28378
In this paper , TiO2 NR arrays are hydrothermally grown on FTO substrate , and are in situ converted into NT arrays by hydrothermally etching .
 TiO2, FTO
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 TiO2, FTO