Molecular engineering of Co ion–imprinted sites on metal–organic frameworks and facile photodeposition for the selective recovery and upcycling of Co(II)

Background The demand for adsorption technologies that facilitate the recovery and upcycling of the valuable metallic element, Co, has been increasing. The recovery of Co from wastewater using metal–organic frameworks (MOFs), which are promising adsorbents, is considerably limited because of the lack of selective adsorption sites. Furthermore, research on the upcycling of Co remains inadequate. Methods Herein, we develop an integrated strategy combining ion imprinting modification and photodeposition for the selective recovery and upcycling of divalent Co ions (Co(II)) using MOF adsorbents. Significant findings First, Co ion–imprinted sites are constructed on a typical MOF adsorbent, MIL-125 (labeled CoIP-ML), via molecular engineering using glycylglycine. Compared with the original aminated MIL-125, CoIP-ML exhibits a superior performance, achieving the maximum adsorption capacity ( q m = 218.6 mg/g) and selectivity (selective coefficient k Co(II)/Ni(II) = 3.61) for Co(II) via the chelation of Schiff base groups and adsorption at terminal carboxyl groups. The Co(II) adsorbed on CoIP-ML is upcycled through a facile photodeposition process into Co oxides, which function as a Fenton-like catalyst. The optimal catalyst effectively activates peroxymonosulfate for the removal of chloroquine diphosphate and chlortetracycline hydrochloride, achieving the upcycling of Co(II). This study presents a unique MOF-functionalization paradigm.