Proton‐Coupled Electron Transfer Over Pd‐Modified ZnIn ₂ S ₄ for Highly Selective Photocatalytic Upcycling of Polylactic Acid Hydrolysate to Acetic

ABSTRACT

Photocatalytic upcycling of polylactic acid (PLA) via a two‐step process‐hydrothermal depolymerization to a lactic acid (LA)‐rich hydrolysate followed by selective photocatalytic oxidation to form value‐added chemicals‐presents a sustainable pathway for plastic waste upgrading. However, the efficient activation of LA molecules and effective generation of key intermediates remain significant challenges. Herein, Pd nanoparticle‐modified ZnIn ₂ S ₄ (Pd‐ZIS) nanosheets were developed to promote selective conversion of PLA hydrolysate to acetic acid (AA). In situ FTIR spectral analysis indicates that Pd nanoparticles promote electron transfer and O ₂ dissociation, accelerating the generation of hydroxyl radicals via proton‐coupled electron transfer (PCET). Furthermore, in situ electron paramagnetic resonance (EPR) results reveal that Pd nanoparticles effectively activate the C _α ─C _COOH bond in LA molecules, promoting the formation of acetyl radical intermediates that subsequently couple with hydroxyl radicals to yield AA. Consequently, the optimized 0.5 wt% Pd‐ZIS catalyst exhibits superior performance, achieving an AA production rate of 4.2 mmol g ⁻¹ h ⁻¹ with a selectivity of 88.7% and an apparent quantum yield of 1.31% ( λ = 380 nm). These performance metrics surpass those reported in most previous studies. This work offers novel insights into catalyst design for waste plastic upcycling, deepening the understanding of the mechanisms to effectively regulate the underlying complex reaction pathways.