Recycled Battery Separators as Low-cost, Selective, and Reusable Adsorbents for Methylene Blue

Recycled lithium-ion battery separators function as effective, regenerable sorbents for methylene blue (MB). Electrolyte exposure “activates” the polyethylene surface—introducing polar/anionic functionalities that enhance uptake relative to pristine-like regions. Equilibrium modeling confirms higher capacity on the electrolyte-enriched domain (\(\:{q}_{\text{m}\text{a}\text{x}}=14.24\) mg g⁻¹) compared with the low-electrolyte-contact fragment (\(\:{q}_{\text{m}\text{a}\text{x}}=5.15\) mg g⁻¹). Van’t Hoff analysis indicates spontaneous, exothermic physisorption with ion-pairing/ion–dipole contributions, while kinetic fits (PFO/PSO, Elovich, Weber–Morris) reveal boundary-layer/heterogeneity effects governing the approach to equilibrium. The sorbent is readily regenerable by a mild acetone rinse and sustains ≥ 92% removal over ten cycles, underscoring a practical route to convert battery plastic waste into a low-cost, reusable adsorbent for wastewater remediation within a circular-economy framework.