Water contaminated with heavy metals is an important environmental concern, especially due to the metals’ cumulative effect in organisms. Metal-organic frameworks (MOFs) are coordination networks of metal ions or clusters linked using organic ligands. The combined effects of the organic and inorganic moieties allow tuning the size of the pores and provide high surface area to mass ratios while ensuring that the material is chemically and structurally stable.
Dipak Rana and colleagues, University of Ottawa, Canada, have developed an efficient membrane containing MOFs that can efficiently remove Pb2+ and Hg2+ ions by filtration of contaminated water solutions. MOF 808, containing Zr6 clusters, and the Fe-based MOF-F300 were enmeshed in nanofibers of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF).
The team concluded that the adsorption of the metals was due to a combination of competitive ion exchange, electrostatic interactions, and pore filling of the MOFs. Removal of Hg2+ and Pb2+ was achieved under controlled acid conditions. The experiments demonstrated that the total negative charge of the deprotonated COOH groups at the metal clusters drags the positive metal ions from the surface into the pore cavity. This was shown by a continuous decrease of the pH as the heavy metal ions promoted the release of protons.
- Metal-organic frameworks supported on nanofibers to remove heavy metals,
Johnson E. Efome, Dipak Rana, Takeshi Matsuura, Christopher Q. Lan,
J. Mater. Chem. A 2018.