N-heterocyclic hyper-cross-linked polymers for rapid and efficient adsorption of organic pollutants from aqueous solution

Three inexpensive N-heterocyclic hyper-cross-linked polymers (HCP-IN, HCP-BZD, and HCP-BTA) were successfully prepared by Friedel−Crafts reaction for the removal of organic pollutants from aqueous solution. Five organic pollutants, i.e., 1-naphthol (1-NO), 4-nitrophenol (4-NP), 4-chlorophenol (4-CP), 2,4-dimethylphenol (2,4-DMP), and phenol were selected. Because of high specific surface area (1023 m2/g), micropore specific surface area (622 m2/g), and good wetting ability, HCP-BTA showed ultra-fast adsorption. Its adsorption capacity can reach up to 490.9 mg/g for 1-NO, 363.2 mg/g for 4-NP, 345.8 mg/g for 4-CP, 310.4 mg/g for 2,4-DMP, and 18,130.9 mg/g for phenol, within 1 min. The process was exothermic, and ΔH had an order of 1-NO (−116.23 kJ/mol) > 2,4-DMP (−89.26 kJ/mol) > 4-NP (−59.74 kJ/mol) > 4-CP (−41.12 kJ/mol) > phenol (−18.61 kJ/mol). The adsorption mechanism was explored as well. Hydrogen bonding, π–π stacking, and hydrophobic interaction might be the significant interactions for the adsorption. Besides, HCP-BTA can be easily regenerated, and the capacity after five cycles still remained 90% of the first adsorption. Above all, the N-heterocyclic hyper-cross-linked polymers may be the promising candidate for the removal of organic pollutants from aqueous solution.