A room-temperature gas sensor based on 2D Ni-Co-Zn ternary oxide nanoflakes for selective and sensitive ammonia detection.

While most of the reports on NH3 gas sensors are either based on metal oxide composites with other 2D materials, polymers or noble metals or involve multi-step-based synthesis routes, this work is the first report on a pristine ternary metal oxide, 2D NiCo2ZnO4 nanoflake based room-temperature (RT) NH3 gas sensor. The 2D NiCo2ZnO4 nanoflakes were prepared by a one-step hydrothermal method. FESEM and TEM images displayed micro-flower like morphologies, containing vertically aligned interwoven porous 2D nanoflakes, whereas XPS and XRD data confirmed the successful growth of this ternary metal-oxide. This sensor revealed a good response, repeatability, linearity (R2 = 0.9976), a low detection limit of 3.024 ppb, and a response time of 74.84 s with excellent selectivity towards NH3 over six other VOCs. This improved performance of the sensor is ascribed to its large specific surface area (127.647 m2 g-1) resulting from the 2D nanoflake like structure, good electronic conductivity, variable valence states and abundant surface-active oxygen of NiCo2ZnO4. Thus, this highly selective 2D NiCo2ZnO4 based RT NH3 gas sensor can be an attractive solution for the fabrication of next-generation NH3 gas sensors.

Graphene Properties, Synthesis and Applications: A Review.

We have evaluated some of the most recent breakthroughs in the synthesis and applications of graphene and graphene-based nanomaterials. This review includes three major categories. The first section consists of an overview of the structure and properties, including thermal, optical, and electrical transport. Recent developments in the synthesis techniques are elaborated in the second section. A number of top-down strategies for the synthesis of graphene, including exfoliation and chemical reduction of graphene oxide, are discussed. A few bottom-up synthesis methods for graphene are also covered, including thermal chemical vapor deposition, plasma-enhanced chemical vapor deposition, thermal decomposition of silicon, unzipping of carbon nanotubes, and others. The final section provides the recent innovations in graphene applications and the commercial availability of graphene-based devices.

Carbon nanotube-tungsten nanowire hierarchical structure for augmented field emission performance.

An increasing number of emitting sites and higher aspect ratios are constantly being added to field emission systems to further improve their properties. Such an ever-growing demand has thrown light on the development of hierarchical field emitters. Tungsten (W) and carbon nanotubes (CNT) have been commonly reported as potential field emitter materials. The present work focused on constructing a hierarchical field emitter structure of CNTs/W nanowires. The structural characterization has been studied using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and x-ray diffraction to confirm the hierarchical structure formation. The carbon nanotube-tungsten nanowire hierarchical structural emitters have demonstrated high current density (31.5 mA cm-2), exceptionally low turn-on field (0.068 Vµm-1), and emission stability for more than 152 h. This excellent performance could be related to the formation of a strong as well as the electrically favourable interface between tungsten nanowires and CNTs.

Development of superhydrophillic tannic acid-crosslinked graphene oxide membranes for efficient treatment of oil contaminated water with enhanced stability.

In the present age of industrialization, oil contamination in the waste water has become a huge global concern due to its several negative impacts on human health and aquatic ecosystem. In order to address this problem, a novel oleophobic and super-hydrophilic graphene-based membrane has been developed using simple and cost-effective vacuum filtration methodology. Prior developing the membranes, the graphene oxide (GO) sheets were crosslinked with tannic acid (TA) molecules in order to improve their mechanical and surface properties. To obtain the structural and morphological information of the membranes and their constituents, Field Emission Scanning Electron (FE-SEM) microscopy, X-Ray Diffraction (XRD), FTIR spectroscopy and Raman spectroscopy was used. When tested with simulated oilfield effluent samples, these membranes exhibited significant reduction in the values of chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS) and turbidity demonstrating low-oil adhesion and preferable oil rejection rates. Moreover, such crosslinked membranes are highly stable which can withstand the pressure of water filtration. In such a way, TA crosslinked GO membranes present a robust and efficient way to treat oil contaminated water released from various industries which can be reused for numerous further applications.

Low-Temperature Chemical Vapor Deposition Growth of Graphene Layers on Copper Substrate Using Camphor Precursor.

A two-step, low-temperature thermal chemical vapor deposition (CVD) process, which uses camphor for synthesizing continuous graphene layer on Cu substrate is reported. The growth process was performed at lower temperature (800 °C) using camphor as the source of carbon. A threezone CVD system was used for controlled heating of precursor, in order to obtain uniform graphene layer. As-grown samples were characterized by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). The results show the presence of 4-5 layers of graphene. As-grown graphene transferred onto a glass substrate through a polymer-free wet-etching process, demonstrated transmittance ~91% in visible spectra. This process of synthesizing large area, 4-5 layer graphene at reduced temperature represents an energy-efficient method of producing graphene for possible applications in opto-electronic industry.

Distinct Levels of Adhesion Energy of In-Situ Grown CuO Nanostructures.

CuO nanostructures were reported for a myriad of applications in diverse areas such as high Tc superconductors, field emitters, catalysts, gas sensors, magnetic storage, biosensors, superhydrophobic surfaces, energy materials etc. In all these applications, structural stability of the nanostructures is very important for efficient functioning of devices with a longer lifetime. Hence, it is necessary to understand the adhesion energy of these nanostructures with their substrates. In this research work, a variety of CuO nanostructures were synthesized directly on Cu foil substrate by varying only the concentration of the reagents. CuO nanostructures, thus grown, were subjected to a nano-scratch test to quantify their adhesion strength with Cu substrate. The adhesion energy was observed to be highest for nanorods and lowest for nanoribbons among all the CuO nanostructures synthesized in this work. Results of this research will be useful in predicting the service life and in improving the efficiency of CuO nanostructure-based devices.

Quantifying bonding strength of CuO nanotubes with substrate using the nano-scratch technique.

CuO is a narrow bandgap semiconductor demonstrating applications in/as catalysts, gas sensors, adsorbents, and superconductors, and as electrodes of photocells, super-capacitors, and lithium-ion batteries. One-dimensional (1D) CuO nanostructures are of particular interest in most of these device applications, owing to their huge surface area. Strong bonding between nanomaterials and substrate is essential for extended device life. Hence, knowledge about the strength of the nanomaterial-substrate bond is highly desired. In this research work, CuO nanotubes were synthesized directly on a Cu substrate, and its adhesion strength was quantified using the nano-scratch-based technique. The adhesion energy of CuO nanotubes (for 7 h of reaction period) on the Cu substrate was measured to be 82 Jm(-2). The bonding strength can be correlated with the structure of the material. Results of this research will be valuable in analyzing and improving the lifetime of CuO nanotube-based devices, and the technique could be further extended to other 1D transition metal oxide nanostructures.

Three-dimensional metal-graphene-nanotube multifunctional hybrid materials.

Graphene was grown directly on porous nickel films, followed by the growth of controlled lengths of vertical carbon nanotube (CNT) forests that seamlessly emanate from the graphene surface. The metal-graphene-CNT structure is used to directly fabricate field-emitter devices and double-layer capacitors. The three-dimensional nanostructured hybrid materials, with better interfacial contacts and volume utilization, can stimulate the development of several energy-efficient technologies.

Controlled growth of single-walled carbon nanotubes for unique nanodevices.

The controlled growth of bent and horizontally aligned single-walled carbon nanotubes (SWNTs) is demonstrated in this study. The bent SWNTs growth is attributed to the interaction between van der Waals force with substrate and aerodynamic force from gas flow. The curvature of bent SWNTs can be tailored by adjusting the angle between gas flow and step-edge direction. Electrical characterization shows that the one-dimensional resistivity of bent SWNTs is correlated with the curvature, which is due to strain induced energy bandgap variation. Additionally, a downshift of 10 cm(-1) in G-band is found at curved part by Raman analysis, which may be resulted from the bending induced carbon-carbon bond variation. In addition, horizontally aligned SWNTs and crossbar SWNTs were demonstrated. To prove the possibility of integrating the SWNTs having controllable morphology in carbon nanotube based electronics, an inverter with a gain of 2 was built on an individual horizontally aligned carbon nanotube.

Carbon nanotubes: how strong is their bond with the substrate?

A reliable quantification technique for interpreting nanomaterial-substrate bond strength is highly desired to predict efficient, long-term performance of nanomaterial-based devices. Adopting a novel nanoscratch-based technique, here we demonstrate quantification of carbon nanotube (CNT)-substrate adhesion strength for dense CNT structure and for patterned carbon nanocone (CNC) structures. Debonding energy for a single CNT is illustrated to range between 1 and 10 pJ, and the variation is strongly dependent on the nature of the interface between CNTs, catalysts, and substrates. Our proposed technique could be adopted for characterization of bonding strength between a wide variety of nanotubes, nanowires, and other one-dimensional nanostructured materials and their underlying substrates.

High capacity and excellent stability of lithium ion battery anode using interface-controlled binder-free multiwall carbon nanotubes grown on copper.

We present a novel binder-free multiwall carbon nanotube (MWCNT) structure as an anode in Li ion batteries. The interface-controlled MWCNT structure, synthesized through a two-step process of catalyst deposition and chemical vapor deposition (CVD) and directly grown on a copper current collector, showed very high specific capacity, almost three times as that of graphite, excellent rate capability even at a charging/discharging rate of 3 C, and no capacity degradation up to 50 cycles. Significantly enhanced properties of this anode could be related to high Li ion intercalation on the carbon nanotube walls, strong bonding with the substrate, and excellent conductivity.

Carbon-nanotube-embedded novel three-Dimensional alumina microchannel cold cathodes for high electron emission.

The present work describes a comprehensive design and scalable micro-fabrication technique for the production of novel 3D cathodes, consisting of chemical-vapor-deposition-grown high-density multi-wall carbon nanotubes along the walls of alumina microchannels. Under high DC and AC electric fields, the 3D cathodes displayed significantly high and moderately stable emission current of approximately 5.25 and approximately 14 mA, respectively. The inherent advantages of the 3D microchannel geometry for cold cathodes are higher emitter area, less ion bombardment and robustness under high voltage conditions. The 3D cathodes are envisioned to offer an entirely new class of miniature electron sources for high current vacuum microelectronics.