A Critical Review on Metal-Organic Frameworks and Their Composites as Advanced Materials for Adsorption and Photocatalytic Degradation of Emerging Organic Pollutants from Wastewater

Abstract

Water-borne emerging pollutants are among the greatest concern of our modern society. Many of these pollutants are categorized as endocrine disruptors due to their environmental toxicities. They are harmful to humans, aquatic animals, and plants, to the larger extent, destroying the ecosystem. Thus, effective environmental remediations of these pollutants became necessary. Among the various remediation techniques, adsorption and photocatalytic degradation have been single out as the most promising. This review is devoted to the compilations and analysis of the role of metal-organic frameworks (MOFs) and their composites as potential materials for such applications. Emerging organic pollutants, like dyes, herbicides, pesticides, pharmaceutical products, phenols, polycyclic aromatic hydrocarbons, and perfluorinated alkyl substances, have been extensively studied. Important parameters that affect these processes, such as surface area, bandgap, percentage removal, equilibrium time, adsorption capacity, and recyclability, are documented. Finally, we paint the current scenario and challenges that need to be addressed for MOFs and their composites to be exploited for commercial applications.

Keywords: adsorption; emerging pollutants; metal-organic frameworks; photocatalytic degradation.

Figure 1

The schematic diagram for the formation of the metal-organic framework (MOF) from metal ion and organic linker as precursors. Reproduced with permission from Reference [57].

Figure 2

Interactions in adsorption of a contaminant (acid orange 7) onto the pores of MOFs. Reproduced with permission from Reference [76].

Figure 3

Publications on the adsorption and photocatalytic degradation of some emerging pollutants using MOFs from 2010–2020. Data were obtained from science direct using the keywords; MOFs; adsorption; photocatalytic degradations; dyes, phenols; pesticides and herbicides; and pharmaceuticals and personal care products PPCPs.

Figure 4

The mechanism for photocatalytic degradation of methyl orange and 4-nitrophenol using composite photocatalyst (MOF-199-NH₂/BaWO₄). Reproduced with permission from Reference [93].

Figure 5

Publications from 2010–2020 on the adsorption and photocatalytic degradation of dyes using MOFs. Data was obtained from the science direct using keywords MOFs; adsorption, and photocatalytic degradations dyes.

Figure 6

(a) Adsorption and photocatalytic degradations spectra of methyl orange dye using Zn and Co²⁺/Zn²⁺ metal-doped MOFs (M(tpbpc)(bdc)0.5·H₂O) and (b) photographs of photocatalytic degradation of the dye using the MOFs under visible light irradiations. Reproduced with permission from Reference [97].

Figure 7

Molecular structures of (a) Perfluorooctanoic acid (PFOA) and (b) Perfluorooctane sulfonates (PFOS).

Figure 8

Diagram for the molecular docking simulation for adsorption of chrysene onto UiO-66(Zr) and NH₂-UiO-66(Zr) MOFs (showing the pollutant in the inner pores of the UiO-66(Zr) and the outer pores of the NH₂-UiO-66(Zr)). Reproduced with permission from Reference [187].

Figure 9

Adsorption capacities of UiO-66(Zr), MOF-808(Fe), and MOF-802(Fe) for the removal of pharmaceutical drugs from water. Reproduced with permission from Reference [224].

Figure 10

(a) Mechanism for photocatalytic degradation of ibuprofen using MIL-88(Fe) and Ag/AgCl@MIL-88(Fe) and (b) the reusability of the composites. Reproduced with permission from Reference [251].

Figure 11

Patents granted from 2010 to 2020 on the adsorption and photocatalytic degradation using MOFs-based materials of (a) some emerging pollutants and (b) dyes. Data obtained from the lens.org using keywords MOFs, adsorption, photocatalytic degradation, dyes, phenols, PPCPs, pesticides, and herbicides.