Role of magnetic substances in adsorption removal of ciprofloxacin by gamma ferric oxide and ferrites co-modified carbon nanotubes

[Display omitted] •The adsorption process on composite adsorbents changed as γ-Fe2O3 was introduced.•The role and importance of each composition in composite adsorbents were clarified.•γ-Fe2O3 reduced the energy and favored the adsorption process of ciprofloxacin.•CNTs and CoFe2O4 affected Co system while CNTs and γ-Fe2O3 ruled Cu and Mn systems.•Adsorption energy followed an order of CNTs > CoFe2O4 > γ-Fe2O3 > CuFe2O4 > MnFe2O4. Antibiotics have been considered an evolving environmental challenge in the last few decades due to their mutagenic and persistent effects. Herein, we synthesized γ-Fe2O3 and ferrites nanocomposites co-modified carbon nanotubes (γ-Fe2O3/MFe2O4/CNTs, M: Co, Cu, and Mn) with high crystallinity, thermostability, and magnetization for the adsorption removal of ciprofloxacin. The experimental equilibrium adsorption capacities of ciprofloxacin on γ-Fe2O3/MFe2O4/CNTs were 44.54 (Co), 41.13 (Cu), and 41.53 (Mn) mg/g, respectively. The adsorption behaviors followed the Langmuir isotherm and pseudo-first-order models. Density functional theory calculations revealed that the active sites preferentially appeared on the oxygen of the carboxyl group in ciprofloxacin, and the calculated adsorption energies of ciprofloxacin on CNTs, γ-Fe2O3, CoFe2O4, CuFe2O4, and MnFe2O4 were –4.82, –1.08, –2.49, –0.60, and 5.69 eV, respectively. The addition of γ-Fe2O3 changed the adsorption mechanism of ciprofloxacin on MFe2O4/CNTs and γ-Fe2O3/MFe2O4/CNTs. CNTs and CoFe2O4 controlled the cobalt system of γ-Fe2O3/CoFe2O4/CNTs, while CNTs and γ-Fe2O3 ruled the adsorption interaction and capacity of copper and manganese systems. This work reveals the role of magnetic substances, which is beneficial to the preparation and environmental application of similar adsorbents.