Improvement of photostability and thermal stability of PVC by carbon quantum dots loaded on TiO2

Titanium dioxide (TiO₂) has a strong oxidation effect when absorbing ultraviolet light. Therefore, when TiO₂ is used as a light stabilizer in polyvinyl chloride (PVC), it will cause the photodegradation of PVC. Herein, carbon quantum dots (CQDs) coated TiO₂ composite (TiO₂@CQDs) was prepared by a one-step hydrothermal method. The prepared TiO₂@CQDs were characterized by transmission electron microscopy (TEM), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The photostability of PVC film containing TiO₂@CQDs was investigated via photodegradation conductivity test, weight loss rate test, and ultraviolet aging test. Due to the down-conversion effect of CQDs under ultraviolet light, its existence can alleviate the photoaging of PVC. In addition, the thermal stability of PVC containing TiO₂@CQDs was studied by conductivity tests and oven thermal aging tests. The presence of CQDs significantly improved the thermal stability of PVC. Meanwhile, the HCl absorption capacity of CQDs could reach 30.8 mg/g_cat. According to the DFT calculations, this high absorption capacity is attributed to the HCl immobilization effect via forming hydrogen bonds between HCl and the keto oxygen, carboxyl keto oxygen in CQDs. The hydroxyl group in CQDs could also combine ZnCl₂ by forming a coordination bond.