Promotion of ciprofloxacin adsorption from contaminated solutions by oxalate modified nanoscale zerovalent iron particles

Abstract

• Oxalate addition greatly enhanced the removal of CIP by Fe 0 from 45.04% to 95.74%. • 0.3 g L −1 of Fe 0 , 0.3 mM of oxalate, pH 7, and 25℃ are the optimal removal conditions. • Oxalate addition promoted the adsorption of CIP instead of oxidation by ROS. • The maximum adsorption capacity of CIP by (Fe 0 /oxalate) system is 294.66 mg g −1 . • Oxalate addition significantly reduced the treatment cost from ¥65.72 to ¥29.12. Water contamination by ciprofloxacin (CIP) is a global and emerging issue because it increases the risk of infection by antimicrobial resistant bacteria. CIP removal from water by iron nanoparticles (Fe 0 ) with the presence of oxalate hasn't been reported yet. The present study demonstrated that the addition of oxalate to Fe 0 nanoparticles improved the removal of 100 mg L −1 of CIP from 45.04% to 95.74% under the following optimum conditions: [Fe 0 ] = 0.3 g L −1 , [oxalate] = 0.3 mM, initial pH = 7, and temperature = 25 ℃. Furthermore, the experimental results illustrated that high concentrations of dissolved oxygen in the aqueous solution greatly decreased the removal efficiency of CIP by (Fe 0 /oxalate) system from 97.69% (N 2 atmosphere) to 67.47%. Similarly, the performance of (Fe 0 /oxalate) system declined from 95.43% to 85.23% because of increasing the ionic strength of the solution from 0 to 100 mM. In contrast, the influence of humic acid (0 – 40 mg L −1 ) on the removal of CIP by (Fe 0 /oxalate) system was neglectable. Also, the negative impact of coexisting ions on the competence of (Fe 0 /oxalate) system was in the following order: Mg 2+ > NO 3 – > SO₄ 2- > Ca 2+ > CO 3 2– > K + . In addition, the desorption experiments and the results of SEM-EDS, XRD, and FTIR revealed that physisorption and chemisorption were responsible for CIP removal by (Fe 0 /oxalate) system as the addition of 0.3 mM of oxalate boosted the surface complexation between Fe 0 nanoparticles and the carboxylic, ketone, and piperazinyl groups in CIP. These results were supported by the outcomes of kinetics, isotherm, and thermodynamic analysis. Moreover, oxalate addition significantly reduced the treatment cost of 1 L of 100 mg L −1 of CIP and the generated sludge by approximately 55.68% and 57%, respectively. Finally, this study proved that (Fe 0 /oxalate) system is inexpensive, practical, and more efficient than most of the reported Fe 0 -based systems with a maximum adsorption capacity of 294.66 mg g −1 .