Photocatalytic upcycling of polylactic acid to alanine by sulfur vacancy-rich cadmium sulfide

Abstract

Abstract Photocatalytic conversion has emerged as a promising strategy for harnessing renewable solar energy in the valorization of plastic waste. However, research on the photocatalytic transformation of plastics into valuable nitrogen-containing chemicals remains limited. In this study, we present a visible-light-driven pathway for the conversion of polylactic acid (PLA) into alanine under mild conditions. This process is catalyzed by defect-engineered CdS nanocrystals synthesized at room temperature. We observed a distinctive volcano-shaped relationship between sulfur vacancy content in CdS and the corresponding alanine production rate reaching up to 4.95 mmol/g catalyst/h at 70 oC. Ultraviolet-visible (UV-vis) spectra, photocurrent spectra, and Fourier-transform infrared (FT-IR) spectra revealed the crucial role of sulfur vacancies in enhancing active sites on the CdS surface. Sulfur vacancy-rich CdS exhibited high stability, maintaining catalytic performance and morphology over several runs, and effectively converted real-life PLA products. This work not only highlights a facile approach for fabricating defect-engineered catalysts but also presents a sustainable method for upcycling plastic waste into valuable chemicals.