Direct upcycling of polyethylene terephthalate (PET) waste bottles into α-Fe2O3 incorporated MIL-53(Al) for the synthesis of Al2O3/Fe3O4-encapsulated magnetic carbon composite and efficient removal of non-steroidal anti-inflammatory drugs

Abstract

The upcycling of polyethylene terephthalate (PET) waste into high-value-added materials can have a significant contribution to global environmental protection. In this study, considering the unique thermal behaviors of PET and metal salts (i.e., Al and Fe) under similar hydrothermal conditions, we proposed a novel solvent-free one-pot approach for the upcycling of PET. In a one-pot hydrothermal reaction at 220 ℃ under self-generated pressure, PET waste was depolymerized into starting monomers (terephthalic acid and ethylene glycol), Al-based metal–organic frameworks (MIL-53(Al)) were fabricated, and iron oxides (α-Fe2O3) were formed simultaneously. X-ray diffraction measurements clearly demonstrated that α-Fe2O3 incorporated MIL-53(Al) (α-Fe2O3/MIL-53(Al)) was successfully synthesized directly from PET waste bottles via a novel green approach. After the annealing process, the α-Fe2O3/MIL-53(Al) precursor was successfully converted to an Al2O3/Fe3O4-encapsulated magnetic carbon composite (Al/[email protected]). The feasibility test proved that the Al/[email protected] prepared at an annealing temperature of 600 ℃ (Al/[email protected]600) effectively removed four common non-steroidal anti-inflammatory drugs, i.e., ibuprofen (96.31%), diclofenac (66.84%), naproxen (87.83%), and ketoprofen (90.07%). Owing to its low removal rate, diclofenac was selected as the target pollutant, and the adsorption parameters were optimized using response surface methodology. Under the optimized conditions (solution pH = 5.0, adsorbent dosage = 1.21 g/L, and contact time = 15 h), the maximum actual diclofenac removal (92.94%) was obtained, which agreed with the maximum theoretical value (93.15%). In addition, Al/[email protected]600 exhibited excellent reusability (removal rate > 85%) after five repetitive adsorption-regeneration cycles. This study demonstrates the promising opportunities for the upcycling PET waste bottles as efficient adsorbents for the removal of emerging environmental contaminants.