Fast decomposition of organic contaminant in wastewater using Zn and Mn bimetallic metal organic frameworks

Metal-organic frameworks (MOFs) exhibit remarkable versatility across various applications including luminescence sensors, adsorption, gas separation, and catalysis due to their tuneable structure and characteristics, especially in the presence of mono- or bi-metal ions. In this study, a comparative analysis of solvothermally synthesized zinc MOF (MOF-5), manganese MOF (Mn-MOF), and bimetallic zinc-manganese MOF (Zn/Mn-MOF) is conducted. Clear distinctions in the properties of these synthesized materials are observed. XRD spectra suggest that MOF-5 and Zn/Mn-MOF exhibit higher crystallinity compared to Mn-MOF. FESEM images reveal that particles of bimetallic MOFs are well-separated, whereas those of monometallic MOF-5 and Mn-MOF are agglomerated. Zn/Mn-MOF display the lowest band gap, measuring 3.03 eV. To assess their efficacy as photocatalysts, their ability to degrade methylene blue under simulated sunlight is evaluated. Reaction kinetics indicate that degradation follows pseudo-first-order linear kinetics for all synthesized samples. Notably, bimetallic Zn/Mn-MOF outperforms its monometallic counterparts in dye degradation processes, exhibiting a rate constant of 0.0535 min−1 and an exceptional degradation rate of ∼91 % in 120 min. Dark condition experiments suggest minimal dye adsorption by the synthesized MOFs, with values of 8.2 %, 5 %, and 2.5 % after 120 min for MOF-5, Mn-MOF, and Zn/Mn-MOF, respectively. Irradiation of the dye solution with a solar simulator enhances methylene blue decomposition. Furthermore, the recyclability studies for MB dye degradation by the Zn/Mn MOF reveal a decline in photocatalytic efficiency to 71.3 % after the fourth cycle, indicating appreciable stability of the material.