High capacity Hg(II) and Pb(II) removal using MOF-based nanocomposite: Cooperative effects of pore functionalization and surface-charge modulation

Here, we applied a novel and simple strategy for high capacity heavy metal ion removal from aqueous solution by modification of urea decorated TMU-32 framework through in-situ synthesis of Fe3O4@TMU-32 composite with aim of controlling the surface-charge of the composite adsorbent toward Hg(II) and Pb(II) ions. [Display omitted] •High capacity heavy metal ion removal by Surface-charge modulation and mult-functionalization strategies.•Fe3O4@TMU-32 hybrid nanomaterials synthesized through encapsulation of Fe3O4 nanoparticles by TMU-32 framework.•Record-breaking rates in removal of Hg(II) (905 mg.g-1) and especially Pb(II) (1600 mg.g-1) ions.•Mechanism evaluation by zeta potential and FT-IR analyses to show the critical roles of surface charge and functionality. Water pollution by heavy metal ions especially Hg(II) and Pb(II) is one of the most important concerns because of their harmful effects on human health and environment sustainability. Here, we developed Fe3O4@TMU-32 metal-organic framework (MOF)-based nanocomposite by applying pore functionalization and surface-charge modulation strategies. Based on synergic effects of these strategies, Fe3O4@TMU-32 nanocomposite shows very high capacity toward Hg(II) and Pb(II) metal ions. TMU-32 (with formula [Zn(OBA)(DPU)]·2DMF·H2O where H2OBA and DPU are (4,4′-oxybis(benzoic acid)) and 1,3-di(pyridin-4-yl)urea)) is decorated with urea functional groups containing carbonyl and amine groups that can interact with metal ions. As results, TMU-32 show very high capacity toward Hg(II) and Pb(II) ions. To improve the TMU-32 capacity toward Hg(II) and Pb(II) cations, we tried to modulate the surface-charge of TMU-32 as a host-framework. Surface-charge modulation strategy had been conducted through encapsulation of Fe3O4 nanoparticles by TMU-32 in an in-situ synthesis procedure and synthesis of Fe3O4@TMU-32 nanocomposite. Fe3O4@TMU-32 nanocomposite shows improved removal capacity (45 % and 54 % toward Pb(II) and Hg(II)) rather pristine TMU-32 framework because of urea decorated framework and charge modulated surface. Fe3O4@TMU-32 nanocomposite adsorb 1600 mg.g-1 of Pb(II) and 905 mg.g-1 of Hg(II) which extremely rare in the literature. Such improvement can be related to the electrostatic interaction between cationic nature of Pb(II) and Hg(II) and negative charge of the Fe3O4@TMU-32 adsorbent.