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In this study , we developed a rationally designed triboelectric nanogenerator ( TENG ) by utilizing the contact electrification between a polytetrafluoroethylene ( PTFE ) thin film and a layer of TiO2 nanomaterial ( nanowire and nanosheet ) array .
 Chemical: polytetrafluoroethylene; Chemical: PTFE; Chemical: TiO2
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: polytetrafluoroethylene; Chemical: PTFE; Chemical: TiO2