From commercial photocatalysts to concentrated solar systems: mechanistic elucidation of cellulose depolymerisation

As the main structural component of biomass, cellulose, which is comprised of glucose units, has significant potential as a low carbon and sustainable feedstock in bioenergy and biochemical applications. Liberating these units is key to unlocking its full potential, and photocatalysis has emerged as a potential technology for cellulose depolymerisation under mild conditions. Despite early conceptual promise, practical applications of photocatalysis remain limited due to challenges such as the scarcity of efficient, commercially available photocatalysts and constraints in process scalability, both of which hinder technological readiness. This study investigated the efficiency of commercially available TiO2 and ZnO to selectively depolymerise cellulose. It went beyond the scope of many previous studies by increasing the standard cellulose model system used, from mono and disaccharides to tri and tetra forms. The results indicate that ZnO has a greater selectivity toward glucose, and that increasing chain length is one of the limiting factors. It also highlights the significant influence of photogenerated holes on this process and elucidates the mechanism and oxidation pathway. Additionally, it conceptually demonstrates that concentrated natural solar irradiation can effectively activate ZnO as part of an efficient depolymerisation system, warranting future investigation into system optimisation.