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Since global oil prices have declined, the price of virgin PET has dropped dramatically, and caused the recycling of PET more challenging. To make the situation worse, the rapid precipitation of terephthalic acid (TPA) from alkaline hydrolysis of PET resulted in very small particles of TPA with unfavorable filtration and drying behaviors. The aim of this work was to engineer product properties of TPA for downstream operations with the existing processing steps. The size effects of TPA crystals/precipitates on filtration, and on drying behaviors, were conducted in terms of specific cake resistance and drying-rate curve, respectively. The whole operating windows was determined for a process optimization by varying operating temperature, feeding strategy, the proportion of water to dimethyl sulfoxide, and the introduction of a cooling operation. Our whole process could be achieved within 8 h at the optimal conditions. As compared to the literature method for chemical recycling of PET, the optimal case exhibited much improved specific cake resistance of ~4.8 × 106 m/g by two orders, and shortened the drying time to 3 h by three times. The TPA crystalline products were also characterized by FTIR for identification, NMR for purity, PXRD for crystallinity, and SEM for particle morphology.

Novel substituted tridentate ligands, which contains a series of pyrazole and pyridine groups as donors, and their cyclometalated complexes have been successfully synthesized. The ligands and complexes were completely characterized by a variety of techniques, such as 1H NMR, UV–Vis, FT-IR, mass spectrometry and elemental analysis. Meanwhile, the single crystal structures of ligand 7 and complex 11 were determined by X-ray crystallography. For ligand 7, due to the effect of delocalization, the C(6)-C(7) bond length in the pyrazole ring is 0.05 A shorter than a normal C-C bond. After coordinating with the metal centre, the configuration was limited by the coordination sphere, so the bond lengths and bond angles of complex 11 are different from those of ligand 7. Through photoluminescence in acetonitrile solution at ambient temperature, two emission bands have been found between 500 and 600 nm for complexes 9 and 10. Moreover, there are several absorbing bands respectively located at 240 to 250 nm and 300 to 310 nm for ligands 7 and 8 (π(L) → π*(L) and n → π*(L)). A red-shift was observed in the UV spectra, on comparing the complexes with electron-donating and electron-withdrawing groups on the ligand, which is due to the electronic effect of the substituent. One absorbing band is also found at 375 to 425 nm for complexes 9 and 10, and this band is attributed to a MLCT (dπ(Pt) → π*(L)).