Effective recovering Pd(II) ions via tuning the Lewis basicity of nanofiber capture vacancy

Recovery of palladium from spent catalysts is of great practical significance for the construction of ecological civilization and resource recycling. However, for environmentally friendly adsorption methods, designing specialized capture vacancies with high capacity and precise selectivity for Pd(II) ions remains a challenge. Herein, a salicylic acid-modified nanofiber (SANF), exhibiting specific spatial configuration and constructing a capture vacancy by "OO" of hard bases, was designed and employed for recovering and separating palladium. The adsorption results indicated that the SANF exhibited a fast capture rate (reaching adsorption equilibrium within 60 min) and a large capture capacity (about 170 mg/g) for Pd(II) ions, and the capture process was exothermic and spontaneous. Additionally, the Lewis basicity of the capture vacancy after tuning better matches the Lewis acidity of Pd(II) ions, which achieves a high-selectivity separation of Pd(II) ions (selectivity coefficient for K(I), Na(I) Ca(II), Mg(II) and Al(III) ions are 1505.2, 10,536.7, 1128.9, 2634.2 and 2873.6, respectively). Practical applications showed that SANF was enabled to recover Pd(II) ions from spent catalyst leachate and achieved four time adsorption-desorption cycles, possessing some industrial promise. Furthermore, the matching mechanism between the Lewis basicity of the capture vacancy and the Lewis acidity of the Pd(II) ions was revealed through series characterization and theoretical calculations. Finally, it is proposed a Lewis basicity tuning strategy founded on a specific spatial structure, provides a new insight for the design and construction of a capture vacancy for Pd(II) ions in the future.