Green and sustainable metal-organic frameworks (MOFs) in wastewater treatment: A review

Metal-organic frameworks (MOFs) possess unique structural, physical, and chemical properties, making them promising materials for wastewater treatment applications, particularly in photocatalysis. However, conventional synthesis methods suffer from drawbacks such as toxic raw materials, high costs, instability, and timeconsuming processes. Addressing these issues, there is an increasing demand for sustainable, eco-friendly, stable, recyclable, and cost-effective methods to produce green and sustainable MOFs. This review explores recent progress in the sustainable synthesis of MOFs and their photocatalytic properties in degrading organic pollutants present in wastewater. Stable MOFs, including MILs, UiOs, and ZIFs, have demonstrated effective photo-degradation capabilities. Enhancing adsorption capacity can be achieved through diverse strategies, such as replacing linkers or metal nodes, selecting suitable metal clusters, adjusting organic linkers and metal clusters, and regulating MOF pores while integrating bio-based ligands, metals, and solvents. Green solvents like water, ethanol, methanol, dimethylformamide, supercritical, and ionic liquids are recommended to improve removal efficiency and reduce environmental impact. Notably, rapid synthesis at ambient conditions is possible using ionic liquids with supercritical CO2. Nonetheless, challenges persist in optimizing the photocatalytic efficiency of green MOFs. This review proposes a combination of strategies, such as ligand functionalization, mixed ligand and metal centers, magnetic material addition, immobilizing metal ions, dye sensitization, carbon or metal decoration, and semiconductor coupling, to overcome these obstacles and create high water-stable green MOFs. Emphasizing the importance of sustainable synthesis methods for MOFs, this review highlights their potential in wastewater treatment through photocatalysis. It identifies areas for further research and development to enhance their performance in environmental applications.