Upcycling Waste Polyethylene and Polypropylene into Carbon Oxides and Hydrocarbons via a Mechanochemistry-Photocatalysis Combined Technology under Mild Conditions

The reaction inertness of polyolefins and poor interface contact between photocatalysts and polyolefin hinder the photocatalytic upcycling of waste polyolefins. In this paper, based on the scientific principle that polyolefins are prone to activation and degradation under stress, waste polyolefins (PP and PE) and photocatalysts were mechanochemically treated through solid ball milling to promote catalyst–polyolefin interaction and enhance the reaction activity of polyolefins, first. Then, by comprehensively utilizing the oxidation ability of photogenerated holes and the reduction ability of photogenerated electrons, PP and PE were first photodegraded into CO 2, and then the generated CO 2 was photoreduced into carbon oxides and hydrocarbons such as CO and CH 4 . After mechanochemistry treatment, the conversion rates of PP and PE to CO increased by 4 and 9 times, respectively. By controlling the reaction conditions (10 M H 2 O 2, 80 °C), the conversion rate of PP to CO increased by nearly 230 times. This mechanochemistry-photocatalysis combined technology still exhibits excellent performance in converting real-world plastic wastes (PE bag, PE bottle, PP box, and PP spoon). This paper provides a new perspective for improving the conversion rate of waste polyolefins and a new combined technology for the upcycling of waste plastics under mild conditions.