Hyper-crosslinked dicationic ionic liquid porous polymers for nitrophenol adsorption

In this work, an imidazolyl dicationic ionic liquid was employed as a monomer to construct a novel nitrogen-rich hyper-crosslinked polymer (HCP–N) for the separation of 4-nitrophenol (4-NP) from wastewater. HCP-N was fabricated through a facile one-pot Friedel-Crafts polymerization, using p-dichloroxylene as cross-linking agents, as well as pore structure regulators. The synthesized HCP-N were randomly stacked by lamellar blocks aggregated by nanospheres. The adsorption kinetic data complied well with pseudo-second-order rate equation while the adsorption isothermal equilibriums conformed to the Freundlich model. At the initial concentration of 1000 mg L−1, the adsorption capacity for 4-NP was up to 437 mg g−1. The influence of acidity, temperature and coexisted metal ions were investigated systematically. Coexisted Pb2+ at low concentration (<150 mg L−1) could significantly increase the adsorption capacity of HCP-N through complexing-bridging mechanism. The mechanism analyses revealed that hydrogen bonding, electrostatic and π−π interaction contributed together to the adsorption of 4-NP on HCP-N. The adsorbent could be recycled at least five times after the adsorbed 4-NP was separated by ethyl acetate extraction.