Enhanced Zn-Co-Fe Layered Double Hydroxides for Effective Levofloxacin Removal: Innovation in Reuse of Waste Adsorbent

Abstract

Purpose

Pharmaceutical waste, particularly antibiotics like levofloxacin, poses a significant threat to aquatic ecosystems and human health due to its persistence and potential to induce antibiotic resistance. This study focuses on the development of Zn-Co-Fe layered double hydroxide (LDH) and its modified form, Cu-Cyanoguanidine-ZnCoFe/LDH, as efficient adsorbents for levofloxacin removal from wastewater. The objective is to provide a sustainable solution for wastewater treatment and antimicrobial resistance management.

Methods

The catalysts were synthesized via co-precipitation and characterized using FTIR, XRD, SEM, TEM, PZC and BET analyses. Adsorption experiments were conducted to evaluate the effects of pH, adsorbent dose, and contact time, while kinetic and isotherm models were employed to elucidate the adsorption mechanisms.

Results

Cu-Cyanoguanidine-ZnCoFe/LDH achieved 90% levofloxacin removal efficiency at pH 9, driven by electrostatic interactions, hydrogen bonding, and π-π stacking. The point of zero charge (PZC) for the adsorbents was determined to be 7.00. The adsorption process followed a mixed 1st and 2nd order kinetic model, with rate constants of k1 = 473.39 min⁻¹ and k2 = 3310.39 g/mg_·min, indicating both physical and chemical adsorption mechanisms. The Langmuir isotherm model revealed a maximum adsorption capacity (Qmax) of 390 mg/g for the modified LDH. Statistical analysis confirmed the significance of the results (p < 0.05). Notably, the adsorbent retained significant antibacterial activity even after levofloxacin removal, as confirmed by antimicrobial assays. Furthermore, the material exhibited excellent recyclability, maintaining 93.9% of its adsorption capacity after four regeneration cycles using NaOH. Cu-Cyanoguanidine exhibited strong antibacterial and anti-biofilm activity, effectively degrading levofloxacin and reducing inflammation. In vitro tests confirmed efficient levofloxacin removal, with treated samples showing no antibacterial activity. In vivo studies on bacterial keratitis demonstrated that Cu-Cyanoguanidine LDH improved treatment efficacy and tissue integrity, even with reduced dosing.

Conclusions

This study highlights the potential of Cu-Cyanoguanidine-ZnCoFe/LDH as a sustainable and cost-effective adsorbent for pharmaceutical wastewater treatment, demonstrating high removal efficiency, robust adsorption mechanisms, and retained antibacterial properties. Its strong performance in eliminating pharmaceutical contaminants underscores its feasibility for large-scale wastewater treatment applications, offering a viable solution to mitigate both environmental pollution and antibiotic resistance. The study further emphasizes the potential integration of LDH-based materials into existing treatment infrastructures, providing an eco-friendly alternative to conventional remediation methods. By addressing critical challenges associated with pharmaceutical pollutants, this research contributes to the advancement of scalable and sustainable wastewater treatment technologies. Future studies should focus on optimizing synthesis methods, evaluating long-term stability under real-world conditions, and assessing large-scale implementation to enhance the practical applicability of this technology.

Graphical Abstract