Review on the application of MOF materials for removal of pollutants from the water (II)

Metal–organic frameworks (MOFs) are a class of organic–inorganic hybrid functional materials generally formed via self-assembly of metal ions or metal clusters and rigid organic ligands with nitrogen and oxygen atoms. The wide range of potential applications of MOF materials includes gas storage and separation, catalysis, sensing, and drug transportation and release, which can be attributed to their versatile designable structures, modifiable chemical functionality, low-density framework, large specific surface area, and functional and permanent pore space. MOF and its composite materials have also been employed to remove various contaminants from the environment in the recent decade. To present the remarkable research progress and outcomes of MOF materials in the removal of pollutants from the water environment, the related studies on the removal of heavy metals and organic pollutants from the water environment were reviewed in this paper. This was the second paper on the topic that mainly introduced the research progress of MOF materials in the removal of organic pollutants in aqueous solution. The previous studies have shown that MOF materials have open metal sites and Lewis acid–base sites; thus, they exhibit a high adsorption performance for dyes, antibiotics, pesticides, and persistent organic pollutants. Hydrogen bonding, π–π interaction, hydrophobic interaction, and electrostatic attraction are the main mechanisms for their adsorption of organic pollutants. In addition, the large pore structure of some MOF materials is conducive to the adsorption of macromolecular organic pollutants. Moreover, some MOF materials that can be used as catalysts for Fenton-like reactions, photocatalytic reactions, and persulfate activation to degrade organic pollutants, exhibit excellent catalytic performance. The degradation of pollutants in photocatalytic reactions can be mainly attributed to the contributions of ·O²⁻, ·OH, and h⁺. In the persulfate system, ·O²⁻, ·OH, SO₄^·−, and ¹O₂ are the main reactive oxide species that cause the decomposition of organic pollutants. Based on the review of previous studies, it is believed that future research will include but will not be limited to the following: (1) the improvement of the performance of MOF in removing organic pollutants and its recyclability; (2) the preparation of new MOF catalytic materials and investigation of catalytic reaction mechanisms; (3) the regulation of the defect structure of MOF to develop new MOF materials with high adsorption and catalytic efficiency; and (4) the analysis of new framework materials, e.g., covalent organic framework materials, and their applications in the field of pollutant purification.