Kinshuk Dasgupta

Nature of the Pd–CNT interaction in Pd nanoparticles dispersed on multi-walled carbon nanotubes and its implications in hydrogen storage properties

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.

Potential of carbon nanotubes in water purification: an approach towards the development of an integrated membrane system

The problems of water shortages and lack of access to safe drinking water have been and will continue to grow as major global problems. To alleviate these problems, water purification technologies are being updated. Recent years have witnessed impressive breakthroughs towards practical application of nanostructured materials such as Carbon Nanotubes (CNTs) in the field of water purification owing to their unique thermal, electrical and mechanical properties. These nanoscale structures need to be arranged into well-defined configurations in order to build integrated systems with high efficiency (the nanotubes being reusable, whereas the traditional membranes foul easily and require frequent replacements), high flux (owing to the hydrophobic super smooth inner surface of nanotubes), and with improvements in chemical selectivity (through suitable chemical functionalisation of the CNTs), so that the idea of using CNTs in separation technology can be made realistic and the potential benefits of practical application of these unique materials can be exploited. This paper assesses the CNTs as an emerging technology in water purification system, particularly with respect to its potential for the removal of arsenic, fluoride, heavy metals and toxic organic components.

Sorption behaviour of Pu4+ and PuO22+ on amido amine-functionalized carbon nanotubes: experimental and computational study

Amido amine-functionalized multi-walled carbon nanotubes (MWCNT-AA) were used for efficient and selective solid phase separation of plutonium(IV) and plutonium(VI). Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Tempkin isotherms were employed for understanding the sorption mechanism and Lagergren first order kinetics, an intra-particle diffusion model, and pseudo second order kinetics were applied to understand the sorption kinetics. The sorption proceeded through monolayer coverage of MWCNT-AA with capacities of 91.2 mg g−1 and 89.4 mg g−1 for Pu4+ and PuO22+, respectively following a Langmuir isotherm while the sorption kinetics followed a pseudo second order reaction with rate constants of 3.86 × 10−5 and 3.19 × 10−5 g mg−1 min−1 for Pu4+ and PuO22+ respectively. This MWCNT-AA showed high radiolytic stability and a method was developed for almost quantitative back extraction of plutonium in both the oxidation states from MWCNT-AA. Finally, the sorbent MWCNT-AA was employed for processing synthetic high level waste solution obtained from a research reactor origin. Moreover, density functional theory calculation was performed to examine the coordination and interaction behaviour of Pu4+ and PuO22+ ions towards MWCNT-AA. The present DFT study reveals that Pu is deca-coordinated (two from each of four nitrates and one AA) in the case of Pu4+ and octa-coordinated (two from each of two nitrates and one AA, and one from each of two oxo groups) in PuO22+. The calculated free energy of complexation was found to be almost three times higher for Pu4+ than PuO22+ both in the gas and aqueous phase, which thus confirms the experimentally observed higher sorption of Pu4+ compared to PuO22+ by MWCNT-AA.

A new approach to fabricate SiC nanowire-embedded dense SiC matrix/carbon fiber composite

A novel and simple sol–gel route has been used for the fabrication of composite structure composed of carbon fibers and silicon carbide nanowires embedded in dense silicon carbide matrix. The carbonaceous silica sol was impregnated in the carbon fiber preform at atmospheric pressure. The sol impregnated carbon preform was cured and heat treated to convert into silicon carbide. The analysis by X-ray diffraction, scanning electron microscopy, X-ray tomography, and transmission electron microscopy indicates that the impregnated carbonaceous silica gel converts to β-silicon carbide with dense and wire morphology. Different morphological silicon carbide was uniformly distributed inside carbon fiber preform and there was no degradation in thermophysical properties of carbon composite during processing. These results reveal high efficient reinforcement of different morphological silicon carbide in carbon composite, demonstrate a new mechanism of carbon composite reinforcement and suggest a new direction to carbon composite reinforcement.Graphical Abstract

Formation of nano-structured core–shell micro-granules by evaporation induced assembly

Nano-structured spherical micro-granules of core–shell morphology have been realized by utilizing the contrasting interfacial interaction of two different types of nano-particles with liquid solvent. By enforcing evaporation induced assembly, a hydrophobic core has been wrapped inside a hydrophilic envelope consisting of correlated nano-particles. This is realized by a one step, fast and facile technique of spray-drying. The evaporation of water in a radially outward direction from mixed-suspension droplets enforces the hydrophobic component to travel towards the core and the hydrophilic component to reside at the surface forming a shell. Mapping the coherent neutron and X-ray scattering length density into reciprocal space, the structure as well as inter-particle correlation in such micro-granules has been characterized over a wide range of wave-vector transfers. Scattering results have been complemented with electron microscopy. Significant enhancement in specific surface-area due to core–shell morphology has been observed by gas adsorption technique. Treating the granules with hydrofluoric acid, the silica shell has been etched to unwrap the meso-porous carbon core. This demonstrates that the hydrophobic component indeed forms the nano-structured core inside the hydrophilic nano-structured shell. In view of the unique characteristics of these synthesized core–shell nano-structured micro-granules, a potential application of such granules has also been discussed.

Diglycolamic acid-functionalized multiwalled carbon nanotubes as a highly efficient sorbent for f-block elements: experimental and theoretical investigations

Diglycolamic acid-functionalized carbon nanotubes were employed for the efficient and selective separation of Pu4+, PuO22+ and Am3+. The sorption occurred through monolayer coverage via chemisorption following the Langmuir isotherm. The sorption of Am3+, Pu4+ and PuO22+ on DGA-CNTs proceeded via a pseudo-second-order rate kinetics with a rate constant in the order Am3+ < Pu4+ < PuO22+. The radiolytic stability for DGA-CNTs and the stripping behaviour of DGA-CNTs were investigated. Luminescence investigations revealed the presence of single species without an inner-sphere water molecule. On complexation, the asymmetry around Eu3+ was found to be enhanced along with the covalency of the metal–ligand bond. Additionally, DFT calculations were performed to investigate the coordination and complexation interaction behaviour of CNT-DGA towards the metal ions. The present DFT study revealed a tridentate coordination mode of the DGA moiety towards Pu4+ and Am3+ and a bidentate coordination mode towards PuO22+. The calculated binding energy of sorption with DGA-CNTs towards Pu4+ was found to be higher than that of PuO22+, in both the gaseous and aqueous phase, whereas for Am3+, it was higher than that for PuO22+ but less than that for Pu4+. The free energy of sorption was also found to be highest for Pu4+ uptake and lowest for PuO22+, in both the gaseous and aqueous phase.

Understanding the sorption behavior of Pu4+ on poly(amidoamine) dendrimer functionalized carbon nanotube: sorption equilibrium, mechanism, kinetics, radiolytic stability, and back-extraction studies

Abstract 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+.

Sorption Behavior of Y(III) from Chloride Medium with Polymer Composites Containing Di-2-ethyl Hexyl Phosphoric Acid and Multiwall Carbon Nanotube

Extractant impregnated polyethersulfone beads have been prepared by phase inversion method and investigated for yttrium recovery from aqueous medium. The effect of experimental parameters on yttrium sorption has been studied. Quantitative sorption of yttrium (> 90%) was attained after 8 hours of equilibration time in the case of D2EHPA impregnated composite beads. Analysis of sorption data by different kinetic and diffusion models suggested that the sorption of Y(III) followed the pseudo-second order model. Stability tests with polymeric composite beads by multiple cycles of sorption and desorption of Y(III) have established the feasibility of reusing the beads for sorption of metal ions.

Dysprosium sorption by polymeric composite bead: Robust parametric optimization using Taguchi method

Polyethersulfone-based beads encapsulating di-2-ethylhexyl phosphoric acid have been synthesized and evaluated for the recovery of rare earth values from the aqueous media. Percentage recovery and the sorption behavior of Dy(III) have been investigated under wide range of experimental parameters using these beads. Taguchi method utilizing L-18 orthogonal array has been adopted to identify the most influential process parameters responsible for higher degree of recovery with enhanced sorption of Dy(III) from chloride medium. Analysis of variance indicated that the feed concentration of Dy(III) is the most influential factor for equilibrium sorption capacity, whereas aqueous phase acidity influences the percentage recovery most. The presence of polyvinyl alcohol and multiwalled carbon nanotube modified the internal structure of the composite beads and resulted in uniform distribution of organic extractant inside polymeric matrix. The experiment performed under optimum process conditions as predicted by Taguchi method resulted in enhanced Dy(III) recovery and sorption capacity by polymeric beads with minimum standard deviation.

Adsorptive Separation of Entrained Di-Nonyl Phenyl Phosphoric Acid from Merchant Grade Phosphoric Acid by Activated Charcoal: Kinetic and Equilibrium Studies

The separation of entrained di-nonyl phenyl phosphoric acid (DNPPA) from merchant grade phosphoric acid (MGA) by adsorption on the coconut shell based activated charcoal has been carried out. The effect of various process parameters, such as DNPPA concentration in aqueous phase of MGA, equilibrium time, amount of activated charcoal and temperature upon adsorption capacity of activated charcoal has been studied. The results showed that the adsorption equilibrium was reached after 240 minutes. The adsorption phenomenon followed pseudo-second order kinetics. Adsorption of DNPPA increased with initial concentration of DNPPA in the range of 50 to 200 mg/L. The experimental data fitted well with the Freundlich isotherm model. Decrease in adsorption with increase in temperature suggests that the adsorption process is exothermic in nature. The value of enthalpy change (ΔH = −35.52 kJ/mol) indicated that DNPPA adsorption on activated charcoal is a physisorption phenomenon. Column operation was carried out to obtain a breakthrough curve. Desorption of DNPPA with 10% NaOH yielded near quantitative regeneration of activated charcoal in three contacts.