Adsorptive removal of herbicides from water over nitrogen-doped carbon obtained from ionic liquid@ZIF-8

Highly porous nitrogen-doped carbon was obtained from the pyrolysis of ionic liquid (IL)-incorporated metal-organic frameworks (MOF, named ZIF-8) (IL@ZIF-8). IL@ZIF-8-derived carbon (IMDC), MOF-derived carbon (MDC, obtained from pure ZIF-8), and commercial activated carbon (AC) were applied in the removal of the toxic herbicides diuron [3-(3,4 dichlorophenyl)-1,1-dimethylurea), DUR] and 2,4-dichlorophenoxyacetic acid (2,4-D) from water. The adsorption capacity of IMDC was found to be the highest for DUR and was also remarkable for 2,4-D compared with any reported adsorbent, including MDC and AC. The maximum adsorption capacities of IMDC for DUR and 2,4-D were 284 and 448 mg·g⁻¹, respectively. The remarkable adsorption efficiency of IMDC is probably due to the abundant number of active sites present on its surface because of nitrogen doping and its relatively high porosity, even though it is less porous than MDC. To determine a plausible adsorption mechanism, not only detailed characterizations of the adsorbents were performed but also adsorptions across a wide pH range were carried out. Hydrogen bonding (IMDC: H-donor; adsorbates: H-acceptor) with hydrophobic and π-π interactions was suggested as a plausible mechanism for adsorption. Moreover, IMDC can be regenerated by a simple solvent treatment and used for successive adsorptive removal of the studied adsorbates. Therefore, IMDC is recommended as a potent adsorbent for the removal of herbicides such as DUR and 2,4-D from water.