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Boron-doped carbon nanotubes (BCNTs) with varying B content (0–8 at%) were prepared by thermo-catalytic decomposition of ethanol in presence of boric acid at 1073 K. It was observed that hydrogen adsorption capacity improved to a critical B content of 3.86 at% and then decreased. Maximum hydrogen adsorption was found to be 0.497 wt% at 273 K and 16 bar with 3.86 at% of boron doping in CNTs. With the help of transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, it was found that in addition to dopant concentration, dopant bonding with carbon structures, crystallinity and defects play pivotal roles in determining the extent of hydrogen adsorption by BCNTs. The thermogravimetric studies revealed the oxidation stability of the BCNTs. The hydrogen adsorption kinetics was found to follow the pseudo-second-order model. The rate constant value was minimum for the BCNT with the highest hydrogen storage capacity.

This paper illustrates the electrochemical exfoliation of graphite for the synthesis of graphene oxide (GO) with few layers. Innovative design and arrangement of electrodes were adopted, which allowed simultaneous exfoliation and re-exfoliation of graphite anode. Electrolyte having different molar concentrations of an aqueous solution of sulfuric acid (H2SO4) and pH offered successful exfoliation of graphite anode with a varying yield of GO. The addition of sodium hydroxide (NaOH) in the solution affected the exfoliation rate and the morphology of the GO sheets. The transition of GO sheets from clumping–scrolling–flat sheet edge rolling to nanoribbons was observed by the change of composition and pH of the electrolyte. GO sheets showed lateral dimensions ranging from 500 nm to 24 μm, and ribbons and scrolls were found to have dimensions up to 50 μm. With the help of transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, a mechanism of exfoliation has been proposed. In situ functionalization of graphene helped in imparting stability to the GO in solvents such as ethanol and water for more than 11 months. This study elaborates on the significance of solvated sulfate ions and provides a window of sulfate and hydroxyl ion combination for tuning of structural morphologies of GO.

Kinetics of formation of carbon nanotube aerogel (CNT-a) by floating catalyst chemical vapor deposition (FC–CVD) has been studied for the first time by thermocatalytic decomposition of ethanol usin...

In this research work, Carbon-carbon composites (CCCs) were fabricated via carbonization of carbon nanotubes (CNTs)-coated carbon textile (CNT-CF) reinforced polymer matrix composites (PMCs) preforms at 600, 900, 1200, and 1500 °C in a tubular furnace. To obtain CNT-CF, MWCNTs were produced radially on the surface of the nano-nickel particles plated carbon textile at 700°C using catalytic chemical vapor deposition method and C2H2 gas as a carbon source. The effects of CNT coating on carbon textiles were evaluated using FESEM, HR-TEM, XRD, Raman, TGA, and BET analysis. The effects of heat treatment temperatures on CNTs coated and uncoated PMCs manufactured using simple hand-layup method subsequently hot compressing were evaluated through XRD, FESEM, density, electrical conductivity measurement, tensile and flexural test, and viscoelastic properties using DMTA. The CNT coated CCCs obtained at 1500°C exhibited ∼ 66, 62, 83, 27, 44, 30, and 36% enhancement in electrical conductivity, storage modulus, loss modulus, tensile strength, Young’s modulus, flexural strength, and flexural modulus of CNT coated CCCs, respectively compare to uncoated CCCs. Moreover, substantial enhancement in thermal stability of PMCs and CCCs make CNT-CF as one of the competent alternate reinforcement for the fabrication of structural parts used in high-performance applications.

The generation IV nuclear reactors Tri-structural isotropic (TRISO) fuel suffer failure due to internal pressure generation, corrosion by fission products and kernel migration under temperature gradient. An innovative fuel particle design was conceptualized and realized for the first time in literature by embedding multi-wall carbon nanotube (MWCNT) into porous buffer pyrolytic carbon layer (B.PyC) of TRISO particle to address above issues. MWCNT embedded in B.PyC was obtained by sequential coating using novel chemical vapor deposition reactor. Scanning electron microscopy shows ~15 μm uniformly dispersed MWCNT into B.PyC layer. Transmission electron microscopy and Raman Spectroscopy analysis of the deposited CNT revealed to be multi walled with good crystalline. Results of small angle scattering technique of the composite layer using X-ray and neutrons (SAXS/SANS) reveal better pore structure and could pave new vistas for TRISO fuel development. Intrinsic MWCNT features offer immense potential to mitigate various shortcoming of TRISO particle during actual Generation IV nuclear reactor operation.

Boron and nitrogen codoped carbon nanotubes (B,N-CNTs) were synthesized by floating catalyst chemical vapor deposition (FCCVD) using ethanol, ferrocene, boric acid and imidazole as carbon source, catalyst, boron and nitrogen precursors, respectively. The samples were analyzed using transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis and X-ray photoemission spectroscopy. 1.5 at% B and 1.34 at% N could be doped in the resultant structure, which has higher length (few μm) with higher thermal stability (621 °C). At pressure 16 bar, hydrogen adsorption for B,N-CNTs was found to be 1.96 and 0.35 wt% at 77 K and 303 K, respectively. Hydrogen storage as function of time was also reported for both the cases. The adsorption process follow pseudo second order kinetics. The present study reveals that the codoping of CNTs aid in tuning properties of CNTs for hydrogen storage application.

Composite armor panels with boron carbide ceramic as striking face, backed with carbon nanotube-ultra high molecular weight polyethylene (CNT-UHMWPE), have been fabricated as lightweight body armors. The armor panels were tested against actual ammunitions through self-loading rifle (SLR) and AK-47. Slip lines were observed in boron carbide with high energy bullets. CNT-UHMWPE composite backing resulted in a low back face signature (BFS) due to the formation of a strong bond between CNT and UHMWPE and high energy dissipation through this composite. The role of CNT in the ballistic protection of this composite armor has been explained with the help of necessary characterization by electron microscopy, X-ray radiography, Fourier transformed infrared spectroscopy and differential scanning calorimetry.

Floating catalyst chemical vapor deposition method was used for the synthesis of boron doped carbon nanotubes (BCNTs) using ethanol, triethyl borate and ferrocene as carbon source, boron source and catalyst precursor, respectively. The synthesized BCNTs were characterized by transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS). The hydrogen adsorption activity was studied for BCNTs along with undoped single walled and multi walled carbon nanotubes. Significant enhancement in the hydrogen storage value was found in doped CNTs as compared to the other undoped CNTs. Hydrogen storage for BCNTs was found to be 2.5 wt% at 10 bar and 77 K. In-situ doped BCNTs gives higher hydrogen adsorption as compared to ex-situ doped BCNTs. The Langmuir adsorption isotherm was found to be suitable for describing the adsorption isotherm as compared with Freundlich isotherm. Maximum adsorption capacity was about 9.8 wt% at 77 K. Pseudo second order kinetics was followed by BCNTs for hydrogen adsorption.

Single walled carbon nanotubes (SWCNTs) have been synthesized from thermocatalytic decomposition of methane by using ferrocene as the catalyst at atmospheric pressure. Floating catalyst chemical vapour deposition using a horizontal two zone reactor was employed to investigate the kinetics. The effects of temperature of synthesis (800–1000 °C), partial pressure (2–40 kPa) of reactant gas and catalyst concentration (0.2–4.6 mol m−3) on the rate of formation of SWCNTs have been studied. The rate is proportional to the partial pressure of methane indicating that the surface reaction of methane on the active site is the rate controlling step. The activation energy was found to be 80.16 kJ mol−1. Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, BET, UV–Vis-NIR and thermogravimetry have been used for the characterization of products. UV–Vis-NIR spectroscopy data reveals presence of 78–82% metallic SWCNTs (m-SWCNTs) in the synthesized samples. The BET surface area of purified SWCNTs were found to be 871 m2 g−1 with pore volume of 0.35 cc g−1 and electrical conductivity of 856–746 S cm−1.

Single and multi-walled carbon nanotubes have been synthesized by floating catalyst chemical vapour deposition technique. Methane, argon, ferrocene and sulphur were used as carbon source, inert gas, catalyst and promoter, respectively. The types of carbon nanotubes (single or multi-walled) were governed by a variety of experimental factors: the ferrocene flow rate, methane flow rate, sulfur flow rate, argon flow rate and reaction temperature. The optimization of the process parameters was carried out to find the parameter 'islands' for the selective formation of single or multiwalled carbon nanotubes. The characterization was carried out by transmission electron microscopy, thermo gravimetric analysis and Raman spectroscopy. A high hydrogen flow rate, low methane flow rate and high sulfur flow rate were crucial factors for selective synthesis of single walled carbon nanotubes. This work provides methodology for optimization of processing parameters for synthesizing high purity single or multi walled carbon nanotubes

Hot pressed boron carbide–carbon nanotube (B4C–CNT) composites have been fabricated as potential materials for armour application. The effect of CNT addition (with 2, 5 and 10 vol%) on the hardness, fracture toughness and flexural strength of the composites has been evaluated. 5 vol% addition of CNT was found to be optimum with superior mechanical properties to that of monolithic B4C. The fracture toughness was improved from 2.56 to 5.65 MPa√m that was attributed to crack branching, crack bridging and crack deflection by CNT as was evident from scanning electron microscopy. Transmission electron microscopy could bring out the clear and continuous interface between B4C and CNT. However, at very high CNT vol% (10 vol %) the mechanical properties slightly deteriorated due to agglomeration. The experimentally obtained data were fitted with suitable mathematical models.

Simultaneous synthesis and densification of boron carbide and boron carbide- graphene nano platelets (GNP) were carried out by reactive spark plasma sintering of amorphous boron and graphene nano platelets at temperature ranging from 1200 to 1600 °C, pressure of 50 MPa and heating rate of 50 °C/min and 100 °C/min. X-ray diffraction and Raman spectroscopy confirmed the formation of required phases. Electron microscopic images revealed the formation of sub-micron and nano sized grains of plate like morphology. Sintered product with high relative density of 96%TD was achieved at a temperature of 1600 °C and heating rate of 50 °C/min for B4C stoichiometric composition and also exhibited maximum hardness of 21.10 GPa.

Doping of carbon nanotubes (CNTs) effectively provides a route to tune their physicochemical properties towards specific applications. Heteroatoms, such as boron (B) and nitrogen (N) can be used as dopants to tune the properties of CNTs. Till now, B as a dopant is relatively less explored but it has a huge potential for applications in various fields. The objective of this review is to shed light on the effects of B doping on different properties of CNTs, on the potential applications of B doped CNTs (B-CNTs), and to draw the future roadmap for the research on B-CNTs. In this review paper, we have presented the chronological development on B doped CNTs. We have analyzed the published literature on the synthesis of B-CNTs using different techniques with more emphasis on the chemical vapor deposition (CVD) method. A methodology has been proposed to find out the reaction mechanism(s) and rate expression(s) for the CVD-based synthesis. The microscopic and spectroscopic analyses (like transmission electron microscopy, Raman spectroscopy, X-ray photoemission spectroscopy, nitrogen adsorption–desorption analysis) for B-CNTs have been extensively discussed. In addition, we have delineated the application of B-CNTs in the field of hydrogen storage, catalysis, electrocatalysis, and sensors in depth. In conclusion, based on the present knowledge base, we have identified the knowledge gaps, and therefore have made recommendations for future work.

We report the development of an ultrasensitive label-free DNA biosensor device with fully integrated standalone carbon nanotube (CNT) aerogel electrode. The multi-directional tenuous network of clustered CNT embedding into the CNT aerogel electrode demonstrates linear ohmic and near isotropic electrical properties, thereby providing high sensitivity for nucleic acid detection. Using this device, the target DNA hybridization is detected by a quantifiable change in the electrochemical impedance, with a distinct response to the single-stranded probe alone or double-stranded target-probe complex. The target DNA is specifically detected with limit of detection (LoD) of 1 pM with a turnaround time of less than 20 min, which is unprecedented for a miniaturized CNT aerogel sensor and impedance spectroscopy without an intermediate DNA amplification step. Moreover, this system is able to differentiate between the closely related target sequences by the distinct impedance response rendering it highly specific. To the best of our knowledge, this is the first report showing the use of standalone bare CNT aerogel electrode without any substrate support, coupled with electrochemical impedance spectroscopy, for the detection of DNA hybridization. Altogether, the results show that our system is fast, sensitive and specific for label-free rapid direct DNA detection, promising a novel avenue for bio-sensing.

A carbon nanotube fiber is formed by interlocking carbon nanotubes that are perfectly aligned to give a continuous long fiber. The production of neat carbon nanotube fibers has paved the way for realization of superior mechanical and physical properties of individual carbon nanotubes at macroscopic scale. In this review paper, we elucidate the state of the art advances in fabrication methods, characterization, modeling of mechanical properties, and applications of carbon nanotube fibers as next generation high performance fibers for composites. Recommendations have been made on the aspects of design and scale-up for large scale manufacturing of carbon nanotube fibers using (a) a stepwise protocol for the determination rate controlling step(s) and the estimation of overall rate of reaction, and (b) computational fluid dynamics. Finally, the challenges and opportunities in carbon nanotube fiber research have been clearly brought out, and suggestions have been made for future work.

Nitrogen doped carbon nanotubes has been synthesized using imidazole and acetylene in a fixed bed reactor by catalytic chemical vapour deposition. Ferrocene was used as a catalyst dispersed on magnesium oxide as a support. Imidazole acted as both carbon and nitrogen source and acetylene was used as an additional carbon source to tune the nitrogen content and increase the productivity. The temperature, flow rate of the reactants, particle size of the support, and height of the boat and partial pressure of acetylene were varied to understand their effect on the rate of formation of nitrogen doped carbon nanotubes. A plausible reaction mechanism was proposed to predict the rate determining step of the reaction and it was found that saturation and supersaturation of the nitrogen doped carbon nanotubes was rate determining. Temperature studies showed surface reaction can be possibly controlling the reaction rate with activation energy of 114 kJ mol −1 . Average particle size of >91 µm depicted pore diffusion control. The products have been characterized by electron microscopy, thermogravimetry, Raman spectroscopy, carbon-hydrogen-nitrogen analysis and surface area analysis.

Feasibility of synthesis of Platinum/Multiwall Carbon Nanotube (Pt/MWCNT) nano-composites has been evaluated using a green chemical approach in the task specific ionic liquid (TSIL), trioctylmethyl ammonium hydrogen phthalate (TOMAHP). Effects of reaction temperature and introduction of functional groups in MWCNT on the dispersion of Pt onto MWCNT have been studied during synthesis. The Pt/MWCNT nano-composites thus prepared have been characterized for their structures, compositions, sizes and morphologies using X-ray diffraction (XRD), small-angle X-ray scattering (SAXS) and transmission electron microscopic (TEM) techniques. The high resolution transmission electron microscopy (HRTEM) and SAXS study showed that the fcc Pt nanoparticles (NPs) prepared at 40 °C are finely dispersed having average particles size of∼3–5 nm. However, most of them were not deposited onto the surface of pristine MWCNT. When functionalized MWCNT was used instead of pristine one, the Pt NPs formed agglomeration and there was wide size distribution. Increase in reaction temperature from 40 °C to 80 °C leads to formation of well dispersed Pt NPs on pristine MWCNT surface with particle size of 1–3 nm. A possible mechanism for formation of Pt/MWCNT in TSIL medium has been discussed.

Few layered graphene (FLG) was synthesized by substrate-free floating catalyst chemical vapour deposition method for the first time. A sensor prepared from the pristine FLG coated over a glassy carbon electrode without further modification showed high sensitivity towards sensing of H 2 O 2 (355 μA mM −1 cm −2 ) with lower detection limit of 0.27 μM and response time of 5 s. Transmission electron microscopy revealed 3–5 layers of graphene sheets with edge defects, which was supported by Raman spectroscopy. X-ray photoelectron spectroscopy confirmed that the defects are due to oxygen present in the FLG in the form of C O, that played important role in sensing.

Amidoamine functionalized multi-walled carbon nanotubes (MWCNT-AA) have been prepared and characterized. Separation of mercury(II) ions from aqueous solution by solid-liquid extraction has been investigated using the synthesized material as an adsorbent. Batch adsorption studies as a function of pH, contact time, initial metal ion concentration, and temperature have been carried out. The best fit for the adsorption equilibrium data was observed with Redlich-Peterson isotherm model and the kinetics data showed superior fitting for pseudo second order model, signifying chemisorption. The adsorbent showed superior selectivity with high adsorption capacity towards mercury as compared to other metal ions present in industrial waste water containing mercury. The MWCNT-AA was successfully used for six adsorption-desorption cycles without significant loss of uptake using 0.05 M EDTA as desorbing agent. A small scale fixed bed column study was demonstrated to test the scale up application. DFT theoretical calculations establish the bi-dentate mode of complexation and correlate the experimental selectivity.

Nitrogen atoms were successfully doped into the lattice of carbon nanotubes (hereafter called N-CNT) by chemical vapor deposition in a fluidized bed reactor using a solid precursor Imidazole. X-ray Photoelectron Spectroscopy estimated that ∼5.4 atom% of nitrogen was doped in the synthesized CNTs. The successful formation of N-CNTs was also confirmed by Fourier Transforms Infrared Spectroscopy. Transmission electron microscopy revealed the morphological features of N-CNTs and their changes with temperature. The use of fluidized bed resulted in the formation of uniform nature of N-CNTs. In-depth studies of influence of nitrogen doping in CNTs for hydrogen storage was studied by comparing with bare CNTs, also synthesized by a the same fluidized bed reactor. The hydrogen storage capacity for N-CNTs (0.8 wt.%) was enhanced significantly at very low temperature (163 K), compared to bare CNTs (0.28 wt.%).

Poly(amidoamine) dendrimer functionalized carbon nanotube was demonstrated as highly efficient sorbent of the Pu4+ from radioactive waste solution. The second generation dendrimer was found to have more efficiency as compared to the 1st generation might be due to the availability of more functionality for coordinating to the Pu4+ ion. Analysis of different isotherm models revealed that, Langmuir isotherm was predominantly operating through chemi-sorption (with the sorption energy 10.07 and 16.95 kJ mol−1 for 1st and 2nd generation dendrimer) with the sorption capacity 89.22 mg g−1 and 92.48 mg g−1 for 1st and 2nd generation dendrimer, respectively. Analysis of different sorption kinetics model revealed that the sorption proceeded via pseudo 2nd order reaction. The 2nd generation dendrimer was found to be radiolytically more stable while oxalic acid was found to be suitable for quantitative back extraction of Pu4+.

Photoelectrochemical performance of bismuth vanadate (BiVO4) photoanode is limited by poor charge separation and transport properties. The roles of carbon nanotube, reduced graphene oxide, or graphitic carbon nitride in BiVO4 composite photoanode were investigated toward enhancing light absorption and reducing overall impedance during photoelectrochemical water oxidation process. X-ray diffraction and Tauc analysis showed that BiVO4 retains its monoclinic phase, n-type semiconductor nature, and band gap in all carbon nanomaterials-incorporated composite photoanodes. It was observed that the carbon nanomaterials incorporation in BiVO4 film increases its surface porosity, ultimately leading to enhanced light absorption. The BiVO4 photoanode with reduced graphene oxide and graphitic carbon nitride showed same bulk charge separation efficiency, whereas the latter showed better charge transfer. It was found that the graphitic carbon nitride formed composite with BiVO4 to provide enhanced light absorption efficiency, i.e., 89% in 350-505 nm range. The BiVO4 with graphitic carbon nitride photoanode showed the best performance with a photocurrent of 2.2 mA cm-2, charge separation efficiency of 67%, and photocurrent of 4.0 mA cm-2 with cobalt-phosphate surface catalyst at 1.23 VRHE for water oxidation under 1 sun illumination. The Mott-Schottky and impedance measurements confirmed the shift of conduction band position toward hydrogen reduction potential and reduction in film resistance, respectively, with carbon nanomaterials addition, and the shift was most significant for graphitic carbon nitride. It is concluded that by concomitant formation of junction during photoanode fabrication between carbon nanomaterials, BiVO4, and fluorine-doped tin oxide glass substrate, better charge separation, transport, and light absorption can be achieved.

Floating-catalyst chemical vapour deposition (FC CVD) is a promising method for large-scale synthesis of single-walled carbon nanotube (SWCNT). The current work focuses on the comprehensive optimization studies with the objective of maximizing the yield and minimizing the diameter of SWCNTs considering the complex dependency and interaction effects between the process parameters. Data-analytics driven process parameter selection criterion was utilized for heat map generation of the eight process parameters. Orthogonal design of experiments encompassing Taguchi L-18 array and subsequent analysis of variance reveals strong interaction effects between the process parameters and demonstrates conflicting nature between the two objectives, yield and diameter of SWCNTs. Pareto optimization was used to capture the conflicting behaviour of the dual objectives in true sense. Artificial neural network (ANN) coupled with Taguchi analysis brings out the interaction effects of process parameters that could predict the output with more than 90% accuracy. The rigorous analysis concludes that the furnace temperature mostly affects the diameter, whereas, methane flow-rate determines the SWCNT yield. The optimum condition for higher SWCNT yield with minimum diameter was obtained at a lower methane and hydrogen flow while keeping furnace temperature and argon flow at the highest level and thiophene at the lowest level.

Efficient interfacial interaction between MoS2 nanosheets and functionalized carbon nanotube (CNT) has been achieved via adopting an engineered, but facile hydrothermal process using ammonium hepta molybdate and thiourea as precursors. The importance of the route lies in enabling strong and easy coupling between Mo7O246− anion and functionalized CNT at low pH, since the zeta potential of CNT has been found to be positive at low pH. The strong interfacial interaction between MoS2 and CNT enhances the overall electronic conductivity and structural stability which leads to better electrochemical performance. The as-developed composite, with just ∼8% carbon, possesses high Li-storage capacity, excellent rate capability and good cycle-life. Impedance spectra indicate least charge transfer resistance in the case of CNT-containing composites, with post-cycling Scanning Electron Microscopic (SEM) images confirms maintenance of integrity after repeated cycling. The cyclic voltammograms, along with x-ray diffraction and Extended X-ray Absorption Fine Structure (EXAFS), confirm that during lithiation step, MoS2 gets converted to Li2S and Mo via formation of LixMoS2 (0

The role of two sulfur sources, such as, thiophene and carbon disulfide, on the structure (graphitic layer) of carbon nanotube cotton (CNT-c) has been investigated during floating catalyst chemical vapour deposition (FC-CVD). The CNT-c assembly at 1200 °C with ferrocene and ethanol as catalyst and carbon precursors respectively was found to be predominantly consisting of (a) single-walled carbon nanotubes (SWCNTs) in the presence of carbon disulfide and (b) multi-walled carbon nanotubes (MWCNTs) in the presence of thiophene. The finding was based on detailed characterization using Raman spectroscopy, transmission electron microscopy and scanning electron microscopy. A possible mechanism for having two different structures has been discussed. The experimental results demonstrated that the interaction of sulfur source with the catalyst particle strongly influenced the number of graphitic layers of CNTs in the CNT-c assembly.

Graphene (Gr) is one of the most preferred reinforcement for polymer matrix, due to its large surface area. However, poor dispersion, due to stacking of Gr sheets, restricts their potential as reinforcement. In the present study, exfoliation of multi-layered graphene sheets is achieved in the presence of nanodiamond (ND), using ultrasonication. High-resolution electron micrographs clearly reveal the role played by ND in hindering restacking of graphene. SPM imaging further quantified exfoliation by measuring the thickness for different combinations of Gr:ND. Improved exfoliation of Gr increases both tensile strength and strain by ~71% and ~113%, respectively, for >0.5 wt% Gr content. Fracture toughness is improved by ~150% with Gr, and an additional 44% with ND decorated Gr. Numerical analysis further confirms the effect of ND assisted exfoliation of Gr in toughening behavior of the composite, which can be explained in terms of improved total interface area, helping in better load transfer.

Addition of carbon nanotubes (CNT) to Graphene (Gr) is seen to have synergistic effect as reinforcement to polymer matrix. This is possible as CNTs inhibit stacking of Gr sheets, thus providing larger surface area nanophase to get bonded with polymer matrix and providing mechanical support through load sharing and crack growth inhibition. However, tube like morphology and high aspect ratio of CNT often lead to entanglement, which restricts their effect in exfoliating Gr. The aim of the present study is to investigate the potential of ND in improving the synergistic effect of Gr-CNT hybrid as a reinforcement to epoxy matrix. This study utilizes the power of ultrasonication technique, which is very simple and scalable, for dispersing and incorporating nanofillers into epoxy matrix. Addition of ND to Gr-CNT epoxy composite improved the tensile strength from ~46% with 0.5 wt% (75Gr:25ND) to ~51% with 0.8 wt% (25Gr:25CNT:50ND) as compared to neat epoxy. While the fracture toughness improved from ~140% with 0.5 wt% (25Gr:75CNT) to 165% with 0.8 wt% (25Gr:50CNT:25ND). Fractured surfaces of composites revealed improved dispersion and strong interfacial interaction with addition of ND to Gr-CNT hybrid. NDs attaches to the surface of Gr inhibit the stacking of Gr sheets by restricting π-π stabilization. NDs also help in bridging the ends of CNTs together into long chains, thereby increasing the aspect ratio of the fiber like reinforcement. This increases the total available surface area of CNTs and Gr, to interact with epoxy matrix, improves the overall efficiency of Gr-CNT hybrid as a reinforcement, resulting into improvement in mechanical properties of the composite structure.

Multiwalled carbon nanotubes (MWCNTs) have been synthesized using methane in a floating catalyst chemical vapour deposition reactor at atmospheric pressure. The catalyst concentration, partial pressure of methane and synthesis temperature have been varied in order to understand their effects on the rate formation of MWCNTs, purity and size of MWCNTs. Reaction mechanism, rate controlling step and overall rate of reaction have been deduced using chemical reaction engineering approach. A systematic study was carried out in order to obtain the kinetic expression based on Langmuir-Hinshelwood type model. The kinetic model was based on the dissociative adsorption pathway of methane and subsequent removal of hydrogen from the adsorbed methyl group with two different active sites. The activation energy for the overall reaction was 46.1 kJ mol−1 in the temperature range of 1073–1273 K. The products have been characterized by transmission electron microscopy, thermogravimetry, BET and Raman spectroscopy. The BET surface area of purified MWCNTs were found to be 157 m2 g−1 with pore volume of 0.176 cc g−1.

Composites with boron carbide (B4C) as the matrix and short carbon fiber (Cf) as reinforcement in 2, 5 and 10 vol% were fabricated by hot pressing route. Microstructural analysis by scanning electron microscopy reveled that Cf got aligned perpendicular to the hot press direction. Agglomeration of Cf was observed at 10 vol% Cf. The addition of Cf improved the flexural strength of B4C-Cf composite and was superior to that of B4C-CNT composite. On other hand, the hardness and fracture toughness of B4C-Cf composite were inferior to that of B4C-CNT composite. The tribological studies revealed that B4C-CNT had superior wear resistance. Both B4C-Cf and B4C-CNT had lower coefficient of friction than monolithic B4C. The possible reasons for deviation of properties due to change in length scale of carbon reinforcement has been analyzed.

The present manuscript deals with the hydrogen absorption properties of multiwalled carbon nano-tubes (MWCNTs) doped with Pd nanoparticles by the conventional wet impregnation method and the polyol method. In the latter method Pd nanoparticles are doped into CNTs based on polyhydroxy organic compounds (polyol) mediated functionalization. The polyol medium reduces palladium chloride to palladium nanoparticles, and also acts as a capping agent to stabilize the Pd nanoparticles. The samples have been characterized using X-ray diffraction (XRD), Energy Dispersive X-ray (EDX) and Infrared (IR) spectroscopy. Hydrogen absorption studies clearly illustrate that Pd doped MW-CNT's prepared by polyol mediated functionalization show much higher hydrogen storage capacity compared to the sample prepared by wet impregnation route. To determine the cause of this behavior, Transmission Electron Microscopic (TEM) studies of the samples were carried out. The results indicate that the dispersion of Pd nanoparticle on the MW-CNT is much better for the sample prepared by the polyol route. An attempt was made to determine the existence of any metal-support interaction using Thermogravimetric Analysis (TGA). The investigation reveals that the higher dispersion of Pd nanoparticles on the CNT support plays a major role for the hydrogen adsorption.

An environment benign process for the separation of rare earths has been delineated for the first time by developing polyethersulfone based composite beads through phase inversion method, where the use of hazardous organic diluents could be circumvented. The porosity and pore structure of these beads were controlled through different additives, of which, polyvinyl alcohol and multiwall carbon nanotubes proved to be the most efficacious. The extraction efficiency of rare earths was ameliorated by four fold with the application of the developed nanotube incorporated beads. The influence of various process parameters, namely, aqueous phase acidity, metal ion concentration, presence of other competitive ions and temperature on the separation of representative yttrium ion has been elaborated in the present investigation. The experimental results attribute to the excellent stability and reusability of the developed beads. The feasibility of employing this novel technology in large scale has been established by successful operation in continuous column mode. The developed assay exhibits profound application towards a greener approach due to the elimination of hazardous organic diluents and prevention of significant organic extractant loss during the process of recovery of rare earths from aqueous media.

Oleyl amine stabilised Pd nanoparticles have been prepared by reverse micro-emulsion method and supported on multi walled CNTs. TEM studies have confirmed that Pd nanoparticles, having sizes in the range of 3–5 nm, are well dispersed on the CNTs. Based on 13C MAS NMR and TG-DTA studies it is inferred that the Pd nanoparticles interact with CNT support to form sp3 carbon species, which get effectively dispersed on the CNTs. Such finely dispersed Pd nanoparticles facilitate the spillover of hydrogen to the CNT support and improve the hydrogen storage capacity.

Carbon nanotubes have been synthesized from acetylene and methane in a fluidized bed by using ferrocene as the catalyst dispersed over carbon black support material. The agglomerate size of carbon black, loading of catalyst, total gas flow rate, partial pressure of reactant gas, temperature of synthesis, and time of synthesis have been varied to understand their effects on the yield of carbon nanotubes. A reaction mechanism consisting of eleven steps and the rate equations for these steps have been proposed. Formation of carbon molecules on the catalyst surface was found to be the rate controlling step in the temperature range of 700–807°C, with an activation energy 47 kJ mol−1, while diffusion through pores in the carbon black was found to be the rate controlling step in the temperature range of 807–1000°C with an activation energy of 7.6 kJ mol−1. A continuous deactivation of the catalyst, represented by an exponential decay, was observed. The products have been characterized by thermogravimetry, electron microscopy, and Raman spectroscopy. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2882–2892, 2014

Selective synthesis of both metallic and semi-conducting single-walled carbon nanotubes (SWCNTs) has been performed using floating catalyst chemical vapour deposition (FC-CVD). It was observed that partial pressure of hydrogen determined the selectivity of SWCNTs being predominantly metallic at lower hydrogen concentration (20 vol%) and predominantly semiconducting at higher hydrogen concentration (80 vol%). The qualitative and quantitative analysis on type of SWCNTs was performed based on UV–vis-NIR, Raman spectra at different wavelengths and SWCNT-based field effect transistor device performance. Transmission electron microscopy was used to get diameter distribution of SWCNTs. Detailed analysis showed that the type of SWCNTs was decided at the nucleation stage that was governed by the collision frequency between hydrogen molecules and iron nanoparticles.

Photo-stability of laser dyes has been an important consideration for dye lasers. In this work, photo-stability of dye and its effect has been investigated as a function of dye laser wavelengths rather than commonly studied photo-chemical degradation pathways upon excitation with pump laser. Here, we report a significant improvement in photo-stability of the liquid dye laser at peak emission wavelength compared to edge wavelengths of the dye gain curve, which was related with an increase in rate of stimulated emission of dye at peak wavelength. Thus, high laser efficiency harmonizes to high photo-stability of the dye at peak wavelength which is useful for the applications of dye lasers. As a representative case, the photo-stability rates of pyrromethene 567 (PM567) dye at different laser emission wavelengths were studied using a 10-Hz Nd-YAG (532 nm) laser-pumped dye laser set-up under lasing and non-lasing conditions. Deterioration of dye laser efficiency on account of photo-degradation of dye molecules was theoretically simulated using a time-dependent rate equation model, which has been found to be in good agreement with the experimental observations.

Carbon nanotube is one of the most talked about materials in recent years due to its unique properties and potential applications in different fields. Out of different techniques, catalytic chemical vapour deposition in a fluidized bed is the most promising technique for bulk production of this exotic material. The objectives of this review are to bring out the science and technology behind this process, the present commercial scenario and to draw a future roadmap. We have critically examined the published literature on the nanoparticle fluidization, different forces involved in it and the hydrodynamics of a nano-agglomerate fluidized bed. The importance of use of discrete elemental method and computational fluid dynamics simulation in the fluidization of carbon nanotubes has also been highlighted. Different preparation routes of catalyst materials have been compiled. The reaction and growth mechanisms of nanotubes, including modeling have been discussed. The data on the effects of different process parameters on the quality and quantity of nanotubes have been critically analyzed. It has been indicated that the available data are scattered in nature and further understanding in the mechanism is required in order to find out the rate controlling step(s) and scale-up of the process. The present commercial scenario of carbon nanotube market has been depicted. At the end, based on the present knowledge gaps, future roadmaps have been suggested.

A combined experimental and theoretical study of the photo-physical, laser properties and molecular structures of three relatively recent Pyrromethene (PM) class dyes, PM597, PM580 and PM567, have been carried out. Laser characteristics of these three PM dyes were compared with three other widely used Rhodamine (RH) class dyes, RH6G, RHB and KRS, using a narrow-band dye laser setup, transversely pumped by the second harmonic (532 nm) of a Q-switched Nd-YAG laser. In addition to generating comparative data of these dyes for optimal use in dye lasers, we observed that unlike the RH dyes, the PM dyes show high efficiencies and wide tunability, despite the low fluorescence yield and high rate of non-radiative decay. Particularly, PM597 dye, in spite of a very low quantum yield of fluorescence (Φ=0.42), high non-radiative decay rate, and a large distortion from planarity in its excited state, when used in a laser cavity it exhibited similar laser efficiency and a beneficially wider tuning curve in comparison to other two PM dyes. Theoretical studies were carried out applying density functional theory and time-dependent density functional theory (DFT/TDDFT) to obtain new information on ground and the first excited state geometrical parameters of the PM dyes. Good correlation between calculated molecular properties and experimental results was observed for the evolution of the longest wavelength absorption maximum.

Many aspects of photophysical, photostability and laser properties of kiton red S dye remain unresolved, particularly for pumping with 578 nm radiation of CVL and 532 nm output of Nd:YAG lasers, and these are studied using different alcohol- and water-based binary solvents. Our results show that methanol is better suited for low and high-repetition-rate KRS dye lasers because of its superior laser efficiency, photostability as well as photothermal properties.

Narrow-band laser performance of alcohol solutions of pyrromethene 567 (PM567) and rhodamine 6G (RH6G) dye was investigated using a home-made GIG-configured dye laser, excited by the second-harmonic radiation (at 532 nm) of a pulsed Nd:YAG laser. Higher laser efficiency was observed with PM567 dye (∼23% peak) in comparison to the commonly used RH6G dye (16.5%), in spite of much lower fluorescence quantum efficiency of the PM567 (0.83) vis-a-vis RH6G (0.98) dye solutions in ethanol. First principle-based electronic structure calculations were performed on PM567 dye in the ground (S0) and excited states (S1) using density functional theory to elucidate the structure and photophysical properties of the dye.

The process parameters (viz. temperature of synthesis, type of catalyst, concentration of catalyst and type of catalyst-support material) for controlling purity of carbon nanotubes synthesized by catalytic chemical vapour deposition of acetylene have been optimized by analyzing the experimental results using Taguchi method. It has been observed that the catalyst-support material has the maximum (59.4%) and the temperature of synthesis has the minimum effect (2.1%) on purity of the nanotubes. At optimum condition (15% ferrocene supported on carbon black at the synthesis temperature of 700 degrees C) the purity of nanotubes was found out to be 96.2% with yield of 1900%. Thermogravimetry has been used to assess purity of nanotubes. These nantubes have been further characterized by scanning electron microscopy, transmission electron microscopy and Raman Spectroscopy. Small angle neutron scattering has been used to find out their average inner and outer diameter using an appropriate model. The nanotubes are well crystallized but with wide range of diameter varying between 20-150 nm.

Micro/nano structures have been obtained by laser surface treatment on sintered LaB6 pellets employing a picosecond pulsed Nd:YAG laser at a pressure of ∼1×10−3 mbar. The X-ray diffraction pattern of the laser treated pellet shows a set of well defined diffraction peaks, indexed to the cubic phase of LaB6 only. The scanning electron microscope studies reveal formation of micro and nano structures upon laser treatment and the resultant surface morphology is found to be strongly influenced by the laser fluence. Field electron emission studies made on the LaB6 pellet, treated with optimized laser fluence, have been performed in a planar diode configuration under ultra high vacuum conditions. The threshold field required to draw an emission current density of ∼10 μA/cm2 has been found to be ∼2.3 V/μm and a current density of ∼530 μA/cm2 has been drawn at an applied field of 5.2 V/μm. The Fowler-Nordheim plot is found to be linear in accordance with the quantum mechanical tunneling phenomenon, confirming the metallic nature of the emitter. The emission current at the pre-set value ∼10 μA shows very good stability over a period of more than 3 hours. The present results emphasize the effectiveness of a picosecond laser treatment towards fabrication of a nano metric LaB6 emitter for high current density applications.

X-ray in-line phase-contrast imaging is an emerging technique made practical by high brilliance synchrotron X-ray sources and high-performance X-ray detectors. This technique is capable of providing improved contrast along with edge enhancement for weakly absorbing samples and hence it is of immense value in study of materials like carbon fiber, carbon composite, etc. This technique is also very useful for determination of coating thickness, uniformity of pyrocarbon coating on the fuel kernel particles. The applications of such fuel kernel particles demand a high-quality of uniformity and precise thickness. The thickness and uniformity of such coatings depends upon several parameters of the system during their preparation. In this paper, we have explored the use of X-ray phase-contrast techniques for the measurement of coating thickness and its uniformity. We present the results of such experiments on SiC and pyrocarbon (PyC)-coated zirconia micro-spheres. This information may be of importance in optimization of the various parameters during the deposition process. The results bring out the importance of the X-ray phase-contrast technique in materials research.

Small angle neutron scattering (SANS) has been utilized to study the morphology of the multi-walled carbon nanotubes prepared by chemical vapour deposition of acetylene. The effects of various synthesis parameters like temperature, catalyst concentration and catalyst support on the size distribution of the nanotubes are investigated. Distribution of nanotube radii in two length scales has been observed. The number density of the smaller diameter tubes was found more in number compared to the bigger one for all the cases studied. No prominent scaling of the structure factor was observed for the different synthesis conditions.

In this paper we report the development of self-standing tubular geometry of aligned carbon nanotubes with very high surface area (∼ 90 m 2 /g). The synthesis involves spray pyrolysis of ferrocene-benzene solution in nitrogen atmosphere. The effects of temperature, ferrocene concentration, flow rate of nitrogen gas and the pumping rate of the liquid precursor were studied. The products were analyzed with transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectroscopy. The optimum condition for formation of macro-tubular geometry was found to be 950 °C, 50 mg/ml ferrocene in benzene, 1.5 ml/min pumping rate of liquid precursor and 5 lpm of nitrogen gas flow rate. The length and the diameter of the macrotube were 5 cm and 1 cm respectively with a thickness of 120 μm. The authors intend to use this tube in separation technology.

Carbon nanotubes (CNTs) were synthesized by catalytic chemical vapour deposition of acetylene diluted with nitrogen. Cobalt formate supported on carbon black was used as the catalyst. The synthesis was carried out at 700 °C in a quartz reactor for 30 min. Thermal analysis was used to determine the CNT yield. The purity of the nanotubes in the deposit was 96% and the yield was 1940% of the weight of the catalyst. Transmission electron microscopic images of as synthesized and oxidized nanotubes supported the thermogravimetric observations regarding the oxidation of CNT. The purity and the yield obtained are one of the highest reported.

Narrowband laser performances and photochemical stability of alcoholic solutions of pyrromethene 567 and rhodamine 6G dyes, under high-repetition rate copper vapour laser (at 510 nm), as well as, high-peak intensity Nd:YAG laser (at 532 nm) excitation have been investigated. We have observed that pyrromethene 567 dye solutions offer higher efficiency, wider tuning range, but lower photochemical stability and higher lasing threshold than that of rhodamine 6G dye solutions. An addition of about 100 mM DABCO, as a singlet oxygen quencher, in pyrromethene 567 dye solutions improved its photochemical stability close to that of rhodamine 6G. The observation of higher slope efficiency, in spite of higher threshold pump energy for pyrromethene 567 dye than that of rhodamine 6G dye solutions, was explained by a predictive model on gain characteristics of both dye solutions as a function of pump energy.

Carbon nanotubes have been synthesized by catalytic chemical vapour deposition of acetylene diluted with argon using three different catalysts, namely, nickel formate, cobalt formate and ferrocene. The synthesis was carried out at 700°C in a quartz reactor for 30 minutes. Thermal analysis was carried out in order to determine the yield of the nanotube. It was found that the deposit contains 86% nanotube, with nickel-based catalyst, which was the maximum. The yield of nanotube was 71 times that of the nickel loading. The TEM images reveal helical type of nanotubes with iron catalyst while cobalt and nickel catalysts yielded straight nanotubes. This technique can be explored for the bulk production of carbon nanotube in an economic way.

Water is an inherently safe solvent for laser dyes and posses far better photo thermal characteristics in comparison to the commonly used organic solvents in dye lasers. However, water solution of dye needs a suitable deaggregating additive to suppress non-radiative dimers and to achieve similar laser efficiency. We have carried out systematic studies on comparative performances of dye lasers, pumped by low-repetition-rate Nd-YAG, as well as high-repetition-rate copper vapour lasers using Rhodamine 6G dye solutions in ethanol and various binary solvents of water. Among different additives in water, for the first time, the results of our studies on the application of water solvent in dye lasers could clearly establish that binary solvent comprising of normal or heavy water and about 18% to 25% n-propanol has produced similar efficiency, better photochemical stability and superior thermo-optic properties than ethanol solvent in high-repetition rate oscillator-amplifier operation.

Metallographic investigation of the microstructure of sintered Thoria pellets necessitates appropriate surface preparation of these pellets. Conventional etching methods involving either chemical or thermal etching techniques being unsuitable for surface etching of irradiated Thoria fuel, laser-based surface treatment was envisaged as a potential alternative technique. Thoria pellets were subjected to laser surface treatment using a pulsed Nd:YAG laser. Our preliminary studies have successfully demonstrated laser etching of sintered Thoria pellets with good reproducibility, clearly revealing grain structures and well-defined grain boundaries. Detailed parametric investigations determining optimum laser parameters for the process, are presented. Our results on ultra-short laser-based etching of sintered Thoria pellets are also discussed.