Urea-Based Metal-Organic Frameworks As High and Fast Adsorbent for Hg and Pb Removal from Water

Water pollution by various toxic heavy-metal ions, particularly mercury and lead, has been considered as a global problem with serious threat to public health. Nowadays, a variety of adsorbents have been used extensively for the removal of heavy-metal ions from water. In this work, two Zn-based metal-organic frameworks (MOFs), named TMU-31 and TMU-32, were successfully synthesized by a solid-state method named mechanosynthesis, which can be considered as a rapid, green, convenient, solventless, and low-cost process. These two MOFs are densely decorated with urea functional groups, which results in rapid, efficient, and selective removal of diverse heavy-metal ions, such as Hg and Pb ions, from wastewater. The sorption capacities of 476.19 mg g in less than 15 min for Hg(II) ions and 909 mg g for Pb(II) metal ions in less than 5 min were obtained effectively by these two structures. In addition, adsorption isotherms of Hg and Pb metal ions are in good agreement with Langmuir model, and also, the experimental adsorption data are well fitted with pseudo-second-order kinetic model ( R = 0.99). This work is the first example of urea-functionalized MOFs as an effective adsorbent for Pb and Hg ions, which shows the best and high efficiency for the removal of heavy metals in less than 15 min.