Specific πδ+–πδ- interaction enables conjugated microporous polymers for highly selective capture of Pd(II)

The targeted capture of heavy metals from wastewater is urgently necessary in response to strategic demands of sustainable resource utilization, but it is severely hampered by the formation of specific adsorbent-adsorbate interactions. Herein, the conjugated microporous polymer CMP-1 with –C≡C– binding sites is introduced for the adsorption of PdCl42- in acid wastewater. The matched interaction between –C≡C– with vertical π bond and electron-rich Pd center with π58δ- exhibits exceptional PdCl42- selectivity in competitive systems with coexisting heavy metals. To regulate the electron density of π bond in –C≡C– to further reinforce the πδ+–πδ- interaction, p-FCMP and o-FCMP adsorbents are rationally designed through the substitution of electro-withdrawing F group at different positions. A joint experimental-simulation exploration reveals that the F-induced electron oriented migration in –C≡C– results in the decreased π-electron density, therefore enhancing the binding of PdCl42-. Notably, o-FCMP possesses the maximum positive charge density at –C≡C– binding sites, which greatly promotes the charge transfer between –C≡C– and PdCl42- for stronger bonding interaction, achieving an optimal adsorption capacity of 447.7 mg g−1 as well as enhanced selectivity. This work provides unique insights into the efficiently targeted removal of heavy metals.