A. K. Singha Deb

Bio: A. K. Singha Deb is an academic researcher from Bhabha Atomic Research Centre. The author has contributed to research in topics: Adsorption & Crown ether. The author has an hindex of 6, co-authored 15 publications receiving 217 citations. Previous affiliations of A. K. Singha Deb include Homi Bhabha National Institute.

Dual mode of extraction for Cs+ and Na+ ions with dicyclohexano-18-crown-6 and bis(2-propyloxy)calix[4]crown-6 in ionic liquids: density functional theoretical investigation

Abstract: The unusually high selectivity of the Cs+ ion over the Na+ ion with bis(2-propyloxy)calix[4]crown-6 (BPC6) compared to dicyclohexano-18-crown-6 (DCH18C6) has been investigated using generalized gradient approximated (GGA) BP86, hybrid B3LYP and meta hybrid TPSSH density functionals, employing split valence plus polarization (SVP) and triple zeta valence plus polarization (TZVP) basis sets in conjunction with the COSMO (conductor like screening model) solvation approach. The calculated theoretical selectivity of the Cs+ ion over the Na+ ion was found to be in accordance with the experimental selectivity obtained using solvent extraction experiments in ionic liquids (IL) and octanol. The distribution constant of the Cs+ ion, DCs with DCH18C6 in the 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIMTF2N) IL phase was found to be significantly large than that in octanol. The experimentally measured DCs value was found to be very large compared to the value of DNa in the IL phase. The presence of the BMIM cation in the recorded UV-visible spectra of the raffinate phase with and without DCH18C6 indicates the BMIM cation exchange with Cs+ and Na+ ions, thus supporting the dual mode of extraction. The dual mode of metal ion extraction observed in the experimental study was complemented by density functional theoretical study. The calculated free energy of extraction, ΔGext, for the metal ion was found to be higher in IL compared to octanol. Further, preferential selectivity of the Cs+ ion over the Na+ ion was established from the free energy difference, ΔΔGext, between the two competing metal ions. The unusually high selectivity of Cs+ over the Na+ ion by BPC6 in IL compared to DCH18C6 is also demonstrated by the free energy difference, ΔΔΔGext, between the two competing ligands which was shown to be free from the complicated metal ion solvation energy.

Adsorption of Eu3+ and Am3+ ion towards hard donor-based diglycolamic acid-functionalised carbon nanotubes: density functional theory guided experimental verification

Abstract: Structure, bonding, energetic and thermodynamic parameters of trivalent Eu3+ and Am3+ with diglycolamic acid-functionalised carbon nanotubes (CNT–DGA) in gas and solvent phases are reported in order to understand their complexation and extraction behaviour. The calculation was performed with generalised gradient approximated BP86 density functional and hybrid B3LYP functional using SVP/TZVP basis set. The free energy of extraction, ΔGext, of Eu3+ and Am3+ was computed using the Born–Haber thermodynamic cycle in conjunction with conductor-like screening model solvation approach. The calculated free energy of extraction was found to be exergonic using an explicit cluster water model for hydrating the ions and it was found to be higher for Eu3+ ion over Am3+ ion. From the estimated distribution constant using synthesised CNT–DGA, it is indisputably established that the Eu3+ ion is preferentially extracted over Am3+ ion and hence confirms the acceptance of the explicit cluster model for ion solvation free ene...

Unanticipated favoured adsorption affinity of Th(IV) ions towards bidentate carboxylate functionalized carbon nanotubes (CNT–COOH) over tridentate diglycolamic acid functionalized CNT: density functional theoretical investigation

Abstract: The hybrid B3LYP density functional and TZVP basis set in conjunction with COSMO solvation approach have been used successfully to predict the free energy of adsorption for Th4+ ions with pristine CNTs, oxidized CNTs (CNT–COOH) and diglycolamic acid functionalized CNTs (CNT–DGA). Experimentally reported values of adsorption capacities of Th4+ by the above three types of CNT indicate that CNT–COOH has the strongest binding with Th4+, whereas p-CNT has the lowest; CNT–DGA shows less adsorption than CNT–COOH, although the former has tridentate ligands on CNTs' surfaces. This experimental observation has been demonstrated by DFT theoretical studies: gas phase calculation does not match with the above experimental fact, whereas, solvent phase calculation in the presence of nitrate ions, a more realistic approach, is able to explain. Free energy of complexation between Th4+ and CNT–COOH is higher than that of CNT–DGA in all available models of complexation reaction viz. bare Th4+ in aqueous nitrate medium, octahydrated Th4+ in nitrate and thorium nitrate ion pair in aqueous solution. The experimental fact that the presence of oxidized fullerene C60 enhances the Th4+ adsorption by oxidized CNT has also been theoretically corroborated as oxidized C60 has a quite high binding energy for Th4+. Present computational calculation in the search for the best nano carbon based Th4+ adsorbent parallel with experimental verification might be helpful for the design of effective nanomaterials to be used in the treatment of radioactive liquid waste.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The Isotope Geochemistry of Zinc and Copper

Abstract: Copper, a native metal found in ores, is the principal metal in bronze and brass. It is a reddish metal with a density of 8920 kg m−3. All of copper’s compounds tend to be brightly colored: for example, copper in hemocyanin imparts a blue color to blood of mollusks and crustaceans. Copper has three oxidation states, with electronic configurations of Cu([Ar]3 d 104 s 1), Cu+([Ar]3 d 10), and Cu2+([Ar]3 d 9). Cu does not react with aqueous hydrochloric or sulfuric acids, but is soluble in concentrated nitric acid due to its lesser tendency to be oxidized. Cu(I) exists as the colorless cuprous ion, Cu+. Cu(II) is found as the sky-blue cupric ion, Cu2+. The Cu+ ion is unstable, and tends to disproportionate to Cu and Cu2+. Nevertheless, Cu(I) forms compounds such as Cu2O. Cu(I) bonds more readily to carbon than Cu(II), hence Cu(I) has an extensive chemistry with organic compounds. In aqueous solutions, Cu2+ ion occurs as an aquacomplex. There is no clearly predominant structure among the four-, five-, and six-fold coordinated Cu(II) species (Chaboy et al. 2006). Hydrated Cu(II) ion has been represented as the hexaaqua complex Cu(H2O)62+, which shows the Jahn–Teller distortion effect (Sherman 2001; Bersuker 2006), whereby the two Cu–O distances of the vertical axial bond (Cu–Oax) are longer than four Cu–O distances in the equatorial plane (Cu–Oeq). The Jahn–Teller effect lowers the symmetry of Cu(H2O)62+ from octahedral Th to D2h. The sixfold coordination of hydrated Cu(II) species is questioned by a finding of fivefold coordination (Pasquarello et al. 2001; Chaboy et al. 2006; Little et al. 2014b …

Synthesis of novel nanomaterials and their application in efficient removal of radionuclides

Abstract: With the development of nuclear energy, large amounts of radionuclides are inevitably released into the natural environment. It is necessary to eliminate radionuclides from wastewater for the protection of environment. Nanomaterials have been considered as the potential candidates for the effective and selective removal of radionuclides from aqueous solutions under complicated conditions because of their high specific surface area, large amounts of binding sites, abundant functional groups, pore-size controllable and easily surface modification. This review mainly summarized the recent studies for the synthesis, fabrication and surface modification of novel nanomaterials and their applications in the efficient elimination and solidification of radionuclides, and discussed the interaction mechanisms from batch experiments, spectroscopy analysis and theoretical calculations. The sorption capacities with other materials, advantages and disadvantages of different nanomaterials are compared, and at last the perspective of the novel nanomaterials is summarized.