Selective Photocatalytic Upcycling of Polystyrene Plastic to High-Value Chemicals by a Single-Atom Fe Catalyst

Chemical upcycling of polystyrene (PS) plastic waste into targeted high-value chemicals is desirable to mitigate plastic pollution and promote a circular economy. However, most of the existing chemical upcycling methods suffer from poor product selectivity due to harsh reaction conditions and an uncontrollable C-C bond cleavage process. Here, we report the selective photocatalytic upcycling of PS into benzoic acid (BA) using a graphitic carbon nitride-anchored single-atom Fe catalyst (Fe-SA/CN). The optimized Fe-SA/CN catalyst achieves 86% conversion of PS with 91% selectivity toward BA in air under visible-light irradiation at room temperature. Electron paramagnetic resonance, in situ infrared spectroscopy, and density functional theory calculations indicate that the atomically dispersed Fe promotes the generation of photogenerated holes, chlorine radical, and reactive oxygen species (•O₂^-/¹O₂), which synergistically facilitate the hydrogen-atom transfer step of the C-H bond and C-C bond cleavage processes. The catalyst can also be extended to convert g-scale real-world waste PS to BA under real sunlight. Preliminary technoeconomic analysis and environmental assessment showed that this catalytic system could significantly reduce carbon emissions and had potential commercial value. This work provides a new catalytic system for the selective upcycling of PS plastic waste into targeted high-value chemicals through the rational design of catalytic active sites, which will help alleviate the global waste plastics challenge and reduce carbon emissions.