Enhanced adsorption of quinoline from aqueous solution by NaOH-treated biochar derived from orange peel: preparation, performance, mechanism, and density functional theory study

Low-cost biochar with a large surface area and enriched oxygen functional groups was prepared by pyrolysis of orange peel and post-NaOH modification. The modified orange peel-based biochar (MOPBC) was examined for its performance in removing quinoline from aqueous solution by adsorption. As high as 197.53 mg/g of adsorption capacity of MOPBC for quinoline was achieved. The quinoline adsorption on MOPBC conforms to the pseudo-second-order kinetic model, well-fitted with the Freundlich isotherm model. Moreover, density functional theory calculation results show that quinoline is more readily adsorbed on oxygen-containing functional groups on the surface of MOPBC, especially hydroxyl groups. The plausible chemisorption mechanisms involve hydrogen bonding, acid-base interaction, π–π, and n–π interactions. This study proves that modified biochar is a prospective adsorbent concerning the disposal of quinoline in wastewater.