Influence of anion hydration status on selective properties of a commercial anion exchange membrane electrochemically impregnated with polyaniline deposits

Abstract

There is currently great interest in the use of polyaniline (PAni) to impart particular properties to anion exchange membranes, employed in several fields. This special polymeric material can be obtained both chemically and electrochemically; however, the latter affords better control of morphology, which could be used to promote some properties of PAni-based membranes, such as their selectivity or hydrophobic/hydrophilic balance. In this work, commercially available membranes were electrochemically modified with PAni to improve their hydrophobic/hydrophilic balance, and this was achieved by cyclic voltammetry in acidic solutions. The performance of the modified membranes in the electrodialysis process of a nitrate-chloride mixture in neutral solutions was then evaluated. The impregnation imparts specific selective properties to the commercial membrane that lead to a greater retention of chloride ions. This property derives from the higher hydrophobicity of the PAni deposited on the membrane, which leads to a more effective exclusion of the more hydrated chloride anions.

Study of Anion Exchange Membrane Properties Incorporating N-spirocyclic Quaternary Ammonium Cations and Aqueous Organic Redox Flow Battery Performance

“…It should be noted that cation hydration [ 48 ] corresponds to the amount of water molecules directly interacting with the cation, whereas hydration shell indicates the number of water molecules surrounding the ion, but not necessarily directly interacting with it [ 49 , 50 ]. For instance, the cation hydration of a chloride ion was reported to be six in water solution [ 51 , 52 ], whereas the cation hydration of poly(DAPCl) has not yet been reported. However, the λ of a PPO-based AEM which has the same structure as ours, in OH − form (2.34 mequiv·g −1 IEC and 101% water uptake at 20 °C), was reported to be 25 [ 36 ].…”

Selective Phosphate Removal from Water and Wastewater using Sorption: Process Fundamentals and Removal Mechanisms

“…It is more difficult for anions with higher hydration energies to overcome this barrier, and hence, their separation from the aqueous phase is inefficient. 34 Another difficulty comes from the complex composition of the aqueous fluid of interest, that is, natural water and wastewater. These environments contain a variety of constituents, including suspended solids, organic matter, anions, cations, and microorganisms.…”

“…Such an energy barrier is related to the hydration energy. It is more difficult for anions with higher hydration energies to overcome this barrier, and hence, their separation from the aqueous phase is inefficient . Another difficulty comes from the complex composition of the aqueous fluid of interest, that is, natural water and wastewater.…”

Aqueous Speciation of Tetravalent Actinides in the Presence of Chloride and Nitrate Ligands

“…Experimental free energy of hydration (Δ G hyd ) values of all the free ligands and proton were used. For Cl – and NO 3 – , the Δ G hyd values were −75.8 and −64.5 kcal mol –1 , respectively. , The hydration free energy of a single water molecule in aqueous medium was −6.3 kcal mol –1 , while that of a proton was −265.9 kcal mol –1 . − All free energies are computed for 1 M solutions using the usual correction term RT ln(24.46) . The concentration of water was always considered to be 55.34 M, which is the bulk water concentration.…”