Metal–Organic Frameworks as Powerful Heterogeneous Catalysts in Advanced Oxidation Processes for Wastewater Treatment

Abstract

Nowadays, the contamination of wastewater by organic persistent pollutants is a reality. These pollutants are difficult to remove from wastewater with conventional techniques; hence, it is necessary to go on the hunt for new, innovative and environmentally sustainable ones. In this context, advanced oxidation processes have attracted great attention and have developed rapidly in recent years as promising technologies. The cornerstone of advanced oxidation processes is the selection of heterogeneous catalysts. In this sense, the possibility of using metal–organic frameworks as catalysts has been opened up given their countless physical–chemical characteristics, which can overcome several disadvantages of traditional catalysts. Thus, this review provides a brief review of recent progress in the research and practical application of metal–organic frameworks to advanced oxidation processes, with a special emphasis on the potential of Fe-based metal–organic frameworks to reduce the pollutants present in wastewater or to render them harmless. To do that, the work starts with a brief overview of the different types and pathways of synthesis. Moreover, the mechanisms of the generation of radicals, as well as their action on the organic pollutants and stability, are analysed. Finally, the challenges of this technology to open up new avenues of wastewater treatment in the future are sketched out.

Sulfate Radical-Based Degradation of Organic Pollutants: A Review on Application of Metal-Organic Frameworks as Catalysts

“…In the presence of halides, PMS gets depleted prior to the oxidation process, which is not observed in the case of PDS . The activation is critical for degradation studies because it increases PS/PMS’s ability to generate reactive oxygen species (ROS), which can initiate the degradation process. , Another study shows 93.6% of PS decomposition side by side with the pollutant degradation because as the decomposition starts, the radicals are generated, leading to the oxidation process. − Table describes the various properties of peroxymonosulfate (PMS) and peroxydisulfate (PDS). The sulfate radical formation reactions involved in the activation process of PMS/PDS are as follows: ,, false( normalPMS false) SO 4 • − + OH − → SO 4 2 − + OH • false( normalPDS false) S 2 O 8 2 − + 2 H 2 O → 2 SO 4 2 − + HO 2 − + 3 H + HO 2 …”

“…This tunability allows for optimization of the active sites for PMS/PDS activation. Figure B depicts the different types of MOF structures like MIL, ZIF, UiO, HKUST, etc . The use of MOFs as PMS/PS activation catalysts offers several advantages, including high catalytic activity, selectivity, and reusability …”

“…Figure 3B depicts the different types of MOF structures like MIL, ZIF, UiO, HKUST, etc. 31 The use of MOFs as PMS/PS activation catalysts offers several advantages, including high catalytic activity, selectivity, and reusability. 43 A study by Yan et al in 2022 explains the underlying mechanism involved in the adsorptive removal of pollutants over MOFs, like electrostatic interaction, acid−base interaction, hydrogen-bonding, ion exchange, etc.…”

“… 12 The activation is critical for degradation studies because it increases PS/PMS’s ability to generate reactive oxygen species (ROS), which can initiate the degradation process. 31 , 32 Another study shows 93.6% of PS decomposition side by side with the pollutant degradation because as the decomposition starts, the radicals are generated, leading to the oxidation process. 33 − 35 Table 1 describes the various properties of peroxymonosulfate (PMS) and peroxydisulfate (PDS).…”

A Review on Carbon Quantum Dots Modified g-C3N4-Based Photocatalysts and Potential Application in Wastewater Treatment

“…Predominantly, wastewater is the key source of water pollution, occurring particularly from chemical industrialization, which is carcinogenic and enormously poisonous in nature due to the presence of extensive large organic complexes [3]. The conventionally utilized environmental remediation processes, such as chemical oxidation, adsorption, incineration, and biological oxidation, have been employed in the mitigation of all types of toxic and organic water contaminants [4][5][6][7]. However, the performance of these techniques is not effective, owing to an incomplete degradation of the persistent organic pollutants and noxious sludge formation [7][8][9].…”