A magnetically recoverable Chitosan-Based nanocomposite for simultaneous removal of tetracycline and antibiotic resistance genes from wastewater

The co-occurrence of tetracycline antibiotics (TCs) (typically 0.1–50 mg/L in hospital wastewater) and antibiotic resistance genes (ARGs) (10⁵-10⁸ copies/mL) in aquatic systems poses serious environmental and public health concerns. This study presents the design and performance of a multifunctional, magnetically retrievable chitosan-carbon quantum dot/ZnFe2O4 nanocomposite (M-Chit/CQD@ZnFe2O4) for the simultaneous removal of TCs and ARGs through synergistic adsorption and visible-light-driven photocatalysis. The unique tri-component architecture integrates: (i) chitosan’s electrostatic DNA-binding capacity, (ii) CQDs’ π-conjugated domains for enhanced TC affinity, and (iii) ZnFe2O4’s dual magnetic recovery and photocatalytic functionality under visible light. The nanocomposite exhibited exceptional tetracycline adsorption capacity (687.4 ± 12.3 mg/g) at pH 7.0 and 25 °C, significantly outperforming conventional materials. Mechanistic studies using DFT calculations and Fe K-edge XANES revealed π-π stacking (binding energy: -9.7 kcal/mol) and Fe³⁺ chelation as dominant adsorption pathways. Efficient removal of tetA gene (98.2 ± 0.7%) was achieved via electrostatic and hydrogen bonding interactions, as confirmed by FTIR and zeta potential analysis. Photocatalytic regeneration under visible light (λ ≥ 420 nm) enabled > 99% degradation of tetracycline and tetA over 20 cycles, maintaining 96.2 ± 1.8% of initial efficiency. Application to real hospital wastewater confirmed the material’s robustness, with tetracycline removal (214.5 ± 23.1 mg/g) outperforming granular activated carbon by 52%, and ARG capture (tetA, sul1, blaCTX-M-15) maintaining > 75% efficiency. Continuous-flow experiments demonstrated scalability (81.3 ± 2.9% TC removal) and magnetic recovery (94%). Toxicity testing showed moderate ecotoxicity (EC₅₀ = 12.7 mg/L for Daphnia magna), within safe operational limits. These findings highlight M-Chit/CQD@ZnFe2O4 as a promising platform for integrated chemical and genetic pollution control in water treatment applications.