperature 650 °C. By increasing the synthesis temperature to 750 °C, planar carbon nanofibres were formed. In order to explore the effectiveness of CNFs towards lowering the decomposition temperature, TPD experiments (at heating rate 5 °C/min) were performed for nano MgH2 with and without CNFs. It was found that the decomposition temperature is reduced to ~334 and ~300 °C from 367 °C for the PCNF and HCNF catalysed nano MgH2. It is also found that HCNF admixed nano MgH2 absorbs ~5.25 wt% within 10 min as compared with pristine nano MgH2, which absorbs only ~4.2 % within the same time and same condition of temperature and pressure. Thus the HCNF possesses better catalytic activity than PCNF. These different levels of improvement in hydrogenation properties of HCNF catalysed nano MgH2 is attributed to the morphology of the CNFs.

In this paper, we describe and discuss the synthesis, structural-microstructural and hydrogen storage behaviour of three AB2 type storage materials namely (a) ZrFe2, (b) Zr(Fe0.75V0.25)2 and (c) Zr(Fe0.5V0.5)2. These alloys were synthesied by radio frequency induction melting in argon atmosphere. X-ray diffraction and transmission electron microscope have been employed for structural and microstructural characterizations. The XRD study reveals that the lattice constants and the unit cell volume of ZrFe2, Zr (Fe0.75V0.25)2, Zr(Fe0.5V0.5)2 alloys, which has C14 type hexagonal Laves phase. The Surface morphology and elemental composition of these alloys were investigated by scanning electron microscope and energy dispersive X-ray analysis. The pressure composition isotherms of these alloys were investigated at room temperature and pressure ranges of 0–100 atm respectively, measured through a fully computerized PCI apparatus. As we increase the concentration of V (substituted for Fe), the total hydrogen storage capacities increased up to 1.45 wt%. This capacity is achieved in Zr(Fe0.5V0.5)2 alloy, while the reversible hydrogen storage capacity decreases due to the formation of a stable hydride phase. It has been found that the lattice constants increase with higher vanadium concentration. This is indicating that the majority of vanadium atoms reside in the B-site. The broader X-ray diffraction peaks observed in Zr(Fe0.5V0.5)2 alloy indicates a higher degree of disorder for alloys with the higher V-content. The yet another interesting feature observed in our present study is that the plateau pressure remains well below 1 atm for all the compositions.

The effect of carbon nanofibres (CNFs) on the de/re-hydrogenation characteristics of 1:2 magnesium amide (Mg(NH2)2) and lithium hydride (LiH) mixture is investigated. It is found that the desorption as well as absorption characteristic of the 1:2 Mg(NH2)2/LiH mixture is improved with admixing of different shaped (planar and helical) CNFs separately. The different shaped CNFs were synthesized through catalytic decomposition of acetylene gas over LaNi5 alloy. The synthesized CNFs contain Ni-metal nano particles. Among two different types of nanofibres namely planar carbon nanofibres (PCNFs) and helical carbon nanofibres (HCNFs), the later was found to act as a better catalyst. The decomposition temperature of the pristine Mg(NH2)2/LiH mixture is ∼250 °C, reduced to 150 and 140 °C for the PCNF and HCNF admixed Mg(NH2)2/LiH mixture respectively. The activation energy for dehydrogenation reaction was found to ∼97.2 kJ/mol, which is further reduced to ∼67 and ∼65 kJ/mol for the PCNF and HCNF admixed Mg(NH2)2/LiH mixture respectively. The lowering of decomposition temperature and enhancement in desorption kinetics, with admixing of different shaped CNFs are described and discussed.

This study reports the synthesis of NaAlH 4 by ball milling of NaH and Al mixture along with 3 mol % Mischmetal (Mm) nanocatalyst under hydrogen atmosphere. It is observed that synthesis of the intermediate phase Na 3 AlH 6 can be achieved by ball milling even under 1 atm hydrogen at room temperature. Ball milling of the NaH + Al with 3 mol % Mm with 3 atm hydrogen in excess of 40 h time did not lead to the formation of NaAlH 4 but charging of the milled material at 100 atm hydrogen pressure at 120 °C lead to formation of NaAlH 4 phase. Direct synthesis of NaAlH 4 was achieved by milling of NaH + Al with 3 mol % Mm under 100 atm hydrogen pressure. Direct synthesis is possible even without any catalyst by high pressure milling. However catalyst is required to improve the hydrogen sorption characteristics of the synthesized material. The as-prepared Mm catalyzed NaAlH 4 is also found to reversibly store hydrogen up to 4.2 wt% hydrogen. Catalytic activity is attributed to defects promoted by ball milling and catalysts.

The present paper reports the catalytic effect of carbon nanomaterials, particularly carbon nanotubes (CNTs) and graphitic nanofibres (GNFs) with two different structure morphology, namely planar GNFs (PGNFs) and helical GNFs (HGNFs) as the catalyst for improving the dehydrogenation and rehydrogenation behavior of sodium aluminum hydride (NaAlH4). It has been observed that HGNFs posses superior catalytic activity than other carbon nanoforms in improving the desorption kinetics and decreasing the desorption temperature of NaAlH4. Temperature programmed desorption (TPD) reveals that HGNFs admixed NaAlH4 undergo hydrogen desorption at a much lower temperature than PGNFs and CNTs (SWCNTs and MWCNTs) admixed NaAlH4. Thus for the heating rate of 2 °C/min, the peak desorption temperature corresponds to initial step decomposition of NaAlH4 admixed with 2 wt.% HGNFs and 2 wt.% PGNFs has been lowered to 143.6 °C and 152.6 °C, respectively (for pristine NaAlH4, it is ∼170 °C). In addition to the enhancement in desorption kinetics, the HGNFs admixed NaAlH4 undergoes fast rehydrogenation at the moderate condition. Microstructural investigation reveals that the HGNFs were present on the surface of NaAlH4 grains, whereas CNTs were tunneled into the grains of NaAlH4 suggesting a distinct catalytic behavior of different carbon nanovariants.

Samples of oxypnictide compound LaO1−x F x FeAs, with x=0.15 and 0.2 corresponding to over- and highly over-doped compositions, respectively, were prepared by solid-state reaction. We present their characterization by XRD and HRTEM, as well as resistivity ρ(T), magnetization M(B) and microwave modulated absorption (MMA) response between 4.2–300 K and applied fields B=0–8 T. With change in x, both the superconducting and magnetic behavior of the samples shows an interesting pattern. The “magnetic anomaly” at T∼130 K, observed in M(T) for x=0, instead of getting totally suppressed shows a tendency to reappear in x=0.2 sample. Both samples typically show ρ(300 K)>2.8×10−3 Ω cm and critical current density J c(5 K, 1 T)

Micron sized hexagon- and flower-like nanostructures of lead oxide (α-PbO2) have been synthesized by very simple and cost effective route of anodic oxidation of lead sheet. These structures were easily obtained by the simple variation of applied voltage from 2–6 V between the electrodes. Lead sheet was used as an anode and platinum sheet served as a cathode. Anodic oxidation at 2 V resulted in the variable edge sized (1–2 μm) hexagon-like structures in the electrolyte. When the applied potential was increased to 4 V a structure of distorted hexagons consisting of some flower-like structures were obtained. Further increment of potential up to 6 V resulted in flower like structures of α-PbO2 having six petals. The diameter of the flower-like structures was ∼200–500 nm and the size of a petal was ∼100–200 nm.

This work deals with the indentation behavior of Zr 69.5 Al 7.5 − x Ga x Cu 12 Ni 11 ( x = 0, 1.5, 7.5 at.%) alloys. A comparison between their nanohardness and reduced elastic modulus values of the as-synthesized glassy phase with their nanocomposites has been made. The indentation characteristics of a novel Ga substituted glass composition corresponding to x = 7.5 have shown significant improvement in regard to hardness and elastic modulus. The evidence of pile up has been observed in case of as-synthesized glassy ribbons. The load ( P ) versus depth ( h ) curves for as-synthesized melt–spun ribbons displayed the presence of displacement burst, which are known as pop-ins. The amount of energy per unit volume required for the shear band formation in glassy state has been estimated based on the pop-ins observed in P – h curve. This seems to decrease with Ga addition. Based on transmission electron microscopic observations of indented glassy specimen, the possibility of nanocrystallization has been ruled out.

The present work describes the preparation characterization and electrical conductivity measurement of carbon–nitrogen (C–N) nanotubes–PEO composites films. CNNTs–PEO composite films have been prepared by using the solution cast technique and characterized by scanning electron microscope (SEM PHILIPS XL-20). The DC electrical conductivity measurements of the composite films revealed that for PEO film conductivity has been found to be ~ 7.5 × 10-8 Scm-1, and for C–N nanotubes (~ 20 wt.%)–PEO film it was found to be ~6.2 Scm-1 at room temperature. Thus, compared to the PEO film, the conductivity of the C–N nanotubes (~ 20 wt.%)–PEO composite film is eight orders of magnitude higher. The same conductivity of ~ 6.2 Scm-1 for the carbon nanotubes (CNT)–PEO composites comes out at 50 wt.% of CNT in PEO as reported earlier by our group. The conductivity increases with the increase of temperature, confirming the semiconducting nature of the C–N nanotubes–PEO composites.

To examine the role of NH3 on bundles of aligned bamboo-shaped carbon–nitrogen (C–N) nanotube were synthesized the pyrolysis of ferrocene (Fe(C5H5)2) and sunflower oil mixtures with NH3 being the source of nitrogen. The concentration of NH3 was varying in volume (vol). Optimized temperature and concentration of ferrocene were 825°C and 10 mg/ml, respectively. With the increase of nitrogen concentration the bundles are breaking in nearly equal parts. With nitrogen doping, the nanotubes have a bamboo-like structure and reveal degraded crystallinity of graphitic sheets. Nitrogen plays key role in generating equal compartments inside the carbon nanotube. The nanotubes were characterized by scanning electron microscopy and transmission electron microscopy that reveal the vertically aligned and hollow structural features of the nanotubes. FTIR shows the incorporation of N atom inside carbon framework and Raman spectrum indicates the enhancement of the defects inside C–N nanotube due to the N atom in C–N nanotube.

In this presentation, we report the indentation behavior of Zr69.5Al7.5−xGaxCu12Ni11(x = 0 and 1.5 at.%) metallic glasses as well as nanoquasicrystal–glass composites. The minor alloying addition in Zr -based glassy alloys greatly influences their mechanical properties. The nanoindentation tests were carried out to study the load (P) versus displacement (h) curves for the determination of reduced modulus as well as their hardness behavior. The formation of shear bands around the indentation periphery has been investigated. The evidence of the pile up was observed. The P − h curve for as-synthesized melt-spun ribbons displayed the presence of displacement burst, which are known as pop-ins. It has been concluded that Ga substitution leads to the improvement of the mechanical behavior of Zr–Al (Ga)–Cu–Ni alloys.

TiO 2 (np) has been found to be an effective catalyst over ZrO 2 (np) for improving the hydrogen storage characteristics of NaAlH 4. TiO 2 catalyst reduces the activation energy of NaAlH 4 to a better extent than ZrO 2. In the reversibly hydrogenated materials, a substantial reduction in the dehydrogenation temperature could be achieved using TiO 2 catalyst. Such effect was not observed through ZrO 2. The activation energy of the reversibly hydrogenated NaAlH 4 catalyzed by TiO 2 nanoparticles obtained in the present study (60 kJ/mol H2 ) is smaller than that of TiO 2: NaAlH 4 starting material (101.9 kJ/mol H2 ). The stability of the intermediate phase Na 3 AlH 6 in the presence of TiO 2 catalyst was studied through TPD and TPA analysis. XRD analysis confirms that only TiO 2 gets reduced during dehydrogenation; therefore, the observed effect is attributed to the consequence of reduction of TiO 2.

In the present investigation, ( Cu, Cr, Fe ) Al 2O4 spinel was synthesized from decagonal quasicrystalline precursor using mechanical milling followed by air annealing. The optimum annealing temperature and time were found to be 600°C and 60 h respectively. The evolution of the spinel structure started upon air annealing at 600°C from the B2 phase formed due to milling of quasicrystalline phase for 40 h. The relevant optical property of mechanically milled and air annealed samples prepared at different temperatures (400°C, 500°C and 600°C) were evaluated by photoluminescence technique. These studies suggested the presence of emission characteristics in blue region i.e. at 430 nm.

We report the comparative study on the effect of Ag doping and admixing on the structure and magnetotransport properties of nanophasic La 0.7 Ca 0.3 MnO 3 (LCMO) manganite to resolve the ambiguous issue of Ag substitution at La -site in LCMO manganite. In this context two sets of samples were synthesized, (a) Ag doped La 0.7 Ca 0.3-x Ag x MnO 3 (x = 0, 0.1, 0.15, 0.2, 0.3) and (b) chemically synthesized Ag nanoparticles admixed La0.7Ca0.3MnO3 (LCMO + x wt.% Ag-NP , x = 0, 10, 15, 20, 30) and were annealed at 700°C in oxygen ambience. XRD study reveals that for Ag doped nanophasic LCMO samples, orthorhombic LCMO transforms to rhombohedral for x ≥ 0.10 while for Ag admixed LCMO no such transformation occurs, rather Ag is present as a secondary phase. Resistivity decreases for both types of samples, In the case of Ag admixed LCMO it is due to the metallic nature of silver while for Ag doped LCMO, increase in the number of holes as silver being mono valent may be the reason for decrease in resistivity. Both the insulator–metal (T IM ) and ferromagnetic–paramagnetic (T C ) transition temperatures increases with Ag . The corresponding increment in these parameters is ~100 K and ~50 K for 30% Ag doped and for Ag admixed (30%) it is ~60 K and ~15 K respectively than that of pure LCMO. Room temperature magnetoresistance (MR) values are higher (6.8% for x = 0.30) for Ag doped LCMO than that of undoped LCMO (~0.5%).

In the present investigation nanoribbons of TiO2 were prepared through the hydrothermal process. In a typical preparation procedure, 2 g of TiO2 powder (average size 100 μm) was added to 50 mL of 10 M NaOH and stirred for 10 min in a beaker. The mixture was then transferred into a teflon lined stainless steel autoclave and heated to 150°C for 48 h. After the autoclave was naturally cooled to room temperature, the obtained sample was filtered and washed several times with distilled water and 0.1 M HCl until the pH value of the solution reached to 7 and then the sample was filtered and dried at 80°C for 8 h. To improve the crystallinity the as dried sample was annealed at 500°C for 4 h. The TiO2 nanoribbons were characterized by SEM, TEM, XRD and UV-Visible spectroscopy. The TiO2 nanoribbons have been used for photoelectrochemical hydrogen production in photoelectrochemical solar cells.

Castor oil (combination of fatty acids) precursor containing hydrocarbon with less amount of oxygen is used first time for synthesis of different carbon nanostructures (i.e., agglomerated carbon nanoparticles, carbon nanobeads and carbon tubular structure). The agglomerated carbon nanoparticles, carbon nanobeads and carbon tubular structure were synthesized by applying CVD method at different temperature using castor oil as new carbon precursor without any catalyst. The synthesis of carbon nanostructure is free from additional catalyst as this hydrocarbon (castor oil) is cheap with abundant sources of carbon. The effect of pyrolysis temperatures on the size, quality and quantity of the synthesized carbon shape were investigated. Interestingly, the morphology of the carbon nanostructures can be controlled in shape from agglomerated carbon nanoparticle to nanobeads to carbon tubular structure just by increasing the temperature from 750°C to 800°C to 850°C, respectively. These nanobeads are chains of uniform size of graphitized carbon spheres. These chains comprised individual carbon particles size of ~ 450 nm. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR).

In this communication, we report the synthesis of helical carbon nanofibres (HCNFs) by employing hydrogen storage intermetallic LaNi5 as the catalyst precursor. It was observed that oxidative dissociation of LaNi5 alloy (2LaNi5 þ 3/2O2 / La2O3 þ 10Ni) occurred during synthesis. The Ni particles obtained through this process instantly interacted with C2H2 and H2 gases, and fragmented to nanoparticles of Ni (w150 nm) with polygonal shape. These polygonal shapes of Ni nanoparticles were decisive for the growth of helical carbon nanofibres(HCNFs)at650 � C.TEM,SAEDandEDAXstudieshaveshownthatHCNFshavegrownon Ni nanoparticles. Typical diameter and length of the HCNFs are w150 nm and 6e8 mm respectively. BET surface area of these typical HCNFs has been found to be 127 m 2 /g. It was

Polycrystalline MgB2 films of different thickness have been prepared by employing spray pyrolysis technique on MgO (1 0 0) substrate. The MgB2 and other phases have been confirmed using X-ray diffraction technique and no trace of impurities phases have been found. The resistivity behavior shows that the superconducting transition temperature lies in the range of 37–39 K with narrow transition width. The transport critical current density vary with films thickness and achieved highest value ∼1.2 × 106 A/cm2 at 20 K for 2.0 μm thick film and its values increase as thickness increases.

In the present investigation, the formation and stability of icosahedral phase in Al70− x Ga x Pd17Mn13 alloys has been explored using X-ray diffraction, scanning, transmission electron microscopy and energy dispersive X-ray analysis. Cast alloys and melt-spun ribbons with x = 2.5, 5, 7.5, 10, 12.5, 15 and 20 have been investigated. In both cases, the alloys up to 5 at% Ga exhibit the formation of pure icosahedral phase. However, for x ≥5 at% Ga content, the cast alloy exhibits the formation of multiphase material, consisting of an icosahedral phase along with AlPd-type B2 and ξ′ crystalline (orthorhombic structure with unit cell a = 23.5 A, b = 16.6 A and c = 12.4 A) phases. In the case of the melt spun ribbon for x = 5 at% Ga, only an icosahedral phase has been found, but for 15 > x > 5 at% Ga, an icosahedral phase is the majority phase with AlPd-type B2 phase being the minority component. For x = 15 at% Ga, a Al3Pd2-type hexagonal phase together with a small amount of quasicrystalline phase is formed. ...

The present study deals with the microstructural changes with respect to the processing parameter (quenching rate) and their correlation with hydrogen storage characteristics of Ti 45 Zr 38 Ni 17 quasicrystalline alloys. The ribbons of the alloy have been synthesized at different quenching rates obtained through different wheel speeds (35, 40, 45 and 50 m/s) and investigated for their hydrogen storage characteristics. The lower cooling rate obtained through low wheel speed (35 m/s) produces, i-phase grains whose size ranges from 300-350 nm, whereas higher cooling rates obtained through high wheel speed (45 and 50 m/s) promote the formation of grains with size ranges from 100-150 nm in Ti 45 Zr 38 Ni 17 ribbons. It has been found that the ribbons synthesized at 35 m/s absorbed ∼2.0 wt%, whereas ribbons synthesized at 50 m/s absorbed ∼2.84 wt. % of hydrogen. Thus the hydrogen storage capacity of ribbon increases for the ribbons produced at higher quenching rate. One of the salient features of the present study is that the improvement of hydrogen storage capacity obtained through higher quenching rates (∼45 to 50 m/s wheel speed) leading to the formation of lower grain size.

Indentation characteristics of melt-spun Zr 69.5 Al 7.5− x Ga x Cu 12 Ni 11 ( x = 0–2.5; in at %) metallic glasses have been investigated. Formation of a nano-quasicrystalline phase by annealing the glass has been found only upto x = 1.5. The substitution of Ga changes the size and shape of this phase. The load dependent hardness behaviour of metallic glasses and nanoquasicrystal-glass composites are reported in detail. It has been observed that substitution of 1.5 at % Ga improved microhardness property of Zr–Al–Cu–Ni alloy. The value of yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. It has been found that microstructural and morphological changes alter the Meyer exponent. Pile up parameters seems to be sensitive to structural and microstructural details.

Bundles of aligned carbon nanotubes (ACNTs) have been synthesised by spray pyrolysis of turpentine oil (inexpensive precursor) and ferrocene mixture at 800°C. Turpentine oil (C10H16), a plant-based precursor was used as a source of carbon and argon as a carrier gas. The bundles of ACNTs have been grown directly inside the quartz tube. The as-grown ACNTs have been characterised through X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopic techniques. Scanning electron microscope images reveal that the bundles of ACNTs are densely packed and are of ∼70–130 µm in length. High-resolution transmission electron microscopy and Raman spectroscopy observations indicate that as-grown multi-walled carbon nanotubes (CNTs) are well graphitised. These CNTs have been found to have outer diameters between ∼15 and 40 nm. This technique suggests a low-cost route for the large-scale formation of ACNTs bundles.

This paper reports the catalytic activity of several metal oxide nanoparticles such as TiO2, CeO2, La2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3 and Gd2O3 for NaAlH4. TiO2 was found to be the most effective catalyst. In order to find the size dependence of TiO2 nanoparticles on the catalytic activity, TiO2 nanoparticles of different sizes such as 5 nm, 25 nm, 150 nm and 200 nm have been used. TiO2 nanoparticles lower the desorption temperature of sodium alanate (NaAlH4) from ∼ 473 K to ∼373 K. Using 5 nm and 25 nm TiO2 catalysts ∼3 wt% hydrogen could be released within 5–7 min at 423 K. TiO2 (25 nm) catalyst lowers the activation energy of NaAlH4 to 67 kJ/mol H2, as compared to 119 kJ/mol H2 for the pristine material. This is better than Ti nanoparticles catalyst of similar size which lowers the activation energy up to 77 kJ/mol H2. The long-term reversible characteristics of 25 nm TiO2 admixed NaAlH4 up to 35 cycles and the phase structural features of the cycled samples are discussed.

Here, we report our studies on the crystal structures, morphologies, and superconductivity in LaFeAsO1 − xFx compounds which were fabricated by solid state reaction. The crystal structures were refined using Rietveld refinement. Superconducting properties, such as critical temperature, Tc, critical current density, Jc, and upper critical field, Hc2, were determined using magneto-transport and magnetic measurements over a wide range of temperature below and above Tc, and in magnetic fields up to 14 T. A peak effect in the Jc versus field is observed at T

The crystallisation behaviour and indentation characteristics of melt-spun (Zr69.5Al7.5Cu12Ni11)100− x Ti x (x = 0–16 at. %) metallic glasses was investigated. Differential scanning calorimetry traces revealed changes in crystallisation behaviour with addition of Ti. Formation of a nanoquasicrystalline phase by annealing the glass was found up to x = 12. Further increase of Ti content gives rise to formation of a Zr2Ni-type crystalline phase. In addition to this, the size of nanoquasicrystals decreases with increasing addition of Ti. The load-dependent hardness behaviour of the metallic glasses and nanoquasicrystal–glass composites is reported in detail. The value of the yield strength of the materials was estimated with the help of hardness values based on the empirical correlations available in literature. The formation of shear bands around the indentation periphery was observed. It was found that microstructural and morphological changes alter the indentation characteristics of glasses as well as comp...

Nonstoichiometric (Cu 2− x Se) and stoichiometric (CuSe, β-Cu 2 Se and Cu 2 Se) copper selenide hexagonal nanoplates have been synthesized using different general and convenient copper sources, e.g. copper chloride, copper sulphate, copper nitrate, copper acetate, elemental copper with elemental selenium, friendly ethylene glycol and hydrazine hydrate in a defined amount of water at 100 °C within 12 h adopting the solvothermal method. Phase analysis, purity and morphology of the product have been well studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray diffraction (EDAX) techniques. The structural and compositional analysis revealed that the products were of pure phase with corresponding atomic ratios. SEM, TEM and HRTEM analyses revealed that the nanoplates were in the range 200–450 nm and the as-prepared products were uniform and highly crystallized. The nanoplates consisted of {0 0 1} facets of top–bottom surfaces and {1 1 0} facets of the other six side surfaces. This new approach encompasses many advantages over the conventional solvothermal method in terms of product quality (better morphology control with high yield) and reaction conditions (lower temperatures). Copper selenide hexagonal nanoplates obtained by the described method could be potential building blocks to construct functional devices and solar cell. This work may open up a new rationale on designing the solution synthesis of nanostructures for materials possessing similar intrinsic crystal symmetry. On the basis of the carefully controlled experiments mentioned herein, a plausible formation mechanism of the hexagonal nanoplates was suggested and discussed. To the best of our knowledge, this is the first report on nonstoichiometric (Cu 2− x Se) as well as stoichiometric (CuSe, β-Cu 2 Se and Cu 2 Se) copper selenide hexagonal nanoplates with such full control of morphologies and phases by this method under mild conditions.

We report a novel method for producing aligned ZnO nanorods (ANR) on self-grown ZnO template in a single step process involving growth of ZnO by vapor transport, followed by quenching of growing ZnO flux in liquid nitrogen. In the present study Zn powder turns into ZnO sheet under oxygen flow at ∼900 °C and bottom surface of the sheet acts as template for the growth of ANR. It is revealed from XRD and EDAX analysis that the bottom of the sheet is Zn rich region and acts as self catalyst for the growth of ANR. The grown nanorods have length up to several tens of micrometers with diameters ranging from ∼100 to 150 nm. Microstructural analysis of ANR indicates the fractal like configuration. The field emission properties have been investigated for ANR with fractal geometry using the ANR on self-grown ZnO template as a cathode directly. The turn-on electric field required to draw current density of ∼1.0 μA/cm2 has been found to be ∼0.98 V/μm. The field enhancement factor based on Fowler–Nordheim (F–N) plot was found to be ∼7815 for ANR. The fractal geometry of ANR has been shown to be advantageous for achieving improved field emission features. The present investigations of synthesis involving formation of ANR over self-grown ZnO template, together with fractal configuration of the as-synthesized ANR, are first of their type.

Superconductivity in a LaOFeAs system is known to get introduced by F-doping (LaO1−xFxFeAs) even under ambient conditions and oxygen deficiency (LaO1−xFeAs) under high pressure conditions. Hitherto unreported, superconductivity in F-free undoped LaOFeAs samples is observed and confirmed for the first time by various characterization tools–resistive ρ(T,B), magnetic M(T,B) and modulated microwave absorption (MMA) measurements. The ρ(T) at B=0 shows a clear superconducting transition with an onset at Tcon∼17 K and a tail-like behavior when R goes to zero at Tc0∼8 K. In the presence of B, the superconducting transition shifts to lower T with a rate ∼−5.5 and −1.65 T/K, depending on whether the ρ(T) has dropped to 90% or 5% of its normal state value, respectively. M(T) in zero field cooling at B=10 mT shows diamagnetic downturn below at ∼12 K. At T Tc0, indicating the presence of weak link superconducting networks in the sample. The sample shows a complex electrical and magnetic behavior in the normal state. For instance, ρ(T) reveals a weak SDW-like anomaly at T∼132 K along with a resistivity minimum at Tmin ∼78 K. M(T) also shows the presence of a magnetic anomaly at T∼130 K. Both below and above Tcon, presence of an additional ferromagnetic component is observed in the isothermal M(B) loop measurements. The superconducting and normal state features of our sample are compared with other undoped and doped LaOFeAs systems reported in the literature.

Anode made of multiwalled carbon nanotubes (MWNT) results in enhancement of exchange current density compared to graphite anode in a conventional alkaline water electrolysis cell. The hydrogen production rate with the nanotubes was measured to be ∼375 lh−1 m−2 at pH ∼ 14 which was nearly double of that obtained from traditional graphitic carbon electrodes at the same overpotential. This effect appears to be caused by defects on the nanotubes which reduces the energy barrier for the dissociation of OH− into oxygen at the anode.

The present paper reports the effect of graphitic nanofibres (GNFs) for improving the desorption kinetics of LiMg(AlH4)3 and LiAlH4. LiMg(AlH4)3 has been synthesized by mechano-chemical metathesis reaction involving LiAlH4 and MgCl2. The enhancement in dehydrogenation characteristics of LiMg(AlH4)3 has been shown to be higher when graphitic nanofibres (GNFs) were used as catalyst. Out of two different types of nanofibres namely planar graphitic nanofibre (PGNF) and helical graphitic nanofibre (HGNF), the latter has been found to act as better catalyst. We observed that helical morphology of fibres improves the desorption kinetics and decreases the desorption temperature of both LiMg(AlH4)3 and LiAlH4. The desorption temperature for 8 mol% HGNF admixed LiAlH4 gets lowered from 159 °C to 128 °C with significantly faster kinetics. In 8 mol% HGNF admixed LiMg(AlH4)3 sample, the desorption temperature gets lowered from 105 °C to ∼70 °C. The activation energy calculated for the first step decomposition of LiAlH4 admixed with 8 mol% HGNF is ∼68 kJ/mol, where as that for pristine LiAlH4 it is 107 kJ/mol. The activation energy calculated for as synthesized LiMg(AlH4)3 is ∼66 kJ/mol. Since the first step decomposition of LiMg(AlH4)3 occurs during GNF admixing, the activation energy for initial step decomposition of GNF admixed LiMg(AlH4)3 could not be estimated.

The crystallization behaviour of melt spun Zr 69.5 Al 7.5− x Ga x Cu 12 Ni 11 ( x = 0–7.5; in at.%) metallic glasses has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The DSC traces showed changes in crystallization behaviour with substitution of Ga. Formation of single nano-quasicrystalline phase by controlled crystallization of glasses has been found only for 0 ≤ x ≤ 1.5. Further increase of Ga content gives rise to formation of the quasicrystals together with Zr 2 Cu type crystalline phase. In addition to this, the substitution of Ga influences the size and shape of nano-quasicrystals. The glass forming abilities (GFAs) of these metallic glasses were assessed by the recognition of glass forming ability indicators, i.e. reduced glass transition temperature ( T rg ) and supercooled liquid region (Δ T x ). The glass transition temperature ( T g ) has been observed for all the melt spun ribbons.

The aim of the present paper is to report results on hydrogenation behaviour of the new composite material Mg 2 Ni: CNT. Admixing of carbon nanotubes (CNT) in storage material Mg 2 Ni leads to noticeable enhancement in desorption kinetics as well as storage capacity. We have found that the composite material Mg 2 Ni–2 mole% CNT is the optimum material. The Mg 2 Ni–CNT composite exhibits hydrogen desorption rate of 5.7 cc/g/min as against 3.0 cc/g/min for Mg 2 Ni alone (enhancement of ∼ 90%) and storage capacity of ∼ 4.20 wt% in contrast to ∼3.20 wt% for Mg 2 Ni alone (increase of ∼ 31%). Feasible mechanisms for the enhancement of hydrogen desorption kinetics and storage capacity have been put forward.

Interactions between nanoparticles of zinc tetra phenyl porphyrin (ZnTPP) with CdSe nanoparticles in dimethyl sulphoxide solvent have been investigated. A ZnTPP–CdSe complex was formed which showed substantial changes in the UV–Vis absorption spectra in the presence of CdSe. Fluorescence measurements showed an interesting behavior at low as well as high concentrations of CdSe. When low concentrations of CdSe nanoparticles were added to the ZnTPP nanoparticles solution, besides two fluorescence bands due to ZnTPP nanoparticles, an intense new band appeared. On the other hand at high concentrations of CdSe one of the fluorescence band of ZnTPP at ∼604 nm increased.

This paper deals with how the Hydrogen Energy may play a crucial role in taking care of the environmental scenario/climate change. The R&D efforts, at the Hydrogen Energy Center, Banaras Hindu University have been described and discussed to elucidate that hydrogen is the best option for taking care of the environmental/climate changes. All three important ingredients for hydrogen economy, i.e., production, storage and application of hydrogen have been dealt with. As regards hydrogen production, solar routes consisting of photoelectrochemical electrolysis of water have been described and discussed. Nanostructured TiO2 films used as photoanodes have been synthesized through hydrolysis of Ti[OCH(CH3)2]4. Modular designs of TiO2 photoelectrode-based PEC cells have been fabricated to get high hydrogen production rate (∼10.35 lh−1 m−2). However, hydrogen storage is a key issue in the success and realization of hydrogen technology and economy. Metal hydrides are the promising candidates due to their safety advantage with high volume efficient storage capacity for on-board applications. As regards storage, we have discussed the storage of hydrogen in intermetallics as well as lightweight complex hydride systems. For intermetallic systems, we have dealt with material tailoring of LaNi5 through Fe substitution. The La(Nil − xFex)5 (x = 0.16) has been found to yield a high storage capacity of ∼2.40 wt%. We have also discussed how CNT admixing helps to improve the hydrogen desorption rate of NaAlH4. CNT (8 mol%) admixed NaAlH4 is found to be optimum for faster desorption (∼3.3 wt% H2 within 2 h). From an applications point of view, we have focused on the use of hydrogen (stored in intermetallic La–Ni–Fe system) as fuel for Internal Combustion (IC) engine-based vehicular transport, particularly two and three-wheelers. It is shown that hydrogen used as a fuel is the most effective alternative fuel for circumventing climate change.

In the present investigation the effect of Fe substitution in Ti 51 Ni 49 alloy has been studied. The alloys were synthesized through radio frequency induction melting. The alloy was characterized through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Mossbauer spectroscopy and positron annihilation techniques. It was found that the Fe substitution stabilized the TiNi type cubic ( a = 2.998 A) phase. The microstructure and presence of the oxide phase in Ti 51 Ni 45 Fe 4 alloy have been investigated by scanning electron microscopy. The positron annihilation measurements indicated a similar bulk electron density in both the as-cast and annealed (1000 °C for 30 h) alloys, typically like that of bulk Ti. Mossbauer spectroscopy studies of as-cast and annealed iron substituted samples showed regions in the samples where nuclear Zeeman splitting of Fe levels occurred and an oxide phase was found to be present in as cast Ti 51 Ni 45 Fe 4 alloy, while annealed sample indicated the presence of bcc iron phase.

In the present investigation, we report the formation of γ-brass type phase in the rapidly quenched Cu50Ga30Mg5Ti15 and Cu50Al30Mg5Ti15 alloys. Rapid solidification of Cu50Ga30Mg5Ti15 alloy shows the formation of simple cubic γ-brass type phase (a = 0.863 nm), which on annealing at 1,023 K for 60 h transforms to disordered type γ-brass phase (a = 0.879 nm). It has been observed that intensity modulation of electron diffraction spots corresponding to simple cubic γ-brass phase is similar to the intensity modulation observed in the mirror orientation of icosahedral quasicrystalline phase. Contrary to the crystalline phase formation in Cu–Ga–Mg–Ti alloy, rapid solidification of Cu50Al30Mg5Ti15 shows the formation of amorphous and nanocrystalline bcc γ-brass type phase (a = 0.870 nm), which on annealing transforms to ordered γ-brass type phase (a = 0.872 nm). The structural and microstructural characterization was done through X-ray diffraction and transmission electron microscopy.

We report the enhanced low field magnetoresistance in broad temperature range (∼70 K) in LCMO:(%x) nano-ZnO (%x = 0, 1, 3, 5, 7 and 10) composites. Nano-ZnO has been synthesized by vapor phase transport technique which then admixed with sol–gel synthesized nano-LCMO that leads to LCMO:nano-ZnO composites. Nano-ZnO admixing does not show any significant change in lattice parameter of the composites. All samples exhibits characteristic insulator–metal (TIM) and para-ferromagnetic (TC) transition temperature, which decreases with increase in nano-ZnO content. Higher nano-ZnO (x ≥ 3%) leads to dual I–M as well as PM–FM transitions. The first transition occurs close to TIM or TC of pure LCMO and another at a significant lower temperature. At x > 7%, the double transitions transforms into a single-broad transition and at then finally disappears for x > 10%. The occurrence of dual transition has been explained on the basis of stress induced phase separation due to nanoglobular ZnO structures that result in formation of intragranular and intergranular regions having different transition temperatures. The interesting and important result for the present LCMO:nano-ZnO composites is the observation of improved MR ∼13–18% at a moderate magnetic field of 3 and 5 kG in a broad temperature range of ∼70 K (80–150 K). The improved broad range low field magnetoresistance (LFMR) has been explained on the basis of grain boundary tailoring due to coating of polar nature nano-ZnO on the LCMO grains.