In situ integrated removal of tetracycline and cadmium from soil/water by the voltaic-cell-effect of the iron (II) sulfide-hydrogel

Tetracycline (TC) and cadmium (Cd(II)) often coexist in environments such as soil and water, posing synergistic toxicity risks. In this study, a Iron (II) sulfide- Enteromorpha prolifera carbohydrate hydrogel (FeS-EP-HD) was synthesized via direct precipitation for the simultaneous removal of TC and Cd(II) from water and soil. The maximum adsorption capacities for TC and Cd(II) were determined to be 213.6 mg/g and 213.8 mg/g, respectively. Mechanisms included precipitation, ion exchange, and coordination for Cd(II), while hydrogen bonding and pore filling for TC. In binary contamination system, FeS-EP-HD possesses co-adsorption sites for both TC and Cd(II). However, Cd(II) exhibited a stronger competitive adsorption affinity, rapidly occupying adsorption sites and consequently inhibiting TC uptake. The formation of FeS-CdS voltaic effect, which further accelerates the adsorption of TC. Additionally, adsorbed TC also provided additional sites for Cd(II) via cation-π interactions. In soil in-situ remediation trials, upon introducing 1.5 ‰ FeS-EP-HD into contaminated soil, reducted in TC and Cd(II) concentrations by 48 μg/kg and 0.6 mg/kg, with removal efficiencies of 50.5 % and 47.9 %, respectively. This work demonstrates the potential of FeS-EP-HD as a efficient, eco-friendly material for co-contaminant remediation.