Novel electrospun metal-organic framework nanofibers (Nickel-coated ZIF-67/Chitosan/Polyvinyl Alcohol) as efficient adsorbents: Isotherm, kinetic and thermodynamic

In this work, Nickel-coated Zeolitic Imidazolate Framework-67 (Ni-ZIF-67) nanoparticles were synthesized via a facile and scalable method and subsequently integrated into a chitosan/polyvinyl alcohol (CS/PVA) nanofibrous matrix through electrospinning and surface-decoration techniques. Structural and morphological characterizations were performed using SEM, EDX mapping, XRD, FT-IR, BET surface area analyses, and UV-Vis spectroscopy. The resulting Ni-ZIF-67-CS/PVA nanofibers exhibited a cactus-like morphology and significantly enhanced surface area. Textural characterization revealed a threefold increase in BET surface area (from 5.38 to 15.51 m2/ g) and a substantial enhancement in Langmuir surface area (from 60.35 to 156.13 m2/g) upon nickel incorporation. Furthermore, BJH analysis showed an increase in total pore volume and pore radius, while t-Plot data confirmed an increase in both microporous and external surface areas, indicating improved accessibility of adsorption sites after Ni coating. Adsorption studies using Acid Red 2 (AR2) as a model pollutant demonstrated that the Ni-coated nanofibers achieved a maximum adsorption capacity of 404.5 mg/g, surpassing that of the uncoated ZIF-67/CS/PVA nanofibers (344.5 mg/g) at an adsorbent dosage of 0.02 g. Kinetic data conformed well to the pseudo-second-order model, and equilibrium adsorption followed the Langmuir isotherm, indicating monolayer chemisorption on a homogeneous surface. Thermodynamic parameters confirmed the spontaneous and endothermic nature of the process, dominated by physisorption mechanisms. After four regeneration cycles, the nanofibers maintained 77.31 % of their initial adsorption efficiency, evidencing excellent reusability and chemical stability. These findings underscore the potential of Ni-ZIF-67-CS/PVA nanofibrous composites as highperformance, environmentally benign adsorbents for dye removal from aqueous media.