ISOTHERM AND KINETIC STUDIES OF SELECTIVE PHOSPHATE AND NITRATE REMOVAL USING POLYETHYLENEIMINE-FUNCTIONALIZED IRON-BASED METAL ORGANIC FRAMEWORKS

Abstract

Nutrient pollution caused by excessive nitrate and phosphate discharge into aquatic environments remains a major environmental challenge due to its role in eutrophication and water quality deterioration. Conventional wastewater treatment methods often suffer from low selectivity, limited adsorption efficiency, and poor regeneration performance. This study developed a structurally optimized and functionally enhanced iron-based metal–organic framework (Fe-UPH.COHSE–NH₂) for selective nutrient removal from aqueous solutions. The synthesis was carried out using a controlled solvothermal method and optimized by varying the precursor ratio of Iron (III) (Fe³⁺) to 1,4-benzenedicarboxylic acid (H₂BDC). Batch adsorption studies integrated with isotherm, kinetic and statistical error analyses were conducted to investigate adsorption mechanisms. The Fe-UPH.COHSE–NH₂ exhibited a high phosphate adsorption capacity of 272.9 mg·g⁻¹ and nitrate uptake of 53.4 mg·g⁻¹ with a maximum BET surface area of 533.94 m² g⁻¹. Isotherm correlation showed phosphate adsorption fitted best into Temkin model (R² = 0.9978), while nitrate adsorption fitted to Freundlich/Halsey models (R² = 0.9745), indicating heterogeneous adsorption behaviour. Kinetic studies confirmed pseudo-second-order behaviour with high correlation coefficient of R2 = 1, suggesting chemisorption governed by electrostatic interactions, Fe–ligand surface complexation and hydrogen bonding. In conclusion, Fe-UPH.COHSE-NH2 exhibits high adsorption capacity for phosphate and strong potential for sustainable and scalable water treatment applications.