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Free - radical photochlorination of graphene is used as an example to investigate the thickness , stacking order , and single - and double - side dependent reactivity in graphene .
 Chemical: graphene; 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