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The results prove that the promoting effect of graphene is strongly dependent on its content ; namely , the efficiency of DSSCs increases and then decreases with increasing graphene content in TiO2 - graphene composites .
 Chemical: graphene; Chemical: graphene; Chemical: TiO2; Chemical: graphene
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: graphene; Chemical: graphene; Chemical: TiO2; Chemical: graphene