An Integrated Plasma–Photocatalytic System for Upcycling of Polyolefin Plastics

Abstract

Nondegradable polyolefin plastics, which account for > 60 % of total plastic waste, trigger severe global concerns and thus demand effective management technologies. However, owing to the chemical inertness of non-polar CÀ C backbones in the polyolefin structure, efficient upcycling of polyolefin plastics under ambient conditions remains a great challenge. This study introduces an integrated plasma-photocatalytic technology, coupling plasma treatment with solar-driven reforming under mild conditions, for the efficient upcycling of polyolefin plastics into value-added hydrogen and gaseous fuels. The first plasma step grafts oxygenated groups, such as À OH, OÀ C=O, and C=O, onto the polyolefin chains, which leads to the formation of a polar and hydrophilic polymer that facilitates the subsequent reforming in the photocatalytic step. Therefore, high hydrogen production activity with a benchmark efficiency of > 100 μmol g À 1 h À 1 was achieved. Moreover, the integrated process also demonstrates high versatility in upcycling different polyolefin plastics including polyethylene, polypropylene and polyvinyl chloride. The findings provide a new avenue for plastic upcycling in an efficient and sustainable way.

Photocatalytic Upcycling of Plastic Waste: Mechanism, Integrating Modus, and Selectivity

“…Some other researchers adopted plasma to pretreat plastic wastes to generate oxygenated groups on the polyolefin chains, and thus improve the hydrophilicity of plastic wastes. [ 107 ] However, this technique requires specific instrument and the species as well as the obtained oxygenated groups are uncontrollable. To make the photocatalytic upcycling process suitable to be efficiently carried out in simple and mild conditions, new strategy to achieve controllable wettability between photocatalysts and plastic wastes is indispensable.…”

Systemically Understanding Aqueous Photocatalytic Upgrading of Microplastic to Fuels

“…Many technologies, like dye-sensitized and plasmon-activated processes, have been developed to broaden the usage of visible light. [30,46] Still, the sensitized process will compete with the generation of free radicals, and the dyes could also be degraded, lowering the efficiency and stability.…”

“…Another example is that Jiang et al have found plasma treatment useful in modifying nonpolar C–C backbones in polyolefin (PE, PP, and PVC) with oxygenated groups, inducing a benchmarking photocatalytic conversion efficiency over 100 μmol g −1 h −1 . [ 30 ] Meanwhile, Hu et al reviewed and compared other advanced oxidation processes, including UVA/UVC‐air, UV, Fenton, O 3 , and Photo‐Fenton, that can promote the generation of oxygenated groups. [ 31 ] In addition, Du et al [ 7 ] used HNO 3 to oxidize PE to oxygenates, and the Reisner group [ 32 ] proposed that the chemical pretreatment for oxygenated groups formation on PE can further benefit the tandem photo/electrocatalytic process.…”

Recent advancement on photocatalytic plastic upcycling

“…1–33 Among these techniques, photocatalysis stands out as a cost-effective, environmentally-benign and green strategy able to upcycle plastic wastes at ambient temperature and pressure utilizing renewable sunlight. 34–79 A photocatalysis reaction conducted in mild conditions is anticipated to accurately activate target chemical bonds, while reserving the other functional groups, thus realizing high selectivity to desirable products. 34–49…”

“…34–79 A photocatalysis reaction conducted in mild conditions is anticipated to accurately activate target chemical bonds, while reserving the other functional groups, thus realizing high selectivity to desirable products. 34–49…”