Photo-Modulating CO 2 Uptake of Hypercross-linked Polymers Upcycled from Polystyrene Waste.

Incorporating photo-switches into skeletal structures of microporous materials or as guest molecules yield photo-responsive materials for low-energy CO 2 capture but at the expense of lower CO 2 uptake. Here, we overcome this limitation by exploiting trans-cis photoisomerization of azobenzene loaded into the micropores of hypercross-linked polymers (HCPs) derived from waste polystyrene. Azobenzene in HCP pores reduced CO 2 uptake by 19 %, reaching 37.7 cm 3  g -1 , but this loss in CO 2 uptake was not only recovered by trans-cis photoisomerization of azobenzene, but also increased by 22 %, reaching 56.9 cm 3  g -1 , when compared to as-prepared HCPs. Computational simulations show that this increase in CO 2 uptake is due to photo-controlled increments in 10-20 Å micropore volume, i. e., adsorption sites and a photo-reversible positive dipole moment. Irradiating these HCPs with visual-range light reverted CO 2 uptake to 33 cm 3  g -1 . This shows that it is feasible to recycle waste polystyrene into advanced materials for low-energy carbon capture.