Developing efficient strategies for the conversion and recycling of polylactic acid (PLA) has gained significant attention in recent years. Literature studies have reported photoreforming strategies that can convert PLA into various liquid products, such as acetic acid, formate, pyruvic acid, and alanine. However, two critical challenges remain: how to efficiently depolymerize and convert PLA under mild conditions, and how to effectively extract products from the complex mixture of impurities present in real-world PLA plastics.
Prof. Zhang Tierui's research group in the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, proposed a synergistic strategy combining photothermal depolymerization and reforming. In this approach, the water vapor generated by the photothermal process facilitates the efficient depolymerization of PLA into lactic acid, while UV light activates the photocatalytic activity of TiO2, efficiently reforming lactic acid into valuable platform chemicals such as hydrogen (H2) and C1 molecules (CO and CH4). This simplifies product separation and avoids contamination from impurities. Through controlled experiments, they identified acetaldehyde and acetic acid as the primary intermediates. H2 production mainly originates from the decarboxylation of lactic acid and the photoreforming of acetaldehyde/acetic acid, while CO and CH4 are primarily produced from the photoreforming of acetaldehyde/acetic acid. Interestingly, in the absence of UV light, the main products obtained are carbon dots and hydrogen, highlighting the importance of UV light introduction.
