Impact of microporous structures of esterified cellulose filter papers on Co (II) rejection in cross-flow microfiltration

Abstract

• Ion rejection by a low-pressure filtration is possible by Donnan exclusion effect. • A microporous structure is important for establishing Donnan exclusion effect. • This phenomenon could be explained by the Gouy-Chapman-Stern (GCS) model. • Highly overlapped EDLs are responsible for developing Donnan exclusion effect. The Donnan exclusion effect is a unique phenomenon in which ions are electrostatically repelled by a surface bearing an identical charge. In this study, cellulose filter papers were esterified by ten different organic acids to systematically evaluate how surface properties regulate the development of the Donnan exclusion effect and subsequent Co(II) rejection. Among the esterified cellulose filter papers, those exhibiting high Co(II) rejection (>80% in 1.0 mg/L Co(II) in 1.0 mM NaCl background electrolyte solution) were noted to simultaneously possess positive zeta potential when in contact with Co(II), low adsorption affinity, and a relatively high microporous environment. This behavior could be explained by the Gouy–Chapman–Stern (GCS) model, in which the ion retention in the overlapped electrical double layers (EDLs) regulates the zeta potential development and consequently the Co(II) rejection. In addition to introducing reactive carbonyl and carboxyl groups, we suggest that the creation of a relatively microporous environment is essential for high Co(II) rejection. Our results are valuable for developing low-energy filtration systems for environmentally friendly water and wastewater treatment.