posted on 2022-11-17, 14:11authored byParveen
K. Verma, Ananda Karak, Pooja Sahu, Vinod K. Aswal, Bholanath Mahanty, Sk. Musharaf Ali, Richard J. M. Egberink, Jurriaan Huskens, Willem Verboom, Prasanta K. Mohapatra
Two tripodal amides obtained from nitrilotriacetic acid
with n-butyl and n-octyl alkyl chains
(HBNTA(LI) and HONTA(LII), respectively)
were studied for the extraction of Th(IV) ions from nitric acid medium.
The effect of the diluent medium, i.e., n-dodecane
alone and a mixture of n-dodecane and 1-decanol,
onto aggregate formation were investigated using small angle neutron
scattering (SANS) studies. In addition, the influence of the ligand
structure, nitric acid, and Th(IV) loading onto ligand aggregation
and third-phase formation tendency was discussed.The LI/LII exist as monomers (aggregarte radius
for LI: 6.0 Å; LII:7.4
Å) in the presence of 1-decanol, whereas LII forms dimers (aggregarte radius for LII:9.3 Å; LI does not dissolve in n-dodecane) in the absence of 1-decanol. The aggregation
number increases for both the ligands after HNO3 and Th(IV)
loading. The maximum organic concentration (0.050 ± 0.004 M)
of Th(IV) was reached without third-phase formation for 0.1 M LI/LII dissolved in 20% isodecanol +80% n-dodecane. The interaction of 1-decanol with LII and HNO3/Th(IV) with amidic oxygens of LI/LII results in shift of carbonyl
stretching frequency, as shown by attenuated total reflectance-Fourier
transform infrared (ATR-FTIR) studies. The structural and bonding
information of the Th-LI/LII complex
were derived from the density functional theoretical (DFT) studies.
The molecular dynamics (MD) simulations suggested that the aggregation
behavior of the ligand in the present system is governed by the population
of hydrogen bonds by phase modifier around the ligand molecules. Although
the theoretical studies suggested higher Gibbs free energy of complexation
for Th4+ ions with LI than LII, the extraction was found to be higher with
the latter, possibly due to the higher lipophilicity and solubility
of the Th-LII aggregate in the nonpolar media.