A synthesis of metal–organic frameworks using terephthalic acid obtained from PET bottles with dye adsorption for application in experimental chemistry classes

In this study, we synthesized Metal–Organic Frameworks (MOFs) using five 3d transition metals: Fe, Co, Ni, Cu, and Zn. The ligand used was Terephthalic Acid (H₂TPA), recovered from PET bottles through alkaline hydrolysis. After its extraction, it was mixed with metal acetates of the respective transition metals, leading to the formation of metal-based MOFs. Rapid adsorption experiments were conducted and analyzed using UV–Vis absorption spectroscopy with solutions of common indicator dyes such as Methylene Blue (MB), Methyl Orange (MO), Nile Blue (NB), and Malachite Green (MG). The adsorption percentage and capacity in aqueous media were evaluated and compared. The interactions responsible for dye adsorption onto the MOFs are governed by physicochemical factors and attributed to forces such as π-π stacking, electrostatic interactions, hydrogen bonding, or coordination. This type of experiment can be applied in undergraduate Chemistry courses, covering rapid and straightforward synthesis, characterization, and application in the adsorption of various molecules while discussing the different types of interactions occurring in MOFs. Additionally, the use of H₂TPA as a ligand derived from chemical recycling adds a sustainable aspect to the experiments, resulting in low-cost and easily executable procedures aligned with the principles of green chemistry.