Chemical Upcycling of Plastic Materials via Photocatalysis

In this work we show proof of concept that useful molecules can be derived from the environmentally friendly decomposition of polyvinyl chloride (PVC) and polylactic acid (PLA), via photocatalysis. Photocatalysis is a sustainable and environmentally friendly process that utilises light through catalysts (photocatalysts) to promote chemical reactions. One of the main current applications of photocatalysis is the degradation of large molecules of pollutants in water into smaller and less toxic molecules. In this work, photocatalysis is used towards the controlled decomposition of plastic materials, specifically PVC and PLA into valuable molecules. A series of plastic/photocatalyst composites were prepared: PVC/TiO2, PVC/TiO2-xFx, PVC/-Fe2O3, PLA/α-Fe2O3 and PLA/-Fe2O3, PLA/TiO2, PLA/WO3. These composites were placed in water and exposed to UV and visible light. After 60 - 90 hours in UV and 90 – 190 hours in visible light we examined the decomposition products of the plastic material released in water via NMR, IC, GCMS and LCMS. A mixture of molecules were produced among which butanoic and propanoic acid are identified from the PVC/photocatalyst composites. The PLA/photocatalyst composites showed that the main reproducible product was the lactide molecule from the PLA composites. Lactide is the monomer used to make PLA via ring opening polymerization. This shows proof of concept that de-polymerisation of PLA can occur in a sustainable and low-cost route.