Advances in metal-organic frameworks for water remediation applications

Abstract

Rapid industrialization and agricultural development have resulted in the accumulation of a variety of harmful contaminants in water resources. Thus, various approaches such as adsorption, photocatalytic degradation and methods for sensing water contaminants have been developed to solve the problem of water pollution. Metal-organic frameworks (MOFs) are a class of coordination networks comprising organic-inorganic hybrid porous materials having organic ligands attached to inorganic metal ions/clusters via coordination bonds. MOFs represent an emerging class of materials for application in water remediation owing to their versatile structural and chemical characteristics, such as well-ordered porous structures, large specific surface area, structural diversity, and tunable sites. The present review is focused on recent advances in various MOFs for application in water remediation via the adsorption and photocatalytic degradation of water contaminants. The sensing of water pollutants using MOFs via different approaches, such as luminescence, electrochemical, colorimetric, and surface-enhanced Raman spectroscopic techniques, is also discussed. The high porosity and chemical tunability of MOFs are the main driving forces for their widespread applications, which have huge potential for their commercial use.

Fig. 1. (A) Different morphologies and methods for the fabrication of MOFs and (B) role played by MOFs in water treatment approaches.

Fig. 2. Different types of MOFs used for water remediation applications.

Fig. 3. Various possible mechanisms for the removal of pollutants using MOFs as adsorbents.

Fig. 4. Effect of pH on adsorption.

Fig. 5. Application of nanofibers/MOFs in the removal of metal ions (reproduced with permission from ref. 115).

Fig. 6. Regenerative MOFs for the reversible uptake of Cd(ii): (1) self-assembly of the 3D framework from the organic ligand and hard metal ion; (2) effective absorption with high capacity; (3) absorption and desorption; (4) reconstruction of the used sample into a fresh sample (reproduced with permission from The Royal Society of Chemistry from ref. 120).

Fig. 7. (A) Schematic representation of TMU-60. (B) Possible pathway for electron transfer in conducting TMU-60-Cd [the golden balls display Cd(ii)] (reproduced with permission from ref. 122).

Fig. 8. Synthesis of Fe₃O₄@AMCA-MIL53(Al) nanocomposite and its adsorption–desorption behavior for metal ions (reproduced with permission from ref. 123).

Fig. 9. Schematic representation of the capture of heavy metal oxoanions by 1-SO₄ with concurrent loss of SO₄²⁻ (reproduced with permission from ref. 131).

Fig. 10. DFT-optimized structures and corresponding magnified views showing the hydrogen bonding interactions of iMOF-3C with different oxyanions and binding energies (reproduced with permission from ref. 134).

Fig. 11. Various interactions simultaneously occurring during the removal of pollutants from wastewater using MOFs.