Hydrogen Bond Disruption-Induced Ion Rearrangement in Acetonitrile–Water–Sodium Sulfate Solutions

Understanding hydrogen bonding and ion-specific interactions in water, sodium sulfate (Na₂SO₄), and acetonitrile (ACN) systems remains challenging due to their complex, dynamic nature. Here, Raman spectroscopy is employed to probe hydrogen bonding networks and ion reorganization in Na₂SO₄ aqueous solutions with different ACN concentrations. The results indicate that, at low ACN concentrations in the ternary solutions, hydrogen bonding between ACN and water molecules disrupts the original hydration structure of the ions, resulting in the formation of small ion clusters via electrostatic interactions. As the ACN concentration increases, the self-association among ACN molecules intensifies, enhancing hydrogen bonding between water molecules and gradually transforming small ion clusters into ion pairs. Upon reaching ACN-water liquid phase separation, ACN molecules predominantly self-associate, weakening ACN-water hydrogen bonding. This shift prompts water molecules to preferentially hydrate ions, transforming ion pairs into ion hydrates. Additionally, the experiment reveals that the regulatory effect of ACN on ions through hydrogen bonds decreased with the increase of Na₂SO₄ concentration. Our research offers insights into the ion reorganization processes and physical mechanisms in ACN-water-salt electrolyte solutions, which provides theoretical guidance for the optimization and design of electrolytes.