A Pair of Strongly Reductive and Oxidative Photocatalysts for the General Upcycling of Biomass Derivatives and Plastic Wastes

Abstract

Tailoring photocatalysts to achieve both strongly reductive and oxidative properties from a common scaffold remains challenging. Herein, we report the development of a pair of photocatalysts, isothiatruxene (ITS) and isosulfonyltruxene (ITSO2), by modulating the valence states of heteroatoms. ITS exhibits highly reducing power, facilitating selective cleavage of C-O bonds in biomass derivatives despite their negative redox potentials. Upon oxidation of ITS, the resultant ITSO2 demonstrates strongly oxidizing capacity, enabling metal-free and acid-free upcycling of plastic wastes even with their high redox potentials. By immobilizing ITS and ITSO2 on polystyrene and oxidized lignin supports, respectively, we have developed recyclable photocatalysts that drive multiple catalytic cycles with high efficiency. Gram-scale upcycling of plastic is achieved by integrating photoredox catalysis with flow chemistry. Mechanistic studies reveal that the excited states of ITS and ITSO2 can directly activate inert substrates, correlating with their strong redox properties. The newly introduced pair of photocatalysts, characterized by their metal-free nature, concise synthesis via trimerization, and dual photocatalytic capabilities encompassing both strongly reducing and oxidizing properties, show great potential for a wide range of applications. Furthermore, this study presents a sustainable catalytic strategy for synthesizing high-value aromatic compounds directly from biomass derivatives and plastic wastes.