A thin film of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) has good flexibility and simple preparation process. More importantly, compared with PVDF, its piezoelectric β-phase can be easily formed without mechanical stretching. However, its piezoelectricity is relatively lower. Therefore, at present, PVDF-TrFE is always compounded with other kinds of piezoelectric materials to solve this problem. The effect of nano-ZnO doping amount on the sensing characteristics of the piezoelectric films was studied. PVDF-TrFE/nano-ZnO films with different nano-ZnO contents were prepared by spin coating process and packaged. The dispersion of nano-ZnO dopants and the crystallinity of β-phase in piezoelectric films with different nano-ZnO contents were observed by scanning electron microscopy and X-ray diffraction, and the piezoelectric strain constants and dielectric constants were measured, respectively. The effect of different nano-ZnO contents on the output performance of the piezoelectric sensor was obtained by a series of impact experiments. The results show that the piezoelectric strain constant and dielectric constant can be increased by doping nano-ZnO in PVDF-TrFE. Moreover, the doping amount of nano-ZnO in PVDF-TrFE is of great significance for improving the piezoelectric properties of PVDF-TrFE/nano-ZnO thin films. Among the prepared piezoelectric films, the output voltage of PVDF-TrFE/nano-ZnO piezoelectric sensor with 7.5% nano-ZnO doping amount is about 5.5 times that of pure PVDF-TrFE. Thus, the optimal range of the doping amount for nano-ZnO is about 4–10%.

Nano titanium dioxide (TiO₂) with photocatalytic activity was firstly modified by diethanolamine, and it was then doped with broad spectrum antibacterial silver (Ag) by in situ method. Further, both Ag doped TiO₂-chitosan (STC) and TiO₂-chitosan (TC) composites were prepared by the inverse emulsion cross-linking reaction. The antibacterial activities of STC composites were studied and their antibacterial mechanisms under visible light were investigated. The results show that in situ doping and inverse emulsion method led to good dispersion of Ag and TiO₂ nanoparticles on the cross-linked chitosan microsphere. The STC with regular particle size of 1–10 μm exhibited excellent antibacterial activity against E. coli, P. aeruginosa and S. aureus under visible light. It is believed that STC with particle size of 1–10 μm has large specific surface area to contact with bacterial cell wall. The increased antibacterial activity was attributed to the enhancement of both electron-hole separations at the surface of nano-TiO₂ by the silver ions under the visible light, and the synergetic and sustained release of strong oxidizing hydroxyl radicals of nano-TiO₂, together with silver ions against bacteria. Thus, STC composites have great potential applications as antibacterial agents in the water treatment field.