Adsorption of Pd(II) ions by electrospun fibers with effective adsorption sites constructed by N, O atoms with a particular spatial configuration: Mechanism and practical applications

The separation and recovery of palladium from electronic waste (e-waste) are of great significance as they can alleviate environmental pollution and avoid resource loss. Herein, a novel nanofiber modified by 8-hydroxyquinoline (8-HQ-Nanofiber) with adsorption sites co-constructed by N and O atoms of hard bases was fabricated, which has good affinity properties for the Pd(II) ions belonging to soft acid in the leachate of e-waste. The adsorption mechanism of 8-HQ-Nanofiber for Pd(II) ions was revealed from the perspective of molecular level relied on a series of characterizations, such as FT-IR, ss-NMR, Zeta potential, XPS, BET, SEM and DFT. The adsorption of Pd(II) ions on 8-HQ-Nanofiber reached equilibrium within 30 min and the maximum uptake capacity was 281 mg/g at 318.15 K. The adsorption behavior of Pd(II) ions by 8-HQ-Nanofiber was described by the pseudo-second-order and Langmuir isotherm models. The 8-HQ-Nanofiber exhibited relatively good adsorption performance after 15 times of column adsorption. Finally, based on hard and soft acids and bases (HSAB) theory, a strategy to regulate the Lewis alkalinity of adsorption sites by specific spatial structures is proposed, which provides a new direction for the design of adsorption sites.