Highly efficient and selective removal of Pb2+ by ultrafast synthesis of HKUST-1: Kinetic, isotherms and mechanism analysis

The relatively high cost, long synthesis duration and low adsorption capacity have limited the application of the primary metal-organic frameworks (MOFs) in the heavy metal removal. Herein, one-minute synthesized primary HKUST-1 MOF with excellent adsorption performance towards Pb2+ has been achieved. The adsorption equi-librium time and maximum uptake capacity of Pb2+ on HKUST-1were 60 min and 819.28 mg/g, respectively. Besides, HKUST-1 exhibited a stronger binding affinity to Pb2+ than the coexisting ions. The adsorption data fitted well with the pseudo-second order model (R-2 = 0.9962) and Langmuir model (R-2 = 0.9919), suggesting the adsorption behavior was dominated by monolayer chemisorption. Further, the destruction of HKUST-1 crystal structure after Pb2+ exposure and strong correlation between the released Cu2+ and adsorbed Pb2+ collectively confirmed the ion exchange could be the potential mechanism. Besides, the coordination interaction between Pb2+ and the free-standing carboxylate groups in the ligands of HKUST-1 also played an important role in the adsorption process. This work not only provides a new idea for Pb2+ removal by primary MOFs based on cation substitution, but also has great implications for constructing green and low-cost MOFs for the treatment of heavy metals contaminated water.

Automated summary

The study successfully synthesized HKUST-1 MOF with excellent adsorption performance for Pb2+ in just one minute. The adsorption behavior was dominated by monolayer chemisorption, with potential mechanisms including ion exchange and coordination interaction. This work not only provides a new idea for Pb2+ removal using primary MOFs, but also has implications for constructing green and low-cost MOFs for heavy metal contaminated water treatment.