23852
Controlling potassium selectivity and proton blocking in a hybrid biological / solid - state polymer nanoporous membrane .
 Chemical: potassium
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: potassium 
Answer:
 Chemical: potassium