Selective Oxidation of H₂S to Elemental Sulfur over Waste PET-Derived Biochar-Supported Metal Catalysts

The upcycling of plastic waste into high-value functional materials offers a sustainable pathway aligned with green chemistry and circular economy principles. In this study, activated carbon (aPAC) was synthesized from waste PET bottles via KOH activation and employed as a support for trivalent metal catalysts (Fe, Bi, and Ce) aimed at low-temperature catalytic oxidation of hydrogen sulfide (H₂S). Among the prepared catalysts, Fe/aPAC exhibited the most promising performance, achieving nearly complete H₂S conversion (∼95%) and a high sulfur yield (∼90%) under humid air at 30 °C. Textural and surface characterizations (X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy, CO₂-temperature-programmed desorption, and scanning electron microscopy [SEM]/EDS) revealed that the presence of Fe₂O₃/FeOOH, abundant oxygenated groups (C-O, CO, O-H), and surface basicity collectively enhanced redox activity and H₂S adsorption. Notably, the catalyst maintained over 80% conversion after three regeneration cycles, demonstrating excellent stability and reusability. Extracted sulfur products were confirmed via SEM and visible recovery. A reaction mechanism involving H₂S dissociation, Fe³⁺/Fe²⁺ redox cycling, and surface-assisted O₂ activation was proposed. This work not only provides mechanistic insights into H₂S oxidation under mild conditions but also proposes a cost-effective and scalable approach for converting PET waste into efficient catalytic materials, offering dual environmental benefits in sulfur recovery and plastic valorization.