Activation of Persulphate by a Waste-Extracted Metal–Organic Framework-Derived Iron Oxide as a Photocatalyst for Effective Degradation of Salicylic Acid

In this research, a novel magnetic recyclable MIL-53(Fe) metal–organic framework (MOF)-derived Fe₃O₄ (wFe) photocatalyst was synthesized using waste polyethylene terephthalate (PET) plastic and iron scraps for efficient activation of persulphate (PS) to degrade salicylic acid (SA). Different characterization techniques thoroughly assessed the physicochemical and photoelectrochemical features of the synthesized photocatalyst. The wFe showed 95.45 ± 3.69% degradation and 56.73 ± 2.25% mineralization of 50 mg L⁻¹ SA within 180 min in the presence of 1 mW cm⁻² of UV fluence, 0.01 mM of PS, and 50 mg L⁻¹ of catalytic dosage. The degradation of SA in wFe/UV/PS followed pseudo-first-order reaction. Moreover, stability of wFe photocatalyst was verified by reusability analysis, which demonstrated that SA degradation and mineralization efficiency slightly declined from 95.45 ± 3.69% to 90.24 ± 2.25% and from 56.73 ± 2.25% to 43.94 ± 1.90% after the sixth run with the highest iron leaching of 0.157 mg L⁻¹, suggesting wFe possesses outstanding stability and recyclability. The findings of radical quenching and Mott-Schottky analysis showed that among different active radicals (i.e., h⁺, ${\mathrm{SO}}_4^{\bullet -}$, ^·OH, ${\mathrm{O}}_2^{\bullet -}$, e⁻), ${\mathrm{O}}_2^{\bullet -}$ was the active species majorly involved in the degradation of SA. In addition, the wFe/UV/PS system showed acceptable efficacy for the degradation of SA spiked in different real-water matrices. Finally, the mechanism involved in the degradation of SA and abatement pathways was established depending on the scavenging and liquid chromatography-equipped mass spectroscopy analysis.