Photocatalytic Hydrolysis─A Sustainable Option for the Chemical Upcycling of Polylactic Acid

Abstract

Plastic waste is a critical global issue, yet current strategies to avoid committing plastic waste to landfills include incineration, gasification, or pyrolysis high carbon emitting and energy consuming approaches. However, plastic waste can become a resource instead of a problem if high value products, such as fine chemicals and liquid fuel molecules, can be liberated from controlled its decomposition. This letter presents proof of concept on a low-cost, low energy approach to controlled decomposition of plastic, photocatalytic hydrolysis. This approach integrates photolysis and hydrolysis, both slow natural decomposition processes, with a photocatalytic process. The photocatalyst, α-Fe2O3, is embedded into a polylactic acid (PLA) plastic matrix. The photocatalyst/plastic composite is then immersed in water and subjected to low-energy (25 W) UV light for 90 h. The monomer lactide is produced as the major product. α-Fe2O3 (6.9 wt %) was found to accelerate the PLA degradation pathway, achieving 32% solid transformation into liquid phase products, in comparison to PLA on its own, which was found to not decompose, using the same conditions. This highlights a low energy route toward plastic waste upgrade and valorization that is less carbon intensive than pyrolysis and faster than natural degradation. By directly comparing a 25 W (0.025 kWh) UV bulb with a 13 kWh furnace, the photocatalytic reaction would directly consume 520× less energy than a conventional thermochemical pathway. Furthermore, this technology can be extended and applied to other plastics, and other photocatalysts can be used.