Transforming Biogenic Iron Oxide into Zero-Valent Iron for Sustainable Doxycycline Removal from Water

The study of biogenic iron oxide (BIOX) produced by Leptothrix bacteria plays a crucial role in sustainable environmental management. As a naturally abundant material, BIOX offers a green alternative to synthetic iron oxides, with promising applications in water treatment, pollution control, and resource recovery. However, its efficacy in removing antibiotic contaminants, specifically doxycycline (DOXY), has not been systematically investigated, representing a clear knowledge gap. Here, we demonstrate that reducing BIOX under either pure H2 or a H2/N2 gas mixture significantly enhances its adsorption capacity for DOXY in both synthetic solutions and real water samples collected from the River Clyde. An increased intensity of zero-valent iron (Fe0) reflections, achieved by extending the reduction duration or raising the temperature, generally correlated with superior performance across various pH levels. A prolonged reduction process lasting 10 hours at different temperatures (700°C, 400°C, and 500°C) achieved adsorption capacity of 455 mg/g. Furthermore, this reductive strategy successfully enhanced the performance of other waste-derived adsorbents, including red mud (RM) and RM-derived α-Fe2O3. These results demonstrate the broad potential of reduced biogenic and waste-derived materials for environmental remediation, highlighting the need for further studies across a wider spectrum of aquatic pollutants.