ABSTRACT
The manuscript presents the results on the sorption of U(VI), Am(III) & Eu(III) from pH medium by a novel amido-amine functionalized multiwalled carbon nanotube (MWCNT). The novel functional group was introduced in the MWCNT by two step processes and characterized by various instrumental techniques like Scanning Electron Microscopy (SEM), Raman and X-ray Photoelectron Spectroscopy (XPS). The sorption process was found to be highly dependent on the pH of the solution with maximum sorption for both 233U, 241Am & 152+154Eu at pH 7.0. Kinetics of sorption was found to be fast with equilibrium reached in â¼15min and the sorption was found to be following pseudo 2nd order kinetics for the radionuclides. The sorption for both 233U and 152+154Eu followed Langmuir sorption model with maximum sorption capacity of 20.66mg/g and 16.1mg/g respectively. This has been explained by DFT calculations which shows that more negative solvation energy of U(VI) compared to Am(III) and Eu(III) and stronger U-MWCNT-AA complex is responsible for higher sorption capacity of U(VI) compared to Am(III) and Eu(III).The synthesized amido-amine functionalized MWCNT is a very promising candidate for removal of actinides and lanthanides from waste water solution with high efficiency.
ABSTRACT
Comparative extraction of trivalent lanthanide and actinide ions (La(3+), Eu(3+), Lu(3+), Am(3+) and Cm(3+)) with tetra-n-octyl diglycolamide (TODGA) was studied and showed the trend: Lu(3+) > Eu(3+) > Cm(3+) > Am(3+) > La(3+). The structure, bonding, energetic and thermodynamic parameters of the trivalent lanthanide and actinide ions (La(3+), Eu(3+), Lu(3+), Am(3+) and Cm(3+)) with a tridentate ligand, tetra-methyl diglycolamide (TMDGA), are reported in the gas and solvent phases in order to understand their complexation and extraction behaviour. The calculations were performed using the generalized gradient approximated BP86 density functional and the hybrid B3LYP functional using SVP and TZVPP basis sets. The calculated structure obtained at the BP86/SVP level of optimization was found to be in close agreement with the X-ray data and also with the structure obtained at the B3LYP/TZVP level of theory. The free energy of extraction was found to be exergonic for the explicit monomer water model. From the solvent extraction experiment the order of extraction was observed as Lu(3+) > Eu(3+) > Cm(3+) > Am(3+) > La(3+), which was in line with the trends predicted based on the free energy changes in the gas phase calculations (ΔGgp). The Born-Haber thermodynamic cycle and the COSMO (conductor like screening model) solvation model were applied to calculate the free energy of extraction, ΔGext, of lanthanide and actinide ions in the aqueous-dodecane biphasic system and ΔGext, however, predicted different extraction trends. After dispersion correction (B3LYP-D3), the free energy of extraction for the metal ions was found to follow the order: Lu(3+) > Eu(3+) > La(3+), which was also observed in the solvent extraction experiments. Both COSMO and DCOSMO-RS models predict the same metal ion selectivity trend. Different bonding analyses indicate the electrostatic and less covalent nature of interactions between the ligands and the metal ions.
ABSTRACT
Mutual radiation grafting technique was employed to graft polyacrylic acid (PAA) onto Polytetrafluoroethylene (Teflon) scrap using high energy gamma radiation. Polyacrylic acid-g-Teflon (PAA-g-Teflon) adsorbent was characterized by grafting extent measurement, FTIR spectroscopy, SEM and wet ability & surface energy analysis. The PAA-g-Teflon adsorbent was studied for dye adsorption from aqueous solution of basic dyes, namely, Basic red 29 (BR29) and Basic yellow 11 (BY11). The equilibrium adsorption data were analyzed by Langmuir and Freundlich adsorption isotherm models, whereas, adsorption kinetics was analyzed using pseudo-first order, pseudo-second order and intra-particle diffusion kinetic models. Equilibrium adsorption of BR29 was better explained by Langmuir adsorption model, while that of BY11 by Freundlich adsorption model. The adsorption capacity for BY11 was more than for BR29. Separation factor (R(L)) was found to be in the range 0 < R(L) < 1, indicating favorable adsorption of dyes. Higher coefficient of determination (r(2) > 0.99) and better agreement between the q(e,cal) and q(e,exp) values suggested that pseudo-second order kinetic model better represents the kinetic adsorption data. The non-linearity obtained for intra-particle diffusion plot indicated, more than one process is involved in the adsorption of basic dyes. The desorption studies showed that ~95% of the adsorbed dye could be eluted in suitable eluent.