Facile modification of hydrochar derived from cotton straw with excellent sorption performance for antibiotics: Coupling DFT simulations with experiments

Highlights: • The modified hydrochars had much oxygen-containing functional groups. • The modified hydrochar had the excellent removal of antibiotics from waste water. • DFT calculations showed an agreement with the sorption process results. • The H-bond, π-π EDA, and electrostatic interactions were the main mechanisms. This study aimed to investigate the sorption of tetracycline (TC) and norfloxacin (NOR) by modified cotton straw hydrochars (CSHC), which would enable the agricultural waste to be processed and recycled. Three kinds of hydrochars were prepared by H₂SO₄, KOH and KMnO₄ modification, showed obvious differences in structures and surface functional groups. The sorption processes contain film diffusion, intraparticle diffusion, and equilibrium. The interaction mechanism between hydrochar and antibiotics include π-π stacking, hydrogen bond, and electrostatic interaction. KMnO₄-modified hydrochar had the largest sorption capacity for TC (58.09 mg/g), while H₂SO₄-modified hydrochar had the largest sorption capacity for NOR (49.64 mg/g). Density functional calculations (DFT) results confirmed that the sorption capacity between hydrochar (HC) and TC was larger than that between HC and NOR. During the sorption process, the TC and NOR were regarded as electron acceptor and electron donor. Generally, CSHC-KMnO₄ and CSHC-H₂SO₄ may be simply prepared and have the potential to eliminate antibiotics from water.