Enhanced cleavage of C–C bonds in polycarbonate plastic wastes to obtain valuable phenolics over a potassium-modified triazine-based strong base catalyst

Abstract

The recycling and upgrading of polycarbonate (PC) plastic wastes have attracted worldwide attention, but the selective cleavage of inert C–C bonds remains a key challenge. Herein, we show that a noble metal-free potassium-modified covalent triazine-based framework (K-CTF), as a strong base catalyst, could efficiently catalyze the cleavage of C–C bonds in various PC plastic wastes to achieve valuable phenolics. Compared with other alkali- and alkaline earth metal (Na, Mg, and Ca)-modified catalysts, K-CTF showed an optimal catalytic performance due to its strong basicity. The total yield of acquired phenolic monomers reached up to 98.1%. The reaction pathway investigation displayed that PC plastics firstly underwent methanolysis to form the bisphenol A (BPA) intermediate. A catalytic amount of strong basic sites then promoted the cleavage of C–C bonds to form phenol and 4-isopropenylphenol (IPP) by the deprotonation activation of the phenolic hydroxyl group in BPA. Thereinto, methanol and H₂O played crucial parts in the PC plastic alcoholysis and C–C bond cleavage, respectively, which acted synergistically for the high-efficiency conversion of PC plastics to monophenols. This work opens new opportunities for the efficient utilization of PC plastic wastes.