Removal of Hg²⁺ heavy metal ion using a highly stable metal-organic framework

The zirconium-based metal-organic framework with 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (H₂TCPP) linker known as PCN-221 was successfully synthesized by the solvothermal method. Characterization of the MOF was performed using various techniques, such as FT-IR, XRD, UV-Vis, and SEM analysis. The MOF has then applied to rapidly and efficiently adsorption of mercury (Hg²⁺) ions using an ultrasonic bath. Different parameters such as initial metal ion concentration, contact time, solution pH and adsorbent dose were investigated. The presence of a nitrogen-functionalized group in the porphyrin ligand in PCN-221 structure contributed to the absorption of mercury ions. The adsorption capacity of 233 mg g^-1 was obtained for this adsorbent in less than 30 minutes at pH = 7. The experimental adsorption data for the PCN-221 MOF are well suited with the pseudo-second-order kinetic model (R² = 0.99), and adsorption isotherms of Pb²⁺ metal ions are in good agreement with the Langmuir model.