Adsorption of ciprofloxacin on iron oxides in the absence or presence of polyethylene microplastic

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 711; p. 136378
• Main Authors: Paludo, Deise, Bonfleur, Eloana Janice, Melo, Vander Freitas, Pasquali, Gean Delise Leal, Bazoti, Suzana Fatima, Corrêa, Rodrigo Studart
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.04.2025
• Subjects: adsorption; ciprofloxacin; energy; Ferrihydrite; filtration; Goethite; Hematite; Inner-sphere adsorption; microplastics; Outer-sphere adsorption; pollution; polyethylene; Specific surface area; surface area; Hematite; Ferrihydrite; Specific surface area; Inner-sphere adsorption; Goethite; Outer-sphere adsorption
• ISSN: 0927-7757
• DOI: 10.1016/j.colsurfa.2025.136378

Antibiotics and microplastics are considered emergent pollutants, with soils serving as critical terminal repository. As such, study aimed to evaluate the outer- and inner-sphere adsorptions of ciprofloxacin on synthetic ferrihydrite, goethite and hematite under three pH conditions (4.7, 6.2, 9.0), both in absent and presence of polyethylene microplastic (40–48 µm, 5 % w/w) (novelty by simulating double environmental contamination with ciprofloxacin and microplastic). Another novelty was estimating the adsorption stability of ciprofloxacin using chemical sequential extractions: i) outer-sphere (0.01 mol L−1 NaOH, pH 12); (ii) low energy inner-sphere (0.1 mol L−1 KH2PO4, pH 4.5); iii) high energy inner-sphere - residual ciprofloxacin. Total ciprofloxacin adsorption capacity (mg g−1) followed decreasing order: ferrihydrite (18.1–20.8) > hematite (5.7–13.8) > goethite (3.5–12.7). When considering adsorption relative to the specific surface area (mg m−2), order shifted to hematite (0.46) > goethite (0.30) > ferrihydrite (0.07) at pH 6.2, where highest adsorption rates were observed. Outer-sphere adsorption, as percentage of total adsorption, was most significant under alkaline conditions (pH 9.0): ferrihydrite (29–55 %) > hematite (8–46 %) > goethite (2–24 %). Conversely, residual adsorption was predominant at pH 4.7 for crystalline iron oxides (hematite, goethite). Maximum ciprofloxacin adsorption capacity on pure microplastic was 7.6 mg g−1, pH 4.7. The inclusion of two crystalline Fe oxides allowed to evaluate the positive effect on ciprofloxacin adsorption of greater exposure of more reactive ferrol groups. Addition of 5 % microplastic to iron oxides did not affect ciprofloxacin adsorption on ferrihydrite, goethite, and hematite. From environmental perspective, Fe oxides, abundant in humid tropical soils, have demonstrated high capacity for ciprofloxacin filtration (characterized by high adsorption energy), even in environments subject to dual contamination with microplastic. [Display omitted] •Synthetic (Sy) hematite was more efficient in total CIPRO adsorption than SY goethite.•The energy of CIPRO adsorption was adequately estimated by sequential extractions.•The CIPRO adsorption on Fe oxides was mainly in more stable inner-sphere complexes.•The high energy inner-sphere CIPRO adsorption was predominant at more acid conditions.•Microplastics did not interfere in total and energy of CIPRO adsorption on Fe oxides.