Peroxymonosulfate activation by polyimide-modified carbon nanotubes supported on melamine sponge for highly efficient bisphenol A degradation

To overcome the limitations of conventional powder catalysts, such as recovery difficulty and aggregation, a three-dimensional polyimide-modified carbon nanotube/melamine sponge composite (PIC-MS) was fabricated via a freeze-drying process and applied for peroxymonosulfate (PMS) activation to degrade bisphenol A (BPA). Structural characterizations, including SEM, FT-IR, and XRD, confirmed the successful integration of polyimide-modified carbon nanotubes with the melamine sponge framework. By combining the high catalytic activity of polyimide-modified carbon nanotubes with the robustness and easy recoverability of the sponge structure, PIC-MS effectively addressed catalyst aggregation, deactivation, and separation challenges. The PIC-MS/PMS system achieved over 97 % BPA removal within 20 min and showed broad-spectrum degradation efficiency toward various organic pollutants. Moreover, the catalyst displayed excellent adaptability across a wide pH range (2.7–9.5) and preserved more than 87 % of its activity after six consecutive cycles, confirming strong stability and reusability. Mechanistic studies demonstrated that singlet oxygen (¹O₂) and superoxide radicals (O₂^•-) were the dominant reactive oxygen species, with ¹O₂ playing the primary role. These species promoted sequential hydroxylation and oxidative ring-cleavage reactions, ultimately leading to complete mineralization of BPA into CO₂ and H₂O. Quantitative structure-activity relationship (QSAR) analysis further indicated that the transformation products had much lower bioaccumulation factors than BPA, suggesting reduced environmental risk during degradation. This work highlights a sustainable strategy for constructing recyclable metal-free catalysts, offering promising prospects for advanced wastewater treatment.