Aniline-functionalized Lithium-ion Battery Separators for Selective Methylene Blue Removal

Polymeric separators recovered from spent lithium-ion batteries were functionalized with an aniline layer to tailor their surface chemistry toward selective dye adsorption. Unlike pristine separators, the aniline-modified material exhibits nitrogen-rich and polar functionalities, as confirmed by FTIR spectroscopy, enabling strong interactions with cationic species. Adsorption experiments using methylene blue (MB) revealed a substantial enhancement in uptake after functionalization, with the Langmuir maximum capacity increasing from 2.53 mg·g⁻¹ for the unmodified separator to 7.19 mg·g⁻¹ at pH 7, rising sharply to 46.33 mg·g⁻¹ at pH 11, and reaching approximately 60 mg·g⁻¹ at 40°C. Kinetic data indicate that conventional pseudo-first- and pseudo-second-order models provide limited descriptions, whereas the Elovich equation accurately represents the adsorption process, evidencing an energetically heterogeneous and coverage-dependent mechanism. Thermodynamic parameters confirm a spontaneous and exothermic adsorption process. Competitive adsorption tests using a methylene blue/Sunset Yellow binary system demonstrate pronounced selectivity toward the cationic dye under alkaline conditions. This study highlights deliberate aniline functionalization as an effective strategy to convert recycled lithium-ion battery separators into high-performance, selective adsorbents for wastewater remediation.