Pooja Sahu

Structural and dynamical properties of Li+-dibenzo-18-crown-6(DB18C6) complex in pure solvents and at the aqueous-organic interface

AbstractMicrostructure of dibenzo-18-crown-6 (DB18C6) and DB18C6/Li+ complex in different solvents (water, methanol, chloroform, and nitrobenzene) have been analyzed using radial distribution function (RDF), coordination number (CN), and orientation profiles, in order to identify the role of solvents on complexation of DB18C6 with Li+, using molecular dynamics (MD) simulations. In contrast to aqueous solution of LiCl, no clear solvation pattern is found around Li+ in the presence of DB18C6. The effect of DB18C6 has been visualized in terms of reduction in peak height and shift in peak positions of gLi-Ow. The appearance of damped oscillations in velocity autocorrelation function (VACF) of complexed Li+ described the high frequency motion to a “rattling” of the ion in the cage of DB18C6. The solvent-complex interaction is found to be higher for water and methanol due to hydrogen bond (HB) interactions with DB18C6. However, the stability of DB18C6/Li+ complex is found to be almost similar for each solvent due to weak complex-solvent interactions. Further, Li+ complex of DB18C6 at the liquid/liquid interface of two immiscible solvents confirm the high interfacial activity of DB18C6 and DB18C6/Li+ complex. The complexed Li+ shows higher affinity for water than organic solvents; still they remain at the interface rather than migrating toward water due to higher surface tension of water as compared to organic solvents. These simulation results shed light on the role of counter-ions and spatial orientation of species in pure and hybrid solvents in the complexation of DB18C6 with Li+. Graphical AbstractDB18C6/Li+ complex in pure solvents (water, methanol, chloroform, and nitrobenzene) and water/nitrobenzene interface

TBP Assisted Uranyl Extraction in Water-Dodecane Biphasic System: Insights from Molecular Dynamics Simulation

Abstract In the PUREX (Plutonium Uranium Recovery by Extraction Process) process, the extraction of uranyl ion from dissolver solution to the organic phase is influenced by co extraction of the other species, such as water and nitric acid and it is assumed that the presence of water or acid droplets in the organic phase intensifies the coordination mechanism of TBP. The present study illustrates the uranyl extraction from the aqueous phase to the organic phase using molecular dynamics (MD) simulation. Here, we consider the biphasic systems to gain insights into the characteristics of the interface and humidity of the organic phase under different acidic and neutral conditions. MD being a force field method, can’t satisfactorily model the bond making and breaking process therefore a priori choice has been made concerning the different status of proton for the acidic phase. Further, the importance of charge species transferability during uranyl-TBP complexation have been investigated considering two different models of uranyl nitrate; united UO2(NO3)2 complex and separate UO22+ and NO3– ions. From the results, it is recommended to use the ionic uranyl model with separate UO22+ and NO3– to study the structural and dynamical properties of extracted uranyl ions in the organic phase. Also, it was noticed that extracted uranyl ions in the organic phase are not completely dehydrated but are surrounded by water molecules. In other words the results show co extraction of other species such as water and acid molecules to the organic phase. Most remarkably, the present study evident that the neutral HNO3 effectively represents the acidity effect for the receiving phase in terms of acid/water extraction and their aggregation to form water droplet, especially when ionic model of uranyl nitrate is considered.

Self diffusion and wetting transition of fluids in carbon nanotubes

Carbon Nanotubes (CNTs) have been shown to be promising for use in fluid filtration and purification processes, as an alternative to commonly practiced polymer based membranes. Recently, it has been shown from the Molecular Dynamics (MD) simulations that the CNTs can be used as a viable alternative of polymer based membranes due to its feasibility to transport the very high flux compared to polymer based membranes. Now, the question naturally arises, what is the reason for fast fluid transport through the nanopores of CNTs of specific diameter. Diffusion of fluids can be used as a signature of transport through nanochannels and MD simulations can be effectively used to calculate the diffusion of fluids. Hence, the present study is aimed at performing the MD simulations to investigate the wetting transition and the diffusivity of polar and non-polar fluids in nanochannels of varied diameters of CNTs.