Electrospun magnetic cobalt-carbon nanofiber composites with axis-sheath structure for efficient peroxymonosulfate activation

Cobalt-carbon nanofiber composites (Co-CNFs) were synthesized by electrospinning and subsequent carbonization and their performance for peroxymonosulfate (PMS) activation was evaluated. Co-CNFs have a large aspect ratio (150 nm in diameter and several millimeters in length) to avoid aggregation and large specific surface area (1304 m(2)/g) to provide more reaction sites for enhancing catalytic activities. Zero valence cobalt was proved to be the main cobalt species of axis or core of the fiber, which might account for its excellent magnetic response, and Co3O4 was the main cobalt species of sheath or coat according to XRD and XPS results. The Co-CNFs exhibited higher catalytic performances than Co3O4 or CNFs for PMS activation and dyes were completely removed in a short time in the Co-CNFs/PMS system. The Co-CNFs derived from cobalt acetate demonstrated the highest catalytic performance and their Co leaking was similar to that of catalysts derived from other cobalt salts. The degradation efficiency increased with the carbonization temperature, cobalt loading, degradation temperature, PMS and catalyst dosage. The dye degradation processes followed pseudo-first-order kinetics. The activation energy of Co-CNFs/PMS/orange G system was derived as 29.8 kJ/mol by the Arrhenius equation. The Co-CNFs exhibited high catalytic performances and excellent stability for five repetitive usage. The possible orange G degradation pathway was proposed based on intermediate detection.