Metallopolymer-based block copolymers for perfluorinated substances (PFAS) and ion removal

Abstract

Similar to the efforts made to combat standard (transition)metal-ion pollution in drinking water, such as chromate or lead, a significant endeavor has been directed towards removing perfluorinated organic substances (PFAS), typically found in very low concentrations. In this study, we have developed asymmetric membranes based on cobaltocenium-containing block copolymers (BCP) that selectively target PFAS but can also be utilized in metal ion removal. These membranes, prepared via the self-assembly and non-solvent-induced phase-separation process (SNIPS), offer a practical and crucial solution to water pollution. Their versatility is demonstrated by their ability to customize the surface and pore size to meet specific filtration requirements and their effectiveness in targeting different pollutants. The metallopolymer membranes we have produced have been tested for applications in a water filtration system and demonstrate a high permeance of 521 ± 49 L h⁻¹ bar⁻¹ m⁻². Furthermore, depending on the settings used for the perfluorooctanoic acid (PFOA) retention experiments, a stable permeance of 48 ± 2 up to 171 ± 26 L h⁻¹ bar⁻¹ m⁻² as well as a PFOA retention decrease of 99.3% at lower and 96.6% at higher water flux was found. The PFAS and metal ion retention capability is followed by ion chromatography (IC) and liquid chromatography coupled with mass spectroscopy (LC-MS). In addition, the ion-capturing is investigated for sodium chromate and lead nitrate for these porous BCP membranes. Here, remarkable retention for both anionic and cationic metallic pollutants of 46.4% and 99.8%, respectively, is verified by inductively coupled plasma mass spectrometry (ICP-MS). For porous membrane recycling, the selective solubility of the cobaltocenium BCPs is furthermore utilized to form new membranes from recycled material. Finally, by up-cycling the used membranes via calcination under reductive or oxidative conditions, we can prepare porous cobalt-containing ceramics with tailorable ceramic composition and well-defined porous architectures, offering a sustainable solution to material utilization and ceramic production.