4-Chlorophenol (4-CP) was obtained from the Beijing Chemical
Corporation (China). 3-Nitrophenol (3-NP) was purchased from the
Shanghai Chemical Reagent Corporation (China). 2-Nitrophenol
(2-NP) was obtained from Sinopharm Chemical Reagent Co.
Ltd. (China). 1-Butyl-3-methylimidazoium hexafluorophosphate
([BMIM][PF6]), 1-hexyl-3-methylimidazoium hexafluorophosphate
([HMIM][PF6]) and 1-octyl-3-methylimidazoium
hexafluorophosphate ([OMIM][PF6]) were supplied by Center
for Green Chemistry and Catalysis, Lanzhou Institute of Chemical
Physics (Lanzhou, China). All reagents were of analytical reagent
grade unless otherwise stated.