A versatile MOF-based trap for heavy metal ion capture and dispersion

Abstract

Current technologies for removing heavy metal ions are typically metal ion specific. Herein we report the development of a broad-spectrum heavy metal ion trap by incorporation of ethylenediaminetetraacetic acid into a robust metal-organic framework. The capture experiments for a total of 22 heavy metal ions, covering hard, soft, and borderline Lewis metal ions, show that the trap is very effective, with removal efficiencies of >99% for single-component adsorption, multi-component adsorption, or in breakthrough processes. The material can also serve as a host for metal ion loading with arbitrary selections of metal ion amounts/types with a controllable uptake ratio to prepare well-dispersed single or multiple metal catalysts. This is supported by the excellent performance of the prepared Pd²⁺-loaded composite toward the Suzuki coupling reaction. This work proposes a versatile heavy metal ion trap that may find applications in the fields of separation and catalysis.

Fig. 1

Schematic illustration of the BS-HMT concept. a The ordered HCOOH in MOF-808 can be substituted by EDTA to form b MOF-808 with ordered EDTA, which can be used as c a BS-HMT for metal ion capture

Fig. 2

Characterization and illustration of MOF-808 and MOF-808-EDTA. a, b Schematic illustration of the structures of the two MOFs. c PXRD patterns. d N₂ adsorption-desorption isotherms. e Pore size distributions. f, g SEM images (Scale bar, 500 nm). h ¹H NMR spectra of (A) alkaline-digested MOF-808-EDTA, (B) alkaline-digested MOF-808, (C) EDTA-2Na, and (D) H₃BTC in KOH/D₂O solution

Fig. 3

Removal efficiency of heavy metal ion in single-component systems. The removal efficiency of hard Lewis metal ions, soft Lewis metal ions, and borderline Lewis metal ions for a–c MOF-808-EDTA, d–f MOF-808-OX, and g–i MOF-808-TGA

Fig. 4

Characterization of MOF-808-EDTA before and after metal ion loading. a–c Wide-scan XPS spectra and d–f FT-IR spectra of MOF-808-EDTA before and after La³⁺, Hg²⁺, and Pb²⁺ loading

Fig. 5

Capture performance of MOF-808-EDTA in multi-component systems. a Simultaneous removal efficiency for 19 metal ions in batch adsorption. b Breakthrough curves in the fixed bed adsorption

Fig. 6

Dispersity of metal ions in MOF-808-EDTA. STEM-HAADF images (scale bar, 100 nm) and the corresponding elemental maps for a MOF-808-EDTA, b–d single-metal systems (MOF-808-EDTA with loaded La³⁺, Hg²⁺, and Pb²⁺, respectively), e binary system (MOF-808-EDTA with loaded Co²⁺ and Ni²⁺), and f ternary system (MOF-808-EDTA with loaded Cu²⁺, Rh³⁺and Ru³⁺)