Simultaneous removal of fluoride and arsenic from water in a fixed-bed column using Fe-Al-MOF/CF composite:...

Fluoride and arsenic contamination of groundwater remains a major concern for drinking water safety, particularly in regions relying on untreated groundwater sources. Although metal-organic frameworks (MOFs) have demonstrated effective adsorption for contaminant removal, their application under continuous-flow conditions remains underexplored, limiting their practical deployment in water treatment systems. In this study, a structured bimetallic Fe-Al metal-organic framework was grown on carbon felt to form a composite (Fe-Al-MOF/CF), which was evaluated for simultaneous fluoride and arsenic removal from water in a fixed-bed column. The composite adsorbent was synthesized through electrochemical deposition, enabling uniform MOF growth on the conductive substrate and improving structural stability during continuous operation. SEM, XRD, and FTIR analyses confirmed that the Fe-Al-MOF/CF structure remained intact after adsorption and regeneration, suggesting that fluoride and arsenic removal is primarily governed by surface complexation at Fe³⁺ and Al³⁺ sites. Response Surface Methodology coupled with a Central Composite Design (CCD) was used to optimize the operating conditions, yielding statistically significant quadratic models (R² = 0.91 for fluoride and 0.94 for arsenic) and achieving fluoride removal above 97% and arsenic removal exceeding 98%. Breakthrough curve analysis indicated favorable column performance, with maximum adsorption capacities of 29.38 mg g^- 1 for fluoride and 14.01 mg g^- 1 for arsenic, as estimated using the Thomas model, while the Yoon-Nelson model predicted 50% breakthrough times of approximately 3,958 min for fluoride and 3,846 min for arsenic. Regeneration experiments demonstrated good reusability, with adsorption capacity retention exceeding 83% for fluoride and 93.7% for arsenic after the fifth adsorption-desorption cycle. Structural and spectroscopic analyses further confirmed the framework's stability after repeated adsorption and regeneration cycles, without compromising its integrity. These results demonstrate that the Fe-Al-MOF/CF composite is an effective structured adsorbent for continuous removal of fluoride and arsenic, highlighting the potential of MOF-based composites for continuous-flow water treatment applications.