(399l) Synchronous Removal of Tetracycline and Heavy Metal Ions By Capacitive Deionization

The combined pollution of antibiotics and heavy metal ions in natural water bodies has become increasingly severe. Particularly, the co-existence of tetracycline (TC) and heavy metal ions (e.g., Ni²⁺, Cr³⁺) forms composite pollutants characterized by high mobility and synergistic toxicity, posing significant threats to ecosystems and human health. Conventional methods struggle to synchronously and efficiently remove such complex contaminants, necessitating the development of novel treatment technologies. Addressing this challenge, this study designed an asymmetric capacitive deionization (CDI) system using modified electrode materials to enhance the simultaneous adsorption of TC and heavy metal ions, while investigating its mechanisms and practical application potential.

Electropositive chitosan-modified activated carbon (CS-AC) anodes and electronegative attapulgite-doped activated carbon (AT-AC) cathodes were synthesized via blending and doping methods. Electrosorption experiments systematically evaluated the electrodes' removal efficiency, selectivity, and stability for Ni²⁺, Cr³⁺, and TC. Results demonstrated that the AT-10-AC cathode (with 10% AT doping) achieved electrosorption capacities of 10.52 mg/g and 10.53 mg/g for Ni²⁺ and Cr³⁺, respectively, representing 34-fold and 4-fold enhancements compared to their physical adsorption capacities. This superior performance was attributed to AT's ion-exchange capability, hydrophilicity, and surface negative charge. In multi-salt solutions, the selectivity coefficients of AT-10-AC for Ni²⁺ and Cr³⁺ reached 2.87 and 3.26, respectively, significantly exceeding those for monovalent ions (K⁺, Na⁺), confirming its preferential adsorption for heavy metal ions. Additionally, the CS-AC anode exhibited a maximum TC electrosorption capacity of 3.73 mg/g, a 46% improvement over physical adsorption, primarily relying on electric double-layer effects and electrostatic interactions, with over 80% desorption-regeneration efficiency after 10 cycles. Crucially, in co-existing TC and heavy metal ions solutions, the adsorption capacities of AT-10-AC for Ni²⁺ and Cr³⁺ decreased by only 0.25%, while CS-AC's TC adsorption capacity declined by 6%, demonstrating minimal mutual interference and validating the feasibility of simultaneous removal of heavy metal ions and TC via the CDI system.

This study innovatively integrates AT- and CS-modified electrodes into a CDI system, offering a novel strategy and technical foundation for the efficient and simultaneous removal of composite pollutants in natural water bodies. Experimental results confirm the system’s practical application potential, particularly in treating low-concentration antibiotic-heavy metal ions co-contaminated wastewater, with significant implications for advancing green water treatment technologies.