Mechanistic insight into the roles of anions and cations in the degradation of poly(ethylene terephthalate) catalyzed by ionic liquids.

Ionic liquids (ILs) have shown high catalytic activity in the degradation of poly(ethylene terephthalate) (PET), but the effects of the anions and cations, as well as the mechanism, remain ambiguous. Glycolysis is an important recycling method that converts waste PET into monomers through various chemical reactions. To reveal the role of ILs and the molecular mechanism of the glycolysis of PET, density functional theory (DFT) calculations have been carried out for the possible pathways for the generation of bis(hydroxyethyl)terephthalate (BHET) catalyzed by isolated anions/cations and ion pairs at different sites. The pathway with the lowest barrier for the glycolysis of PET is the cleavage of the C-O ester bond, which generates the BHET monomer. The synergistic effects of the cations and anions play a critical role in the glycolysis of PET. The cations mainly attack the carbonyl oxygen of PET to catalyze the reaction, and the anions mainly form strong H-bonds with PET and ethylene glycol (EG). In terms of the mechanism, the H-bonds render the hydroxyl oxygen of EG more electronegative. The cation coordinates the carbonyl oxygen of the ester, and the hydroxyl oxygen of EG attacks the ester group carbon of PET, with proton transfer to the carbonyl oxygen. A four-membered-ring transition state would be formed by PET, EG, and the IL catalyst, which regularly accelerates the degradation of PET. These results provide fundamental help in understanding the roles of ILs and the mechanism of IL-catalyzed PET degradation.

Time-multiplexed stereoscopic display with a quantum dot-polymer scanning backlight.

We fabricate a time-multiplexed stereoscopic display, which is composed of a quantum dot-polymer (QDP) scanning backlight, 120 Hz liquid crystal display (LCD), and shutter glasses. Blue LEDs, which can excite QDP film to produce white light, are adopted to replace the traditional white LEDs. The QDP scanning backlight, LCD, and shutter glasses can be controlled by the synchronization signal and work together, enabling viewers to obtain parallax views. Crosstalk is about 1%, and luminance through the shutter glasses is higher than 150 nit. The color gamut can be widely extended to 77.98% rather than the traditional 55.75% in the ITU-R Recommendation BT.2020 (Rec.2020) color space, due to the excellent properties of QD material.