Solar-Driven Upcycling of Polylactic Acid to Alanine over Pt/CdS-TiO₂ Heterojunction Single-Atom Photocatalyst

The application of solar photocatalysis under mild conditions offers a promising approach to mitigating plastic pollution. In this study, a Pt single-atom catalyst (Pt SAs) supported on a CdS-TiO₂ heterojunction (CTA) was synthesized to enable the efficient one-pot conversion of polylactic acid (PLA) into the high-value chemical alanine via integrated depolymerization, oxidation, ammonification, and reduction reactions. The Pt SAs-CTA catalyst achieved an outstanding alanine production rate of 12.1 mmol g_cat^-1 h^-1. Structural and optical characterizations, along with theoretical calculations, reveal that a two-channel electron transfer mechanism (TCETM) synergistically promotes charge separation and transport while suppressing electron-hole recombination, thereby enhancing the redox capability of the photocatalyst. Moreover, Pt SAs-CTA also exhibits excellent performance in the conversion of commercial-grade PLA under solar-simulated irradiation. This work elucidates the atomic-level charge dynamics of Pt single atoms in heterojunction photocatalysis and offers a viable strategy for upcycling plastic waste into value-added chemicals.