Hierarchical porous polymeric ionic liquids with excellent adsorption performance for phenolic compounds

In this work, polymeric ionic liquids (PILs) based on imidazolium ionic liquid monomer , which possessed hierarchical porous structure and rich Lewis basic sites, could effectively adsorb both large-sized and small molecular phenolic compounds from aqueous solution. The maximum adsorption capacities of the as-synthesized PILs for tannic acid (TA), 4-nitrophenol (4-NP) and 4-chlorophenol (4-CP) reached as high as 911 mg/g, 460 mg/g and 433 mg/g, respectively. The capacity for TA was the highest among the existing adsorbents. The abundant Lewis basic sites (N-atom and Cl − ) provided by imidazolium ionic liquids and the special hierarchical porous structure of PILs were responsible for its excellent phenolic adsorption performance. The adsorption equilibrium data of 4-NP and 4-CP fitted well with the Freundlich model while those of TA complied better with the Langmuir model. The mechanism analysis indicated that the adsorption for 4-NP and 4-CP was mainly due to π–π interactions, and that for TA was dominated by H-bonding and electrostatic interaction. The PILs could be easily regenerated. This study provided a novel material for the treatment of phenolic wastewater.