Zn²⁺-urea synergistic enhance hydrothermal carbonization of PVC: Dechlorination with Zn loading, photocatalytic...

Hydrothermal carbonization (HTC) is a promising approach for dechlorination of PVC plastic wastes. However, the high dechlorination temperature is one of the key obstacles to the application of it. This work introduced Zn^2 + and urea into the hydrothermal process to lower the dechlorination temperature of PVC plastic and investigated the photocatalytic performance of the derived zinc-loaded solid products. It was revealed that Zn²⁺ and urea acted synergistic effects to open up the porous structures and prevent PVC particle agglomeration, so as to facilitate the penetration of hydroxyl and Zn²⁺ in to the particles, catalyzing the elimination and substitution of PVC. Particularly, it achieved a remarkable dechlorination efficiency of 99.96 % by HTC at 200 °C in 120 min. By modulating the hydrothermal parameters, the Zn₅(OH)₆(CO₃)₂ was simultaneously loaded onto the PVC-derived porous hydrochar. After that, the zinc-loaded hydrochar was pyrolyzed into a porous ZnO-C composite material. Serving as a carbon dopant source, the PVC-derived hydrochar reduced the band gap of ZnO, broadening its light absorption range. Benefiting from this bandgap narrowing and extended light absorption, the ZnO-C composite achieved 92.22 % degradation efficiency for TMX in aqueous solution under simulated natural light and maintained high activity over 5 cycles (retaining ∼70.17 % efficiency). This work pioneered a pathway for low-temperature hydrothermal dechlorination of PVC and demonstrated the potential practical application of the derived ZnO-C composites in photocatalysis.