Waste PET-derived MOF-5 for high-efficiency removal of tetracycline

Polyethylene terephthalate (PET) accounts for 40 % of discarded plastics, and its recycling products have outstanding environmental protection and energy-saving performance, so how to improve the current low recycling rate of waste PET has caught increasing attention. In this paper, waste PET plastic was depolymerized to prepare terephthalic acid (TPA) as an organic linker to synthesize MOF-5. MOF-5 was applied to the adsorption of tetracycline (TC). The batch experiments exhibited that kinetic and isotherm data best fitted the pseudo-first-order model and Langmuir isotherm model with a maximum adsorption capacity of 2325.55 mg g-1. The regeneration rate of MOF-5 at the fifth cycle was 85.51 %. X-ray photoelectron spectroscopy (XPS) technique and Fourier Transform Infrared (FTIR) spectroscopy both indicated the main adsorption mechanism of MOF-5 toward TC could be attributed to hydrogen bonding and the ionic interactions between the unsaturated bonds (C=O and O-C=O) in MOF-5 and TC molecules. Alginate hydrogel with 30-150 mg MOF-5 loading provided better adsorption performance toward TC than MOF-5 powder, and 90 mg MOF-5 loaded hydrogel performed the highest removal rate of 66.28 %. This work proposed a novel method using waste plastics as raw materials to synthesize pollutant adsorbent, which had an enlightening effect on pollutant treatment.