Specific spatial transfer PdCl42− to [X-Pd-Y] by strong coordination interaction in a 3D palladium ion-imprinted polymer with footprint cavity

Abstract

Selective extraction of target metal ions from contaminated water is always the concern in the absorbent application. Herein, a palladium ion-imprinted polymer (Pd-IIP-AHTB) absorbent was designed and fabricated through radical-induced polymerization of Schiff based functional monomer (3-Allyl-2-hydroxybenzaldehyde thiosemicarbazone, AHTB) to selectively recover Pd2+ from water. Pd-IIP-AHTB shows a high distribution coefficient Kd (850.46 mL g−1) which is up to 110 times higher than that of interference metal ion like Zn(II). pH 3.0 was chosen as an optimum pH in the adsorption operation. The maximum adsorption capacity on Pd-IIP-AHTB is 60 mg/g, which is 2 times that of the non-imprinted polymer (NIP) (30.33 mg/g) at 25 °C. Dubinin-Ashtakhov (DA) based site energy distribution model (F(E*)) confirms that more accessible sites are binding with Pd2+ on Pd-IIP-AHTB than NIP (Q0(F(E*)Pd-IIP-AHTB > Q0(F(E*)NIP, and E0*Pd-IIP-AHTB > E0*NIP). We elucidated a new Pd2+ adsorption mechanism that involves a strong coordination interaction between Pd2+ and binding site (X->CN and Y->CS) in a 3-D Pd-IIP-AHTB with memoryeffect cavity. Notably, the strong coordination enables the specific spatial transfer PdCl42− to [X-Pd-Y] in aqueous solution byfixed bed adsorption experiments verification, and no Cl− ions are retained on the absorbent. This finding provides new insight into the recovery of highly purified Pd on fixed bed packed Pd-IIP-AHTB absorbents and renewal hydrochloric acid solution in practical application.