Highly efficient methyl orange adsorption by UV-012, a new crystalline Co(ii) MOF

Abstract

This work presents three scientific contributions: the new metal organic framework (UV-012) crystal structure, the evaluation of this new material for dye adsorption and a new mechanism that explains the excellent and selective anionic dye adsorption by this material. UV-012 was synthesized by a solvothermal method and characterized by single crystal and powder XRD, scanning electron microscopy (SEM) and FT-IR. Methyl orange (MO) adsorption experiments in water were completed, obtaining the maximum adsorption capacity (1410 mg g⁻¹) determined by Langmuir's mathematical model. The value obtained is one of the highest reported to date for a MOF or a coordination polymer; this exceptional performance is attributed to the MOF–dye electrostatic interaction, which is associated with bpp linkers in the MOF structure. The adsorption kinetics is described by a pseudo-second-order model. The pH effect was studied, which indicated that the adsorption capacity decreases proportionally when the pH increases. UV-012 presents high potential to adsorb other anionic dyes such as Congo red or indigo carmine; however, its cationic dye adsorption performance (methylene blue) was not significant, which indicates selectivity toward anionic dyes. The most important conclusion of this work is: MOFs constructed from pyridinic linkers will present high adsorption capacity in the removal of anionic dyes, due to the strong electrostatic interaction between this type of linker and the negative charge of the dye. To the best of our knowledge, this conclusion has not been published previously.