Combined Classical and AIMD Simulations for Understanding the Extraction Mechanism of Li/Na/K Ions Using p-toluene Sulfonate/4-(trifluoromethyl) Benzene Sulfonate in Aqueous Medium

The demand for environmentally sustainable and easily transportable energy sources in various industries, such as electrical, automotive, and aerospace, has driven continuous attention of the research communities towards lithium (Li) ion-operated batteries. The conventional industrial method used for Li-ion extraction involves pumping mechanisms to bring Li brine to the surface, which is subjected to chemical treatment, facilitating the segregation of the metallic component from the liquid phase. This process suffers many disadvantages, such as groundwater contamination due to chemicals, and can potentially result in decreased water availability. Therefore, to overcome these drawbacks, scientists have recently discovered that para-toluene sulfonate (PTS) can be used for Li recovery and can be potentially exploited for Li-ion extraction. In the present study, we have carried out combined classical and ab-initio molecular dynamics simulations focusing on the interactions of various ions (Li, Na, K) with PTS and 4-(trifluoromethyl) Benzene Sulfonate (TBS) in water. From the analysis of radial distribution functions and potential of mean force, we found that the sulfur group present on both PTS and TBS actively interacts with Li-ion followed by Na and then K. The ion-sulfur interaction can be attributed to the efficient extraction of Li from the Li-PTS and Li-TBS aqueous solutions. We believe that tuning the side groups on the benzene ring may result in increasing the extraction efficiency.