REGENERATION EFFICIENCY AND LONG-TERM STABILITY OF FE-MOFS FOR REPEATED NUTRIENT ADSORPTION CYCLES

Umoh, Enobong T.; Udeh, Ngozi U.

Authors

Umoh, Enobong T. Centre for Occupational Health, Safety and Environment, Faculty of Engineering, University of Port Harcourt, Port Harcourt, Nigeria
Udeh, Ngozi U. Department of Civil Engineering, Faculty of Engineering, University of Port Harcourt, Port Harcourt, Nigeria

Keywords:

Fe-MOF; adsorption regeneration; phosphate removal; nitrate removal; adsorption stability; nutrient remediation; reusable adsorbent; wastewater treatment.

Abstract

The sustainability and practical implementation of metal–organic frameworks (MOFs) for water treatment depend largely on their regeneration efficiency, structural stability, and adsorption reusability under repeated operational cycles. This study evaluates the regeneration performance and long-term adsorption stability of an iron-based metal–organic framework (Fe-MOF), Fe-UPH.COHSE–NH₂, for repeated phosphate and nitrate removal from aqueous solutions. The experiments concerning the nutrient recovery and reusability of the adsorbent have been done using batch adsorption-desorption process using diluted sodium hydroxide as the regenerating agent. Methods such as adsorption capacity test, kinetics modeling, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), BET surface area analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) have been employed to monitor the adsorption capacity, structural stability, and physicochemical stability. The regenerated Fe-MOF after several adsorption-desorption cycles retains its high phosphate removal efficiency (>85%) indicating high structural stability and regeneration ability. Phosphate adsorption remained predominantly governed by chemisorption and inner-sphere complexation, while nitrate adsorption exhibited comparatively weaker retention due to electrostatic interaction mechanisms. It was discovered that partial pore clogging, active site saturation, and minimal framework distortion were responsible for the small decreases in adsorption capability after successive regeneration processes. The adsorbent recovered from successive regeneration processes retained its heterogeneous active sites and favorable adsorption thermodynamics as revealed by the kinetic and isotherm studies. Finally, it can be stated that the findings indicate that Fe-UPH.COHSE-NH₂ is a sustainable adsorbent with high regeneration capability and stability, which makes it an excellent candidate for nutrient removal and wastewater treatment.