Adsorption characteristics of individual and binary mixtures of ciprofloxacin and Cr(VI) in water using MnO₂ colloidal particles

In the present study, the MnO₂ adsorbents with a crystal structure, the components of approximately 59% Mn and 40% O, and the specific linkages of -OH and O-Mn-O were characterized by the techniques XDR, EDX, and FI-IR, respectively. Especially, the individual and simultaneous adsorptions of chromium, Cr(VI), and an antibiotic, CFX, on the manganese dioxide (MnO₂) material were systematically investigated. Compared with the individual adsorption, the CFX adsorption efficiency was significantly reduced in the Cr(VI) presence due to the Cr(VI)-CFX complexation formed by the Cr₂O₇²⁻ or HCrO₄⁻-NH₂⁺ electrostatic attractions. The optimal experimental conditions for the Cr(VI)-CFX simultaneous adsorption were found to be pH 6, 1 mM NaCl, 60 min contact time, and 50 mg.mL⁻¹ MnO₂ dosage. The maximum adsorption efficiencies of the Cr(VI) and the CFX on the MnO₂ were achieved at 98.1 and 87.5%, respectively. The maximum adsorption capacities of the Cr(VI) and CFX were correspondingly extrapolated to be 144.5 and 100.1 mg.g⁻¹ by the Langmuir adsorption model. The Cr(VI)-CFX simultaneous adsorption was adequately described by the Freundlich isotherm and the pseudo-second kinetic models. The chemisorption of Cr(VI)-CFX governed the simultaneous adsorption with the formation of multiple adsorbed layers.