Mechanism Insights Into High-Performance Cu2+ Adsorption by ZIF-8/PAN Nanocomposite Fibers: Coordination and Ion Exchange Dynamics

The accumulation of copper ions in the environment can devastate the ecological systems and threaten the health of organisms. Consequently, the development of effective adsorbents to extract Cu2+ from aqueous solutions is urgently needed. Here, the Zeolitic Imidazolate Framework-8 (ZIF-8)/polyacrylonitrile (PAN) nanocomposite fibers were synthesized by electrospinning and further characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). ZIF-8 powders were uniformly distributed on the surface of the nanocomposite fibers, and amide CO=NH bonds were formed between the -NH2 groups of ZIF-8 and the C=O groups of PAN. The ZIF-8/PAN nanocomposite fibers demonstrated an exceptional Cu2+ adsorption capacity of 275.7 mg g-1 at pH = 4.0. The adsorption process adhered to the pseudo-second-order kinetics and the Langmuir isotherm model. The adsorption mechanism, as conformed by FTIR and X-ray photoelectron spectroscopy (XPS) analysis, involves the coordination of the -NH2 and C=O groups with Cu2+ and the ion exchange processes between Cu2+ and Zn2+ for the nanocomposite fibers. This study provides a novel approach for the removal of Cu2+ from aqueous solutions and addresses the challenge of recovering powder materials in wastewater treatment.