Efficient upcycling of iron scrap and waste polyethylene terephthalate plastic into Fe3O4@C incorporated MIL-53(Fe) as a novel electro-Fenton catalyst for the degradation of salicylic acid

The current research demonstrates the efficiency of a low-cost MIL-53(Fe)-metal-organic framework (MOF) derived Fe3O4@C (MIL-53(Fe)@Fe3O4@C) electrocatalyst in a batch-scale electro-Fenton (EF) process for the degradation of salicylic acid (SA) from wastewater. The electrocatalyst was prepared from the combination of polyethylene terephthalate (PET) and iron scrap wastes. The result showed 91.68 ± 3.61% degradation of 50 mg L−1 of SA under optimum current density of 5.2 mA cm−2, and pH of 7.0 during 180 min of electrolysis time. The degradation of SA from waste catalyst was similar to the chemical-based MIL-53(Fe)-derived Fe3O4@C (cFe) cathode catalyst. The presence of chloride ions (Cl−) in the water matrix has shown a strong inhibitory effect on the elimination of SA, followed by nitrate (NO3−), and bicarbonate (HCO3−) ions. The multiple cyclic voltammetry (CV) analysis and reusability test of waste cathode catalyst showed only 8.03% drop of current density at the end of the 20th cycle and 5% drop of degradation efficiency after 6th cycle with low leaching of iron. The radical scavenging experiment revealed that the HO• generated via electrochemical generation of H2O2 had a prominent contribution in the removal of SA compared to HO2•/O2•−. Besides, possible catalysis mechanism and degradation pathways were deduced. Furthermore, a satisfactory performance in the treatment of SA spiked in real water matrices was also observed by waste-derived Fe3O4@C cathode catalyst (wFe). Additionally, the total operating cost and toxicity analysis showed that the as-synthesized wFe cathode catalyst could be appropriate for removing organic pollutants from wastewater in the large-scale application.