Polyelectrolyte Microcapsules: An Efficient and Rapid Adsorbent for Uranine

Fluorescein-based tracers like uranine are extensively used in hydrogeology, textile marking, and cosmetics, yet their discharge generates dilute wastewater streams that challenge conventional treatment due to low removal efficiency and high operational costs. This study evaluates the sorption potential of polyelectrolyte microcapsules (PMCs) fabricated via a green, aqueous layer-by-layer (LbL) assembly on sacrificial CaCO3 templates for uranine decontamination. The PMCs achieve rapid equilibrium within ≤5 min, with kinetics governed by the pseudo-second-order model and equilibrium data described by the Langmuir isotherm, yielding a maximum capacity of 12.1 mg/g. Sorption is highly efficient at neutral to mildly acidic pH (3.0–7.0) and low ionic strength (≤0.15 M NaCl), providing 98–100% removal from dilute streams (C0 ≤ 10 mg/L) and consistently reducing effluent concentrations to <0.05 mg/L. Saturated capsules exhibit low spontaneous dye release (≤10%) in deionized water under the tested conditions. Although limited regenerability precludes multi-cycle industrial use, the rapid sorption kinetics and high uranine removal efficiency make PMCs well suited for single-use polishing applications. By offering a scalable, solvent-free synthesis and targeted removal of emerging fluorescent pollutants from low-concentration effluents, this work presents a sustainable, low-energy alternative for advanced wastewater treatment, aligning with green chemical engineering and circular water management principles.