A novel defect-rich Prussian blue analogue based on controlled doping strategy: Exceptional adsorption performance of platinum group metals and enhanced stability

Abstract

The efficient separation of platinum group metals (PGMs, mainly Pd, Ru, and Rh) from high level liquid waste (HLLW) is of growing significance for resolving challenges in radioactive waste treatment and achieving sustainable development. Based on Prussian blue analogues (PBAs) with tunable compositions and morphologies, a defect-rich but also excellently stable cobalt-doped aluminum hexacyanoferrate (Co/KAlFC) was successfully synthesized for the separation of PGMs using defect engineering. Interestingly, the defects in Co/KAlFC induced an increase in active sites and vacancies, leading to a remarkable enhancement of PGM adsorption capacity compared to the undoped KAlFC. While maintaining the same excellent Pd(II) adsorption capacity, the convenient access provided by the defects led to a reduction of the Pd(II) adsorption equilibrium time to 30 min, as well as a 3-fold and 7-fold increase in the adsorption capacity for Ru(III) and Rh(III), respectively. The experimental and characterization results revealed that the adsorption mechanism of defect-rich Co/KAlFC on PGM was mainly a synergistic effect of ion-exchange and chemical complexation, and the enhanced electrostatic interaction promoted the adsorption process. The valence state of Fe shifted from divalent to trivalent during the adsorption process, which affected the strength of coordination interaction between PGMs and Fe-CN- at N-atom. Overall, this study not only demonstrated that Co/KAlFC is an excellent candidate for the removal of PGM from HLLW but also provided a new idea for the rational design and development of inorganic materials with exceptional properties and stability.