Bipyridine covalent organic framework aerogel for highly selective recovery of palladium in wastewater

Palladium (Pd), a rare and precious metal, is highly valued due to its non-renewable nature and significant cost. Therefore, recovering palladium from industrial wastewater is of great importance but remains a challenge. Herein, a composite aerogel adsorbent has been developed by linking a bipyridine covalent organic framework, termed TpBpy, with chitosan (CS) through robust covalent bonds. The resulting TpBpy/CS aerogel is employed for the selective separation and recovery of palladium at low concentrations in real wastewater. Experimental results reveal that the maximum adsorption capacity of the TpBpy/CS aerogel for Pd(ii) is 274.4 mg g^-1 at pH 1. Additionally, even in the presence of other coexisting ions at concentrations 100 times higher than Pd(ii), the adsorption efficiency for Pd(ii) remains above 99%. Mechanistic investigations indicate that the adsorption of Pd(ii) by the TpBpy/CS aerogels primarily occurs through the coordination between pyridine N and Pd(ii), as well as the electrostatic interaction between protonated amino groups and Pd(ii). Moreover, the TpBpy/CS aerogel demonstrates exceptional reusability, maintaining an adsorption efficiency for Pd(ii) above 99% after nine adsorption-desorption cycles. Overall, the TpBpy/CS aerogel is a promising monolithic adsorbent for the efficient recovery of Pd(ii) from acidic industrial wastewater due to its exceptional adsorption capacity and selectivity, demonstrating substantial potential for practical applications.