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.

Influence of the auxiliary acceptor and π-bridge in triarylamine dyes on dye-sensitized solar cells.

Four metal-free organic dyes (AFL7-AFL10) based on triarylamine donors and different π-bridges with or without a benzothiadiazole auxiliary acceptor have been synthesized. The dyes' photophysical and electrochemical properties, theoretical calculations, and dye-sensitized solar cell (DSSC) performances have been investigated. Electrochemical measurement data indicate that varying the π-conjugacy system can tune the HOMO and LUMO energy levels. A high molar extinction coefficient combined with a broad absorption spectrum helps to reinforce the dyes' light harvesting ability; therefore, it could help to increase the JSC of the DSSCs. Among the four dyes, AFL7 bearing the bithiophene bridge achieves the best photocurrent performance with a JSC value of 16.94 mA cm-2, corresponding to an overall conversion efficiency η of 7.92% under standard AM 1.5 G conditions (that of N719 dye was 8.53% under the same conditions). The results show that the dyes based on the triarylamine donor containing fluorenyl and biphenyl moieties are promising candidates for improving the performance of DSSCs.

Study of the volatile constituents in radix flemingiae macrophyllae and a substitute by gas chromatography-mass spectrometry and chemometric methods.

A combined approach of subwindow factor analysis and spectral correlative chromatography was used to analyze the volatile components in Radix Flemingiae Macrophyllae and Flemingiae Latifolia Benth, one of its substitutes. After extraction by a water distillation method, the volatile components in Radix Flemingiae Macrophyllae and Flemingiae Latifolia Benth were detected by GC-MS. Then the qualitative and quantitative analysis of the volatile components in Radix Flemingiae Macrophyllae was completed with the help of subwindow factor analysis resolving two-dimensional original data into mass spectra and chromatograms. Sixty five of 82 separated constituents in the total ion chromatogram of the volatile components in Radix Flemingiae Macrophyllae were identified and quantified, accounting for about 88.79% of the total content. Then, spectral correlative chromatography was used to extract correlative constituents in Flemingiae Latifolia Benth. Fifty one correlative components were recognized in essential oil of Flemingiae Latifolia Benth. The result proves the combined approach is powerful in the analysis of complex herbal samples. The developed method can be used to compare the sameness and differences of Radix Flemingiae Macrophyllae and its substitutes and it can also be used for quality control of Radix Flemingiae Macrophyllae.