Selective Liquid Chemical Production in Waste Polyolefin Photorefinery by Controlling Reactive Species

Photocatalytic upcycling of waste polyolefins into value-added chemicals provides promise in plastic waste management and resource utilization. Previous works demonstrate that polyolefins can be converted into carboxylic acids, with CO2 as the final oxidation product. It is still challenging to explore more transformation products, particularly mild-oxidation products such as alcohols, because of their instability compared with polymer substrates, which are prone to oxidation during catalytic reactions. In this work, we propose an efficient strategy to regulate the product type through precise control of radicals, intermediates, and reaction paths. Taking the commonly used photocatalyst C3N4 as an example, its major products are carboxylic acids and CO2. When MoS2 is introduced to construct a Z-scheme heterostructure, gas products are significantly reduced and alcohols appear with a high yield of 1358.8 μmol gcat-1 and a high selectivity up to 80.3%. This is primarily attributed to the presence of •OH radicals from oxygen reduction, acting a key role in alcohol formation while simultaneously suppressing the competing pathways oxygen to •O2- and 1O2, thus reducing the overoxidation products. The β-scission of the C-C bonds in the polymer chains generates intermediate alkyl species, followed by the combination with •OH to produce methanol, which is more energetically favorable for MoS2/C3N4. In contrast, alkyl species couple with oxygen species to form formic acid, which is favorable for C3N4. This work provides new approaches for controlling the product types and offers new insights into the reaction pathways involved in polyolefin photorefinery.