Global production of polystyrene (PS) exceeds 20 million tons annually—accounting for approximately 6% of total plastic output—yet less than 1% is recycled due to its chemical inert nature and strong C-C/C-H bonds. Conventional recycling methods are energy-intensive, while elemental sulfur (S8), an abundant by-product of petroleum refining, remains underutilized in high-value applications.
Recently, a research team led by Prof. CHEN Qingan and Associate Prof. LIU Heng from the Dalian Institute of Chemical Physics (DICP), in collaboration with the team of Prof. HU Jianshe and Associate Prof. CHEN Zhangpei from Northeastern University, developed a novel solar-driven co-upcycling strategy, which enabled the synergistic upcycling of PS and S8, integrating clean solar energy with the high-value utilization of industrial byproducts. This study offers a promising new pathway for controlling plastic pollution and for the comprehensive utilization of sulfur resources.
The research findings were published in the Journal of the American Chemical Society.
Solar-driven upcycling of polystyrene enabled by elemental sulfur (Image by LIU Yong and LIU Heng)
Leveraging the dual role of elemental sulfur as both a photothermal agent and a reactant, concentrated sunlight rapidly heats the mixture of waste PS and S8 to temperatures above 320 °C within two minutes. Under these conditions, the eight-membered ring of S8 molecules underwent ring-opening to generate reactive sulfur radicals, which initiate PS chain scission via hydrogen atom abstraction. The in-situ formation of degraded polystyrene and char further sustained a self-catalytic photothermal cycle, enhancing the overall conversion efficiency.
This solvent-free and noble metal-free method enabled the selective transformation of PS into high-value utilizations, including 2,4-diphenylthiophene (34% yield) and 1,3,5-triphenylbenzene (16% yield, over $400 per kilogram). Additionally, the strategy was compatible with a wide range of post-consumer PS wastes—such as disposable tableware, packaging materials, and lab consumables—as well as substituted PS derivatives, SAN, and ABS copolymers, highlighting its applicability to mixed plastic systems.
"This work transforms two low-value feedstocks into high-value products while harnessing solar energy to reduce reliance on fossil resources," said Prof. CHEN, "A promising step toward sustainable plastic recycling and circular economy".