Evaluation of waste polyethylene terephthalate bottles as ligands for the synthesis of manganese-based metal-organic framework and removal of tetracycline antibiotics from aqueous solutions

Water resources are decreasing day by day due to the discharge of various wastes into underground and surface waters. In order to ensure ecological sustainability, wastewater must be treated before being discharged. In this study, used waste polyethylene terephthalate (PET) bottles were depolymerized to obtain benzene dicarboxylic acid (BDC), an intermediate product. The resulting BDC was used as a linker in manganese-based metal organic framework (MOF) synthesis. At the same time, manganese-based MOF containing commercial BDC-TPA was also synthesized. BDC linker for the synthesis of the manganese-based MOF. Tetracycline was removed from aqueous solutions by batch adsorption method by using the synthesized Mn-PET-MOF and Mn-TPA-MOF materials as adsorbents. Characterization of the synthesized adsorbents was carried out by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), Brunauer-Emmett-Teller (BET), zeta potential and scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDX) analyses. To determine the optimum conditions, the effects of various parameters (adsorbent amount, adsorption time, tetracycline solution concentration, temperature, pH, different ion-NaCl/NaNO3) on the adsorption process were investigated. The tetracycline adsorption capacity (qe) of Mn-PET-MOF is 8.27 mg/g and qe value of Mn-TPAMOF is 8.55 mg/g when adsorbent quantity is 1 mg. The mechanism and equilibrium conditions of the adsorption system were investigated by establishing Langmuir and Freundlich isotherm equilibrium models and Pseudo 1st order, 2nd order and Bangham kinetic models. The maximum adsorption capacities (qm) for tetracycline/Mn-PET-MOF and Mn-TPA-MOF adsorption systems were calculated as 13.51 mg/g (25 degrees C) and 15.92 mg/g (25 degrees C), respectively. Both adsorption systems fit the Pseudo 2nd order kinetic model better with higher R2 values (>= 0.95). The rate constants of Mn-PET-MOF and Mn-TPA-MOF are 0.029 g/mg min and 0.020 g/mg min, respectively. At the same time, Langmuir and Freundlich models were found to be suitable isotherm models with high R2 values (>= 0.97). Generally evaluated, PET-based adsorbent has shown performance as an alternative to commercial TPA-based adsorbent for the removal of tetracycline from aqueous solutions and is promising as an environmentally friendly adsorbent.