Bis-Imidazolium-Based Poly(Ionic Liquid)-Functionalized Hydrochar for Efficient Sorption of Methyl Orange and Sodium 2,4-Dichlorophenoxyacetate

Environmentally friendly hydrochar demonstrates excellent performance in the treatment of cationic pollutants, yet its capability to address anions is limited. Cationic imidazolium ionic liquids carry a positive charge, and modification of the surface of hydrochar can increase its positive charge, thereby improving its ability to remove anions. Herein, bis-imidazolium-based poly(ionic liquid)-functionalized hydrochar (BIPIL-HC) was prepared using hydrochar derived from the hydrothermal carbonization of bamboo powder and <i>N</i>,<i>N</i>'-methylene-bis(1-(3-vinylimidazolium)) chloride via free radical polymerization and characterized using different instruments. The behavior of BIPIL-HC in adsorbing methyl orange (MO) and sodium 2,4-dichlorophenoxyacetate (2,4-D Na) was studied by using batch adsorption experiments, including the effects of initial concentration and temperature, solution pH, contact time on adsorption, and regeneration experiments. The adsorption kinetics and isotherms conformed to pseudo-second-order kinetics and Langmuir models. The adsorbing capacity of BIPIL-HC for MO and 2,4-D Na reached 554.91 and 565.50 mg·g^-1, respectively. BIPIL-HC is also effective in removing MO and 2,4-D Na under diverse pH values and is highly reusable. Mechanism analysis shows that hydrogen bonding, ion exchange, electrostatic, and π-π interactions promote the adsorption of the two pollutants by BIPIL-HC. Particularly, the imidazolium group of BIPIL-HC is decisive in its capture ability of the two anionic pollutants through anion exchange and electrostatic interaction. These results confirm that the use of ionic liquid functionalization as a method for modifying hydrochar can effectively enhance the treatment capacity of hydrochar for anionic wastewater, and the obtained BIPIL-HC shows promising value in anionic wastewater handling.