Effective and Sustainable Removal of a Model Fluorescent Brightener Using Bicarbonate-Loaded Polyelectrolytes in a Closed-Loop CO₂ Cycle

Abstract

Fluorescent brighteners (FBs), currently recognised as emerging contaminants, require effective removal from aquatic environments. However, no practical methods exist due to their high water solubility, the formation of toxic byproducts upon decomposition, and the lack of repeatable absorbent regeneration. This study demonstrates the efficient removal of a fluorescent brightener from water using cationic polyelectrolytes loaded with bicarbonates. Poly(allylammonium bicarbonate) (PAAm-BC), obtained from commercially available poly(allylamine) (PAA) by capturing carbonic acid, effectively removed disodium 4,4ʹ-bis(2-sulfostyryl)biphenyl (DSBP) from water through ion exchange. The removal efficiency reached nearly 100%, independent of the molecular weight of PAAm-BC. The bicarbonate-loaded polymer incorporated DSBP as an electrostatic cross-linker; the incorporated DSBP aligned within the polymer composites, generating directional regions in their morphology. Under basic conditions (pH 12), the composites completely released DSBP, regenerating PAA, which reloaded bicarbonates upon CO₂ introduction and enabled subsequent removal. This reversible removal process, achieved through repeated basification and CO₂ introduction in a closed-loop CO₂ cycle, is potentially applicable to a wide range of anionic pollutants and offers a promising strategy for improving aquatic environments.