A closed-loop strategy: Simultaneous upcycling of waste PET and electronic wastewater into multifunctional MOF photocatalysts for metal recovery and CH₃SH control

This study presents a sustainable and integrated strategy for converting waste polyethylene terephthalate (PET) and electronic wastewater into low-cost, high-performance multi-metal metal-organic frameworks (MOFs) for simultaneous metal recovery and environmental sensing applications. Terephthalic acid recovered from waste PET was employed as the organic ligand, while metal ions (Cu, Fe, Al, Ni, Sn) were efficiently extracted from electronic wastewater via hydrothermal synthesis. The process achieved over 99.999% metal ion recovery, producing treated effluent that meets China's Class IV water discharge standards. The synthesized multi-metal MOFs integration with carbon cloth electrodes demonstrated excellent visible light driven photocatalytic activity, completely degrading with 100 ppm methyl mercaptan within 25 min. This enhancement is attributed to improved charge transfer, as evidenced by electrochemical impedance spectroscopy. The improvement stems from three key factors: the conductive support, the defect-rich structure of the MOFs derived from recycled ligands, and the in-situ formation of a multifunctional Z-scheme heterojunction (CuO_x@multi-metal-MOF). Moreover, a portable and cost-effective MOF-based sensor was developed, enabling accurate detection of CH₃SH in the 5–400 ppm range and reliable recognition of safe exposure levels (< 10 ppm). This work establishes and economically viable pathway for sustainable resource recovery, photocatalytic pollutant degradation, and selective gas sensing, with promising potential for broader volatile organic compound (VOC) monitoring and environmental remediation.