Preparation And Solid-phase Photocatalytic Degradation Activity Of Photodegradable Polyvinyl Chloride Composite Films

White pollution has become a global environmental issue in recent years. Solid-phase photocatalytic degradation of waste plastics can lead to an eco-friendly disposal of polymer wastes, which has extensive worthiness of research and applicable prospects in the field of white pollution control. In this thesis, in order to facilitate the TiO2 electron-hole separation and increase the TiO2 solid-phase photocatalytic efficiency, many attempts have been carried out to modify nano-TiO2 by surface modifiers such as vitamin C (VC), polyoxometalate (POM) and BiOI. Moreover, the solid-phase photocatalytic activity of perchlorinated iron (II) phthalocyanine (FePcCl16) has also been investigated. The main content of the thesis is as follows:1. Four types of photodegradable composite film such as PVC-VC/TiO2, PVC-POM/TiO2, PVC-BiOI/TiO2 and PVC-FePcCl16 were prepared by embedding modified nano-TiO2 or FePcCl16 photocatalyst into the commercial PVC plastic. The solid-phase photocatalytic degradation behaviors of these composite films were investigated, which show that all composite films have high photocatalytic degradation activity in the ambient air.2. Nano-TiO2 modified by VC forming a Tiâ…£-VC charge-transfer complex having a five-member chelate ring structure, not only enhances the ultraviolet photoresponse of TiO2, but also shifts the onset of the photoresponse of TiO2 up to visible region. This complex can greatly promote a rapid photogenerated charge separation under light irradiation and the photogenerated electrons transfer from VC to conduction band of TiO2, the active oxygen species could be formed acceleratively. Therefore, the PVC-VC/TiO2 composite film shows a high photocatalytic degradation activity, for example, the weight loss rate of PVC-VC/TiO2 composite film reaches about 71% after 216 h UV-irradiation, which is 2 times higher than that of PVC-TiO2 composite film; Moreover, the weight loss rate of PVC-VC/TiO2 composite film reaches about 12.9% 6under sunlight irradiation for 12 d, which is 1.5 times higher than that of PVC-TiO2 composite film. The optimal mass ratio of VC to TiO2 is found to be 1/2.3. In the POM/Ti02 associate system, POM can mediate photogenerated electron transferring from TiO2 conduction band to molecular oxygen and speeds up the transferring of photogenerated electron of TiO2 conduction band in the solid-phase photocatalytic process. Thus, PVC-POM/TiO2 composite film has much higher photocatalytic degradation activity than PVC-TiO2 composite film. For example, the weight loss rate of PVC-POM/TiO2 composite film reaches about 29.5% after 216 h UV-irradiation, which is 1.3 times higher than that of PVC-TiO2 composite film. The optimal mass ratio of POM to TiO2 is found to be 2%.4. BiOI modified nano-TiO2 forms BiOI/TiO2 composite, which expands the photoresponse range of nano-TiO2. The valence band of BiOI becomes the trap of TiO2 photogenerated hole in the BiOI/TiO2 composite under light irradiation, which can effectively promote the separation of TiO2 photogenerated electron-hole pair. Thus, PVC-BiOI/TiO2 composite film has a high photocatalytic degradation activity. For example, the weight loss rate of PVC-BiOI/TiO2 composite film reaches about 21.9% after 216 h UV-irradiation, which is 1.6 times higher than that of PVC-TiO2 composite film. The optimal mass ratio of BiOI to TiO2 is found to be 0.75%.5. The PVC-FePcCl16 composite film was prepared by homogeneous embedding FePcCl16 into the commercial PVC plastic, PVC-FePcCl16 composite film not only has strong absorption in ultraviolet region, but also shifts the photoresponse up to visible region. Therefore, PVC-FePcCl16 composite film was revealed to have much higher photocatalytic degradation activity than pure PVC film owing to the FePcCl16. For example, the weight loss rate of PVC-FePcCl16 composite film reaches about 10.4% after 192 h UV-irradiation, which is 2.5 times higher than that of pure PVC film, moreover, FePcCl16 has good photostability in the solid-phase photocatalytic process. Both dehydrochlorination and further photooxidative degradation contribute considerably to the photodegradation of PVC-FePcCl16 composite film. Under light irradiation, the energy absorbed by the excited FePcCl16 could be transferred to the chemical groups in the polymer chain by intermolecular energy transference. The energetic transference increases the dehydrochlorination and formation of conjugated double bonds in PVC. On the other hand, the intermolecular interaction between excited FePcCl16 and triplet ground molecular oxygen can generate singlet oxygen (102) via energy transfer, which can react quickly with the unsaturated bonds in polymer forming by the dehydrochlorination, thus FePcCl16 promotes further photooxidative degradation of PVC.