Equilibria and Dynamics of Sodium Citrate Aqueous Solutions: The Hydration of Citrate and Formation of the Na₃Cit⁰ Ion Aggregate

Abstract

Sodium citrate (Na 3 Cit) has a crucial role in many biological and industrial processes. Yet, quantitative information on its hydration and the ion association between Na + and Cit 3− ions in a broad range of salt concentrations is still lacking. In this work, we study both ion association equilibria and relaxation dynamics of sodium citrate solutions by combining potentiometry, spectrophotometry, and dielectric spectroscopy. From photometric and potentiometric measurements, we detect the formation of the NaCit 2− ion-pair and the neutral Na 3 Cit 0 ion aggregate in a wide range of ionic strengths (0.5−4 M). Due to its remarkable stability, the latter becomes the prevailing species at higher salt concentrations. In the dielectric spectra, we observe the dipolar relaxation of Cit 3− and NaCit 2− and two solvent-related processes, associated with the collective rearrangement of the H-bond network (cooperative water mode) and the H-bond flip of water molecules (fast water mode). Unlike numerous other salt solutions, the relaxation time of the cooperative mode scales with the viscosity indicating that the strongly hydrated anion fits well into the water network. That is, the stabilizing effect of anion−solvent interactions on the H-bond network outweighs the destructive impact of the cations as the latter are only present at low concentration, due to strong ion association. In conclusion, the affinity of citrate toward Na + binding not only governs solution equilibria but also has a strong impact on water dynamics.

Enhanced SO2 Absorption Capacity of Sodium Citrate Using Sodium Humate

“…Moreover, the desulfurization time increased by 15 min. The causes of this phenomenon are various [33]. In addition to the hydrolysis of HA-Na to generate hydroxide ions, it can also ionize the acid radical ions (carboxylate), thus consuming H + to move the dissolution balance to the right and cooperating with Ci-Na to absorb more SO 2 .…”

Long-Life Zn Anode Enabled with Complexing Ability of a Benign Electrolyte Additive

“…NaCit has a regulating effect on the solvation structure of Zn 2+ . Cit – preferentially adsorbs on the zinc surface, occupying the active site of water-induced corrosion and hydrogen evolution and rearranging the electrode–electrolyte interphase . Cit – can interact with Zn 2+ to induce zinc deposition along the Zn(002) plane, effectively regulating Zn ion migration behavior and thereby promoting uniform deposition and inhibiting side reactions.…”