Selective photocatalytic upcycling of polylactic acid hydrolysate to pyruvic acid via modulating oxygen adsorption on defective CdS

Sulfur vacancies increase Cd site charge density, favoring end-on O 2 adsorption. • End-on adsorption inhibits O O bond cleavage, suppressing •OH radical formation. • Overoxidation of pyruvic acid is prevented, leading to 91.4% selectivity. The photocatalytic valorization of polylactic acid (PLA) into high-value pyruvic acid (PA) represents a sustainable pathway toward a circular carbon economy. However, the generation of non-selective reactive oxygen species (ROS) typically compromises product selectivity. Herein, we report a sulfur-vacancy-modified CdS photocatalyst (CdS v ), which was synthesized via a facile co-precipitation method and engineered to precisely regulate ROS generation. Experimental and theoretical analyses reveal sulfur vacancies (S v ) enrich the localized electron density at adjacent Cd sites. This electronic modulation promotes molecular oxygen (O 2 ) capture at these Cd centers and concurrently drives a shift in the binding geometry from a side-on to an end-on orientation. The specific adsorption configuration significantly inhibits O O bond cleavage to form hydroxyl radicals (•OH) through the oxygen reduction reaction, thereby effectively suppressing the overoxidation of PA. Consequently, remarkable PA generation efficiency is achieved over the optimized CdS v catalyst, yielding 13.2 mmol g −1  h −1 with a high selectivity of 91.4%, which significantly surpasses most previously reported results. This work provides a molecular-level paradigm for the selective upcycling of plastic waste by regulating the formation of specific ROS through vacancy engineering. Sulfur vacancies intrinsically enrich the electron density at proximal Cd centers, thereby favoring molecular oxygen (O 2 ) adsorption and shifting its adsorption configuration from side-on to end-on. This specific adsorption configuration of O 2 suppresses O O bond cleavage during the oxygen reduction reaction, thereby steering the pathway toward preferential superoxide radicals (•O 2 − ) generation and mitigating the hydroxyl radical (•OH)-induced over-oxidation. Download: Download high-res image (160KB) Download: Download full-size image