Effect of dopants in polyaniline-coated capacitive deionization electrodes on anion selectivity

This study explores the viability of employing polyaniline (PAni) coatings doped with different anions in capacitive deionization (CDI) electrodes for ion recovery purposes. Multiple CDI electrodes were fabricated by electrodepositing PAni in the presence of four mineral acids (HCl, HNO₃, H₂SO₄, and H₃PO₄) to incorporate the corresponding anions into the PAni network. The results highlight the critical role of dopants and polymerization conditions in determining ion adsorption behavior. Notably, the PAni/H₂SO₄ electrode achieved approximately 20 % reduction in chloride adsorption while maintaining consistent sulfate adsorption compared to the control. The behavior of PAni/HCl, PAni/HNO₃, and PAni/H₃PO₄ systems were not as pronounced compared to the PAni/H₂SO₄ system, under tested parameters, highlighting the dopant-dependent influence of polymerization conditions. Specifically focusing on the PAni/H₂SO₄ system, various polymerization conditions were investigated, and their ion adsorption characteristics were evaluated using a CDI system. It was observed that reducing the monomer concentration or the polymerization duration can enhance the selective properties of the coated electrode in this specific scenario. Additionally, distinct differences in polymer morphology based on polymerization conditions and dopants were observed, underlining the need for further research to understand the influence of these variables on the morphology of the PAni network and the resulting ion adsorption behavior of the coatings.