Suneel Kumar Srivastava

Nanostructured anode materials for lithium ion batteries

High-energy consumption in our day-to-day life can be balanced not only by harvesting pollution-free renewable energy sources, but also requires proper storage and distribution of energy. In this regard, lithium ion batteries are currently considered as effective energy storage devices and involve the most active research. There exist several review articles dealing with various sections of LIBs, such as the anode, the cathode, electrolytes, electrode–electrolyte interface etc. However, the anode is considered to be a crucial component affecting the performance of LIBs as evident from the tremendous amount of current research work carried out in this area. In the last few years, advancements have been focused more on the fabrication of the nanostructured anode owing to its special properties, such as high surface area, short Li+ ion diffusion path length, high electron transportation rate etc. As the work in this area is growing very fast, the present review paper deliberates the recent developments of anode materials on the nanoscale. Different types of anode materials, such as carbon-based materials, alloys, Si-based materials, transition metal oxides, and transition metal chalcogenides, with their unique physical and electrochemical properties, are discussed. Various approaches to designing materials in the form of 0, 1 and 2D nanostructures and their effect of size and morphology on their performance as anode materials in LIBs are reviewed. Moreover, the article emphasizes smart approaches for making core–shell particles, nanoheterostructures, nanocomposites or nanohybrids with the combination of electrochemically active materials and conductive carbonaceous or electrochemically inactive materials to achieve LIBs with high capacity, high rate capability, and excellent cycling stability. We believe the review paper will provide an update for the reader regarding recent progress on nanostructured anode materials for LIBs.

MoS2–MWCNT hybrids as a superior anode in lithium-ion batteries

Molybdenum disulfide (MoS(2))-multiwalled carbon nanotube (MWCNT) hybrids have been prepared by simple dry grinding. Excellent initial charge capacity (1214 mA h g(-1)) and ~85% retention after 60 discharge-charge cycles at different current densities (100-500 mA g(-1)) make MoS(2)-MWCNT (1 : 1) hybrids a superior anode in Li-ion batteries.

Synthesis and characterization of Na-montmorillonite-alkylammonium intercalation compounds

Some organophilic montmorillonites (OPMNTs) have been synthesized from Na-montmorillonite (Na-MNT) using ammonium salts of methyl, propyl, butyl, and dodecyl amine. Thermogravimetric (TG), infrared (IR), and X-ray analyses of the compounds were carried out. Microstructural parameters such as crystallite size and root mean square strain (rms) ( 1/2) have been calculated by X-ray line profiles analysis. TG analysis in the temperature range 20–100°C show a weight loss for pure Na-MNT and OPMNTs of about 11% and 2.8%, respectively, indicating the organophilic properties of the OPMNTs. IR and X-ray analyses confirm the formation of OPMNTs by an ion exchange reaction. It is also observed that the crystallite size and rms strain increase with increase carbon number (nc) in the amines.

In situ deposition of Sn-doped CdS thin films by chemical bath deposition and their characterization

In-situ Sn-doped CdS thin films have been deposited successfully by the chemical bath deposition method using tartaric acid as a complexing agent. The films have been characterized by x-ray diffraction for structure determination, and microstructural parameters like crystallite size, rms strain and dislocation density have been calculated using x-ray line profile analysis. The composition of the films has been determined by x-ray photoelectron spectroscopy and energy dispersive x-ray analysis. Optical studies show that the band gap decreases significantly for pure CdS (2.39?eV) to 3.8?mol% of Sn-doped CdS (1.84?eV). A detailed PL study of CdS when doped with varying Sn concentrations has also been discussed. Temperature variation of the electrical resistivity of Sn-doped CdS thin films confirmed their semiconducting behaviour similar to the pure CdS. It also shows that doping of Sn in CdS makes a pronounced drop in the room temperature resistivity value from 1010?103???cm for pure CdS to 3.8?mol% of Sn-doped CdS, respectively.

Magnetic Ni/Ag core–shell nanostructure from prickly Ni nanowire precursor and its catalytic and antibacterial activity

A microemulsion template assisted hydrazine hydrate mediated wet chemical reduction of nickel chloride hexahydrate at 70 °C has been used for the fabrication of prickly nickel nanowires. Subsequently, the nanowire surfaces are modified with silver using the well known Tollens reagent to form Ni/Ag core–shell nanostructures. X-Ray diffraction studies confirm the formation of face centered cubic type structures of nickel as well as silver in Ni/Ag nanostructures individually and they are found to be devoid of any trace of contamination. Low magnification field emission scanning electron microscope (FESEM) images confirm the wire-like morphology of nickel as well as Ni/Ag core–shell nanostructures. However, the high magnification FESEM and transmission electron microscopy images show the prickly surface of nickel nanowires consisting of cone-like nanostructures, where small spherical silver particles are deposited. Vibrating sample magnetometer (VSM) studies show well defined ferromagnetic behavior of the Ni as well as core–shell Ni/Ag structures. In addition, these nanostructures have been proved to be efficient catalysts at room temperature for the reduction of p-nitrophenol compared to bare Ni nanowires, and the magnetic behaviour serves as an added advantage in its easy separation from the reaction mixture so that it can be reused. Furthermore, Ni/Ag nanostructures also exhibit excellent antibacterial properties, which are significantly better than commercially available antibacterial materials.

Nanostructured copper sulfides: synthesis, properties and applications

Among different metal chalcogenides, copper sulfides have been extensively studied in the past few years due to their semiconducting and non-toxic nature, making them useful in a wide range of applications from the energy to the biomedical fields. A series of stoichiometric compositions of copper sulfides from Cu-rich, Cu2S to Cu-deficient, CuS2 exist with different crystal structures as well as phases, resulting in different unique properties. The suitable band gap values in the range of 1.2–1.5 eV and unique optoelectronic properties indicate that the material is photocatalytically active and exhibits excellent plasmonic behavior. The material is also known for promising thermoelectric properties, converting waste heat into electricity through the Seebeck effect. The nanodimensional form of copper sulfides promotes their use to a more advanced level, tuning their properties with the size of the materials. In view of this, the present review article is focused on the compositions, phases and crystal structures, and different synthetic methodologies involved in the fabrication of 0D, 1D and 2D nanostructured copper sulfides. Moreover, recent advancements on their use in various applications will also be briefly discussed.

EVA/clay nanocomposite by solution blending: Effect of aluminosilicate layers on mechanical and thermal properties

Ethylene vinyl acetate (EVA)/clay nanocomposites were synthesized by blending a solution of ethylene vinyl acetate copolymer containing 12% vinyl acetate abbreviated as EVA-12 in toluene and dispersion of dodecyl ammonium ion intercalated montmorillonite (12Me-MMT) inN,N-dimethyl acetamide (DMAc). X-ray patterns of sodium montmorillonite (Na+-MMT) and 12Me-MMT exhibited d001 peak at 2θ?=7.4° and 2θ?=5.6° respectively; that is, the interlayer spacing of MMT increased by about 0.39 nm due to intercalation of dodecyl ammonium ions. The XRD trace of EVA showed no peak in the angular range of 3–10° (2θ). In the XRD patterns of EVA/clay hybrids with clay content up to 6 wt% the basal reflection peak of 12Me-MMT was absent, leading to the formation of delaminated configuration of the composites. When the 12Me-MMT content was 8 wt% in the EVA-12 matrix, the hybrid revealed a peak at about 2θ?=5.6°, owing to the aggregation of aluminosilicate layers. Transmission electron microscopic photograph exhibited that an average size of 12–15 nm clay layers were randomly and homogeneously dispersed in the polymer matrix, which led to the formation of nanocomposite with delaminated configuration. The formation of delaminated nanocomposites was manifested through the enhancement of mechanical properties and thermal stability, e.g. tensile strength of an hybrid containing only 2 wt% 12Me-MMT was enhanced by about 36% as compared with neat EVA-12.

Dehydration transformation in Ca-montmorillonite

The present work deals with the dehydration transformation of Ca-montmorillonite in the temperature range 30°–500°C. Thermal, infrared (IR), and X-ray diffraction (XRD) analyses were used to describe the thermal transformation. The microstructural and layer disorder parameters like crystallite size, r.m.s. strain (〈e2〉1/2), variation of interlayer spacing (g), and proportion of planes which were affected by the defect (γ), have all been calculated from the (001) basal reflection using the method of variance and Fourier line shape analysis. These investigations revealed that sample underwent transformation from hydrated phase to dehydrated phase at 200°C, and as a consequence, its basal spacing collapsed from 1602 Å (30°C) to around 10 Å (200°C). This transformation occurred through a wide range of temperature, i.e. within the range 120°–200°C. The crystallite size was maximum at room temperature (30°C), however, the size decreased with increasing temperature in the hydrated phase, whereas the size increased with increasing temperature for the dehydrated phase. Theg, γ and 〈e2〉1/2 of the hydrated and the dehydrated phase increased and decreased, respectively with increase of heating temperature.

Low temperature micelle-template assisted growth of Bi2S3 nanotubes

The growth of Bi(2)S(3) nanotubes through a simple soft chemical route using the surfactant Triton-X 100 as the template at the relatively very low temperature of 115 degrees C/12 h has been reported for the first time. These nanotubes are nearly uniform in dimensions, with diameter around 120 nm and length up to 8 microm, their nature being single crystalline. The reaction conditions are optimized. Development of nanotubes and nanoparticles from the same precursor is discussed. The optical properties of the nanotubes are studied by means of UV-visible and photoluminescence spectra. The band gap calculated from the absorption spectra is found to be 1.76 eV, indicating a considerable blue shift relative to the bulk.

Studies on layer disorder, microstructural parameters and other properties of tungsten-substitued molybdenum disulfide, Mo1−xWxS2 (0≤x≤1)

Abstract The present paper deals with the preparation of tungsten-substituted molybdenum disulfide, Mo 1− x W x S 2 (0≤ x ≤1) compounds and their characterization by various physicochemical methods. X-ray studies confirmed that these compounds crystallized in a layer type of hexagonal structure. X-ray line profile analysis techniques such as the method of variance and Fourier analysis have been used for microstructural characterization of these compounds to find out information about particle size, r.m.s. strain, variability of interlayer spacing, fraction of planes affected by such defects, dislocation density, stacking fault probability and radial distribution function analysis for calculating coupling constants and mean-square displacements, etc. Room-temperature magnetic susceptibility measurements and thermoelectric power experiments and temperature variation of conductivity (25–350°C) confirmed, respectively, diamagnetic n- and p-type semiconducting behaviour for Mo 1− x W x S 2 . Thermal stability behaviour of these compounds in air and inert atmosphere has also been carried out up to 1000°C. These studies indicated that the compounds are nearly stable up to 1000°C in inert atmosphere, whereas, in air, oxidative degradation of these compounds started at 400°C. The nature of the oxidized products has also been studied by X-ray analysis. Scanning electron micrograph studies are also reported here.